Gia o Trinh Cam Quan

7/31/2019 Gia o Trinh Cam Quan

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NGUYN HONG DNG

Gio trnh

Thc hnh nh gi Cm quan

TRNG I HC BCH KHOA

TP. H CH MINH2005


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Mc lc

1 Nhng hiu bit c s v nh gi cm quan 3

1.1 Nhm ngi th cm quan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

1.2 Sn phm-Mu th . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

1.3 La chn php th . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

1.4 Phng nh gi cm quan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

1.5 Thi im nh gi cm quan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

2 Mt s php th "n gin" 7

2.1 Php th Tam gic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

2.2 Php th ph hp - AnotA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

2.3 Php th ABX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

2.4 Php th 3-AFC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

2.5 Php th so hng . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

2.6 Php th phn nhm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92.7 Php th cho im . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

2.8 Php th th hiu . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

2.9 Vit bo co nh gi cm quan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

2.9.1 Nhng iu cn trnh . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

2.9.2 Nhng phn khng th thiu ca bo co . . . . . . . . . . . . . . . . . . . . . 10

3 Cc th nghim cm quan 13

3.1 Th nghim 1. Nhng iu kin c bn . . . . . . . . . . . . . . . . . . . . . . . . . . . 133.2 Th nghim 2. La chn hi ng . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

3.3 Th nghim 3. So snh cc php th phn bit . . . . . . . . . . . . . . . . . . . . . . 18

3.4 Th nghim 4. Xc nh ngng . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

3.5 Th nghim 5. Xc nh tn hiu . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

3.6 Th nghim 6. Php th c lng ln . . . . . . . . . . . . . . . . . . . . . . . . . 25

3.7 Th nghim 7. Phng php Thi gian-Cng . . . . . . . . . . . . . . . . . . . . . 27

3.8 Th nghim 8. M t mi-v . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

3.9 Th nghim 9. Xy dng thut ng . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 323.10 Th nghim 10. Phn tch m t . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

3.11 Th nghim 11. Php th th hiu . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

3.12 Th nghim 12. Tng tc mi-v . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

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3.13 Th nghim 13. Ti u ha thc n . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

3.14 Th nghim 14. nh gi cht lng . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

Ph lc 49


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LI M U

Mn hc nh gi cm quan bt u c a vo ging dy cc trng i hc trn th gii tnhng nm 60 ca th k trc nh vo ng gp to ln ca Gio s Rose Marie Pangborn (UCDavis-Hoa K). Vit Nam, GS. Lu Dun v PGS. H Duyn Tt lu c bit n nhnhng ngi u tin t nn mng cho mn hc ny cc trng i hc c chuyn ngnh o tok s Cng ngh Thc phm. Ti liu "K thut phn tch cm quan"[1] ca tc gi H Duyn T tr thnh mt quyn sch gi u cho nhiu th h k s cng ngh thc phm Vit Nam cngnh cc bn c quan tm n ngnh khoa hc cn rt tr ny. Ti liu trn trnh by mt cch cng nhng kin thc c bn v l thuyt cng nh thc hnh ca nh gi cm quan trong tcgi dnh nhiu s ch n cc php th cm quan. Vi mong mun tp hp v b sung mt sthng tin trong lnh vc khoa hc cm gic (sensory science) trong thi gian hn 10 nm qua, chngti khng mun nhc li nhng g c trnh by trong n phm trn, m dnh nhiu s ch n phn thc nghim c bit l cc bi tp mang tnh tnh hung. y l gio trnh dnh cho sinhvin ngnh K s Cng ngh Thc phm ca trng i hc Bch khoa Tp. H Ch Minh.

Nh trnh by trn, do ch ch n kha cnh thc nghim nn cc phn lin quan nc s tm-sinh l ca hot ng ca h thng c quan cm gic bao gm cu to, hot ng, qutrnh hnh thnh nhn thc, cc hin tng tm l, c s ca cc php o, ... xin mi cc c giquan tm tm c trong ti liu ca PGS H Duyn T [1] & [2] hoc trong cc ti liu khc clit k trong phn ti liu tham kho. Vi mc ch cung cp cho sinh vin h k s ngnh cng ngh

thc phm mt s k nng c bn s dng cc php th cm quan (sensory test) thng dng, cngnh k nng t chc cc nghin cu cm quan t khu u tin l chun b mu n khu cui cngl vit mt bo co th nghim, gio trnh ny c chia lm 3 phn chnh: Phn 1: Nhng iu cnphi bit trc khi tin hnh mt php th cm quan; Phn 2: Mt s php th thng dng v Phngphp vit mt bo co th nghim cm quan; Phn 3: Mt s bi th nghim cm quan.

y l ln u tin mt ti liu tng t c bin son, mc d c nhng c gng nhtnh, nhng chc l s khng trnh khi mt s sai st. Chng ti rt vui lng lng nghe nhng gp ca c gi vi hy vng nhng ln ti bn sau, gio trnh s hon chnh hn. Nhng kin nggp ca c gi s rt b ch cho mt ti liu v nh gi cm quan m chng ti ang hp tc binson [8]: Cm nang nh gi cm quan.

Xin chn thnh cm n GS.TSKH Lu Dun, PGS.TS. ng Th Anh o ng gp nhiu kin qu bu cho gio trnh ny. Tc gi xin chn thnh cm n GS. Harry Lawless (Trng ihc Cornell, Hoa K) cho php s dng mt s ti liu thc hnh. Cm n cc em Lm o TrungHiu, Nguyn Nh gip thit k trang ba v hon chnh bn tho ca gio trnh.

Tp. H Ch Minh, ngy 25 thng 5 nm 2004,Tc gi

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MI GP XIN GI V

Nguyn Hong DngB mn Cng ngh Thc phm-Khoa Cng ngh Ha hcTrng i hc Bch khoa268 L Thng Kit, Q. 10 Tp. HCMEm@il: [email protected]

Phin bn in t ca gio trnh ny bn c c th tm thy trn website ca PTN Cm quan, trngi hc Bch khoa Tp HCM: www2.hcmut.edu.vn/dzung


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Chng 1

Nhng hiu bit c s v nh gi cmquan

Theo ti liu chuyn mn, tn ti kh nhiu nh ngha v nh gi cm quan (Jellinek[4]; H DuynT[1]; Sauvageot & Catherine[12]; ...), tuy nhin theo chng ti quan im ca Stone & Sidel[15] ltng qut v chnh xc nht v ASTM (American Society for Testing and Materials) cng s dngquan im ny lm nh ngha chnh thc v nh gi cm quan.

"Sensory evaluation has been defined as a scientific method used to evoke, measure, analyze,and interpret those responses to products as perceived through the senses of sight, smell, touch, taste,and hearing."

nh gi cm quan cho php gii quyt nhng bn tm ca nh sn xut thc phm trongcc qu trnh kim tra nguyn liu, qu trnh sn xut, nh gi nh hng ca cc yu t cng nghv k thut n sn phm cui cng, cng nh xc nh mi quan h gia bao b v cht lng, xcnh vng i ca sn phm v cui cng l pht trin sn phm mi (hnh 1.1).

Cng ging nh nhng phng php phn tch thc phm khc, nh gi cm quan phi tuntheo mt s nguyn tc c bn nhm m bo kt qu thu c l chnh xc v ng tin cy. Nhngnguyn tc s c trnh by mt cch tm tt trong chng m u ca ti liu ny.

1.1 Nhm ngi th cm quan

Mt trong nhng im tng ng gia cc ngnh phn tch s dng thit b vi phn tch cm quan l mt th nghim cm quan khng th tin hnh nu thiu dng c o l ngi th (Who). Tuynhin, nu nh cc phng php thit b ch cn mt thit b o, th trong nh gi cm quan, clp vi "uy tn" ca ngi th (chuyn gia) vic s dng mt hi ng gm nhiu thnh vin tr

Hnh 1.1: V tr ca nh gi cm quan trong cng nghip thc phm [5]

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4 CHNG 1. NHNG HIU BIT C S V NH GI CM QUAN

thnh iu khng th thay th 1. Mt vn c t ra tip theo (khng ch i vi cc em sinhvin m c vi nhng ngi tng t chc cc th nghim nh gi cm quan) l s lng thnhvin trong mt hi ng. S l khng chnh xc khi a ra mt con s c th mc d iu thamn tt hn cu hi trn y, nhng trong nh gi cm quan, xc nh s lng ngi tham giahi ng, trc ht cn phi xc nh r mc ch th nghim.

Nu nh bn mun xc nh nhng tnh cht cm quan ca mt sn phm thc phm th cnphi tp hp mt nhm gm 8-12 ngi qua la chn v hun luyn. Ngc li, nu mc ch th

nghim ch n gin l tm hiu nhn bit ca ngi th v s ging, khc nhau gia hai hoc vinhm sn phm th s lng ngi th cn kim tra lc ny phi nhiu hn 50 ngi. Nhng thnhvin ny cng cn c la chn v hun luyn nhng v mt thi gian v khi lng th "nh nhng"hn nhm "phn tch" bi mc ch yu cu cng n gin hn: h ch cn tr li l nhng sn phmny ging hay khc nhau. Ch rng iu ny hon ton khng c ngha l cc php th thuc loiny l n gin. Xin mi c gi quan tm tm n bi vit gn y ca OMahony[16].

Nu nh mc ch th nghim l nh gi s a thch ca ngi tiu dng i vi mt snphm th cn phi vt qua con s 100 ngi th kt qu thu c c gi tr. tnh ton s lngngi th cn cho loi php th ny, c rt nhiu cng thc c ngh tuy nhin nhng iu kin p dng chng cn l mt cuc tranh ci ln; v trong hu ht cc trng hp, con s 100 xuthin vi tn s nhiu nht.

1.2 Sn phm-Mu th

Quy tc "vng" th nht ca cc phng php phn tch i hi cc mu kim tra ( What) phi "idin" cho tp hp mu. Ngoi ra, cc phng php ly mu cn phi c chun ha m bokt qu o c c th khi qut cho c tp hp. Phng php ly mu, s lng mu v nhng vn lin quan bn c c th tm thy trong ti liu K thut phn tch thc phm(H Duyn T[3]).Cng vi yu cu "i din", mu th phi c chun b theo mt cch thng nht. Mt li khuyn:mi khu chun b phi c vn bn ha nhm trnh mi sai st khng ng c. Vic vn bn ha

ny cn l mt c s tt ngi t chc php th c th i tm gii p cho kt qu thc nghim.Quy tc "vng" th hai l cc mu phi c trnh by di dng v danh (nude-trn tri).Trong mi trng hp mu em i th khng c c bt k mt mi lin h no vi tn thng mi,nhn hiu, ngun gc,... nhm loi tr c nh hng ca hnh nh cm gic v sn phm c trcca ngi th n kt qu nh gi cui cng. Thng thng, cc mu th c m ha bi mt sgm 3 ch s ngu nhin (Ph lc 8).

1.3 La chn php th

La chn php th (How) l khu rt quan trng ca mt th nghim nh gi cm quan. Bn c

c th tm thy s la chn cc php th c trnh by chi tit trong SSHA[14]. Mt cch tmtt, chng ta cn phi tun theo trnh t: Php th Phn bit Php th M t Php th Thhiu. Trong ti liu ny, chng ti s trnh by nguyn tc ca mt s php th thng dng m ccbn c th s dng ty theo vn c th m bn gp phi.

Bn c hai sn phm v bn mun kim tra xem chng c khc nhau hay khng:

Php th tam gic

Bn mt sn phm v bn mun kim tra xem sn phm ny ging hay khc sn phm mu:

Php th ph hp

Bn c nhiu sn phm; nhng sn phm ny khc nhau mt tnh cht, bn mun sp xp cc snphm ny theo tnh cht khc nhau :

1c gi quan tm n vic nn s dng chuyn gia hay khng chuyn gia trong nh gi cm quan xin tham khocc ti liu ca Lawless & Heymann[5]; Nguyn et al. [9]...


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1.4. PHNG NH GI CM QUAN 5

Php th so hng

Bn c nhiu sn phm khc nhau nhiu tnh cht, bn mun xp chng vo trong cc nhm c nh ngha trc:

Php th phn nhm

Bn c nhiu sn phm khc nhau nhiu tnh cht, bn mun c lng s khc nhau :

Php th cho im

1.4 Phng nh gi cm quan

So vi cc phng php phn tch thit b, nh gi cm quan i hi mt s iu kin tng i khtkhe v c s vt cht (Where). Phng th nghim (PTN) phi c t ni yn tnh, nhit dchu (khong 20 25C). iu kin ny gip cho ngi th c th d dng tp trung lm vic. Bncnh , PTN phi m bo ngi th khng b lm phin bi cc mi l, cng nh b lm phin bi

nhng ngi xung quanh. Vic xy dng cc vch ngn gia ngi th l cn thit thu c cutr li c lp. c gi c th tm thy mt trong nhng thit k ca PTN cm quan hin i trongti liu ca Meilgaard [6], Lawless & Heymann [5], cc tiu chun ca ISO v ASTM v Nguyn et al.[8].

1.5 Thi im nh gi cm quan

Thi im nh gi cm quan (When) cng l mt vn lm cho nhiu ngi bn khon. Theothng l, ngi ta chp nhn rng mt th nghim cm quan tt nht nn c t chc vo khong10h-11h30 v 15h-17h, tuy nhin cc khong thi gian trn y cn thiu nhng c s thc nghim.

Trong mt nghin cu gn y, di sc p v thi gian v ngi th, chng ti t chc thc hincc th nghim ngoi khong thi gian ni trn nhng khng quan st thy bt k kt qu bt thngno. Ngc li, khi cn so snh kt qu ca mt ngi th qua nhiu bui th nghim th nhng ktqu ny phi c thu thp vo cng mt thi im trong ngy (Sauvageot & Catherine[12]).

Hot ng ca ngi th trong PTN cn ph thuc vo thc nghim vin ( tnv). Nhim v catnv khng ch l gii thch cc hng dn, cch thc tin hnh thc nghim, m cn gip cho ngith trong trng thi thoi mi nht, lng nghe nhng gp ca h, t chc cc bui tho lun vduy tr mc ch ng cao ca ngi th trong sut thi gian th nghim. ng vai tr tnvc thl nhn vin ca phng th nghim cm quan hoc l ngi t chc th nghim.


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6 CHNG 1. NHNG HIU BIT C S V NH GI CM QUAN


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Chng 2

Mt s php th "n gin"

2.1 Php th Tam gic

2.1.1 Mc ch

Php th tam gic c s dng nhm xc nh s khc nhau gia hai sn phm m khng cn bitbn cht ca s khc nhau . Php th ny c s dng trong trng hp s khc nhau gia haisn phm l tng i nh.

2.1.2 Nguyn tc

C ba mu th c gii thiu, hai mu l ging nhau (c chun b t mt loi sn phm), muth ba c gi nh l khc hai mu cn li v c chun b t mt loi sn phm khc. Ngi thc yu cu phi xc nh mu khng lp li trong s 3 mu th.

Gi s A v B l hai sn phm cn phn bit; 6 t hp trnh by mu xut pht t cc thp ca A&B bao gm: AAB/ABA/BAA/BBA/BAB /ABB. m bo kt qu thu c c tincy cao, trong k hoch trnh by mu, s ln xut hin ca mt trong s su t hp trn phi gingnhau.

2.2 Php th ph hp - AnotA

2.2.1 Mc ch

Php th ph hp cn c gi l php th AnotA cho php xc nh liu mt sn phm c gingvi mt mu chun hay khng. Php th ny rt thch hp trong tnh hung bn mun kim tra xemsn phm lm ra c ging vi mt sn phm ang bn trn th trng hay khng.

2.2.2 Nguyn tc

Gi s A l mu chun v "not"A l sn phm ca bn. Trong giai on u tin ngi th phi c"hc" cch nhn bit mu A. Tip theo, ngi th s phi th mt dy cc mu c m ha baogm c mu A v mu notA. Ngi th phi xc nh mu no l A v mu no l notA.

2.3 Php th ABX

2.3.1 Mc ch

Khi bn cn i chiu mt mu vi mu chun(matching-to-sample), ngoi php th AnotA, chngta cn c th s dng php th ABX. Ngc vi php th duo-trio(hai-ba)[5], trong php th ny c

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8 CHNG 2. MT S PHP TH "N GIN"

hai mu chun c gii thiu. Tuy nhin theo OMahony [17] khi s khc nhau v cm gic cgii thiu mt cch tng minh, ngi th c kh nng tp trung s ch vo mt hoc nhiu tnhcht cm gic khc bit v l c s c th tin hnh cc so snh i chiu chnh xc. Hn thna, do ch c mt mu chun c gii thiu nn c th gim bt s mt mi cm gic, thch nghi,...

2.3.2 Nguyn tc

Trong php th ABX ngi th nhn c hai mu "A&B", trong c mt mu chun v mt munghin cu (mu ny c th c hnh thnh do thay i cng ngh). Mu "X" c th l mt tronghai mu "A, B". Ngi th cn phi ch ra cp mu no l ging nhau. Xc sut a ra cu tr lingu nhin l 50% v php th ny thuc nhm php th mt chiu.

2.4 Php th 3-AFC

2.4.1 Mc chKhi chng ta cn phi nh gi s khc nhau gia hai sn phm v mt tnh cht cm quan xc nh,vic ng dng phng php tam gic khng cn ph hp na, trng hp ny chng ta phi s dngphp th 3-AFC (3-Alternative Forced Choice).

2.4.2 Nguyn tc

Phng php 3-AFC tng t nh phng php tam gic c nh hng, trong php th ny ngi

th nhn c mt cch tun t 3 mu v phi xc nh mu no c cng cm gic ca mtch tiu c th ln hn hoc b hn hai mu cn li. Khc vi phng php tam gic, trong phngphp 3-AFC, ch c mt trong hai nhm - mi nhm gm 3 t hp ca hai mu- c gii thiu: hocAAB, ABA, BAA hoc BBA, BAB, ABB. Khi gii thiu mu, phi m bo trt t trnh by mucn bng i vi nhm ngi th. Trong thc t, c th mt tnh cht cm quan thay i s lm thayi cc tnh cht cm quan khc (nh quan h gia hm lng ng v v chua [10]) v vy vic sdng php th 3-AFC trong thc phm i hi mt s suy xt k cng.

2.5 Php th so hng

2.5.1 Mc ch

Php th so hng c s dng khi bn nghi ng cc sn phm khc nhau mt tnh cht (v ngt,mi hoa houblon). Php th ny cng c th s dng vi mc ch xc nh mc a thch cangi th i vi mt nhm sn phm cng loi.

2.5.2 Nguyn tc

Nhim v ca ngi th l sp xp cc mu theo mt trt t tng dn (hoc gim dn) v "chtlng" (v d nh v ngt) hoc theo mc a thch. Theo kt qu ca mt nghin cu gn y nht[8], trong trng hp ngi th phi nut mu( nh gi ch tiu mi v) th khng nn yu cu hsp xp qu 7 mu. S lng ny c th nng cao khi ngi th lm vic vi cc cht kch thch vtl (v d khi cn so hng cc sn phm theo ch tiu mu sc).


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2.6. PHP TH PHN NHM 9

2.6 Php th phn nhm

2.6.1 Mc ch

Php th phn nhm c s dng so snh nhiu sn phm b nghi ng l khc nhau nhiu tnhcht. Cc nhm c xc nh bng mt hoc nhiu tnh cht v khng c mi quan h logic nogia cc nhm. V d php th ny c s dng khi bn cn xc nh hng v ch o ca mt s

sn phm nc tri cy hn hp. Cc nhm c xc nh trc bao gm: cam, chanh, i, to, du,chanh dy (fruit de passion).

2.6.2 Nguyn tc

Ngi th phi sp xp mt dy mu vo nhng nhm khc nhau bng cch tr li "c" khi mu thc tnh cht thuc nhm nh gi v "khng" khi mu th khng c tnh cht ny. Cc tnh cht canhm c xc nh trc bi nh sn xut v chng phi c mt ngha nh nhau i vi mi ngith.

2.7 Php th cho im

2.7.1 Mc ch

Logic ca php th cho im l lng ha cng cm nhn ca mt tnh cht cm quan. V vy,php th ny gip m t s khc nhau gia cc sn phm. Ch rng php th ny ch c s dngkhi m cc sn phm c nh gi l khc nhau v chng ta cng c nhng nghi ng v nhngtnh cht m chng khc nhau. Php th ny i hi hi ng phi c xy dng t nhng thnhvin qua hun luyn. So vi php th so hng, php th cho im khng i hi phi th mt lc

tt c cc sn phm, tuy nhin ngi th phi c mt tr nh tt v thang im nh gi.

2.7.2 Nguyn tc

Ngi th s dng mt thang im nh gi cng cm gic. Thang o c th l mt onthng gii hn hai u mt bi cc t kha: "rt yu" v "rt mnh". Ngi th phi th hin cmnhn ca h bng cch vch vo mt v tr trn thang (thang khng cu trc). Ngoi loi thang ny,c th s dng mt loi thang c cu thnh t mt dy s (thang c cu trc) cho im. Cng cm nhn thp nht s tng ng vi gi tr b nht trn thang; ngc li chng ta c cng cm nhn mnh nht.

2.8 Php th th hiu

2.8.1 Mc ch

Php th th hiu cho php xc nh thi ca ngi s dng i vi mt sn phm nht nh.Logic ca php th ny ng thi da trn kh nng cm nhn v c kinh nghim s dng sn phmca ngi tiu dng "o" mc hi lng, chp nhn, a thch ca h.

Trong lnh vc thc phm v hng tiu dng, c hai cch nh gi cm gic ca ngi tiu

dng: l nh gi mc u tin (preference) trong la chn sn phm v nh gi mc chpnhn - acceptance[5]. Vi loi php th u tin, ngi tiu dng c quyn la chn l thch mt snphm hn mt sn phm khc; cn trong php th mc chp nhn ngi th ghi li mc athch ca h trn mt thang im. Khc vi php th u tin, php th chp nhn c th c thchin vi ch mt sn phm.


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2.8.2 Nguyn tc

i vi php th u tin, ngi th c th nhn c 2 mu (php th cp i u tin) v chn ratrong s sn phm h a thch nht. H cng c th nhn c nhiu mu (php th so hng utin) v phi xp cc mu ny theo mc a thch tng dn. i vi php th chp nhn, ngith nh gi mc a thch ca h i vi sn phm trn mt thang im, thng thng l thang9 im (im 0: "Cc k ght", im 9: "Cc k thch")[6].

2.9 Vit bo co nh gi cm quan

Son tho bo co th nghim l mt khu quan trng ca nghin cu cm quan. Thng qua bo cony, bn c th trao i kt qu thc nghim vi ng nghip; ng thi cng l mt t liu tracu tt dnh cho bt c ai mun lp li th nghim ca bn. Mt th nghim khng dn n vic vitmt bo co khoa hc th th nghim khng c ngha.

2.9.1 Nhng iu cn trnh

- Vit mt bo co "dy cp" v nhiu li chnh t: kt qu l s chng c ai mun c "cngtrnh" ca bn. Mt iu hin nhin l chng ta s mc nhiu li khi vit mt bn bo co 100trang hn l 10 trang.

- Vit mt bo co "gy guc" v kt qu l khng c ai nh gi ng nhng iu bn lm.V l , bo co ca bn phi cha tt c nhng yu t ngi c c th nhn ra rng bn nm vng php th v nu nh c gi mun lp li th nghim th h cng s thu c ktqu nh bn.

2.9.2 Nhng phn khng th thiu ca bo co

Trong mt bo co cm quan c bn phn quan trng khng th thiu l: mc ch th nghim,iu kin th nghim, kt qu v kt lun. Mc d ni dung ca cc phn ni trn c th khc nhaunhng chng u quan trng.

Mc ch

Mt gii thiu r rng l do ca th nghim chng t sinh vin nm vng vn h gii quyt. Phnmc ch ch nn trnh by khng qu 5 trang trong nu ngn gn v chnh xc mc ch thnghim. Hy trnh a ra nhng khi nim qu rng hoc chung chung kiu nh: "Nghin cu cht

lng cm quan c ph" (Cht lng cm quan th c mi, v, mu sc, trng thi; vy bn quan tmn cht lng no ?) hoc l xc nh s khc nhau ca 3 loi c ph (s khc nhau no ? Nu nh l mu sc v bn bt ngi th bt mt th lm sao h xc nh c ?)

iu kin thc nghim

Nhng ni dung cn nu trong phn ny bao gm:

- Sn phm: tt c nhng chi tit lin quan n sn phm c trnh by trong phn ny khicn thit, ngi khc c th lp li th nghim.

- Ngi th: nhng thng tin quan trng cn nu c th bao gm s lng, tui, gii tnh, tui trung bnh (cng vi phn tn),... cng nh cch tuyn chn, hiu bit ca ngi thv sn phm v phng php nh gi cm quan m bn s dng. Phn ny cng khng nntrnh by qu 5 dng.


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2.9. VIT BO CO NH GI CM QUAN 11

- Php th: trong nhiu bo co khoa hc ca lnh vc cm quan phn php th v cu hi dnhcho ngi th c a vo ph lc. y thc s l mt sai lm ln. Trong thc t cu hi lmt phn t "kha" th hin trao i gia ngi lm th nghim v ngi t chc th nghim,cng nh vi sn phm,... v cng chnh t y nhng sai lch trong thc nghim (experimentalbias) th hin r nht.

- iu kin thc nghim: hy trnh by mt cch tm tt nhng iu kin tin hnh thcnghim nh nh sng, thi gian, mu nh gi trc ,...

Kt qu

Sau khi thu thp s liu, nhng bng s liu th sp xp s phi c chuyn vo phn ph lcca bo co. Ch nhng bng s liu c tnh tng kt mi c a vo phn kt qu, y l nhngthng tin c ngha v c th "thao tc c". Sau bng s liu ny l nhng gii thch cng vinhng kt qu kim nh thng k m bn s dng (phn tch phng sai, kim nh t-Student,kim nh 2,...). Trong phn ny ngi vit bo co phi a ra nhng gii thch thng k r rng ngi c c th hiu c th nghim tin hnh. ng qun a bng s liu tng kt trc khia ra nhng kim nh thng k.

Kt lun

Khng nn trnh by phn ny di qu 5 trang. Thc ra, y l mt bn sao ca nhng ni dung vit trong phn mc ch th nghim vi mt im thay i nh l ngi vit bo co phi tr limt cch r rng nhng vn c nu ra trong phn mc ch th nghim. Cui phn kt lun cth xut nhng hng nghin cu tip theo tuy nhin khng nn qu sa n mc lm cho ngic c suy ngh rng nghin cu ca bn l khng c ngha hoc qu hn ch dn n mt ktlun c ngha.


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Chng 3

Cc th nghim cm quan

3.1 Th nghim 1. Nhng iu kin c bn

3.1.1 Mc ch

- n li nhng nguyn tc c bn ca php th cm quan;

- Tho lun v xc lp iu kin v phng php chun b mu;

- Thit k phiu ghi kt qu, cu hi v hng dn.

3.1.2 C s

Hai yu t ht sc quan trng ca nh gi cm quan c trnh by 1.2 v 1.4. Trong phngphp trnh by mu, cn ch n nhit mu, kch thc, th tch mu, nh sng, dng khngkh,... trong s nhng iu kin c bit khc ca iu kin th nghim. Trong mi trng hp, cchng dn th nghim cn c vn bn ha nhm quy nh c th nhng cng vic m ngi thphi thc hin. V d hng dn i vi ngi th h c th sc ming hay s dng cht thanhv ty vo phng php th. Trong mt s nghin cu, ngay c vn tc th mu cng cn phi ckim sot (v d i vi mt s sn phm nng nh tiu, mt s v c th lu thi gian di, ...).

Phng php trnh by mu phi theo mt thit k th nghim chn sn. V d vic nhgi lp li c th phi c tin hnh tng nhy cm ca php th hoc kim tra s lp li cangi th. Trt t gii thiu mu c th l cn bng hoc ngu nhin. Trt t cn bng l phngphp s dng khi m mi mu xut hin tng v tr nh gi vi s ln nh nhau. Hnh vung Latin(Bng 3.1) l mt phng php thng c s dng cho cch gii thiu ny. Trt t ngu nhin cs dng khi ngi th phi nh gi cc sn phm theo nhng th t khc nhau (Ph lc, Bng 8).Phiu "Cu hi" a cho ngi th phi bao gm tt c cc hng dn lin quan n mu v cchth mu (v tr, trt t nh gi, mu c c th li hay khng ?...) v phi ch r rng cc m hamu s dng cho sn phm nh gi, cng nh m s ca ngi th.

Bng 3.1: Quy hoch Hnh vung LatinTasting Position

1 2 3 4

Ngi th A 456 787 945 342Ngi th B 787 945 342 456Ngi th C 945 342 456 787Ngi th D 342 456 787 945

13


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14 CHNG 3. CC TH NGHIM CM QUAN

3.1.3 Tho lun nhm v Bo co

Tnh hung: Mt nh sn xut sa, mong mun a ra th trng mt loi sn phm t bo v tngt so vi loi sn phm truyn thng rt bo v rt ngt. Ngi tiu dng s dng sn phmny bng cch lnh v rt ra cc ung. Nh sn xut ny mun bit liu c s khc nhaugia cc sn phm mi v sn phm ang c trn th trng hay khng.

Yu cu: Hy thit k mt php th tam gic xc nh s khc nhau c th c gia sn phm t

bo v sn phm nguyn bo v s khc nhau c th gia sn phm t ngt v ngt nhiu. Trongbo co phi trnh by tt c nhng chi tit quan trng ca th nghim cn theo di v kimsot. Phng php chun b v gii thiu mu phi c m t t m v chnh xc. Phng phpny s c a vo ti liu ca PTN v c s dng nh mt qu trnh tiu chun cho phpth s dng v sn phm sa. Nhng vn sau y phi c a vo bo co th nghim:

- M mu v nhn;- Trt t trnh by;- Kch thc mu v nhit nh gi mu;- Phng php chun b;

- Phng php s ch v ch bin (c phng tin v dng c s dng);- Cu hi/cu tr li (bao gm c hng dn, ch dn cch th nm);- Thi gian (gia hai ln th, thi im a ra kt qu);- Phng php ghi kt qu;- iu kin phng th;- Yu cu i vi ngi th, phng php la chn;- Yu t nhit tnh (motivation);- Nhng yu t an ton m ngi th v k thut vin (ktv) phi ch .

Phng php: Sinh vin lm vic theo nhm (3-4 ngi). Tho lun theo tnh hung v chun bmt bo co th nghim ngn (np theo c nhn) sau tho lun nhm. Cc nhm lm vic trongiu kin th nghim nh sau:

- khng c h thng thu thp s liu bng my tnh (dng phiu cu hi v cu tr li)- sinh vin chun b hng dn th nghim mt cch c th sau chuyn nhng hng dn

ny cho mt ktv tin hnh php th.- Ktvch c chuyn ngnh ha phn tch v khng c kinh nghim cm quan.


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3.2. TH NGHIM 2. LA CHN HI NG 15

3.2 Th nghim 2. La chn hi ng

3.2.1 Mc ch

- Tho lun phng php la chn thnh vin (panellist) c nng lc;

- Kim tra cc loi tests xc nh tn cc mi vi s c mt hoc khng ca cc thng tin v cc

cht mi;- Kim tra cc tests xp hng v cng nh nhng tests la chn thnh vin.

3.2.2 C s

La chn ngi th l mt cng vic rt quan trng trong phn tch cm quan. Ngay c i vi ccth nghim nh gi th hiu ngi tiu dng, ngi th cng phi c la chn theo tiu ch sdng sn phmhoc mt trong s cc sn phmthuc nhm sn phm iu tra. H cng phi cnh gi l nhng ngi s dng thng xuyn v thch mt sn phm no trc khi tham gia.i vi cc php th phn bit v i vi hi ng m t, thnh vin phi c la chn da trnkh nng sinh l(v d khng b hn ch hoc bt hot lin quan n sn phm), v mc sn sng(availability) nht l i vi ngi ang i lm. Yu t nhit tnh (motivational qualification) cngl mt im ht sc quan trng i vi vic la chn ngi th cm quan. Khc vi suy ngh thngthng, nh gi cm quan l mt cng vic khng nh nhng v i hi mt s tp trung, v trongmt s trng hp l lp li v mt mi. Bn cnh cc yu cu trn, schnh xc v cm giccngl mt yu t m ngi th cn phi c. i vi cc php th phn bit, thnh vin cn phi ckim tra m bo rng h thng c quan cm gic ca h hot ng mt cch bnh thng. iuny cng c th c s dng nh mt kim tra xc nh xem mt ngi th c th lm theo hngdn hay hiu cc thut ng trong nh gi hay khng.

Trong phn tch m t hay trong kim tra cht lng, cc thnh vin c la chn sphi thc hin mt s tests kim tra chnh xc cm quan ca h. Trong thc t, ngi ta thng

s dng cc mu kim tra l nhng sn phm m ngi th s phi nh gi v sau m khng dngcc loi "m hnh". Trong bi tp sau, chng ta s xem xt hai phng php la chn kiu sng lc(screening): (1) xc nh tn mi nhm nh gi mc chnh xc cm gic ; v (2) xp hng xcnh kh nng phn bit cng cm gic.

Xc nh tn mi l mt kh nng c bn ca ngi nh gi cm quan. Cng vic ny khngn gin do chu nh hng ca nhiu yu t trong c iu kin mi trng, s mong i,... Tuynhin ngay c khi nhng yu t ny mt i, ngi th ch c kh nng nhn ra chnh xc mt natrong s cc mi c gii thiu [5]. Mc d vy, mt khi cc thng tin ny c gii thiu nh mtbi tp matching (tc l tn ca mi c a ra v ngi th phi gn ng mt mi vi tn can) kh nng xc nh chnh xc tn mi c th ln n 75%. T l ny cn c th tng ln khi ngith c lm vic vi nhng mi quen thuc. S ci thin kh nng nhn dng mi trong php thmatching cho thy kh khn ca con ngi khi lin kt cm nhn khu gic vi qu trnh x l ngnng trong tr nh.

Xp dy cng cm gic l mt k nng c bn khc ca ngi th. Nhng thnh vin cahi ng m t, nhn vin kim sot cht lng thng c kim tra kh nng phn bit cng ca mt ch tiu c th. Mc d hi ng nh gi m t thng cho im hn l xp dy nhng hvn phi c hun luyn s dng thang mt cch hp l v chnh xc. Khi mt thnh vin chatri qua giai on hun luyn, mc chnh xc ca kt qu nh gi trn thang l khng cao. V l, nh gi vic sp xp cc sn phm theo cng l mt cng c hu hiu v thch hp kimtra mc chnh xc ca ngi th giai on u tin.

3.2.3 Nguyn liu v Tin trnh bui thXc nh tn mi:

1. Nguyn liu


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- Mt dy 6 l y np, trong mi l ch cha mt mi duy nht (tt c k hiu "A", tngl c m ha bng mt s c 3 ch s).

- Mt dy mu th hai c 6 l y np v trong mi l cng ch c mt mi (k hiu "B,"c m ha bng mt s c 3 ch s).

- Phiu tr li l mt trang trng (cho mi "A") v mt danh sch cc tn mi (cho mi"B")

2. Tin trnh:Ngi th bt u th nghim free-choice (la chn t do) vi dy mu "A" v ngi mi trongtng l c k hiu "A". H c yu cu xc nh tn ca tng mi bng mt hoc hai tm t c th v chnh xc nht v vit ln phiu tr li. Ch m bo m 3 ch s trn np lv thn l khp vi m ca dng tr li trong phiu. Tip theo ngi th tin hnh th nghimmatching vi cc mi trong dy "B". H phi ngi mi trong dy, c gng xc nh tn catng mi theo danh sch xut ca phiu. Khi hon thnh hai th nghim, ngi th aphiu tr li cho k thut vin ghi kt qu. Hc vin s dng danh sch mic cung cp website ca PTNCQ tng hp v nh gi kt qu.

So hng cng v

1. Nguyn liu

- Ba mu nc to gm:+ Nguyn mu+ B sung 1% sucrose+ B sung 2% sucrose

- Ba mu nc to gm:+ Nguyn mu+ B sung 0.1% tartaric acid+ B sung 0.2% tartaric acid

2. Tin trnhNgi th c yu cu xp dy 3 mu nc to u tin theo cng v ngt tng dn (3=ngt nht; 1= t ngt nht). Sau xp dy 3 mu nc to th hai theo cng v chua tngdn (3= chua nht; 1= t chua nht). S dng danh sch v trn website ca PTNCQ tnghp v nh gi kt qu.

3.2.4 Bo co

Sinh vin lm vic theo nhm (3-4 ngi). Tho lun theo tnh hung v chun b mt bo co thnghim ngn (np theo c nhn) sau tho lun nhm. Yu cu ca bo co phi c cc phn sau:

Xy dng th phn b (histogram) s lng cu tr li chnh xc tn mi bi sinh vin tronglp t bng kt qu xc nh tn mi (cc th c xy dng ring r cho cc phn th nghimfree-choice v matching);

Tin hnh mt kim nh cp t-test (s dng cng s liu trn y) so snh gi tr trungbnh ca xc nh chnh xc mi trong hai trng hp free-choice v matching. Gi tr trungbnh cao hn ca mt phng php c ngha g ? Tnh gi tr tng quan gia hai phng phpxc nh mi.

Mt ngi c kh nng xc nh tt tn mi trong mt iu kin th c kh nng nh vy trongiu kin kia hay khng ?

C th t hp hai kh nng ny thnh mt i lng nh ch s im (index-score) ca tng cnhn c khng ? V sao c v v sao khng ?


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3.2. TH NGHIM 2. LA CHN HI NG 17

Lp bng s lng so hng chnh xc cho v ngt, chua v c hai. Xy dng histogram i vikt qu so hng v ngt v v chua (taste ranking data).

Tin hnh mt phn tch 2 nhm xc nh kt qu so hng c phi l ngu nhin hay khng.

Gi tr dng(cutoff) c la chn nh th no nu mc ch ca th nghim l tm ngi thcho cng tc kim tra cht lng (Quality Control)?

Cho bit nhng xut v vic t chc php th kt qu thu c tt hn.


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3.3 Th nghim 3. So snh cc php th phn bit

3.3.1 Mc ch

- Lm quen vi 4 php th phn bit;

- So snh nhy tng i ca 4 php th phn bit;

- Chun b mt bo co kt qu phng th nghim theo mu bo co cho x nghip.

3.3.2 C s

Trong cng nghip, s khc nhau nh gia cc sn phm thng c kim tra bng php th phnbit la chn bt buc (forced-choice). Trong nhng php th nh vy, ngi th c yu cu lachn mt trong hai hay nhiu mu c t nhiu nhng tnh cht c bit hoc l nhng mu ny khcnhau. Dng kim nh s khc nhau tng qut ny bao gm cc php th tam gic, duo-trio (hai-ba)v so snh vi mu chun (AnotA), cn dng c bn th bao gm so snh i v phng php lachn bt buc 3 mu (3-AFC).

Cc php th phn bit thng c s dng xc nh liu mt s thay i nh v thnhphn v/hoc cng ngh cng nh phng php bao gi c lm thay i tnh cht cm quan ca mtsn phm hay khng. iu ny c th xut pht t mun thay i cng ngh ca nh sn xuthoc do thay i nh cung cp nguyn liu vi mc ch gim gi thnh sn phm. Tuy nhin v vn "thng hiu" (branding) m nh sn xut hy vng rng nhng thay i trn y khng dn ns khc nhau v tnh cht cm quan ca sn phm. c th nm c thng tin ny h s dngphp th phn bit. Nhng khng phi bt k php th phn bit no cng cho php pht hin skhc nhau nh gia cc sn phm. i vi mt s phng php, nh phng php tam gic, ngith gp nhiu kh khn khi so snh cc mu: h phi thc hin ba cp so snh cho bit mu nokhng lp li. Nhng php th khc, nh so snh i, n gin hn bi l ch i hi ngi tr li"trt" cm gic ca h xc nh xem mu no mnh nht hay yu nht. V vy, vi mt nng lc

tng ng, mt php th c th nhy cm hn cc php th khc. Php th so snh i, nhy cmi vi s khc nhau hn l php th duo-trio, thm ch khi m hai php th ny c nng lc tngng (chng hn p[sai s]=0.5)[5].

Trong bi tp sau, ngi th c yu cu nh gi s khc nhau ca hai sn phm thngqua 4 php th phn bit bao gm:

- Tam gic

- ABX

- 3-AFC

- So snh i

Php th s c thc hin bi tng sinh vin theo trt t trn y. Nhng thng tin b sungv cc php th c th tm thy trong ti liu ca tc gi H Duyn T[1], Lawless & Heymann[5].

3.2.3 Nguyn liu v Phng php

1. Nguyn liu:

- Chun b mt khay trng cha 11 mu bt nc qu. Ch kim tra m bo m mu

trn khay v m mu c trong phiu tr li phi ging nhau;- Bn phiu tr li (cho 4 php th) vi hng dn tng ng;- Nc, bnh thanh v, khn giy v cc nh.

2. Phng php: Thc hin cc php th nh hng dn trong phiu tr li theo trt t sau:


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3.3. TH NGHIM 3. SO SNH CC PHP TH PHN BIT 19

- Tam gic- ABX- 3-AFC- So snh i

Sau khi thc hin xong cc php th, chuyn kt qu cho ktv tnh s lng cu tr li chnhxc cho tng php th. S liu v keyca m, mu v m t vic xp ngu nhin cc mu kimtra s c cung cp.

3.2.4 Bo co

Sinh vin lm vic theo nhm (3-4 ngi). Tho lun theo tnh hung v chun b mt bo co thnghim ngn sau tho lun nhm. Trong bo co phi tin hnh cc phn tch sau trn kt qu cnhn t a ch email ca PTNCQ ([email protected]):

- Xc nh phn trm cu tr li chnh xc cho tng php th.

- Xc nh xem liu cc php th tm thy s khc nhau gia hai mu theo cng mt kt qu. Sdng bng 1 (Ph lc) tnh ton s lng cu tr li chnh xc.

- Tnh s ngi thc s pht hin s khc nhau gia cc mu (discriminators) cho tng phngphp vi kt qu tm c bng cng thc sau:

C = D +p(ND)

Trong : C = s cu tr li chnh xc; D = s discriminators; N = s ngi nh gi; v p =mc sai s ca php th. V d vi mt php th tam gic gm 30 ngi, 16 ngi a ra cutr li chnh xc. Kt lun l c s khc nhau c ngha mc p < 0.05. S discriminators s l:

16 = D + 1/3(30D) = 2/3D + 10 D = 9

- Cho bit php th no nhy cm nht? V sao ?

Vit hai trang bo co da trn kt qu th nghim trn. Bao gm cc phn sau:

- Tc gi/Tiu /Ngy

- C s (bn c th t ngh ra mt u bi)

- Kt lun

- Khuyn co- Phng php

- Kt qu

- Ti liu tham kho


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3.4 Th nghim 4. Xc nh ngng

3.4.1 Mc ch

- Lm quen vi mt phng php nhanh xc nh ngng ca mi hoc v ca mt nhm.

- Hiu s khc nhau gia cc c th v s chnh xc cm gic ha hc.

- Lm quen vi mt phng php ca ASTM (American Society for Testing and Materials).

3.4.2 C s

Ngng thng c coi l nng nh nht ca cht kch thch m ti ngi ta thu c 50 %cu tr li chnh xc. Thc t ngng l i lng phc tp v kh xc nh. lch ca cu trli (response biases), xu hng lun tr li "c" hoc "khng" i vi nhng tnh hung khng chcchn, s hiu chnh suy on, la chn mc ngha v chi tit ca qu trnh gii thiu mu l nhngyu t tuy t nhng lm phc tp thm nh ngha v ngng. Mc d vy, vic xc nh ngng lrt cn thit bit c nng nh nht ca mt cht kch thch m a s ngi th cm nhn

c. ng dng c th ca ngng xc nh trong khoa hc cm gic bao gm:

- xc nh kh nng kch thch cm gic ca mt thnh phn mi v trong thc phm;

- xc nh s c mt ca mt s ly nhim hoc mt mi v l (off-flavour) trong thc phm hng;

- xc nh mc chp nhn nh nht ca s ly nhim hoc mt mi v l;

- xc nh mc nhy cm ca mt c th i vi mt thnh phn mi v m chng ta quantm.

Con ngi khng ging nhau v nhy cm i vi cc cht gy mi, v. i vi mt s ngi cccht phenylthiocarbamide (PTC) [IUPAC:phenilthiourea] v propylthiouracil (PROP) khng c v,cn i vi mt s ngi th chng c v ng. Hin nay c nhiu phng php c khuyn co xc nh ngng [5]&[1]. Trong bi tp sau, chng ta s kim tra hai phng php: ASTM E-679-79[5] v phng php c lng ngng t nhm cc php th la chn bt buc. Mt php th 4-AFCcng c pht trin da trn nguyn tc ca php th ny nh gi vai tr ca yu t vnha n kh nng nhy cm mi ca ngi th[11].


1. Nguyn liu:Chun b by mu c nng ca ng saccarose trong nc lc nh sau:- Mu 1: 0.50g/l- Mu 2: 0.71g/l- Mu 3: 1.00g/l- Mu 4: 1.41g/l- Mu 5: 2.00g/l- Mu 6: 2.83g/l- Mu 7: 4.00g/l

2. Phng phpSinh vin lm vic theo nhm hai ngi trong mt ngi ng vai tr "thc nghim vin"trc cn ngi kia l "cm quan vin". Mt khi kt thc th nghim, hai ngi thay i vai tr"thc nghim vin" v "cm quan vin" cho nhau.


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3.4. TH NGHIM 4. XC NH NGNG 21

Nhng m s mu dng cho cc ln lp s khc nhau cho "cm quan vin" v "thc nghimvin" hai i tng ny khng on c kt qu ca cc i tng kia khi c hai ng vaitr "cm quan vin". Sinh vin ng vai tr "thc nghim vin" s nhn c t ktvcc dngc th nghim sau:

- Khay trng cha 14 mu 10ml nc lc (mu trng) v 7 mu 10ml dung dch ng (ttc cc mu l ging nhau v c xc nh bi mt s ngu nhin 3 ch s)

- Mt phng php tng dn vi mt s lng gii hn phiu tr li cha m ca 21 muc gom thnh 7 nhm 3 mu.- Mt bng kha cho bit mu no trong nhm 3 mu l cha ng. Nc sc ming, cc

nh, khn v bnh trng ming.

"Cm quan vin" s khng nhn thy phiu tr li v KHA. "Thc nghim vin" a cho "cmquan vin" ln lt tng mu h th (t mc 1 n mc 7), hng dn "cm quan vin"nm mu theo trt t ca cu hi (tri sang phi), v yu cu "cm quan vin" xc nh muno trong nhm 3 mu c v ngt nht. Nu "cm quan vin" khng th quyt nh mu notrong s 3 mu c v ngt nht, h phi on. "Cm quan vin" s phi sc ming bng nc vch khong 30 giy gia cc nhm 3 mu th (Phng php thc nghim ny phi c nhc

li trong phn hng dn th nghim). Khi "cm quan vin" tr li, "thc nghim vin" s vngtrn s mu m "cm quan vin" xc nh l ngt nht trong nhm 3 mu. Khi tt c 7 nhmmu c th xong, "thc nghim vin" tng kt s cu tr li chnh xc ca "cm quanvin". Kt qu cui cng c gi li ktv tp trung thnh kt qu ca nhm.

3.4.4 Bo co

S dng s liu hng tin hnh cc phn tch sau:

- V th phn b ngng c th v kim tra xem y c phi l phn b chun hay khng.- Tnh ngng ca nhm bng cch tnh trung bnh hnh hc ca ngng cc c th. Ch

: trung bnh hnh hc c th c biu din nh l trung bnh s hc ca gi tr log,v d [-4.25 + -5.75 + ...]/n = -4.25; hoc c th c biu din di dng moles/litersbng nghch o log ca gi tr trung bnh logarithmic ca ngng, hay 104.25 = 56.23micromoles/liter. KHNG tnh log ca log gi tr trc !

- V mt th ca t l cu tr li chnh xc ca nhm (trc Y) theo hm s ca nng ng (trc X).

- V ng hi quy (s dng MS Excel hoc mt phn mm khc) qua s liu ca tn s cutr li chnh xc ca nhm v ni suy t ng ny gi tr nng ng c 67% cu trli chnh xc.

- Hai phng php nh gi ngng ca nhm c thng nht vi nhau khng ?

- Nhng ch khi s dng cc phng php ny xc nh ngng. Cu hi ph: Lmth no ta c th c lng c mc sai s xung quanh hai php o ? (Ch : sai s phic biu din di dng n v nng , X moles/lit).


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Hnh 3.1: th xc nh tn hiu[5]

3.5 Th nghim 5. Xc nh tn hiu

3.5.1 Mc ch- Lm quen vi phng php s dng trong l thuyt xc nh tn hiu;

- Hiu v lch ca cu tr li, hiu lc ca php th v ng lc ca ngi th;

- Hiu l thuyt xc nh tn hiu nh l mt l thuyt ca phng php xc nh ngng cin.

3.5.2 C s

L thuyt xc nh tn hiu l c s ca cc php th phn bit. y l mt l thuyt c bit caphng phng php xc nh ngng c in v cc php th phn bit c bn (Th nghim 6). imc bit ca phng php ny l cho php tch phn lch ca cu tr li ra khi phn phn bit thcs. L thuyt xc nh tn hiu c th c s dng phn bit hai cht kch thch hoc c sdng o kh nng cm gic ca ngi th. Khi cn phn bit mt cht kch yu i vi mt mutrng hoc i vi mt mu c s, phng php xc nh tn hiu c th c dng nh mt phngphp thay th cho phng php o ngng. L thuyt xc nh tn hiu hot ng di nhng githit sau:

- Cm nhn i vi mu trng v mu nh gi bin i theo phn b chun (tc l i lngny c th mnh hn, hoc yu hn gi tr trung bnh). Nhng phn b c tnh gi thit ca

kinh nghim ch quan ny c gi ln lt l phn b "ting n" v "tn hiu"- Ngi th a ra mt "im dng" (cut-off) mt ni no dc theo continuum cng m

mt cu tr li tch cc c a ra cho mt cm gic mnh hn v mt cu tr li tiu ccc a ra cho cm gic yu hn.

Trong khun kh ca cc gi thit trn y, s phn bit ca mt mu v mu trng c tnh bngkhong cch gia gi tr trung bnh ca phn b "tn hiu" v phn b "ting n". Gi tr ny cxc nh bng t l ca "hits" (chnh xc- l tr li "C" khi mu chun c gii thiu) v tl ca "false alarm" (hay l sai lm loi 2-tr li "C" khi m ch c noise). Nhng t l ny tngng vi min gii hn trong hnh 3.1. P(Hits) l min di phn b tn hiu n pha phi ca "im

dng-cutoff", trong khi P(False Alarms) l min di phn b ting n n pha tri ca imdng-cutoff. Bc tnh ton cui cng l chuyn i cc vng thnh khong cch tm mc khcnhau gia cc gi tr trung bnh ca hai phn b. iu ny c thc hin bi chuyn i t l hitsv false alarms thnh gi tr Z (xem bng p-& Z-scores) v v mt ton hc cng chng li vi nhau.Do gi tr Z c lp bng, iu ny c thc hin bng cch tr. Cng thc cui cng ca s


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3.5. TH NGHIM 5. XC NH TN HIU 23

khc bit loi tr s lch ca cu tr li (response bias) c biu din di dng "d":

d = Z(Hits) Z(FalseAlarms)

Vic tnh d l mt im c li ch n loi tr c cu tr li lch l h qu ca phng phpxc nh ngng yes/no. Cc c th c th l bo th (conservative) hoc d dng (lenient) tr li"C" cho mi cht kch thch. Trong biu 3.1, xu hng ny s nh hng v tr ca ng dng"cutoff". Ngi c xu hng tr li "C" thng xuyn hn s c gi tr dng "cutoff" v pha trica ngi c xu hng tr li "Khng" mt cch thng xuyn hn. Tuy nhin, khng quan tm nv tr tng i ca "im dng" gia cc c th, s tch bit gia gi tr trung bnh ca phn bn v gi tr trung bnh ca phn b tn hiu vn gi nguyn v gi tr d s khng thay i (theo lthuyt). Nu mt ai "d di" hn, ngi s c c gi tr hits nhiu hn, nhng cng s c nhiuhn false alarms. Nu ngi ny tr nn "bo th" hn, gi tr false alarm s gim nhng ng thigi tr hit cng s gim theo. Tm li, gi tr "im dng" c th trt sang tri hoc phi nhng gitr d vn khng thay i. Trong bi tp ny, chng ta s xem hiu ng thay i "im dng" bngcch iu chnh phn "b" v phn "pht" (payoffs - penalties) ln lt ca cu tr li chnh xc vkhng chnh xc bng cch s dng bin payoff matrices.

c th hiu v lm c bi th nghim ny, yu cu sinh vin xem li phn tnh i lng

Z trong cc ti liu thng k.


1. Nguyn liu

- Hai chai mu nu cha ct hoc mt nguyn liu tng t. Mt chai cha 200g nguyn liuc k hiu l S (standard-Mu chun) v mt chai cha 208g nguyn liu c k hiuH (heavy-Mu nng hn) ; cc k hiu S&H c ghi di y chai.

- 30.000VND thng v pht thnh vin theo kt qu th nghim ca h;

- Mt tm chn gia thc nghim vin v cm quan vin, payoff matrices, hai phiu tr li(mt dnh cho ch tiu bo th v mt dnh cho ch tiu linh hot).

2. Phng php Sinh vin lm vic theo cp (nh cc v d trc) trong mt sinh vin lm vicnh "Thc nghim vin" cn ngi kia l "Cm quan vin". Mt khi kt thc c hai trnghp ch tiu bo th v linh hot, hai sinh vin thay i vai tr cho nhau v lp li th nghim.Mt na cc chai mu ( c gn trc bi ngi hng dn) s c bt u vi ch tiubo th, trong khi mt na kia s bt u vi ch tiu linh hot. Sau khi thay i vai tr,sinh vin bt u bi ch tiu c thc hin sau cng trong cp ca mnh. Danh sch tt ccc nguyn liu trn, sinh vin c th nhn c thng qua ktv hoc t website ca PTNCQ."Cm quan vin" v "Thc nghim vin" phi ngi i din qua bn v cc chai, cu hi v matrn phi c xp sau tm chn ch c "Thc nghim vin" c th quan st c.

Mu th: (P1 - P10 trong phiu)

- Bt u vi ch tiu c ch dn bi ngi hng dn (ch tiu bo th hoc linh hot).

- a cho ngi th chai c ch ra trong php th P1 ("S" hoc "H") lm sao cho ngi thkhng thy c nhn ca chai.

- Bo cho ngi th: y l "Mu chun" hoc y l "Mu nng hn" (mu tng ng) khi bna tng mu cho ngi th. Hy cho ngi th mt lc h nh gi trng lng ca mu.

- Ly mu v v thc hin php th tip theo cho n php th P10.Mu th nghim:(P1-P50 trong phiu)

- Thng cho cm quan vin 5.000VND nh phn im khi ng ca h. Gi li 25.000VND;


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- a cho ngi th mt chai c k hiu 1 ging nh trong phn th. Khng cho cm quanvin bit tn ca chai (tc l "S" hoc "H"), nhng phi yu cu cm quan vin nh gi trnglng ca chai v quyt nh l "Mu chun" hay l "Mu nng hn";

- Khi Cm quan vin tr li, ly chai li, ghi cu tr li vo v tr thch hp trn phiu v tr1.000VND cho Cm quan vin nu l cu tr li ng v pht tin (1.000VND) nu lcu tr li sai vi kt qu cho trong payoff matrix;

- Tin hnh mt cch tng t cc php th tip theo cho n khi bn kt thc dy mu th(mu 50). Sau chuyn n ch tiu khc v khi bn kt thc ch tiu ny th hy chuyn ivai tr "thc nghim vin" v "cm quan vin" ri lp li tin trnh th nghim trn cho c haich tiu.

Khi kt thc tp hp s liu, hy tnh s lng hits v false alarms:

- Mt kt qu HIT c c khi m "cm quan vin" tr li "Mu nng hn" khi m thc s Munng hn c gii thiu. iu ny khng bao hm tt c cc cu tr li chnh xc m ch ctnh khi mu nng hn c gii thiu (c ngha l cu tr li tch cc cho tn hiu);

- Mt kt qu FALSE ALARM c c khi "cm quan vin" tr li "Mu nng hn" khi thc tMu Chun c gii thiu. iu ny cng khng bao gm tt c cc cu tr li khng chnhxc m ch i vi trng hp Mu Chun c gii thiu (tc l cu tr li tch cc i vimu ch c ting n-noise trials).

Tip theo, xc nh t l ca hai i lng ny bng cch chia s lng cu Hits cho s lng ca"Mu nng hn" c gii thiu (25) v chia s lng False Alarms cho s lng ca Mu chun cgii thiu (25). Chuyn hai t l ny thnh Z-scores bng cch s dng bng cho sn, v tnh d thngqua cng thc trn (Khong trng dnh cho cc php tnh ny nm trong payoff matrices) Cui cng,sinh vin a kt qu tnh ton ktv h kim tra v ghi kt qu. Kt qu ca nhm s c a lnmng ngay sau khi th nghim kt thc.

3.5.4 Bo co

Trong mt bo co ngn gn, sinh vin phi tr li cc cu hi sau:

- T l ca hits v false alarms ca tng ngi thay i nh th no trong hai iu kin pht vthng ? iu ny c cn ng i vi c nhm ni chung ?

- Tnh ton gi tr trung bnh ca d i vi c hai trng hp. Hai gi tr ny c khc nhaukhng ?

- Phng php ny c th p dng c trong iu kin cc x nghip cng nghip khng ?- Vai tr ca cc mu trng trong th nghim xc nh tn hiu.


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3.6. TH NGHIM 6. PHP TH C LNG LN 25

3.6 Th nghim 6. Php th c lng ln

3.6.1 Mc ch

- Lm quen vi hai phng php cho im: cho im trn thang v c lng ln;

- Kho st hm s tm sinh l m t mi quan h cht kch thch-tr li ca hai phng php

trn;- Nm c tm quan trng ca n v o khi a ra kt lun v kh nng to mi v.

3.6.2 C s

Trong nh gi cm quan c nhiu phng php lng ha cng cm gic. Trong s phngphp thng c s dng nhiu nht khoa hc thc phm l c lng cng cm gic trnmt thang tuyn tnh. Trong phng php ny, ngi th th hin cng cm gic c lng cca mnh bng cch nh mt vch trn thang. bit c ln ca cng cm gic, ngita tin hnh o khong cch t vch n im cui ca thang. Khong cch ny cng tng th hincng cm nhn cng tng mt cch tuyn tnh (c ngha l khong cch khc nhau gia cc sbng nhau biu din nhng s chnh lch nh nhau v cng cm gic). Mt phng php khccng hay c s dng l nh gi cng bng cch s dng mt thang c nhng s c nh(t 1 n 9 hay t 1 n 15) biu din nhng bc nhy bng nhau trong cm nhn cng camt ch tiu. Loi thang ny c gi l thang nhm (category scaling). Mt cch tip cn khc ivi thang nhm hoc tuyn tnh l nh gi cng cm nhn tng quan vi mu chun bngcch s dng mt thang ratio hoc phng php t l. Nhng t l bng nhau gia cc gi tr cdng m t cng (v d 1-phn-2 hoc 5-phn-10) biu din nhng t l bng nhau v cng cm nhn tng i. Dng thang ny c gi l c lng ln.

Cc loi thang phn nhm, thang on thng, c lng ln c phn tch v bnh

lun kh nhiu v tnh khng tuyn tnh trong cch s dng cc s [5]&[6]. Bn thn cc thang nycng khng tng quan tuyn tnh khi kt qu nh gi c v theo hm ca nng cht kchthch. S liu trn thang phn nhm v on thng thng thng i theo quy lut log (tc l c miquan h ng thng khi v theo hm nng cht kch thch), trong khi thang c lng lnli theo quy lut hm ly tha (tc l c mi quan h ng thng khi log s liu c v theo logca nng cht kch thch)[5].

Theo cc ti liu khoa hc thc phm, vic xc nh ngt tng i ca cc loi ng vcht ngt cng cao thng gy nn nhiu kh khn cho cc nh nghin cu. Nhng kh khn nyxut pht t cc n v o khc nhau. Mt monosaccharide nh fructose hoc glucose c th ngthn l mt disaccharide l sucrose mt t l tng ng (1-1) v khi lng. Nu mt nh ch binhoc sn xut thc phm, mua cht to ngt theo khi lng v quan tm n cc mc khc nhau ca

v ngt, th khi lng c th l i din tng i ph hp cho s so snh. Nhng nu mt nh haphn tch quan tm n qu trnh kt ni gia cc phn t v trung tm cm nhn v to nn v ngtth mt s so snh da trn n v mole (molarity-s lng phn t trn khi lng) tr nn thchhp hn. Bi tp sau yu cu sinh vin so snh ngt tng i ca sucrose (mt diasaccharide) vfructose (mt monosaccharide) theo c t l trng lng-trng lng v moles-trng lng.


1. Nguyn liu

- Bt tri cy lm ngt bng sucrose theo nng :

+ 2.5% w/v(0.073 M)+ 5.0% w/v(0.146 M)+ 10.0% w/v(0.292 M)+ 20.0% w/v(0.585 M)


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- Bt tri cy lm ngt bng fructose theo nng :+ 2.5% w/v(0.139 M)+ 5.0% w/v(0.278 M)+ 10.0% w/v(0.556 M)+ 20.0% w/v(1.111 M)

2. Tin trnh

Xp cng v ngt ca tng nng trong s 8 dung dch trn s dng c hai thang onthng v c lng ln vi dung dch 5.0% w/v sucrose c dng nh l mu chun (gncho gi tr 10). Mu chun s c nm trc mu th nht, th 3, th 5 v mu th 7 trongbi tp c lng cng . Tt c mi nh gi phi c tin hnh trn mt thang trckhi chuyn sang mt thang khc. Mt na nhm tin hnh trn mt mt loi thang trc khichuyn sang thang cn li. Sinh vin lm vic theo cp v thay i vai tr cm quan vin vthc nghim vin cho nhau khi nhim v hon thnh. Ktvs cung cp trt t gii thiu mu m bo trt t gia cc cht gy ngt l ngu nhin nhng hai ng khng ln ln vi nhau.Khi kt thc phn nh gi, ghi li kt qu ghi trn thang on thng bng cch o khongcch t im u mt tri n v tr nh du ca ngi th theo millimet. Sau a tt cs liu vo mt bng ln cho c hai phng php. Ktvs tnh gi tr trung bnh, lch chun

v sai s chun t cc s liu ny. Bng tnh cha kt qu ca s liu trn s c gi cho sinhvin qua email cng vi m mu v nng ng.

3.6.4 Bo co

Xy dng th sau da trn kt qu thu c:Trc X v trc Y

a) nng khi lng-trn-khi lng ca thang on thng

b) nng khi lng-trn-khi lng ca thang c lng ln

c) nng moles trn thang on thngd) nng moles trn thang c lng ln

e) logarith nng moles ca thang on thng

f) logarith nng moles ca thang c lng ln

g) log ca molaritylog thang on thng

h) log ca molaritylog ca thang c lng ln

Biu din ng thi kt qu ca hai cht gy ngt trn mt th c th so snh cng tng

i. Giy th semilog c th s dng cho semilog plots (e & f) v giy th log-log c th s dngcho th log-log plots (g & h). Biu din thanh lch chun trn th s hc (a - d).

Tr li v tho lun cc cu hi sau:

- ng no ngt hn sucrose hay fructose?

- S thay i v n v o ko theo thay i g v mi quan h gia ngt ca hai ng nghincu ?

- n v o no thng dng hn theo quan im thng mi ?

- n v no c ngha hn theo quan im ha sinh ?

- Gii thch kh nng to ngt tng i ca hai loi ng ?- Hm tm sinh l no ph hp nht i vi tng phng php cho im ?

- Nhn xt th logarit.


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3.7. TH NGHIM 7. PHNG PHP THI GIAN-CNG 27

3.7 Th nghim 7. Phng php Thi gian-Cng

3.7.1 Mc ch

- Lm quen vi phng php thi gian-cng (time-intensity);

- Lm quen vi hai phng php thu nhn cu tr li thi gian-cng : bng giy v bng my

tnh;- Chng minh s khc nhau gia hai sn phm khi xem xt ng cong thi gian-cng

3.7.2 C s

Bn cht ca qu trnh cm nhn cc tnh cht mi, v, hng-v, cu trc ca thc phm l ng chkhng phi l mt qu trnh tnh. iu ny xut pht t qu trnh nhai, th, tit nc bt, chuynng ca li v nut (Dijksterhuis, 1996). V l , cng cm nhn ca cc thng tin cm gicthay i t thi im ny sang thi im khc. Trong phng php profile cu trc, cm gic trngthi ca sn phm s thay i r rng trong ln cn u tin, nhai v phn d (Brandt et al., 1963).

Vn ny cng c th bt gp trong nh gi ru vang. Do hng v ca ru vang thay i nhiutheo thi gian khi tip xc vi khng kh, ngi th nm ru vang thng tranh lun v cm gicru vang "opens in the glass". S chp nhn ca ngi tiu dng i vi nhng cht ngt c cng khc nhau ph thuc vo s tng t ca profile thi gian ca chng i vi profile ca ngsucrose. Nhng cht ngt cng mnh c thi gian lu li trong ming lu c th t c ngitiu dng a thch. Ngc li, nu ko cao su (chewing-gum) c thi gian mi lu li cng lu hocru vang c thi gian kt thc mi v cng di th cng c ngi tiu dng a chung. Cc v dtrn cho thy profile thi gian ca mt thc phm c th l mt kha cnh quan trng ca gi tr cmquan ca chng.

Cc phng php cho im cm gic thng yu cu ngi th s ha cng cm nhn(gn cho cng cm nhn mt ch s). Nhim v ny i hi ngi th phi tnh gi tr trung

bnh hoc tch hp nhng cm nhn bin i ca h a ra mt gi tr cng duy nht hocch c lng cng ln nht. S gii hn ny lm mt i mt s thng tin quan trng. Haisn phm c th c cng profile cc tnh cht c trng nhng c th khc nhau v trt t xut hincc tnh cht hoc thi im cc tnh cht t cng cm nhn cc i. nh gi cm quan thigian-cng (TI) l mt c hi ngi th cn i cm gic cm nhn c theo thi gian. Vvy phng php ny cung cp cho chuyn gia cm quan v ngi s dng ca d liu nhng thngtin tc thi c ngha quan trng v cm gic cm nhn c. Khi theo di cm nhn ca ngi thi vi mt cht kch thch, t thi im bt u n khi cm gic kt thc, nh khoa hc cm gicc kh nng lng ha nhng bin i v cm nhn ca mt thuc tnh no theo thi gian. Khinhiu thuc tnh c theo di, profile ca mt t hp ca hng hoc cu trc thc phm c thcho thy nhng khc nhau gia cc sn phm v s thay i theo thi gian trong khi cc phng

php mt im duy nht ch cho php nh khoa hc cm gic bit cng ca thuc tnh ctch hp qua thi gian hoc l gi tr trung bnh theo thi gian ca ngi th.

Mt s nghin cu gn y[5]&[6] cho thy cng mt im tng quan tt vi gi tr cci TI, iu gi rng ngi th khng tch hp cm gic theo thi gian m ch nh gi cng cm nhn ln nht. Tuy nhin, gi tr TI cho php nh khoa hc cm gic quan st c bin ica cng cm nhn ca mt thuc tnh theo thi gian. i vi phn ln cm gic, cng cmnhn tng v ri gim dn, nhng i vi mt vi cm gic, nh cng cm nhn c ca tht,cm gic ch tng theo thi gian. Tng t, cm nhn ca s chy c th ch tng cho n khi t ntrng thi chy hon ton. Khi tin hnh mt nghin cu TI, chuyn gia cm gic c th thu cnhng thng tin sau y cho tng mu v cho tng ngi th: cng cm nhn cc i, thi gian

t cng cc i, vn tc v dng v ca s tng ca cng n im cc i, vn tc v dngv ca s gim cng n mt na cng cc i v n im kt thc v tng thi gian cacm gic. Mt vi thng s chung thi gian-cng c m t trong hnh 3.2.

Nhng thng tin b sung rt ra t TI l c bit hiu dng khi nghin cu cht to ngt hocsn phm nh chewing-gum, cht dng da,... l nhng sn phm c profile theo thi gian khc nhau.


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Hnh 3.2: th Thi gian-Cng [5]&[6]

Nhng thng s rt ra t TI nh "vn tc tng" v "vng di ng cong" l nhng c lng thuc vi gi thit ng TI c dng mt hnh tam gic. n v o ca "vn tc tng" l cng trn thi gian (thng l giy) cn ca "vng di ng cong" l mt i lng khng c th nguynv c rt ra bng cch s dng cng thc 1/2bh.


Nguyn liu

- Ko cao su (chewing-gum) b sung hng (qu, cam, chanh, bc h,...)

- Nc sauce Knor ( nhit phng)

- Nc tng Chinsu (cay)

- Nc trng ming, bnh crackers

Phng phpMi sinh vin s thc hin bi th nghim thi gian-cng cho tng sn phm vi hai phng php:s dng phiu tr li v phn mm Fizz (mt cng c thu thp s liu t ng) hoc trn mtmodun ca R c thit kt bi Sbastien L. Sinh vin chia lm hai nhm c kch thc nh nhau,mt na tin hnh th nghim bng Fizz hoc R (trong phng th nghim cm quan), trong khi nhmkia tin hnh th nghim trong iu kin phng hc vi cc phiu cu hi. Khi tt c sinh vin ktthc phn cho im, cc nhm i vai tr cho nhau.

Qu trnh di y c tin hnh bi tng sinh vin cho c hai phng php thu thp s

liu.* Th nghim vi ko cao su: a mt ming ko cao su vo ming v bt u nhai. Tip tc nhai

ko trong vng mt pht ca qu trnh nh gi. i vi nhm s dng phiu tr li, hy chobit nh gi ban u v cng mi qu ti thi im bt u nhai v thc hin 6 nh gilin tc cch nhau mi ln 10 giy. Sinh vin t "canh gi" cho mnh bng ng h eo tay hocng h treo tng. Nhm sinh vin s dng Fizzhoc R th lm theo hng dn trn mn hnh.

* Th nghim vi nng tng v nc xt: t 3 git nc tng Chinsu nhit phng lntrn bnh cracker v cho c ming bnh vo ming. Nhai ming bnh cracker trong vng 1 phtv nh gi, hoc l cho n khi khng cn cracker trong ming. Cho im "cay nng" ca

nc tng bng hai cch m t trn. Sinh vin ch t nht 3 pht sau ln nh gi utin hoc ch n khi cm gic trong ming tr nn bnh thng mi c bt u th mutip theo. Ngi th c th dng nc v/hoc n mt lng va crackers trong khong thigian ngh thanh v. Khi m bo chc chn trong ming khng cn crackers th tip tc thnghim trn vi nc sauce Knor.


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3.7. TH NGHIM 7. PHNG PHP THI GIAN-CNG 29

3.7.4 Cu hi tho lun

Vit mt bo co vi phn trnh by ngn gn mc ch, phng php, copy ca cc th kt quv sau tr li cc cu hi tho lun sau. Sinh vin c th s dng mt hoc hai ti liu tham kho.

- Trong hai phng php thu thp s liu (phiu tr li v Fizz/R), phng php no tt hn ?V sao ?

- Lm th no c th so snh cc kt qu cng mt nhit ? (Cu hi ny c th c trli thng qua vic s dng cc thng s ca TI: Imax, Tmax, Vn tc tng, Vng di ngcong,...)

- Cm gic nng thay i nh th no theo nhit ?

- Nhng sn phm no c th thch hp vi phng php TI ?


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3.8 Th nghim 8. M t mi-v

3.8.1 Mc ch

- Gii thiu cch tip cn cht lng thc phm thng qua mt hi ng m t

- Tham gia vo mt qu trnh phn tch cm quan

- nh gi cht lng ca vt liu lm chun trong phn tch cm quan

3.8.2 C s

Phng php m t mi-v (flavor profile) c ngun gc t nhm t vn Arthur D. Little vo cuinhng nm 1940. Vo thi im , nhm ny cung cp mt cng c chung nh gi tnh cht ctrng hng-v ca mt thc phm, v thay th phng php s dng chuyn gia th nm bng mthi ng gm cc thnh vin c hun luyn. Phng php ny chng t gi tr ca vic nh ginhng s khc nhau v hng-v gia cc sn phm thc phm ph thuc vo thnh phn v/hocvo nhng thay i v cng ngh.

Khng ging cc phng php thc nghim hin i, phng php lun ca flavor profile sdng mt qu trnh "ng thun" (consensus) . Nhm cc thnh vin hun luyn thng qua tho luns quyt nh thc phm c nh gi nh th no trn nhiu phng php khc nhau (cng cla chn bi nhm). Nhng nh gi ring bit ca nhm bt u bng lm vic c lp vi nhaunhng sau li tp hp li trong mt nhm kt thc flavor profile.

Trong thc t, phn tch thng k ca nhng nh gi ring l thng c s dng nhiu hnnhng qu trnh da trn s ng thun, mc d vy phng php flavor profile vn cn s dng mt vi phng th nghim. Trong th nghim tip sau y, sinh vin s a ra mt flavor profile camt loi nc qu bng cch s dng mt nhm nh vi c cht lm chun v sn phm cui cng.Nhng nguyn liu lm chun (nhng thnh phn ring l ca nc qu) c s dng nhm xcnh mt cch r rng v chnh xc thnh phn hng v m chng ta thng thy nht trong ncqu.

Th nghim ny s ch ra lm th no m mt sn phm phc hp, mt sn phm thc phmcui cng c th c phn mnh trong tm tr mt ngi th thnh nhng thnh phn mi v v.


Nguyn liu (cho tng nhm)Bt nghin hoc thnh phn nc qu:

- Nc p Tomato

- Pureed c ci ng (ti v qua ch bin nhit);

- Pureed carrots (ti v qua ch bin nhit);

- Pureed cn ty (ti);

- Pureed rau mi ty (ti);

- Pureed rau dip (ti);

- Pureed spinach (ti v qua ch bin nhit);

- Pureed ci xoong (ti);- Mui n, nc qu p;

- Ngoi cc ph gia khong 1 tha plastic cho tng ngi trong nhm, cn c nc, cc nh, khnlau v bnh trng ming.


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3.8. TH NGHIM 8. M T MI-V 31

Phng phpSinh vin lm vic theo nhm gm 4-5 ngi. Tng nhm bt u bng vic th cc thnh phn canc qu cho trn y (nm tng thnh phn v khng th nc qu cho n khi c yu cu).Cc thnh phn c th c th theo cc trt t bt k. Tp trung ch vo cc hng-v c trongtng thnh phn, ghi li cm nhn nu thy cn thit. Khi tt c cc thnh vin trong nhm thtt c cc thnh phn, sinh vin c th bt u thit lp flavor profile ca nhm:

- Bt u th mu nc qu. Tip tc lm vic c lp, ghi li tt c nhng hng-v cm nhnc trong nc qu theo trt t xut hin ca chng vo phiu tr li;

- S dng thang cho im sau ghi li cng ca tng cm gic:

)(= ngng, va cm nhn c.1= yu2= va phi3= mnh*** sinh vin c th s dng na im trn thang ny nu thy cn thit

- Khi tt c cc thnh vin trong nhm kt thc nh gi profile ca h v tha mn vi ktqu t c th tin hnh bc thng nht trong nhm. La chn ra trng nhm tp hpkt qu cc thnh vin v ng vai tr ca ngi "pht ngn".

- Thng qua tho lun ca nhm, so snh im cng hng-v ca nc qu. C gng tn s thng nht (ng thun) gia nhm ca bn v cng ca tng hng-v. S ngthun khng ch n gin l mt vic ly gi tr trung bnh ca cc nh gi ca cc thnh vintrong nhm (iu ny c th lm bng thng k rt n gin) m phi bao hm vic lm chott c cc thnh vin trong nhm t n s thng nht v mt im cng cho mt tnhcht hng-v ca profile.

- Mt khi nhm t n s ng thun, ghi li profile ca nhm trn phiu tr li chng va cho ktv.

3.8.4 Bo co

Tp hp cc bng kt qu ca tt c cc nhm v flavor profile ca sn phm nc qu. Tho lunv mc thng nht gia cc nhm khc nhau:

- Cc nhm c cng tm thy nhng hng-v chnh ca nc qu ?

- Cc nhm c xu hng thng nht v cng tng i ca cc ch tiu ?

- Nhn xt s thng nht ca cc nhm v hng-v mnh v hng v yu?- Nhng vn nhm gp phi trong qu trnh i tm s ng thun ca nhm ? Vic t n s

thng nht trong nhm v cng ca mt ch tiu no l d dng hay kh khn ? Tholun nhm dn n mt m t chnh xc v sn phm hay l phng din thng k (tnh trungbnh ca cc thnh vin) ? V sao c v v sao khng ?


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3.9 Th nghim 9. Xy dng thut ng

3.9.1 Mc ch

- Lm quen vi cc phng php s dng xy dng thut ng;

- Lm quen vi cc tiu chun a cc thut ng vo phiu cu hi;

- Lm quen vi vic thc hin cc ti nghin cu theo nhm.

3.9.2 C s

Trong hu ht cc tin trnh phn tch m t hin i, mt bc quan trng l la chn cc thutng (ch tiu) cn a vo phiu phn tch hay cn gi l ballot. iu ny c hon thnh thng quamt qu trnh sng to c gi l "group brainstorming" trong tt c nhng t c th c sdng m t sn phm hoc nhm sn phm c la chn t mt nhm ngi th.

Trc ht, trng nhm s a ra mt vi hng dn trng tm trong bc "group brain-storming"bng cch n nh mt s nhm cc tnh cht m t v sn phm nh tnh cht b ngoi,

hng, hng-v, cu trc v phn d, hu v. Mt khi tp hp xong danh sch tt c cc thut ngtim nng, s lng cc thut ng c gim bng cch loi tr cc thut ng trng hp v chngcho nhau, nhng thut ng c ngha rng v nhng thut ng th hin cm tnh (thch/khng thch).Thm vo , cc thut ng c ngha phc hp c th c phn tch thnh cc thnh phn ngin hn nu c th. Danh sch ca cc thut ng tip tc c lm tinh gim hn c th thng quanhiu bui hun luyn, cho n khi c hi ng thng nht v ngha ca tng thut ng v rngdanh sch thut ng m t mt cch y (tha ng) sn phm hoc l nhm sn phm quantm. Cui cng, nhm ngi th phi la chn thut ng "neo" cho u mt thp v cao ca thang.Nhng thut ng "neo" ny, cng vi cc mu chun nu cn thit, gip cho nhm nh gi nhngcm gic tng t trn nhng cc vng tng t trn thang.

Trong bi tp sau y, ktv ng vai tr trng hi ng v sinh vin s ng vai tr thnhvin ca hi ng. Mt phiu cu hi s c pht trin t mt tp cc sn phm nc qu v sau s c s dng nh gi mt tp nh hn cc loi nc qu ny. Sinh vin tham kho thmti liu ISO[18] c thm thng tin v phng php ny.


Nguyn liu: Ba loi c ph c t l cc thnh phn robusta:arabica ln lt l 25:75, 50:50 v 75:25.Cc mu c chun b trong iu kin ca PTNCQ.

Phng php: Ngi th nh gi sn phm th nht v ghi li trn mt t giy trng ttc cc thuc tnh cm quan m h t cm nhn c. Cc nhm cm gic nh b ngoi, hng,hng-v,... s c lc bi trng hi ng. Trng H s tp hp tt c cc thut ng t nhm tho lun. Vic tho lun theo nhm s tin hnh loi cc thut ng trng lp, khng c th vth hin cm tnh. Sn phm th hai s c tip tc th v sinh vin cng nh trng nhm li lpli cng vic trn y. Danh sch cc thut ng c th m rng thm hoc chi tit ha hn vi thngtin thu c t sn phm th hai. Thm vo , do th mt chui mu, nhm c th bt u c tng v nhng thut ng "neo" c th s dng cho tng thang v liu nhng chun vt l c cnhay khng lm sng t ngha ca cc thut ng c bit. Nu thi gian cho php, bi tp trn cth c lp li bng cch s dng sn phm th 3 lm tinh hn danh sch thut ng trn phiucu hi. Mc ch cui cng ca bi tp l khi qut ha mt phiu cu hi s dng cho bi tpsau ca lab.

3.9.4 Bo co

Sinh vin nhn mt bo co mu ktv. Cc nhm tp hp kt qu v vit mt bo co chung. Sosnh vi kt qu c sn ca cc nghin cu trc v a cc nhn xt sau vo bo co:


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3.9. TH NGHIM 9. XY DNG THUT NG 33

Lp bng tn s s dng cc ch tiu cho tng loi sn phm. Dng phng php phn tch yut (package FactoMineR, phn mm R) quyt nh danh sch cc ch tiu s la chn.

Tho lun phng php loi cc ch tiu cng m t mt tnh cht;

Tho lun v vai tr ca nhm trong vic xc nh danh sch cc ch tiu;

So snh phng php s dng v phng php ca ISO[18]. Cho bit u nhc im ca hai

phng php.


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3.10 Th nghim 10. Phn tch m t

3.10.1 Mc ch

- Lm quen vi phng php thu thp s liu ca php th m t1;

- Lm quen vi vic tin hnh mt ti nghin cu trong lnh vc cm quan.

3.10.2 C s

Trong phng php phn tch m t, cc thnh vin lm vic c lp lng ha cng cmnhn ca mt nhm thuc tnh ca mt sn phm hoc mt nhm sn phm. Nhng thuc tnh cla chn v lm "tinh" bi mt nhm lm vic trong bc generation (Th nghim 9). Mt hi ngc th c th nhiu ln sn phm cc bui th khc nhau m bo rng tng thnh vin tronghi ng s dng cc thuc tnh v thang nh gi theo cng mt cch. Vic a vo cc bui thtrn sn phm trc tip c th gip loi b nhng sai s nh hiu lm v nh ngha cc thut ng,cc thut ng "neo" v cch s dng thang.

Nhng nh gi hin ti c thc hin trn thang nhm (thang c cu trc) hoc thang onthng (thang khng cu trc). S liu c phn tch bng phng php Anova hoc t-Student nuch c hai sn phm c em i so snh. Phn tch m t bao gm gi tr trung bnh, lch chunc tnh cho tng ch tiu v sn phm. Cc so snh sau th nghim (post-hoc) c thc hin khi c3 hoc nhiu hn cc gi tr trung bnh c em i so snh nhm xc nh s khc nhau thc t mAnova khng pht hin c. Mt s kim nh post-hoc c th bao gm: Test so hngca Duncanv Test khc nhau nh nht c ngha.

Mt khi thng k m t c tnh ton v so snh, s liu c v trn th c thso snh bng mt mi quan h gia cc gi tr trung bnh v cc tnh cht. Mt dng th c sdng thng xuyn l th hnh mng nhn (spider) hoc th trc phn khc cho thy nhiugi tr trung bnh ca cc sn phm ln trn mt h trc c chia n v t tm. Mi trc (hoc bnknh hoc "spoke") trn th biu din mt thuc tnh trong phn tch m t. Nu t 5 n 8 thuctnh c biu din trn mi th, gi tr trung bnh s i din bi mt ng a cnh. Mt v cad th mng nhn (spider) c th tm thy trn website hoc trong ti liu ca PTNCQ. Trongbi tp sau y, sinh vin s nh gi 3 loi nc qu, s dng cu hi pht trin t trc trong thnghim th 9. Nhng nh gi s c thc hin trn phn mm Fizzca Sensory Lab. Sau khi thuthp s liu, vi s tr gip ca ktv, sinh vin tin hnh cc phn tch thng k m t (PCA, HCA,...)v Anova kt qu thc nghim, sau s dng th spider biu din s liu phn tch. Mt s vd ca v phng php phn tch Anova c th tm thy trong ti liu ca OMahony[17].


Nguyn liu: Ba mu c ph c chun b tng t nh trong th nghim 9.

Phng php: Tin hnh php th vi 8 ngi mt nhm trong PTN Cm quan. Ktv s acho sinh vin 6 mu tt c, mi mu c m ha bng mt s c 3 ch s. nh gi 6 mu bngFizz hoc s dng phiu tr li. Khi nhm cui cng thc hin xong vic nh gi, ktv s tin hnhphn tch Anova v phn tch m t nh vo Fizz, R hoc SAS ri v th mng nhn. Kt qu sc thng bo trn mng.

3.10.4 Bo co

Sinh vin gp ktv tham kho bo co mu. Nhng kt qu sau cn phi c a vo bo co;

- Bng cu hi phn tch QDA c ph1s dng kt qu ca th nghim 9


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3.10. TH NGHIM 10. PHN TCH M T 35

- Kt qu phn tch Anova;

- th mng nhn (spider) ca d liu thu c;

- Hnh chiu sn phm trn mt phng chnh th nht, vng trn tng quan cc ch tiu v ktqu phn nhm HCA.


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3.11 Th nghim 11. Php th th hiu

3.11.1 Mc ch

- Lm quen vi hai php th chp nhn v a thch;

- nh gi mt s yu t nh hng n s a thch;

- nh gi hin tng phn nhm th hiu ca ngi tiu dng.

3.11.2 C s

C hai phng php thng c s dng nh gi thi ca ngi tiu dng (thch hay ght;mua hay khng mua) i vi sn phm thc phm. Nhng phng php ny bao gm vic cho immc chp nhn v nh gi mc u tin (php th la chn). Php th u tin thng nhycm hn i vi s khc nhau gia cc sn phm; hai thc phm c th c nh gi cng mc chp nhn nh nhau tuy nhin ngi tiu dng vn thch sn phm no hn da vo s khcnhau rt nh c th pht hin c trn thang chp nhn. D liu ny dng nh ch cho ngi

ta bit sn phm no ngi tiu dng thch hn di mt iu kin cho sn. Trong khi , nh gimc chp nhn l mt php o n tng tng qut ca ngi tiu dng v vic h thch hay ghtnh th no mt sn phm (hoc mt kha cnh ca sn phm). nh gi mc chp nhn thngc tin hnh vi thang hedonic 9 im c pht trin bi Quartermaster Corps of the U.S. Army.Thang ny c gii hn bi mt u mt bi "cc k thch" v u i din bi "cc k ght" vi7 khong trng bng nhau c m t bi nhng mc a thch khc nhau. Kt qu ca nh giny c phn tch bng Anova hoc t-Student ([5]&[17]). Cc mu c th c trnh by theo bacch: 1) Theo trt t monadic nghim ngt: mt mu c nh gi trong mt bui th. 2) Theotrt t monadic tun t: nhiu sn phm c nh gi trong mt bui th. Ti mt thi im xcnh; ngi th ch nh gi mt mu v khng c quay ngc tr li mu nh gi trc .3) Theo trt t so snh: nhiu sn phm c trnh by ng thi cho ngi th v h c quyn quay

tr li mu nh gi.Thang o c th s dng 3 loi chnh: thang khng lin tc bao gm thang semantic 7&9 im,

thang khng lin tc dng s, thang lin tc dng on thng v thang khng lin tc dng hnh nh.

Php th u tin bao gm cc dng la chn a thch gia mt cp hai sn phm hoc chomt chui cc sn phm. Ty vo s lng mu m ngi th nhn c mt thi im xc nhm ngi ta phn bit:

Php th so hng 2 mu, thng c gi l so snh i: ngi th nhn 2 mu;

Php th so hng 3 mu hoc nhiu hn: ngi th nhn c nhiu hn 2 mu.

Khi s lng mu cn nh gi ln hn 2 m ta vn mun trnh by cho ngi th ti mt thi imxc nh 2 mu th, th vn c th s dng mt k thut thng gi l cp bi: mt cch tun t,ngi th nhn c mt phn hoc tt c p(p-1)/2 cp mu th c th t hp c t p sn phm;i vi tng cp mu, ngi th phi cho bit mu no h thch hn. Vic quyt nh loi php thty thuc vo tnh cht ca sn phm, ln s khc nhau gia cc sn phm, s sn phm v lngsn phm s dng trc khi a ra quyt nh v s a thch.

S liu ca php th a thch c phn tch bng thng k s dng lut nh phn. Cc phpth u tin c th bao gm mt qu trnh la chn bt buc khi tng thnh vin phi la chn snphm m h thch trong nhm gm 2 sn phm (hoc la chn theo mt trt t a thch ca mtnhm nhiu hn hai sn phm). Php th u tin c th s dng la chn "khng thch" hoc l

"khng xp hng". Tuy nhin vic s dng la chn "khng thch" s dn n nhng kh khn khix l s liu; phn b nh thc s khng cn ph hp na. Mt cch thch hp hn khi s dng lachn "khng thch" l dng mt thang nh gi mc a thch vi la chn "khng thch" nm gia thang (tng t vi thang chp nhn v ch khc mt ch l thang ny khng s dng cct "neo" a thch. D liu ca thang a thch ny c th c x l theo kiu c thng s da trn


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3.11. TH NGHIM 11. PHP TH TH HIU 37

gi thit Ho rng gi tr trung bnh ca tp hp nm gia thang. Trong bi tp di y, sinh vins lm thc nghim vi 3 nhm sn phm gm nc cam, bnh snack v phomat. C hai sn phmtrong mi nhm, cc sn phm ny s c nh gi thng qua hai nhm php th chp nhn v athch (cho im mc a thch).

thu c cu tr li tc th v nhanh chng ca ngi th, ch nn t mt cu hi v nhgi chung ca ngi th th hin qua mt im hoc mt v tr ca sn phm trn thang. Mc d vy,ngi t chc th nghim th hiu thng mong mun thu thp thm nhiu d kin c th hiu

c kt qu thu c. Bn cnh cc phng php phn tch chuyn bit nhpreference mapping,conjoint analysis, ngi t chc c th t ra cc cu hi, cho d n c th ch mang li t thng tin,vo thi im khi ngi th a ra nh gi cui cng. Cc dng cu hi c th t ra bao gm:

Cu hi m: cho php ngi th gii thch nhng g lm h thch hoc khng thch ca snphm h va nh gi. Trong trng hp ny khng c nh hng s ch ca ngi thvo mt tnh cht c bit ca sn phm. V d trong php th cp i th hiu khng nn tcu hi v hng-mi. Nu h mun, cu hi ny phi c a ra khi ngi th nh gi mudi dng: " Anh ch thch mi ca sn phm no hn?".

Cu hi ng: (ch c dng cho loi php th cho im th hiu), loi cu hi ny yu cu

ngi th cho bit kin v cc tnh cht mu, mi, trng thi,... ca sn phm nh gi. trnh hiu ng Halo, nn t chc hai ln nh gi khc nhau vi mt ln v nhn xt chung vmt ln v nhng nhn xt cc tnh cht. i khi thay v hi v cc tnh cht sn phm, ngita hi v nh mua hoc s dng sn phm. y l dng cu hi khng c khuyn co dokhng gip gii thch c th hiu ca ngi th v hn th, ngi th khng y thng tin(v gi c, nhn mc, bao gi,..) tr li cu hi trn. Cc thng tin lin quan n ngi th(thi quen tiu dng,...) ch c t ra sau khi ngi th nh gi tt c cc sn phm vcu hi ny phi c trnh by trn mt phiu ring.


Nguyn liuHai sn phm trong cc nhm sn phm sau c k hiu bng mt s ngu nhin 3 ch s:

- Nc cam

- Bnh snack

- Phomat

Phng php

Thc hin tun t php th chp nhn, php th u tin cho tng nhm sn phm theo trtt trn. Trc ht sinh vin nm sn phm u tin, nh gi mc chp nhn v cho im mc chp nhn tng qut sau nm v nh gi sn phm th hai. Tip tc th li hai sn phm nitrn theo th t ghi sn trn phiu v sp xp mc a thch (nu c) ca tng sn phm. Nghgii lao chng 1 pht gia hai nhm sn phm. S dng bnh cracker hoc nc trng ming nu cn thanh v hon ton. Tip tc th nghim ging nh lm vi nhm sn phm u tin cho nkhi hon thnh vic nh gi mc chp nhn v u tin i vi 3 nhm sn phm.

3.11.4 Bo co

Gii m v vit bo co gm mt s thng tin sau:

- T nh gi u tin ca hai sn phm ca tng c nhn, ngoi suy mu ny c a thch trongtng nhm sn phm. Ghi li m ca mu ny vo ct "sn phm a thch" ca phiu kt quca tng ngi. Nu bn nhn c la chn "khng a thch" cho mt nhm sn phm cbit no , ghi "NP" vo v tr thch hp trong phiu tng kt.


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- Chuyn phiu ghi kt qu ca c nhn cho ktv tng kt v tnh ton.

Thc hin cc phn tch sau y trn s liu thu c (phiu kt qu 1 v phiu kt qu 2):

- V th phn b mc chp nhn ca tng c th ( th ring r cho tng nhm sn phm).C tn ti nhng nhm khc nhau trong phn b chung?

- Tin hnh t-tests cp trn mc chp nhn i vi tng nhm sn phm. C s khc nhau cngha gia cc sn phm v mc chp nhn ?

- V th phn b mc u tin ca tng c th ( th ring cho tng loi sn phm). Cnhng nhm khc nhau khng ?

- Tin hnh t-Student cp trn mc u tin i vi tng nhm sn phm. C s khc nhau cngha gia cc sn phm v mc a thch ?

- Phn tch quyt nh la chn u tin ca sn phm s dng phn b nh phn (gi thit Ho:khng a thch). Chia phn tr li "khng a thch" thnh nhng phn bng nhau cho cc snphm hai nhm.

Tho lun cc cu hi sau y trn s liu thc nghim:

- C s phn nhm mc u tin ca nhm hay khng (rt thch mt trong hai sn phm trongnhm) ? C s nghch o mc u tin gia cc c th ?

- Nhn xt trn c thay i theo 3 cch nh gi mc u tin hay khng ? (cho im chpnhn, cho im a thch v a thch theo bin nh phn)

- Cho bit kin nu phi s dng php th u tin cp i (la chn bt buc) thay cho viccho im mc a thch. Lm th no c th d bo c l s liu s thay i di nhngiu kin nh vy ?

- C th thay i phng php trn y nh th no kim nh nhiu sn phm trong mtnhm ?


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3.12. TH NGHIM 12. TNG TC MI-V 39

Hnh 3.3: nh hng ca mi du ty n cng v ngt [10]

3.12 Th nghim 12. Tng tc mi-v

3.12.1 Mc ch

- Lm quen vi phng php nh gi cng trn thang im khng cu trc;

- Gii thiu khi nim tng tc cm gic mi v

- Gii thiu khi nim v nh hng yu t khung cnh (contextual effects) n cng cm

nhn;

3.12.2 C s

Mi tng tc mi-v thng gp trong cuc sng hng ngy ca chng ta nhng li t c ch n. Hin tng ny c ngun gc do s tch hp ca cc thng tin v gic v khu gic vng x lthng tin ca no b. S tch hp ny th hin nhiu hin tng tm sinh l, bao gm c s tnghoc gim cng v nhn bit v. Chnh iu dn n nhng ng nhn v v ca mt mi(mi vanilla c v ngt, mi chanh c v chua,...). Yu cu sinh vin tham kho ti liu ca Lawless[5], Nguyn[10] hiu thm c ch ca hin tng ny. Tng tc mi v chu nh hng ca yu ttm sinh l [10], tuy nhin iu khng n thun ch ph thuc vo trng thi ca ngi th mcn ph thuc vo iu kin th nghim (skewed & context effect) v s lng cc ch tiu cn nhgi. Nu ngi th khng c c hi m t cm nhn h s tch hp (chng-dumping) cc cm gictng t nhau to nn s tng cng v (Hnh 3.3). Hin tng ny c ngun gc sinh l l s giaothoa ca cc thng tin v gic v khu gic vng orbital-frontal cortex ca no ngi[10].

Hin tng tng tc mi v c nh hng n phng php lng ha cht lng QDA(sensory profile) thng c s dng trong nh gi cm quan. Khi s dng phng php ny, nudanh sch cc ch tiu cn phn tch khng y nhng thng tin cm gic m ngi th c thcm nhn c th kt qu nh gi cng s t nhiu b nh hng. V vy loi b hin tngtng tc mi v th nht thit ngi th phi c bit trc (hun luyn) cc ch tiu cn nh

gi. Sinh vin t chc bui th nghim lm hai phn, mt phn c nhng yu t thun li v mtphn c nhng yu t bt li hin tng tng tc c th xy ra. nh gi cng c thdng phng php so hng (t thp n cao) hoc phng php cho im trn thang cng . Cccht kch thch s dng c th thuc nhm kt hp (vanille-ng, chanh-chua) v khng kt hp(vanille-axit, chanh-ng).


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Nguyn liu:

Mi chanh (nng : 200ppm)

Mi vanille (nng : 400ppm)

Dung dch ng (nng : 85.6g/l) Dung dch axit citric (nng : 0.48g/l)

Sinh vin chun b cc dung dch th vi s tr gip ca ktv. Cc cht kch thch trn c chun btrong nc lc tinh khit v bo qun lnh trong vng 24h trc khi tin hnh th nghim.

Phng phpChia bui th thnh hai phn. Trong phn th nht ngi th nh gi cng ca cc mu c vkhng c cht mi, trong phn ny ngi th ch c nh gi mt ch tiu l cng cm gicv. Trong phn th hai, nhim v ca ngi th khng thay i tuy nhin h s c nh gi ttc cc loi cm gic c th cm nhn c. Sinh vin chia lm hai nhm, mt nhm ng vai tr

ngi chun b mu (pha dung dch, chun b m ha mu v gii thiu mu) v mt nhm ng vaitr ngi th. Sau khi th nghim hon thnh, cc nhm i vai tr cho nhau. S dng phng phpcho im trn thang khng cu trc v so snh bt buc 2-AFC thu nhn nh gi ca ngi th.Ngi th c hng dn cch cho im trn thang cng : h lm quen vi hai mu chun tngng vi cng cm gic thp nht v mnh nht trn thang im; tip theo h c hng dncch cho im cm gic trn thang ny. Sau khi s dng phng php cho im, ngi th nh gimu no c cng ngt hn bng phng php 2-AFC. Trong qu trnh chun b cch trnh bymu, ngi chun b th nghim ch tm cch khng ch hiu ng context bng cch xc nh trtt gii thiu mu thch hp. Cc nhm ln lt lm vic vi bn cp cht kch thch mi-v.

3.12.4 Bo coChuyn kt qu nh gi trn thang thnh im. Nhp s liu theo tng nhm ngi th trong cciu kin thc nghim. Biu din cng cm nhn v theo mi. S dng phn tch ANOVA xcnh nh hng ca cc mi n cng cm nhn v ngt v chua. Trnh by bo co theo nhmvi mt s tho lun sau:

Cho bit nh hng ca hai iu kin thc nghim n hin tng tng tc;

Phng php nh gi c nh hng n hin tng tng tc mi-v hay khng ? V sao?

Hin tng mi kch thch cm nhn v mnh nht quan st c vi nhng cp cht kch thch

no ? V sao ? Liu c th loi c hiu ng dumping hay khng ?

Hin tng tng tc mi v c nh hng g n phng php QDA s dng trong phn tchcm quan ?


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3.13. TH NGHIM 13. TI U HA THC N 41

3.13 Th nghim 13. Ti u ha thc n

3.13.1 Mc ch

- Lm quen vi phng php iu chnh ti u v thang "va " (just-about-right scale-JAR);

- Gii thiu khi nim v nh hng yu t khung cnh (contextual effects) n s a thch;

3.13.2 C s

iu chnh ti u l mt qu trnh trong mt thnh phn c b sung vo hoc ly ra khi thcphm sn phm ph hp vi tiu chun hoc ti u ha t n v tt nht. iu ny thngc thc hin vi mt vi thnh phn n gin ca cc sn phm cng loi nh l vic b sungng hoc axit vo mt loi ung. ung c th c ha trn (hoc iu chnh) v v v thnhphn ca ng hoc axit cui cng c th o c bng refactometer, pH, hoc cc thit b phntch khc. Kt qu ca phng php c th c nh gi thng qua vic so snh th tch hoc khilng ca sn phm trc v sau b sung mt thnh phn no .

Phng php iu chnh ny chu nh hng ln ca yu t khung cnh (context effect). Qutrnh b sung mt gia v v bn thn vic mong mun t n mt v no c th a n cm gicrng thc phm t n mt v ring tt hn trc khi c b sung gia v. iu ny xut phtt quy trnh thc nghim trong ngi th so snh nhng trng thi v gy ra bi nng longhn so vi mc hin ti. Khi c nh gi trong iu kin c nng long nh vy, mc hin tic th mnh hn gi tr thc ca n (10C thng Ging m hn 10C thng Su). Tng t nhvy, khi pha long xung t mt nng m c hn, ngi lm ra cng thc ny c xu hng dngli qu sm bi nng hin ti t ra qu i lp vi nng ban u. Nhng thng tin b sung vphng php ny sinh vin tm c trong ti liu ca Lawless & Heymann[5].

Mt phng php khc ca ti u ha l s dng thang JAR, i khi cn c gi l thang"Goldilocks". Cc mu c th c nh gi trn thang JAR nh l "qu yu", "qu mnh" hoc

l "va " theo mt continuumc bit no nh l v ngt hoc v chua. S liu thu c tuntheo phn b chun xung quanh gi tr trung tm ca thang (im "va ") cng l ch dn camt mc ti u v nng ca cht ph gia. Khi p dng k thut ny cn phi kim sot phn bca s liu th. V d, mt nhm ngi th c th bao gm mt nhm nh thch sn phm khng cv mn v nhm khc li thch xp c v rt mn. Nu nh hi ng ny th mt loi xp c v mnva phi, nhm s a ra kt qu gn vi im "va " tuy nhin khng c gi tr no xung quanhim tm c.

K thut s dng thang "va " cng thin v mt sai s gi l "sai s ti tm". Cho mtchui nng , nng ti tm s c kh nng c nh gi gn tm ca thang. Nh vy, JAR cth a ra mt n tng sai v v tr thc ca im "va "; n c th lm sai lch i mt t phthuc vo chui nng la chn. Phng php c lng im "va " thc thng s dngnhiu chui nng v nhng chui ny trng tm xung quanh nhng nng khc nhau. im "va" thc c ni suy t nhng c lng "va " ca tng chui nng .

Thc nghim sau bao gm mt ti u ha bng qu trnh iu chnh v mt thang JAR. Trongbi tp ti u ha, sinh vin b sung mt nc qu c nng ng cao vo mt nc qu longhn cho n khi nc qu c pha long gn vi ngt va (ti u). Pha long mt loi ncqu m c hn n mc ti u v o nng ng ca dung dch ti u ny bng refactometer.

Trong th nghim th hai, v ngt ca hai dy dung dch nc qu ngt c nh gi trnthang JAR. Gi tr im "va " thc s s c ni suy t bi tp ny.

3.13.3 Nguyn liu v Phng phpTi u ha bng iu chnhNguyn liu

Bn cc cha hn hp bt tri cy c ng, m ha v cha:


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- 100 ml ca bt tri cy khng ng(cc "Pha long")

- 100 ml bt nc tri cy rt ngt(cc "Conc.")

- 300 ml bt nc tri cy khng ngt (cc "")

- 300 ml bt nc tri cy rt ngt (cc "++")

Phng php

Sinh vin bt u vi cc c nhn "Pha long" hoc "Conc." theo s ch dn ca ktv. Sinhvin c yu cu nm dung dch trong cc, sau b sung mt lng nh hn hp trong cc k hiu"++" nu mun lm m c dung dch pha long hoc b sung lng nh hn hp k hiu ""nu mun pha long dung dch m c. Nm li dung dch trong cc "Pha long" hoc "Conc." mtcch u n cho n khi ngi th tin l t n mc optimal v ngt. Nu ngi th cm thy hi qu nng v ngt ti u, th c th b sung mt lng nh mu trong cc "" vo cc"Pha long" hoc mt lng nh ca mu trong cc "++" vo cc "Conc." Cho n khi ngi ththu c ngt ti u. Mt khi c cng v ngt ti u trong mu "Pha long" hoc mu"Conc.", hy ti u ha cng v ngt ca cc cn li bng phng php va thc hin. Mt khingi th ti u ha hai dung dch ("Pha long" v "Conc."), a hai mu ny cho ktv o nng

ng trong tng cc bng refractometer. Sinh vin gp ktv tham kho s liu quan h tuyntnh gia nng ng v brix tnh nng ng c trong mu. Bng kt qu s c thngbo ngay vi cc nhm th nghim.

Thang "va "Just-About-Right-ScalingNguyn liu

Bt gii kht hn hp c chia lm hai dy nng v ngt ca saccarose nh sau:

Dy pha long

- 2% w/v sucrose

- 5% w/v sucrose

- 8% w/v sucrose

Dy m c

- 8% w/v sucrose

- 12% w/v sucrose

- 16% w/v sucrose

Phng php

Di s tr gip ca ktv, sinh vin chun b mt tp phiu tr li v 6 mu hn hp ncung. M ha tng mu bi mt s gm 3 s ngu nhin. Nm cc mu theo trt t c ghi trnphiu cu hi v nh gi cm nhn v ngt ca tng mu trn thang JAR. Ngi th ngh gii laokhong 3 pht sau khi bn th xong mu th 3. Gii m kt qu bng cch gn cho mt gi trt 1-7 trong u mt tri (khng ngt) c gn cho im 1 v u mt phi (qu ngt) cgn cho im 7. Phng php ni suy c lng JAR thu c cho c hai dy nng s dng th mu v cch tnh cng c th tm thy trn website. Chuyn phiu ghi kt qu v th kt quJAR tnh c cho ktv. Bng kt qu s liu th v c lng ca tng c nhn trong nhm s cgi n tng ngi trong bui th nghim tip theo.

3.13.4 Bo coThc nghim ny phi c vit di dng mt bi bo gi ng tp ch khoa hc. Dng ca boco nh sau:

Phn tch s liu


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3.14 Th nghim 14. nh gi cht lng

3.14.1 Mc ch

Tip cn khi nim cht lng ton phn ca thc phm;

Lm quen vi phng php cho im cht lng theo tiu chun Vit nam TCVN 3215-79;

Nhn thc vai tr ca chuyn gia trong nh gi cm quan.

3.14.2 C s

Cht lng thc phm c cu thnh bi nhng tnh cht c trng v th hiu ca ngi tiu dng.Cc phng php phn tch cht lng trnh by th nghim 9, 10, 11 cho php tip cn hai khacnh trn ca cht lng thc phm thng qua vic phn tch cc thuc tnh v nh gi th hiungi s dng. Mc d c ng dng rng ri trn th gii, phng php phn tch m t (sensoryprofile) hm cha mt gi nh c bit: cc ch tiu nh gi c cng chung mt h s quan trngi vi cht lng chung ca thc phm. Thc t nghin cu th hiu ngi tiu dng cho thy, mc

a thch chung ca ngi tiu dng ch t l thun vi mt s tnh cht nht nh ca thc phm,c bit l cc tnh cht mi v v. Nguyen et al. [9] khi s dng phn tch hi quy bn phn nh nht(Past Least Square-PLS) cho thy mc a thch ca ngi tiu dng i vi sn phm c phch ph thuc vo mt s t (1/3) cc tnh cht cm quan ca c ph. Tiu chun TCVN 3215-79 lmt cch tip cn cho php nh gi cht lng tng hp ca mt thc phm da trn c s "nhgi cm th xut hin theo loi v cng ca cm th "[19].

Thc cht TCVN 3215-79 l mt phng php lng ha cht lng, cho php nh gi chtlng thc phm tng qut v qua phn hng cht lng sn phm. Phng php ny thc hinc bi cc chuyn gia l nhng ngi th "c kh nng nh gi khch quan, c kh nng phn bitcm gic tt, c kin thc chuyn mn tt v kin thc phn tch cm quan"[19]. Mt trong nhngim khc bit na ca phng php ny so vi sensory profile l cc tnh cht cm quan c

nh gi theo nhm (v d tnh cht mi, tnh cht v, mu sc, trng thi,...) v tng nhm ch tiuny c mt h s quan trng c xc nh t trc. V d i vi sn phm bia chai cc ch tiunh gi v h s quan trng ln lt l: Mu sc, trong: 0.4; to bt: 0.8; Mi: 0.8; V: 2.0. Ccchuyn gia nh gi cc ch tiu trn mt thang im c cu trc t 0: "sn phm hng" n 5:"snphm tt". im ca ch tiu l 5 nu nh "trong ch tiu ang xt, sn phm c tnh tt c trngv r rt cho ch tiu , sn phm khng c sai li v khuyt tt no" v im 0 nu " Sn phm ckhuyt tt v sai li mc rt trm trng, sn phm b coi l hng v khng s dng c na".Nh vy, hai tiu ch cn c cho im cc ch tiu tng hp l mc c trng v mc sai li, khuyt tt ca ch tiu. Da trn nn tng ca tiu chun 3215-79, mt s tiu chun khc c pht trin nh gi cht lng cm quan cc thc phm c th (ch, bia, ru, thuc l,...)

Trong th nghim sau sinh vin s dng phng php TCVN 3215-79 v 3218-93 nh gicht lng cm quan 5 sn phm ch xanh. Sinh vin tham kho thm cc tiu chun nm vngcc iu kin cn thit ca php th v phng php nh gi.


3.14.3.1 Nguyn liu

5 sn phm ch xanh theo vng nguyn liu v nh sn xut(Kim Anh, Bo Lc, Cu Tre,...);

B th ch loi c dung tch 150ml;

Cn ( chnh xc 0.5g), ng h ct, khay ng mu, giy trng; m in, tha, cc ng nc trng tha, khn tay;

Sinh vin chun b mu theo tiu chun 3218-93[20].


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3.14. TH NGHIM 14. NH GI CHT LNG 45

3.14.3.2 Phng php

Sinh vin chia lm hai nhm, mt nhm chun b mu cng vi ktvv mt nhm ng vai tr ngith. Cht lng ca ch c nh gi theo bn ch tiu vi h s quan trng ln lt l: ngoi hnh(1), mu nc pha (0.6), mi (1.2), v (1.2). Cc ch tiu ny c nh gi ring r trn thang 5 im(ch : im thp nht l 1 v im cao nht l 5) vi chnh xc n 0.5. im ca sn phm ctnh bng tng ca im trung bnh ca tng ch tiu c trng s. Sinh vin tham kho Bng 5[20]

nm mc cho im cc ch tiu ca sn phm. Phng php nh gi c th cc ch tiu ca chc th tm tt nh sau[20]:

Ngoi hnh: Ngoi hnh ca ch c nh gi bng cch mu ch ln khay c lt giy trng.Ch n ng u v mu sc v kch thc ca sn phm, t l cc phn gy v. Snphm c cht lng cao phi ng u v mu sc, khng c mu bc cnh, ngoi hnh hp dn.

Mu nc pha: Nc pha c chun b t 3g ch, c hm trong cc s trong vng 5 pht bngnc un si sau rt ra bt s nh gi. Dng mt quan st mu nc, m c, vinvng quanh bt s, c v tp cht. im 5 ca ch tiu ny ng vi mu "trong sng, snh,c trng".

Mi ch: nh gi ch tiu ny ngi th phi dng mi ngi nc pha v b ch. Cc sai lithng gp l mi ngi, khi, kht, i chua, mi l. Mi tt c th m t nh mi ca hoahng, mt ngt, qut, hnh nhn, cm. Ch nh gi tnh bn ca mi.

V: V ch c nh gi bng cch ung mt ngm nh, rt mu qua k rng, nh gi v cht, huv v hng ca mu ch. Ch n c

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