Technology of Preservation by Freezing

7/24/2019 Technology of Preservation by Freezing

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Technology of Preservation byFreezing


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COLD PRESERVATION:COLD PRESERVATION:

QQ1010=(K=(K1010+T+T) / K) / KTT

1010 ooC lowerin o! "e#$er%"&re #%'e el! li!e %l#o"C lowerin o! "e#$er%"&re #%'e el! li!e %l#o"

*o&le*o&le,,Cill "or%eCill "or

%e: 0 "o -: 0 "o - ooC. onl $ro"ro$ %n rowC. onl $ro"ro$ %n row

rel%"iel lowl, e,, ener%"ion "i#e !or $e&*o#on%rel%"iel lowl, e,, ener%"ion "i#e !or $e&*o#on%

%%il%le in !i i 234 o&r %" -%%il%le in !i i 234 o&r %" - ooC o#$%re* "o 52 r %" 0C o#$%re* "o 52 r %" 0ooC,C,

A "e "e#$er%"&re i lowere* "e $l%#% #e#r%ne o! "eA "e "e#$er%"&re i lowere* "e $l%#% #e#r%ne o! "e

or%ni# &n*eroe $%e "r%ni"ion !ro# li6&i* r"%llineor%ni# &n*eroe $%e "r%ni"ion !ro# li6&i* r"%lline

"o "e el in wi "r%n$or"%"ion o! ol&"e i e7"re#el"o "e el in wi "r%n$or"%"ion o! ol&"e i e7"re#el

*i!!i&l",*i!!i&l",

8eo$ile %n row %" illin "e#$er%"&re &" no"8eo$ile %n row %" illin "e#$er%"&re &" no"

nee%ril 'ille*, Cer"%in $ro"ro$e & %nee%ril 'ille*, Cer"%in $ro"ro$e & %

$e&*o#on% *o row %n* %&e !oo* $oionin,$e&*o#on% *o row %n* %&e !oo* $oionin,9

8oi"&re lo 9 % #% or role#, Pro"e"e* eer%l " e


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L%re $iee o! #e%" %re o!"en $%'e* in $l%"i % orL%re $iee o! #e%" %re o!"en $%'e* in $l%"i % or

$r%e* wi" %rio& #oi"&re rei"%n" o%"in, E %re$r%e* wi" %rio& #oi"&re rei"%n" o%"in, E %re

o%"e* wi" e*ile oil wi e%l "e #in&"e $ore in eo%"e* wi" e*ile oil wi e%l "e #in&"e $ore in e

ell, ;ee! %ein %" , !or eer%l wee' %" 5ell, ;ee! %ein %" , !or eer%l wee' %" 5 ooCCi "re%"e* wi" ?V r%,i "re%"e* wi" ?V r%,

@REEINB@REEINB: Te #o" $o$&l%r #e"o* %n* ro&": Te #o" $o$&l%r #e"o* %n* ro&"

oneniene %" o#e, @oo* #%"eri%l ein "o !reee inoneniene %" o#e, @oo* #%"eri%l ein "o !reee in

*ere%e, Peri%le !oo* %re "ore* %" 314oC or elow*ere%e, Peri%le !oo* %re "ore* %" 314oC or elow,,


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Freezing preservation Effective for retaining color, flavor and nutritive

value and oderately effective for retention of

te!ture" #n freezing process teperature of product is

reduced to $1% &' or bello( and crystallization

of the part of (ater and soe of solutes ta)esplace"

*upercooled or under cooled + teperature of(ater is lo(ered belo( its freezing point (ithoutany occurrence of crystallization and E-'E-. #/P0#/E-T of food uality" *o, changesduring freezing is attributable to (ater$ice

transforation not to reduction in teperature"


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ater ice transforation leads to crystall$foration of a systeatically organised solidphase fro solution 5solute and (ater6 or elt

5ice and (ater6" 'rystallization$ nucleation $ association ofolecules into tiny ordered particle of size

sufficient to survive and serve as the site for thegro(th of crystal"

#nitial freezing point $ teperature at (hicha tiny crystal of ice can e!ist in euilibriu(ith the liuid phase"


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T(o types of nucleation8 hoogeneous

and heterogeneous or catalytic occurs in

food aterials (hich involves foration ofnuclei ad9acent to suspended foreign

particles, surface fils or on the (alls of

containers + necessitates soe super cooling$teperature is lo(ered to soe critical value,

nucleation begins and further decrease in

teperature results in abrupt increase in

nucleation rate"


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'rystal gro(th$

it occurs 9ust bello( the elting pointteperature" 0t teperatures near the elting

point, (ater olecules add to e!isting nuclei inpresence to for ne( nuclei" ';*T0


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Teperature 5o'6

#nitial *upercooling

ate of ht reoval

&

1ateof

-ucleation

oo - $&o


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Teperature 5o'6

#nitial *upercooling

ate of ht reoval

&

1

ateof'rystal

gro(th

oo $&o


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*uspended atter or cellular coponents are

unable to igrate and ice crystals either for

around the or push the aside" ence infoods 5high oisture6, rate of ice crystal gro(th

is generally not liited by ass transfer

process, e!cept during the late stage of

freezing (hen teperature is lo(, viscosity is

high and unfrozen (ater is lo("

ence, heat transfer liits the rate of

crystallization because of large latent heat of

crystallization of (ater" ?ro(th rate is increased

greatly (ith increase of heat reoval"


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*lo( freezing8 1 & ' to 1& & '@h

'oercial freezing8 1& & ' to & & '@h

Altra rapid freezing8 above 1&& & '@hBuring freezing of tissues, (ater fro the solution istransferred into ice crystals of a variable but ratherhigh degree of purity" -on aueous constituents are

therefore concentrated in a diinished uantity ofunfrozen (ater" Anfrozen phase changes significantlyin p, titratable acidity, ionic strength, viscosity,freezing point, surface and interfacial tensions etc" .2

and '.2 ay be e!pelled out fro solution,acroolecules are forced closer together, (aterstructure and (ater solute interactions ay bedrastically altered"


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*lo(freezing

apid

freezing


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Colue changes

'oposition

*olutes or suspended atter + substitution

effect + reduce the fraction of (ater in syste"

intracellular air spaces + coon in planttissue + can probably accoodate gro(ing

crystals and thereby iniize changes in the

e!terior diensions"

Fraction of (ater that fails to freeze + bound or

supercooled (ater does not contribute to

e!pansion during freezing" Dind at" of solutes

influence at" of bound (ater tendenc for *'


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Teperature range under study + .bserved

changes in volue is a function of teprechange"

'ooling of the food prior to freezing 5concn

6 #ce foration 5e!pansion6

'ooling of ice crystals 5concentration6 *olute crystallization 5concentration6

'ooling of solute crystals present in

eutectics 5concentration6

'rystallization and cooling of non solutes

such as fat 5concentration6


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/a9or point + #ce crystals are relatively pure even

(hen they originate fro a cople! syste"

Proper to assign an e!pansion value appro! >

to the nty of (ater that freezes" Colue changesis not unifor through out the food + because

ost other constituents contract as the tep is

lo(ered + leading to localised areas of e!pansion5ice crystals6 and localised areas of concentration

+ li)elihood of stresses and possibility of

echanical daage + ore li)ely in plant tissues(ith its rigid structure and poorly aligned cells

than in uscle (ith its pliable consistency and

parallel arrangeent of cells 5fibers6"


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Effect of initial concentration on the decrease in

volue and the increase in /olality of the

Anfrozen PhaseAnfrozen51 liter6

Frozen

51 liter6

S S

S

S S S

S

S

S S S S

S

S

S S S

S

S

S

S

ice

SS S

S

SS

#ce

'onc in unfr s per liter 1 s per liter

'onc in unfr ph of fr sl 3& s per liter 3& s per liter

#ncrease in conc by fr 7G 2G

Colue of unfr ph aft fr 1@7 liter H liter0ount of ice fored @7 liter H liter


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Eutectic point or Eutectic teperature 0s the freeze concentration process

progresses solutes reach or e!ceed theirrespective saturation concentrations and

siultaneous crystallization of ice and solute

becoes possible" The teperature at (hicha crystallized solute can e!ist in euilibriu

(ith ice and the unfrozen phase is )no(n as

the eutectic point or eutectic teperature of

the solute"

-a'l8 $21"13&' sucrose8 $14&'

glucose8 $&' -a2'.3$2"1&'


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during the freezing and since only soluteconcentration in the unfrozen phase is

increased to a oderate level 5slight depressionof freezing point6, K$' e!ists as a long plateau(ith a negative slope" Buring the early stages offreezing, (ater separates as pure or nearly pure

ice crystals" Buring the late stages of part K$'and the entire '$B, eutectic i!tures and othertypes of cople! solids of largely un)no(nstructures and coposition ay for" Theseportions are especially cople! in tissuesbecause gro(ing ice crystals e!ist in and@oraong cells, thereby copeting (ith


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each other for space and for diinishing supply

freezable (ater" Keyond point ', each successive

gra of ice fored is responsible for a substantial and

successively larger increase in olality of the unfrozen

phase 5lo(er freezing point6" Kesides, reoval of a

given aount of heat energy can effect a uch

greater reduction of saple teperatures during theportion '$B than K$' because the saple at point '

contains uch less freezable (ater than it had initially"

Anless the teperature is (ell belo( the sapleJs

final eutectic point, the saple usually contains soefreezable (ater even after cooling to the point B" Fro

the other curves, it is clear that increased rates of heat

reoval causes the various stages of cooling and


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freezing becoes less distinct" 0t very great

rates of heat reoval they becoe

indistinguishable"


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freezing becoes less distinct" 0t very great

rates of heat reoval they becoe

indistinguishable" Freezing point depression8 the teperature at

(hich the first ice crystals can appear (hen

cooling is carried out under euilibriuconditions"

B t ti lt ti t t i i hi h


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Benaturation8 an alteration to protein in (hich

interolecular cross lin)ing ta)es place that

peranently changes the physical and cheical

properties of the protein" Brip8 the e!pressible fluid fro fish flesh" The volue

of drip increases denaturation"

Fatty fish8 ac)erel herring etc" contain a

considerable uantity of stored lipids" addoc) and

cod fish are non fatty or lean fish"

Freezer burn8 describes the area of a frozen product

in (hich the ice has subliated leaving the productdehydrated, porous and spongy" The phenoenon

can affect the entire surface and penetrate deeply

into the product"

T i i i th t t f th


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Tepering8 raising the teperature of the

frozen fish or product bet(een $&c and $1&&c

to perit echanical processes, such as

slicing"

?lazing8 it is carried out by uic)ly iersing

the frozen fish in very cold (ater iediately

after freezing (hich produces a protectiveshell of ice"

F i


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Freezing process8

Prefreezing treatents

Freezing

Frozen storage

Tha(ing

Each phase is

iportant toproduce food

products of

a!

ualityFruits and vegetables treatents8$ Luality of

fruits and vegetables follo(ing the freezing

process depends greatly on8variety chosen, gro(ing conditions, and

stage of aturity at harvest

ature for fruits and iature for vegetables

hi di ti tti d


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o ashing, grading, sorting, cutting, and proper

pac)aging are soe of the obvious operations"

o Deeping the aside soe eans ust beeployed to control enzye activity"

o Else undesirable changes in flavour, colour,

te!ture, and nutritive value (ill occur duringfrozen storage"

ocontrol of enzye activity is generally achieved

by blanching + e!posing to hot air or (ater"

o Enzye catalysed 5polyphenolo!idases6

o!idative bro(ning + light coloured fruits + deep

colouration + not b heatin + chan es desirable

. l ti ti f f it 'h i l


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.rganoleptic properties of fruits" 'heical

additives + inhibit enzyes + alter enzye

substrates + liits entrance of o!ygen" *.2,

sulphites, sulfurous acid, citric acid, alic acid

etc" inhibit activity of polyphenolo!idases or

reacts (ith substrate"

0scorbic acid + costly, effective agent for

controlling enzyatic bro(ning + also a valuable

nutrient + inhibits bro(ning by aintaining

polyphenolic substances to a reduced and

colourless state" 6"3 00 in sugar syrup reuired

for coplete effectiveness"


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*ucrose or sugar syrups + added to fruits + prior

to freezing + accoplishes several purposes 8

to contribute s(eetness

to retain volatile aroas

To decrease at of (ater frozen at any given

subfreezing tep

to lessen enzynatic bro(ning by acting as a

barier to the entrance of o!ygen"'ut fruits ust be protected + iersion in a

dilute sol of -a'l 51$36 is a ethod often used"

PP. are inhibited by chloride ions"

El i th f it i & 2 - *. f 4


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Else ierse the fruit in &"2 -a*.3for 4

sec follo(ed by in dip in &"2 D2P.45p

%"%6"

Prior to freezing overly soft fruits is fired to

soe e!tent by brief iersion in a sol

containing 'a2M

$ divalent calciu ions forcrosslin)s bet(een negatively charged polyers

of pectic substances"

Fi h L lit f f th d ) d fi h


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Fish8$ Luality of frozen$tha(ed$coo)ed fish +

*pecies

coposition especially fat content

size

ho( and (here caught

elapsed tie in the live state bet(n harvest fr"

the state of rigor (hen frozenuality (hen frozen

details of the freezing process

/a9or probles during freeze processing of fish


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/a9or probles during freeze processing of fish

.!idative deterioration

Behydration

Toughening

loss of 9uiciness

e!cessive tha( e!udate or drip

icroorganis

autolysis

To iniize contraction and lessen increase in

desirable that rigor ortis is copleted at a lo(


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desirable that rigor ortis is copleted at a lo(

non freezing teperature prior to freezing"

Freezing during rigor is undesirable" *tate of rigor

at the tie of freezing is less iportant (ith(hole fish than it is (ith fillets and saller pieces"

ence, freezing proptly after the catch or

harvest 5prerigor6 is recoended for (hole fish"

Andesirable o!idative changes ay be iniized

eliinating .2 5vacuu or flushing (ith inert

gases6 or providing a barrier to the entrance of .2

such as protective coating

avoiding containation (ith o!idative catalysts

adding antio!idants


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adding antio!idants"

0voiding irradiation including light"

Asing very lo( storage teperature or shortstorage tie"

0void dehydration by8$

applying a suitable protective coating to the

fish" ?enerally by ice glaze, gelatinous coating,

or conventional pac)age"educe Brip loss or tha( e!udate by

controlling the rate and e!tent of glycolysis prior

to freezin "

applying suitable cheicals 5polyphosphates6


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applying suitable cheicals 5polyphosphates6

follo(ing recoended practices for freezing,

frozen storage, and tha(ing"ater fr" to ice Tep ater fr" to ice Tep

56 o' 56 o'

& $2" $2"7

1& $2": 1 $2">

2& $3"1 2 $3"3

3& $3" 3 $3">4& $4"2 & $"2

7& $7"% :& $>"

%& $14"% >& $3&

*torage life of frozen foods at 1% o'


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*torage life of frozen foods at +1% o'

Products (ith storage lives of 3 ths or less +

/aalian eats, Ka)ery products etc"Products (ith storage lives of 3 to 7 ths +

/aalian eats, poultry, etc"

Products (ith storage lives of 7 to 12 ths + Ceg"

Fish, aalian eats, poultry, ba)ery products

Products (ith storage lives of 12 ths or ore +Fruits 5sugared6, vegetables, aalian eats,

fish, eggs,ba)ery products etc"


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Freezers

Priary freezers8 product is in contact (ith

refrigerant in the for of a cryogenic gas orliuid or solid"

/erits + very uch suitable for sall and thin

product, very sall ice crystals, insignificantdehydration, color, flavor, structural changes,

drip loss on tha(ing"

Beerits$ ay induce considerable theralstresses, large product ay display severe

crac)ing due to e!treely uneven cooling at

the surface and interior"


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*econdary freezers8 plate freezers refrigerantreoves heat by circulation (ithin the plates those arein contact (ith the product"

/erit$ different refrigerants are used to cool air (hichcan be used"

Beerits$ irregular shaped product are very difficult tofreeze, tie of freezing is very high, larger ice crystalare fored"

Tertiary freezing8 air blast freezers (hich is in turncirculated over the product"

/erit$ varied and irregular shaped product can befrozen, (ide variety of shapes, sizes are available"

Beerit$ freezer burn, drip loss etc"

#ndividual Luic) Freezing 5#LF6


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'ryoicroscopy8

icroscopical observations of cheical andbiological systes during cooling" /olish discovered

(ith ice@salt freeze i!ture no( a days coputercontrolled at &"&1 to 1&&&c per in cooling rate isavailable"

Teperature of ice nucleation in tissue

*ize shape and location of ice crystals around and(ithin cells or tissues

ate and echanis of propagation of ice crystallizn

/echanical effects of e!tracellular ice crystals on cells Coluetric response of cells during freezing

/orphological alterations occurring during freezing

Effects of cooling rate, cheical additives and otherfactors"


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Technology of Preservation by Freezing

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