Foods Under the Microscope
55
FOODS UNDER THE MICROSCOPE Updated: February 2, 2009. New information. Introduction Microscopy is a scientific discipline, the objective of which is to enlarge minute particles or structures in order to study them. Depending on whether the objects are biological, geological, or metallurgical, there is a wide variety of instruments and techniques suitable to achieve the objective. A good starting point on the Internet is the Microscopy in Wikipedia. There are many reasons to examine foods under a microscope. Low-magnification dissecting microscopes function as magnifying glasses and may be used for better views of the food structure. They show details of meat fibres or seed surfaces and spices which may be captured on film or a video tape using various attachments. They are the first microscopes to be used when examining a particulate food contaminant. Microscopy at a higher resolution helps to understand what happens to the original biological materials such as grains, muscles, or milk when they are processed into bread or pasta, ham or steak, yogurt or cheese. With industrial food production, developers of new foods need to know what causes a particular food to be elastic or spreadable (e.g.: string cheese and processed cheese) or why some foods, which are smooth under normal conditions, become gritty (e.g.: ice cream stored for too long in a freezer). Optical microscopes provide a higher resolution than dissecting microscopes and open completely new views at the specimens examined. They are relatively easy to use. Their price makes them affordable to any laboratory - even individual enthusiasts and students. Magnifications up to 2000x are achieved using this kind of microscopes. With a higher magnification,
description
SEM and TEM food analysis
Transcript of Foods Under the Microscope
FOODS UNDER THE MICROSCOPEUpdated: February 2, 2009.New !"#r$at#!.I!tr#du%t#!M%r#&%#py & a &%e!t"% d&%p'!e, t(e #b)e%t*e #" w(%( & t# e!'ar+e $!ute part%'e& #r &tru%ture& ! #rder t# &tudy t(e$. Depe!d!+ #! w(et(er t(e #b)e%t& are b#'#+%a', +e#'#+%a', #r$eta''ur+%a', t(ere & a wde *arety #" !&tru$e!t& a!d te%(!,ue& &utab'e t# a%(e*e t(e #b)e%t*e. - +##d &tart!+ p#!t #! t(e I!ter!et & t(e M%r#&%#py ! ./peda.T(ere are $a!y rea!& t# e0a$!e "##d& u!der a $%r#&%#pe. 1#w2$a+!"%at#! d&&e%t!+ $%r#&%#pe& "u!%t#! a& $a+!"y!+ +'a&&e& a!d $ay be u&ed "#r better *ew& #" t(e "##d &tru%ture. T(ey &(#w deta'& #" $eat "bre& #r &eed &ur"a%e& a!d &p%e& w(%( $ay be %aptured #!"'$ #r a *de# tape u&!+ *ar#u& atta%($e!t&. T(ey are t(e "r&t $%r#&%#pe& t# be u&ed w(e! e0a$!!+ a part%u'ate "##d %#!ta$!a!t.M%r#&%#py at a (+(er re'ut#! (e'p& t# u!der&ta!d w(at (appe!& t# t(e #r+!a' b#'#+%a'$atera'& &u%( a& +ra!&, $u&%'e&, #r $'/ w(e! t(ey are pr#%e&&ed !t# bread #r pa&ta, (a$ #r &tea/, y#+urt #r %(ee&e. .t( !du&tra' "##d pr#du%t#!, de*e'#per& #" !ew "##d& !eed t# /!#w w(at %au&e& a part%u'ar "##d t# be e'a&t% #r &preadab'e 3e.+.: &tr!+ %(ee&e a!d pr#%e&&ed %(ee&e4 #r w(y $e "##d&, w(%( are &$##t( u!der !#r$a' %#!dt#!&, be%#$e +rtty 3e.+.: %e %rea$ &t#red "#r t## '#!+ ! a "ree5er4.Opt%a' $%r#&%#pe& pr#*de a (+(er re'ut#! t(a! d&&e%t!+ $%r#&%#pe& a!d #pe! %#$p'ete'y !ew *ew& at t(e &pe%$e!& e0a$!ed. T(ey are re'at*e'y ea&y t# u&e. T(er pr%e $a/e& t(e$ a""#rdab'e t# a!y 'ab#rat#ry 2 e*e! !d*dua' e!t(u&a&t& a!d &tude!t&. Ma+!"%at#!& up t# 20000 are a%(e*ed u&!+ t(& /!d #" $%r#&%#pe&. .t( a (+(er $a+!"%at#!, +reater deta'& are re*ea'ed but &$a''er area& are &(#w!. I! addt#! t# &tru%tura' deta'& &u%( a& +'#bu'e& #r "bre&, &pe%"% &ta!!+ pr#%edure& $a/e t p#&&b'e t# d&t!+u&( pr#te!& "r#$ "at&, &tar%(, %e''u'#&e, $!era' %#$p#!e!t& et%. - b##/ e!tt'ed F##d M%r#&%#py by O'+a F'!t 3R#ya' M%r#&%#p%a' S#%ety M%r#&%#py Ha!db##/ 60, 7#& S%e!t"% Pub'&(er&, O0"#rd, U8 999:4 pre&e!t& !&tru%t#!& #! "##d &a$p'e preparat#! "#r $%r#&%#py a!d (e'p& t# !terpret t(e re&u't&. It & ''u&trated wt( $a!y $%r#+rap(&.E'e%tr#! $%r#&%#pe& are t(e &ub)e%t #" t(& &te. T(ey pr#*de a %#!&derab'y (+(er re'ut#! t(a! '+(t 3#pt%a'4 $%r#&%#pe&. H#we*er, &!%e e'e%tr#!&, a!d !#t p(#t#!&, are u&ed t# e!'ar+e t(e *ew& #" t(e &pe%$e!&, t(e re&u't!+ p(#t#+rap(& 3$%r#+rap(&4 are b'a%/ a!d w(te #!'y. F#r edu%at#! a!d ''u&trat#! purp#&e&, !d*dua' &pe%$e! %#$p#!e!t& &u%( a& &tar%( +ra!u'e&, "at +'#bu'e&, $u&%'e "bre&, %e'' wa''&, $%r##r+a!&$& et%. ! &u%( $%r#+rap(& $ay be (+('+(ted by "a'&e %#'#ur&. E'e%tr#! $%r#&%#py pr#*de& a $ar/ed'y (+(er $a+!"%at#! at a %#!&derab'y better re'ut#! t(a! '+(t $%r#&%#py but & $u%( $#re e0pe!&*e t# per"#r$. I!&tead #" '+(t, a bea$#" e'e%tr#!& +e!erated "r#$ a! !%a!de&%e!t tu!+&te! #r 'a!t(a!u$ (e0ab#rde 31a7;4 e'e%tr#de & u&ed t# $a+!"y t(e $a+e #" t(e &a$p'e. T(e e'e%tr#!& are !e+at*e'y %(ar+ed part%'e& w(%( be(a*e '/e radat#! (a*!+ a *ery &(#rt wa*e'e!+t(. T(ere are tw# $a)#r e'e%tr#! $%r#&%#py $#de& 2 &%a!!!+ e'e%tr#! $%r#&%#py 3SEM4 a!d tra!&$&! e'e%tr#! $%r#&%#py 3TEM4. T(ee'e%tr#! bea$ & "#%u&&ed u&!+ $a+!et% 'e!&e& ! b#t( /!d& #" $%r#&%#pe. I! t(e &%(e$at% da+ra$ #! t(e 'e"t, < 'e!&e& are &(#w! "#r TEM a!d #!'y tw# "#r SEM. T(e &pe%$e! ! p'a%ed !t# t(e pat( #" t(e e'e%tr#! bea$ 3S4 ! t(e TEM but ! t(e SEM t & p'a%ed at t(e e!d #" t(e "#%u&&ed e'e%tr#! bea$ pat(. T(e $a+e 3I$4 & pr#du%ed ! t(e "#r$ #" a &(ad#w #! a "'u#re&%e!t &%ree! ! TEM. =reater deta' #! $a+e "#r$at#! ! t(e TEM & a' a*a'ab'e. I! SEM, re"'e%ted a!d &e%#!dary e'e%tr#!& are pr#%e&&ed by a! e'e%tr#! dete%t#r t# "#r$ a ,ua& t(ree2d$e!!a' $a+e #! a $#!t#r &%ree!. S!%e t(e e'e%tr#!& w#u'd be ea&'y abrbed by ar, t(e $%r#&%#p% e0a$!at#! & %arred #ut ! *a%u#. T# e!&ure t(at t(e e'e%tr#!& w'' pe!etrate a t(! &e%t#! #" t(e &pe%$e! #r t& rep'%a, t(e e'e%tr#! bea$ & a%%e'erated ! t(e $%r#&%#pe. -! a!#de wt( a! #r"%e ! t& %e!tre & p#&t*e'y %(ar+ed. T(e !e+at*e e'e%tr#!& ru&( t#ward t a!d t(#&e w(%( are ! t(e %e!tre "'y, a%%e'erated, t(r#u+( t(e #r"%e t#ward t(e &pe%$e!. -%%e'erat!+ *#'ta+e #" 6 t# 20 /> (a& bee!u&ed t# d# SEM a!d ;0 t# ?0 /> (a*e bee! u&ed ! TEM #" "##d&.E!*r#!$e!ta' &%a!!!+ e'e%tr#! $%r#&%#pe& 3ESEM4 %a! be u&ed t# e0a$!e (ydrated 3water2%#!ta!!+4 &pe%$e!& at a redu%ed ar pre&&ure. I! t(& way, t(ere & !# !eed t# dry #r "ree5e t(e &pe%$e!. T(& & part%u'ar'y u&e"u' wt( *ery "ra+'e &pe%$e!& &u%( a& $#u'd& 3"u!+ a!d t(er &p#re&4 a!d p'a!t &pe%$e!& &u%( a& "rut& a!d *e+etab'e&. ESEM $%r#+rap(& (a*e bee! %#!trbuted by Mr. -.2F. @a!+. Tradt#!a' e'e%tr#! $%r#&%#py re,ure& t(at t(e &pe%$e! $u&t !#t re'ea&e a!y +a& #r *ap#ur w(e! !&erted !t# t(e tra!&$&! #r &%a!!!+ e'e%tr#! $%r#&%#pe. E0%ept "#r p#wdered "##d& &u%( a& "'#ur, &u+ar, #r $'/ p#wder, $#&t "##d& %#!ta! water. Dry!+ #r "ree5!+ at a *ery '#w te$perature #" 2900AC e!&ure t(at t(e %#!dt#! #" !#t re'ea&!+ +a& #r *ap#ur & $et.Tra!&$&! e'e%tr#! $%r#&%#py %a! by per"#r$ed u&!+ *ar#u& te%(!,ue&. T(e $#&t %#$$#! %#!&&t& #" e$bedd!+ t(e &pe%$e! ! a re&!, %utt!+ t(! &e%t#!& 39< t# 90 !$ t(%/4 u&!+ a $%r#t#$e, &ta!!+ t(e &tru%ture& wt(! t(e &e%t#!& 3u&!+ (ea*y $eta' &a't& &u%( a& #&$u$, 'ead, a!d ura!u$4, a!d p'a%!+ t(e &e%t#!& !t# t(e pat( #" t(e e'e%tr#! bea$. Ot(er TEM $et(#d& !%'ude !e+at*e &ta!!+, w(%( & a re'at*e'y &$p'e pr#%edure w(ereby $!ute part%'e& &u%( a& %a&e! $%e''e&, detary "bre, ba%ter#p(a+e, #r ba%tera are $0ed wt( a (ea*y $eta' &a't 'ut#! a!d app'ed #! a t(! e'e%tr#!2tra!&pare!t "'$. T(e &pe%$e! a!d t(e &a't 'ut#! are dred a!d p'a%ed !t# t(e $%r#&%#pe. T(e (ea*y $eta', w(%( &urr#u!d& t(e #r+a!% &pe%$e!, abrb& e'e%tr#!& but t(e e'e%tr#!& w(%( pa&& t(r#u+( t(e #r+a!% &pe%$e! "#r$ a B!e+at*e'y &ta!edB $a+e. Meta' &(ad#w!+ & a!#t(er &$p'e te%(!,ue w(ereby t(e &pe%$e! & dred #! a tra!&'u%e!t "'$ a!d t(e! & B&(ad#wedB wt( p'at!u$ *ap#ur ! *a%u#. T(e t(%/!e&& #" t(e %#at!+ 3'e&& t(a! 0.00< $%r#$eter4 depe!d& #! t(e a!+'e #" t(e &ur"a%e &(ad#wed. T(e $a+e & "#r$ed by t(e e'e%tr#! bea$ w(%( pa&&e& t(r#u+( t(e d""ere!t t(%/!e&& #" t(e %#at!+ w(%( depe!d& #! t(e t#p#+rap(y #" t(e &pe%$e!B& &ur"a%e. Free5e2"ra%tur!+ a!d "ree5e2et%(!+ te%(!,ue& are t(e $#&t 'ab#r#u&. T(ey $a/e t p#&&b'e t# e0a$!e t(e &pe%$e! wt(#ut a'ter!+ t %(e$%a''y 3"0at#!4 #r p(y&%a''y 3de(ydrat#!, $pre+!at#! wt( a re&!, dry!+4. T(e &pe%$e! & rapd'y "r#5e!, t(e! & "ree5e2"ra%tured at a te$perature be'#w 2990AC a!d t(e "ra%ture p'a!e & rep'%ated wt( p'at!u$ a!d %arb#! et(er $$edate'y #r a"ter a %erta! per#d #" "ree5e2et%(!+, dur!+ w(%( a t(! 'ayer #"%e ! t(e &pe%$e! &ub'$e& #"" a!d re*ea'& u!der'y!+ &tru%ture&. T(e &pe%$e! & t(awed a!d t(e rep'%a & &eparated "r#$ t(e &pe%$e!, %'ea!ed "r#$ &pe%$e! re&due&, a!d e0a$!ed ! t(e $%r#&%#pe.I! &%a!!!+ e'e%tr#! $%r#&%#py 3SEM4, t(e &pe%$e! & e0a$!ed by a "#%u&&ed e'e%tr#! bea$. S#$e #" t(e&e e'e%tr#!& are re"'e%ted a!d #t(er& +e!erate& &e%#!dary e'e%tr#! "r#$ t(e +#'d %#at!+. 3- +reat *arety #" #t(er !tera%t#!& a' ta/e& p'a%e4. Se%#!dary e'e%tr#!& 3#r, ! #t(er app'%at#!&, ba%/&%attered e'e%tr#!&4 are u&ed t# "#r$ a! e!'ar+ed $a+e #" t(e &pe%$e! &ur"a%e. T(e !%de!t e'e%tr#!& %arry a !e+at*e %(ar+e a!d ! #rder t# be B!eutra'5edB a"ter t(ey (a*e %#$p'eted t(e e0a$!at#!, t(e &pe%$e! &(#u'd be e'e%tr%a''y %#!du%t*e. T(& & a%(e*ed et(er by %(e$%a' pr#%edure& w(%( $pre+!ate t(e &pe%$e! wt( #&$u$ #r, $#re "re,ue!t'y, by p(y&%a''y %#at!+ t& wt( +#'d, a +#'d2pa''adu$, p'at!u$, #r rdu$ 2 #%%a!a''y b#t( pr#%edure& are %#$b!ed. Meta' %#at!+ pr#*de& a pat( "#r t(e e'e%tr#!&. I" t(& pat( & !terrupted 3by !%#$p'ete $eta' %#at!+ #r by %ra%/&4, t(e e'e%tr#!& &t ! t(e area t(u& 'ated a!d repe' a!y e'e%tr#!& ! t(e !%de!ta' bea$ ! a%%#rda!%e wt( t(e ru'e t(at e'e%tr%a''y %(ar+ed part%'e& #" t(e &a$e %(ar+e repe' ea%( #t(er. T(u& t(e area #%%uped by t(e &tat#!ary !e+at*e %(ar+e & by2pa&&ed a!d %a!!#t be e0a$!ed. .(te &p#t& #r '!e& de*e'#p ! &u%( p'a%e& a!d t(e $a+e & %(ara%ter5ed a& &u""er!+ "r#$ %(ar+!+ art"a%t&.SEM &(#w& &pe%$e! &ur"a%e&. T# t(e u!!tated, &u%( $a+e& $ay appear "a$'ar, &!%e t(& & t(e way ! w(%( we per%e*e #ur e!*r#!$e!t, w(ere we a' &ee &ur"a%e&, "#r e0a$p'e, $'/ p#wder part%'e&. T(e $a+e& are #b&er*ed #! a $#!t#r a!d p(#t#+rap(ed u&!+ a 6e'/y I -, 8a'Hb M: E!%ap&u'at#! #" *&%#u& (+(2"at "##d& ! %a'%u$ a'+!ate +e' tube& at a$be!t te$perature. F##d Stru%ture 9, 9ar#u& rapd "ree5!+ pr#%edure&, part%u'ar'y (+(2pre&&ure "ree5!+, (a*e a' bee! de*e'#ped 2 deta'& $ay be "#u!d ! b##/& '&ted at t(e e!d #" t(& &e%t#! 2 ! "a%t, at pre&e!t, t(e pr!%p'e& a!d app'%at#!& &ee$ t# be better e0p'a!ed ! t(e #'der b##/& t(a! #! t(e .eb4. Ne+at*e &ta!!+ #" !"'ue!5a *ru& wt( a$$#!u$ $#'ybdate by M. Ner$ut F2G:T#p: Spe%$e! "ree5e2dred7#tt#$: Spe%$e! ar2dred7ar& !d%ate 0.9 O$ Fr#5e! &pe%$e!& are u&ua''y "ree5e2"ra%tured ! #rder t# e0a$!e t(e !ter!a' &tru%ture by SEM. Free5e "ra%tur!+ $ay be d#!e ! a &pe%a' apparatu& %a''ed t(e %ry#2&ta+e, atta%(ed t# t(e &%a!!!+ e'e%tr#! $%r#&%#pe. - bre" per#d #" "ree5e et%(!+ re$#*e& a t(! 'ayer #" t(e "r#5e! %e by &ub'$at#! t(u& a''#w!+ t(e 'd &tru%ture& t# e$er+e. T(e "r#5e! &pe%$e! & t(e! %#ated wt( +#'d. Free5e "ra%tur!+ $ay be %#$b!ed wt( %#!*e!t#!a' SEM. T(e &pe%$e! & %(e$%a''y "0ed, de(ydrated ! ab'ute et(a!#', "r#5e! a!d "ree5e2"ra%tured ! ',ud !tr#+e! 3et(a!#' d#e&!#t pr#du%e %ry&ta'& w(e! "r#5e!4. T(e "ra+$e!t& are t(awed ! ab'ute et(a!#', %rt%a'2p#!t dred, $#u!ted #! SEM &tub&, %#ated wt( +#'d, a!d e0a$!ed by %#!*e!t#!a' SEM. T(e be!e"t& #" t(& pr#%edure (a*e bee! #ut'!ed &e*era' para+rap(& be'#w a!d e'&ew(ere. Spe%$e!& de&t!ed "#r TEM $ay #r $ay !#t be "ree5e2et%(ed a!d t(e! rep'%ated wt( p'at!u$ a!d %arb#!. T(e &pe%$e! & t(e! re$#*ed a!d t(e rep'%a & %'ea!ed, %aptured #! a +rd, a!d e0a$!ed. Free5!+ & a' ad*a!ta+e#u& t# !e+at*e &ta!!+ #" $e &pe%$e!&. -r2dry!+ u&ed $#&t "re,ue!t'y d&t#rt& e*e! $!ute part%'e& &u%( a& &p(er%a' *ru&e&. Free5!+ t(e$ wt( t(e t(! 'ayer #" t(e !e+at*e &ta! &t'' #! t(e &upp#rt!+ "'$ a!d "ree5e2dry!+ pre&er*e& t(e +'#bu'ar &(ape& #" t(e *ru&e& a& (ad bee! &(#w! by M. Ner$ut ! F2G. Free5e2dry!+ & &$'ar'y u&e"u' wt( &pe%$e!& de&t!ed "#r $eta' &(ad#w!+ a& (ad a' bee! &(#w! by t(e &a$e aut(#r. T(e&e pr#%edure& w#u'd be u&e"u' wt( %a&e! $%e''e& a!d #t(er $!ute (ydrated %#rpu&%u'ar "##d %#$p#!e!t&.C#u'd "r#5e! %e %rea$ be e$bedded ! a re&!M H. D. =#"" pr#*de& t(e a!&wer a!d de%rbe& a! $p#rta!t preparat#ry pr#%edure %a''ed "ree5e &ub&ttut#!.I!"#r$at#! ! +reater deta' $ay be "#u!d ! t(e&e a!d #t(er b##/&:9. E'e%tr#! $%r#&%#py #" "##d& M. 8a'ab !: P(y&%a' Pr#perte& #" F##d&, M. Pe'e+ a!d E. 7. 7a+'ey 3ed&.4, pp. :6290:, ->I Pub'. C#., I!%., .e&tp#rt, CT, US-, 99?6.2. Free5e2Et%(!+ Te%(!,ue& a!d -pp'%at#!& E. 1. 7e!edett a!d P. Fa*ard 3ed&.4, 2D: pp., S#%QtQ Fra!Ra&e de M%r#&%#pe S'e%tr#!,ue, Par&, Fra!%e, 99D6.6. Free5e "ra%ture: Met(#d&, -rt"a%t&, a!d I!terpretat#!& K. E. Ra&( a!d C. S. Hud! 3ed&.4, 20: pp., Ra*e! Pre&&, New @#r/, US-. 99D9.:. Free5e2Fra%ture Rep'%at#! #" 7#'#+%a' T&&ue& C. St#'!&/ a!d -. S. 7reat(!a%(, 9D6 pp., -%ade$% Pre&&, 99Drtua' 1brary: M%r#&%#py pr#*de& '!/& t# *ar#u& te%(!,ue&, e,up$e!t &upp'er& et%. Y -!#t(er &te e0p'a!& *ar#u& /!d& #" $%r#&%#py a!d re"er& t(e reader& t# *ar#u& &upp'er&. Y 1!/& t# *ar#u& $%r#&%#py &te&.Y 1!/& t# *ar#u& &%e!t"% 'brare&.Su++e&t#!& "#r aut(#r& #" &%e!t"% rep#rt& a!d $a!u&%rpt& w(%( $ay $pr#*e t(er wrt!+ &/''& are pr#*ded at a!#t(er .eb &te.MI18M'/ a!d It& C#!&ttue!t&FOODS UNDER THE MICROSCOPEE*eryb#dy /!#w& t(at $'/ & ',ud. 7ut w(y & t #pa,ue a!d w(teM Or d#e& t (a*e a ye''#w&( t!tM .(y a!d w(e! d#e& t %urd'eM .(at & a%tua''y %urd'!+M I" y#+urt a!d %(ee&e areb#t( $ade "r#$ $'/, w(y are t(ey d""ere!t "r#$ ea%( #t(erM I& t true t(at t(ere are ba%tera ! b#t( y#+urt a!d %(ee&eM .(y are t(ey t(ereM -!&wer& t# t(e&e ,ue&t#!& $ay a'ready be "#u!d #! t(e I!ter!et.M'/ & pr#du%ed by a'' $a$$a' "e$a'e& t# "eed t(er !ewb#r!& a!d t(e ',ud "#r$ & $#&t %#!*e!e!t. T(& $ea!& t(at t(e %#!%e!trat#! #" !utre!t& & re'at*e'y '#w %#$pared t# "##d& %#!&u$ed by adu't&. C#w $'/ %#!ta!& 6 t# :E pr#te!, : t# :.
![[William J. Croft] Under the Microscope](https://static.fdocuments.net/doc/165x107/577c82ec1a28abe054b2d492/william-j-croft-under-the-microscope.jpg)
