TRNG I HC S PHM K THUT TP.HCMKHOA CNG NGH HO HC THC PHMMN HC: Ha Hc Thc Phm

ti: ENZYME LM SM MU TRONG THC PHMGing vin hng dn: ThS. ng Th Ngc DungNhm thc hin:STTH tn sinh vinMSSV

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Trng i Hc S Phm K Thut Tp.HcmKhoa Cng Ngh Ho Hc Thc PhmMN HC: Ha Hc Thc Phm ti:ENZYME LM SM MU TRONG THC PHMGing vin hng dn: Nguyn ng M DuynNhm thc hin:STTH tn sinh vinMSSV

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TP. H Ch MinhEnzyme lm sm mu trong thc phmThang 04/201424

NHN XT CA GING VINim s:

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TP.HCM, ngy..thng..nmCh k ca ging vin

LI CAM NLi u tin nhm xin cam n Khoa cng ngh ha hc thc phm a m mn hoc Ha Hc Thc Phm tao iu kin cho chung ti hoc hoi va tng hp nhng kin thc, ky nng a c hoc co th thc hin mt bi bo co hon chnh.ng thi, chng ti xin gi li cam n chn thanh n c ThS. ng Th Ngc Dung vin b mn cng ngh ch bin lng thc. C a mang n cho chng ti rt nhiu kin thc va kinh nghim thc t b ch. Hn th na, C rt nhit tnh gip nhm gii quyt nhng vn , thc mc gp phi v cho chng ti nhiu kin nh gi, nhn xt rt qu gi. Nh o, nhm co th thc hin bi bo co nay mt cach tt nht va hoan thanh ung thi han. Tuy nhin, do kin thc chuyn mn con han ch v cch hnh vn cha tt nn khng th tranh khoi nhng thiu sot, chng ti xin chn thanh on nhn y kin ong gop cua giang vin cun bo co sau hoan thin hn.

LI M U

Cuc sng ngy cng pht trin th nhu cu v thc phm ca con ngi cng tng ln. Nu nh trc kia, cng ngh bo qun thc phm ch cn m bo ch thc phm khng b h hng, m bo hm lng cht dinh dng l c th nay i hi cng ngh lm sao cho thc phm vn gi cht lng trong qu trnh bo qun vn chuyn m cn m qun v mt cm quan, hnh thc ti ngon. Trong s cc sn phm yu cu cn thit l rau qu v hi sn phi ti. Nhng cc sn phm ny thng c xu hng sm mu nhanh chng sau khi thu hoch. C hai nguyn nhn dn n s sm mu l do s oxi ha bi enzyme v oxi ha bi cc tc nhn khng bi enzyme. M thc cht yu t ch yu l do enzyme, bi v cc phn ng do enzyme nhanh, gy tc ng tc th. Hiu v bn cht, nguyn nhn v cch c ch enzyme sm mu ny l cn thit trong bo qun. Qua bi ny chng ta s bit c l enzyme g, c ch v ng dng chng trong cng ngh thc phm v cc ngnh lin quan.

TI LIU THAM KHOHa sinh cng nghip L Ngc Twww.fao.orgwww.wikipedia.orghttp://www.food-info.net/uk/colour/enzymaticbrowning.htmhttp://www.buzzle.com/articles/enzymatic-browning.htmlhttp://videosdigitals.uab.es/cr-vet/www/21254/Enzymatic%20Browning.htmwww.wholefoodsmagazine.comwww.biomedcentral.com/1471-2164/13/395

MC LC

ContentsNHN XT CA GING VIN3LI CAM N4LI M U5TI LIU THAM KHO6MC LC6Chng 1: Gii thiu v enzyme71.1 Gii thiu v enzyme71.2 Enzyem lm sm mu trong thc phm101.3 C cht ca phn ng sm mu(Polyphenol)101.4 Tc hi ca enzyme lm sm mu131.5 Li ch ca enzyme lm sm mu13Chng 2: Tnh cht, c ch v phn loi enzyme lm sm mu152.1 Tnh cht v c ch152.2 Phn loi162.3.1 Monophenol oxidase(Tyrosinase)172.2.2 O-diphenol oxidase(Catechol oxidase)172.2.3 Laccase17Chng 3: Vai tr sinh l ca enzyme lm sm mu(PPO)183.1 i vi thc vt183.2 i vi ng vt18Chng 4: Cc yu t nh hng ti qu trnh sm mu ca enzyme203.1 Nhit 203.2 pH213.3 Nng oxy21Chng 5: Cc bin php cng ngh kim hm s sm mu do tc dng ca enzyme trong qu trnh ch bin v bo qun225.1 Cac phng phap vt ly235.1.1 Phng php chn235.1.2 Phng php lm lnh265.1.3 Phng php ng lnh265.1.4 Phng php lm mt nc275.1.5 Phng php chiu x295.1.6 Phng php ch bin bng p sut cao305.1.7 X l bng phng php siu lc (UF)325.1.8 X l bng sng siu m335.2 Cac phng phap ha hc345.2.1 Tc ng n cc enzyme345.2.2 Loi b kim loi355.2.3 Loi b oxi365.2.4 c ch s to thnh melanin39Chng 6: ng dng ca enzyme lm sm mu PPO trong thc phm v cc ngnh cng nghip khc416.1 Trong ngnh cng nghip thc phm416.2 Trong ngnh cng nghip giy v bt giy416.3 Trong cng ngh mi trng416.4 Trong lnh vc y t426.5 Trong ngnh cng nghip dt may426.6 Trong cc ngnh cng nghip khc42Cu hi43

Chng 1: Gii thiu v enzyme

1.1 Gii thiu v enzymeTrong cuc sngsinh vtxy ra rt nhiuphn ng ha hc, vi mt hiu sut rt cao, mc d iu kin bnh thng v nhit , p sut, pH. S d nh vy v n c s hin din cacht xc tcsinh hc c gi chung l enzym. Enzymlcht xc tcsinh hcc thnh phn c bn lprotein.Nh vy, enzym l ccproteinxc tc cc phn ngha hc. Trong ccphn ngny, ccphn tlc bt u ca qu trnh c gi l c cht (substrate), enzym s bin i chng thnh ccphn tkhc nhau. Tt c cc qu trnh trong t bo u cn enzym. Enzym c tnh chn lc rt cao i vi c cht ca n.Hu ht phn ng cxc tcbi enzym u c tc cao hn nhiu so vi khi khng c xc tc. C trn 4 000phn ng sinh hac xc tc bi enzym. Hot tnh ca enzym chu tc ng bi nhiu yu t. Cht c ch l cc phn t lm gim hot tnh ca enzym, trong khi yu t hot ha l nhng phn t lm tng hot tnh ca enzym.

Tnh cht ca enzyme: Enzym c bn cht lproteinnn c tt c thuc tnh l ha ca protein. a s enzym c dng hnh cu v khng i qua mng bn thm do c kch thc ln. Tan trong nc v cc dung mi hu cphn cckhc, khng tan trongetev cc dung mi khng phn cc. Khng bn di tc dng ca nhit , nhit cao th enzym b bin tnh. Mi trngaxthaybazcng lm enzym mt kh nng hot ng. Enzym c tnh lng tnh: ty pH ca mi trng m tn ti cc dng:cation,anionhay trung ha in. Enzym chia lm hai nhm:enzym mt cu t(ch cha protein) nh pepsin, amylase... v ccenzym hai cu t(trong phn t cn c nhm khng phi protein)

Trong phn t enzym hai cu t c hai phn Apoenzym: phn protein (nng cao lc xc tc ca enzym, quyt nh tnh c hiu) Coenzym: phn khng phi protein (trc tip tham gia vo phn ng enzym), bn cht l nhng hp cht hu c phc tp.

Trung tm hot ng ca enzyme: Trong qu trnh xc tc ca enzym vng cu trc khng gian c bit tham gia trc tip vo phn ng kt hp vi c cht gi l "trung tm hot ng". Cu to c bit ca trung tm hot ng quyt nh tnh c hiu v hot tnh xc tc ca enzym. Trong "enzym 1 cu t", cc acid amin thng phn b trn nhng phn khc nhau ca mch polypeptid nhng nm k nhau trong khng gian to thnh trung tm hot ng. S kt hp ca cc nhm chc ca cc acid amin, thng gp l -SH ca cysteine, -OH ca serine, vng imidazol ca histidine, w-COOH ca aspartie v acid glutamic, -COOH ca cc acid amin cui mch... Trong "enzym hai cu t" ngoi mch polypeptid m cc nhm chc kt hp to trung tm hot ng, cn c cc nhm chc coenzym v cc nhm ngoi khc kt hp to thnh trung tm hot ng enzym cha kim loi, cc ion kim loi cng tham gia vo vic to trung tm hot ng Trong cc nhm chc tham gia to trung tm hot ng cn phn bit hai nhm: "tm xc tc" (tham gia trc tip vo hot ng xc tc ca enzym) v "nn tip xc" (gip enzym kt hp c hiu vi c cht) Mt enzym c th c 2 hoc nhiu trung tm hot ng, tc dng ca cc trung tm hot ng khng ph thuc vo nhau.

Cc c cht kt hp vi trung tm hot ng to phc hp enzym-c cht (ES)E + S ES->ES E + PS: c chtP: sn phm Yu cu: E v S phi b sung v mt khng gian v hp nhau v mt ha hc, c kh nng hnh thnh nhiu lin kt yu vi nhau. Chng lin kt sao cho c th to ra v ct t s dnh nhau c gy nn do bin ng nhit ngu nhin nhit thng.

Trong mt s enzym cn c "trung tm d khng gian" - nhng phn enzym khi kt hp vi cc cht c phn t nh no s lm bin i cu trc bc ba ca ton b phn t enzym lm cu trc trung tm hot ng thay i bin i hot tnh ca enzym.

Tnh c hiu ca enzyme:Enzym ch tc dng ln mt s c cht v mt s kiu ni ha hc nht nh trong phn ngtnh c hiu c hiu lp th: ch tc dng ln mt dngng phn quang hc. Enzym cng th hin tnh c hiu vi ccng phn hnh hc: ch tc dng ln mt dng ng phn cis hoc trans c hiu tuyt i: Enzym ch c kh nng tc dng ln mt c cht nht nh. Cu trc trung tm hot ng ca enzym phi kt hp cht ch vi cu trc ca c cht, mt khc bit nh v cu trc ca c cht cng lm enzym khng xc tc c. c hiu tng i: enzym c tc dng ln mt kiu ni ha hc nht nh trong phn t c cht m khng ph thuc vo bn cht ha hc ca cc cu t tham gia to thnh lin kt c hiu nhm: Enzym c kh nng tc dng ln mt kiu lin kt nht nh khi mt hay hai cu t tham gia to thnh lin kt ny c cu to nht nh. Enzyme c chia thnh 6 nhm ln: Oxydoreductaza: Xc tc c phn ng oxi ha kh. Transferaza: Chuyn v mt nhm no t cht ny sang cht khc. Hydrolaza: Xc tc phn ng thy phn Isomeraza: Chuyn ha gia hai dng ng phn ca mt c cht. Liaza: Xc tc qua trnh phn ct mt nhm no ra khi hp cht m khng c s tham gia ca H2O. Ligaza: Xc tc phn ng kt hp ca hai phn t km theo s ct t mi lin kt pirophosphat cao nng lng ATP.1.2 Enzyem lm sm mu trong thc phm

Hnh thc b ngoi, hng v, kt cu v gi tr dinh dng bn thuc tnh c coi l ngi tiu dng khi a ra la chn thc phm.Trong hnh thc b ngoi, mu sc l yu t u tin m ngi tiu dng nh gi cht lng sn phm. Mu sc c th b nh hng bi cc sc t t nhin nh chlorophyll, carotenoid v anthocyanin trong thc phm, hoc bi cc cc phn ng t enzyme v cc phn ng khng enzym. Sm mu do enzyme l mt trong nhng phn ng mu quan trng nht nh hng n cc loi tri cy, rau qu v hi sn. Sm mu do enzyme l mt qu trnh ha hc, thng xy ra trong tri cy v rau qu v nhm nh enzyme polyphenol oxidase, thuc nhm ln enzyme oxydoreductaza, c kh nng xc tc qu trnh oxi ha phenolic to thnh melanin, gy sm mu thc phm. S tc ng sm mu do enzyme ny c nghin cu nhiu nht trong tri cy, rau v hi sn. Ngoi ra, cc nh khoa hc v thc phm(rau qu, thc vt v sinh l sau thu hoch), vi sinh vt v thm ch v c sinh l cn trng v ng vt gip xc v ang nghin cu phn ng ny v s tc ng nhiu mt ca n.1.3 C cht ca phn ng sm mu(Polyphenol)Polyphenol, cn c gi l hp cht phenolic, l nhm cc cht ha hc c trong thc vt (rau qu) ng vai tr quan trng trong qu trnh nu ha bi enzyme, bi v n l cht nn cho mu nu.Cc hp cht phenolic chu trch nhim cho mu sc ca nhiu loi thc vt, chng hn nh to, n l mt phn ca hng v v hng v ca ung (nc to, tr), v rt quan trng chng oxy ha trong cc nh my.Polyphenol l nhng cht hu c thng phc tp, c cha nhiu nhm phenol (acid carbolic):

Cu trc 1: Phenol

Hnh 4: Cu trc 2 Theaflavin, mt polyphenol trong tr(Ngun)Polyphenol c th c chia thnh nhiu loi ph khc nhau, chng hn nhanthocyans(mu sc trong tri cy), flavonoid (catechin, tannin trong tr v ru) v khng flavonoid thnh phn (axit galic trong l ch).Flavonoid c hnh thnh trong cc nh my t cc axit amin thm phenylalanine v tyrosine.

Hnh 5: Mu sc ca to l do polyphenolBng 1:C cht ca phn ng sm mu thc phm c trong cc loi rau qu(Ngun t FAO)NgunCht phenolic

Toaxit chlorogenic (tht), catechol, catechin (v), axit caffeic, 3,4-dihydroxyphenylalanine (DOPA), axit benzoic 3,4-dihydroxy,p-cresol, 4-methyl catechol, leucocyanidin,p-coumaric axit, flavonol glycosides

B4-metyl catechol, dopamine, pyrogallol, catechol, acid chlorogenic, axit caffeic, DOPA

Chui3,4-dihydroxyphenylethylamine (Dopamine), leucodelphinidin, leucocyanidin

Cacaocatechin, leucoanthocyanidins, anthocyanins, tannin phc tp

Ht c phaxit chlorogenic, axit caffeic

C tmaxit chlorogenic, axit caffeic, axit coumaric, dn xut ca acid cinnamic

Nhocatechin, axit chlorogenic, catechol, acid caffeic, DOPA, tannin, flavonol, axit protocatechuic, resorcinol, hydroquinone, phenol

Tmtyrosine

Xoidopamine HCl, 4-methyl catechol, acid caffeic, catechol, catechin, axit chlorogenic, tyrosine, DOPA,p-cresol

Nmtyrosine, catechol, DOPA, dopamine, adrenaline, noradrenaline

oaxit chlorogenic, pyrogallol, 4-methyl catechol, catechol, axit caffeic, axit galic, catechin, dopamine

Laxit chlorogenic, catechol, catechin, axit caffeic, DOPA, axit benzoic 3,4-dihydroxy,p-cresol

Nho khaxit chlorogenic, catechin, axit caffeic, catechol, DOPA

Khoai tyaxit chlorogenic, axit caffeic, catechol, DOPA,p-cresol,p-hydroxyphenyl axit propionic,p-hydroxyphenyl acid pyruvic,m-cresol

Tmtyrosine

Khoai langAxit chlorogenic, axit caffeic, caffeylamide

Trflavanol, catechin, tannin, dn xut ca acid cinnamic

1.4 Tc hi ca enzyme lm sm muS ha nu do enzyme l mt trong nhng phn ng tc ng nghim trng i vi nhiu loi tri cy v rau qu, c bit l ging nhit i v cn nhit i. Ngi ta c tnh rng hn 50% tn tht l kt qu ca enzyme gy nu ha (Whitaker v Lee, 1995).Nhng s tn tht ny ng quan ngi v khin ngi ta mun bit r v enzyme ny v cch kim sot chng trong thc phm.Rau dip, khoai ty, khoai lang, nm, to, l, chui, nho, o, v mt lot cc loi tri cy v rau qu nhit i v cn nhit i khc, rt nhy cm vi mu enzyme gy nu ha v do gy ra thit hi kinh t cho nng hc. Mu nu cng c th nh hng xu n hng v v gi tr dinh dng.V vy s kim sot ca mu nu t thu hoch n ngi tiu dng l rt quan trng gim thiu thit hi v duy tr gi tr kinh t trong nng hc v thc phm. Hnh 1: Qu b sm mu do enzymeNgoi ra s ha nu do enzyme cn xy ra trong cc loi thy sn c bit l ng vt gip xc nh tm, cua, c bit nh cc sn phm c gi tr cao nh tm hm th cng d b tc ng xu bi enzyme ny. Mc d cc sn phm b nu ha ny khng c hi v khng nh hng n hng v v mi hng, nhng ngi tiu dng s khng chon cc sn phm ny, v h thng ngh n bao hm s h hng. C rt nhiu v d v cc sn phm thy sn nhp khu vo Hoa K, tr gi hng triu la, b gim ng k hoc mt hon ton gi tr do enzyme gy nu. Tht khng may, a s cc n phm ny c ngun gc cc nc ang pht trin, ni m thiu c khoa hc k thut ln c s h tng ngn chn, c ch enzyme ny.1.5 Li ch ca enzyme lm sm mu

Khi nhc ti enzyme gy sm mu trong thc phm, ngi ta thng c ci nhn tiu cc v n v thng suy ngh ti nhng nh hng c hi. Tuy nhin, mt s phn ng enzyme gy sm mu rt c li cho cc sn phm tr, caf, cacao, v cc sn phm tri cy kh nh nho, mn. Cc sn phm ny sau khi enzyme polyphenol oxidase kch hot phn ng pht trin mu nu c trng, n mt ngng mu theo yu cu, sau s cho c ch enzyme gi mu nu, gim thiu mt mu.

Hnh 2: Mu nu c trng ca socola.Ngoi ra, c nhiu nghin cu khng nh rng sn phm melanin ca qu trnh oxy ha cc hp cht phenolic nh enzyme PPO c kh nng khng khun, chng ung th v l cht chng oxy ha. V vy theo cc chuyn gia th khuyn khch chng ta s dng cc sn phm c cc hp cht phenolic v cc sn phm oxi ha t n nh enzyme PPO.

Chng 2: Tnh cht, c ch v phn loi enzyme lm sm mu2.1 Tnh cht v c chPolyphenol oxidase l mt tetramer c cha bn nguyn t ng trn mi phn t, lin kt gia cht thm v oxy. Enzyme xc tc qu trnh o-hydroxyl ca monophenols (phn t phenol trong vng benzen c cha mt nhm th hydroxyl n) to thnh o-diphenols (phn t phenol c cha hai nhm th hydroxyl). Chng tip tc xc tc qu trnh oxy ha ca o-diphenol to ra o-quinon. y l qu trnh polyme ho nhanh o-quinon to ra sc t en, nu hoc (polyphenol) l nguyn nhn ca mu nu tri cy.Axit amin tyrosine c cha mt vng phenolic duy nht m c th b oxy ha do tc ng ca PPO hnh thnh o-quinone. Do , PPO cng c th c gi l tyrosinases.(Ngun Wikipedia)PPO l c pht hin u tin nm v phn b rng ri trong t nhin. Chng c trong plastic v lc lp ca thc vt, mc d tn ti t do trong t bo cht ca senesing hoc tri cy chn. PPO c ng vai tr quan trng trong vic khng chng vi khun, virus v iu kin kh hu bt li. Ngoi ra, PPO cng c tm thy ng vt v c cho l lm tng kh nng khng bnh cn trng v ng vt gip st.

Hnh 2: Hnh thnh mu nuKhi s c mt ca oxy khng kh, cc enzyme xc tc nhng bc u tin trong vic chuyn i sinh ha ca phenol sn xut quinon v tri qua trng hp mang li mt dng polyme mu ti, khng ha tan gi l melanin. Cc melanin hnh thnh ro cn v c c tnh khng khun, ngn chn s ly lan ca s nhim trng hoc bm tm trong m thc vt. thc vt, nhng ging chu c iu kin khc nhit c mc PPO cao hn rt nhiu so vi cc ging mn cm hn.Mt v d v s hnh thnh ca melanins t mt polyphenol n gin, tyrosine, c th hin trong hnh bn di:

Hnh 3 : Hnh thnh melanins t tyrosine(ngun Hnh nh Ngun: fao.org).Polyphenoloxidase xc tc hai phn ng c bn: hydroxyl ha v qu trnh oxy ha.C hai phn ng s dng oxy phn t (khng kh) nh l mt ng cht nn.Phn ng khng ch ph thuc vo s hin din ca khng kh, m cn v pH ( axit).Phn ng khng xy ra ti acid (pH 8) iu kin.

2.2 Phn loiPPO bao gm monophenol oxidase, diphenol oxidase bao gm o-diphenol oxidase v p-diphenol oxidase(laccase). Monophenol oxidase gip thy phn gc monophenol to thnh gc o-diphenol. Oxidase diphenol oxy ha diphenol chobenzoquinones. T l ca oxidase monophenol v diphenol trong cy thng l 1:10 hoc thp hn 1:40.2.3.1 Monophenol oxidase(Tyrosinase)Monophenol oxidase xc tc qu trnh thy phn o-diphenols to thnh monophenols.Enzyme c gi l tyrosinase ng vt, L-tyrosine l cht nn monophenolic ln.Trong cy, cc enzyme i khi c gi l cresolase do kh nng ca cc enzyme s dng oxi ha cc cht nn monophenolic, cresol.2.2.2 O-diphenol oxidase(Catechol oxidase)Qu trnh oxy ha ca cht diphenolic to quinon vi s c mt ca oxy c xc tc bi diphenol oxidase.Oxidase diphenol nhn c nhiu s ch do t l xc tc cao v lin kt ca n vi s hnh thnh ca quinon, hnh thnh cc sc t mu nu, melanin.Khi s c mt ca ba yu t oxi, diphenol v enzyme diphenol oxidase th mt qu trnh phn ng xy ra to thnh quion(mu sm), tip tc qua qu trnh trng hp to thnh melanin. C ch ca phn ng oxidase diphenol vn cn cha bit v khng c trung gian cc gc t do c hnh thnh v oxy lin kt vi cc enzyme trc khi rng buc caocht nn-diphenolic. 2.2.3 LaccaseLaccase (p-diphenol oxidase, EC 1.10.3.2) (DPO) l mt loi c cha ng polyphenol oxidase.N c kh nng c o ca oxy hap-diphenols, do cho php n c phn bit vio-diphenol oxidase nh catechol oxidase.Laccases l mu xanh m mu trong trng thi tinh khit.Laccases l cc glycoprotein c trng lng phn t khc nhau, t 60 n 80 kDa, v mt hm lng carbohydrate khc nhau t 15-41%.Laccases tm thy trong nhiu loi nm phytopathogenic v trong mt s thc vt bc cao (Mayer v Harel, 1991).Laccases t thc vt bc cao v laccases t nm c bit n c trong t bo cht.Ngoi tr o (Harelet al. 1970) v m (Dijkstra v Walker, 1991), laccases khng xy ra trong tri cy v rau qu.Laccase l mt thnh phn ca h thng tng hp lignin trong m g (Boet al. 1993).Tuy nhin n l khng lin quan n ligninolysis trong mt s nm.Laccase tAspergillus nidulansc lin quan n s tng hp sc t (Hermannet al. 1983).Laccase sn xut bi cc loi nmBotrytis cinereacng lin quan n bnh tt truyn nhim m dn n nhim trng thi mm trong da chut (Viterboet al. 1993).

Chng 3: Vai tr sinh l ca enzyme lm sm mu(PPO)

cho cc nh khoa hc thc phm hiu r hn lm th no ngn chn enzyme nu ha, iu quan trng l phi hiu l do ti sao polyphenol oxidase hin din trong m thc vt v ng vt.Mc d bit v gi thuyt mt s chc nng ca PPO trong cc m, cc nh nghin cu vn ang c gng gii p chc nng ca enzyme ny trong c hai h thng ng vt v thc vt.3.1 i vi thc vtPolyphenol oxidase ln u tin c pht hin nm v thc t th chng phn b rng ri trong t nhin. Chng c tn ti trong platid v lc lp ca thc vt, ng thi tn ti t do trong t bo cht qu tri cy chn(Vaughn v Duke, 1984).PPO ng vai tr quan trng gip cho cy phng chng b nhim trng do vi khun, virus v iu kin kh hu bt li. Phenolics nh axit chlorogenic, axit caffeic v scopolin, cc cht nn ca enzyme ny c chng minh c biu hin tnh dit nm. PPO tn ti trong lc lp cn hp cht phenolic tch ly trong khng bo, khi cy b tn thng cc cht ny kt hp vi nhau, di s c mt ca oxi khng kh to quion v sau l to melanin gip ng t m cy, to thnh ro cn v c c tnh khng khun, ngn chn s ly lan ca nhim trng hoc bm tm trong m thc vt.Mc nhiu hay t PPO th hin tnh chng chu ca cy trc nhng iu kin bt li. cc cy m s chng chi vi nhng iu kin bt li c cha PPO nhiu hn gp nhiu ln so vi cc ging cy mn cm hn. H thng cc enzyme khc trong cy nh chitinase, peroxidase, lipoxygenase, phenylalanine ammonia lyase,b-1,3-glucanase, cng c biu hin tng khi cy b stress.3.2 i vi ng vtNgun: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC22812/Polyphenol oxidase tn ti trong c cn trng v ng vt gip xc nh mt zynogen hoc hnh thc propolyphenol oxidase v cng c cho l c kh nng khng bnh. Enzyme ny cho l lin quan ti min dch v nhn thc.Khi xm nhp vo c th ng vt, cc vi sinh vt tit protease, gy phn hy protein, gy bnh cho c th. Khi , propolyphenol oxidase c kch hot bi protease to thnh PPO, chng li s xm nhp ca cc vi sinh vt ny. Cht chuyn ha th cp khc c sn xut bi cc vi sinh vt, chng hn nh glucans, glycoprotein, laminarins, lipopolysaccharides, cng c th gy ra s kch hot propolyphenol oxidase.Ngoi tc dng l khng khun, PPO trong ng vt gip xc v cn trng cng lin quan ti qu trnh lm cng lp v kitin trong chu trnh tng trng. Cc enzyme ny cn nm trong lp biu b v hemolymph di dng propolyphenol oxidase. Khi lt xc, lc c th yu nht, cc prophenol oxidase c kch hot cho PPO. Cc diphenols b oxy ha to cc quion tng ng.Quinon hnh thnh phn ng vi cc nhm phn t protein lin k lin kt chng li vi nhau to mt mng cng, gip bo v c th trc nhng tc ng xu t bn ngoi.PPO trong ng vt gip xc phn b ch yu trong cc mai, tip theo l b xng ngoi bng, u ngc, PPO c lin quan n s hnh thnh m en ca ng vt gip xc sau khi cht. Hnh thnh m en l mt trong nhng cc vn quan trng ca ng vt gip xc, n lm gim ng k th hiu ca ngi tiu dng v cht lng sn phm. Cng hc t hnh thnh trong ng vt gip st thay i theo loi, do s khc bit ca cht nn v nng enzyme. Do , cn c mt s hiu bit r rng c tnh sinh ha v ng hc ca PPO l cn thit kim sot v hn ch hot ng ca n.

Chng 4: Cc yu t nh hng ti qu trnh sm mu ca enzyme

Phn ng sm mu do enzyme xc tc l phn ng rt thng xy ra trong qu trnh ch bin cc sn phm thc phm c ngun gc thc vt nh rau qu cc sn phm hp rau qu, cc sn phm ch thuc l... C nhiu yu t nh hng n phn ng ny nh cc nhn t sau : Nng c cht phenol Hm lng v trng thi ca polyphenoloxydase Nng oxy Nng quinon pH Nhit 3.1 Nhit

T l phn ng ca cc enzyme polyphenoloxydase c kim sot bi nhit Khi nhit tng, tng nng lng ng hc ( tn s va chm pht trin) tn s phc hp enzyme - c cht pht trin trn mt n v thi gian do tc phn ng tng qu trnh sm mu ca enzyme din ra nhanh hn. Khi nhit tng n khong 1000C s lm bt hot enzyme polyphenoloxydas hn ch qu trnh lm sm mu ca enzyme. V d qu vi: Hot ng polyphenoloxidase cao nht 20 C, v gim lin tc khi nhit tng cao cho n khi ngng hot ng hon ton 60 C.PPO vn cn hot ng trong thi gian 120 pht 40 v 50 C v c bt hot sau 10 pht 60 C

Biu nhit hot ng ca enzyme PPO trong qu vi

Bng 2: nhit bt hot ca mt s enzymeEnzymenh hng n thc phmNhit bt hot ca enzyme(0C)

Lipolityc acyl hydrolaseGy mi hi~ 75

LipoxygenaseGy mi hi~ 80

PolyphenoloxidaseLm sm mu~ 100

PeroxidaseGy h hng~ 135

Nu nhit thp --> qu trnh sm mu ca enzyme din ra chm hn.

3.2 pH

pH mi trng nh hng r rt n qu trnh sm mu ca enzyme v n nh hng n mc ion ha ca c cht, s hot ng ca enzyme polyphenol oxydase v nh hng n bn protein enzyme. H thp pH n 4,0 s lm c ch hot ng ca enzyme polyphenol oxydase.

S nh hng ca pH ti PPO trong qu vi3.3 Nng oxy

Nng oxy cng cao phn ng oxy ha polyphenol xc tc bng enzyme polyoxydase xy ra cng nhanh. Vic ngn chn s tip xc gia oxy vi b mt ct ca tri cy hoc rau hn ch cc phn ng sm mu do enzyme.

Chng 5: Cc bin php cng ngh kim hm s sm mu do tc dng ca enzyme trong qu trnh ch bin v bo qun(ngun ti liu tham kho : chng trnh cng ngh thc phm v an ton thc phm cai hc Wageningen, H Lan v cc trng i hc i tc ; Enzymatic Browning in Fruits, Vegetables and Seafoods Maurice R. Marshall1, Jeongmok Kim2and Cheng-I Wei3 )

S sm mu do tc dng ca enzyme khng xy ra khi t bo thc vt cn nguyn vn, iu ny xy ra khi t bo b tc ng nh ct,nghin,gt v, h hng. S sm mu xy ra do s oxy ha cht hp phenolic c trong khng bo ca t bo thc phm vi xc tc l enzyme polyphenol oxydase c mt trong t bo cht ca t bo thc phm. c tnh cm quan v ha sinh ca tri cy v rau qu chu nh hng bi s hnh thnh sc t. T l enzyme gy hin tng ha nu trong tri cy v rau c iu chnh bi cc hot ng polyphenol oxidase trong thnh phn ca cc m, thnh phn phenolic ca m, pH, nhit v hot tnh ca oxy trong m. Nh m t trong Chng 1, enzyme polyphenol oxidase xc tc qu trnh oxy ha ca phenol o-quinon, l cc hp cht c hot tnh cao. O-quinon, theo cch c hnh thnh thng qua qu trnh trng hp t nhin to ra cc hp cht cao phn t hoc cc cht mu nu (melanins).. Cc melanins c th phn ng vi axit amin v protein to ra mu nu. Nhiu nghin cu tp trung vo vic c ch hoc ngn chn hot ng oxidase polyphenol trong thc phm. K thut v c ch khc nhau c pht trin trong nhng nm qua kim sot cc hot ng enzyme khng mong mun. Nhng k thut ny c gng loi b mt hoc nhiu thnh phn thit yu (oxy, enzyme, Cu, hoc cht nn) t phn ng. Vic ngn chn s tip xc ca Oxy vi b mt ct ca tri cy hoc rau s lm hn ch cc phn ng ha nu. S sm mu do tc dng ca enzyme xy ra nhanh chng khi tip xc vi oxy. Hn ch s tip xc vi oxy c th bng cch ngm trong nc, xi-r, ngm nc mui, hoc bng cch x l chn khng. Enzyme polyphenol oxidase l mt tetramer c bn nguyn t ng. Vic loi b ng s lm thay i cu trc ca enzyme PPO, t lm mt kh nng xc tc ca n => hn ch s sm mu do tc dng ca enzyme . Cch hiu qu nht trong vic loi b ng l dng cc cht to phc. Bt hot oxidase polyphenol bng x l nhit nh chn hi nc c p dng trong vic kim sot hin tng ha nu trong tri cy v rau c ng hp hoc ng lnh. Tuy nhin x l nhit khng c p dng trong vic bo qun cc sn phm ti sng. Polyphenol oxidase xc tc qu trnh oxy ha ca cht phenolic nh axit caffeic, axit protocatechuic, axit chlorogenic, v tyrosine. Tuy nhin thay i tnh cht ha hc ca cc cht c th ngn chn qu trnh oxy ha. Mt s hp cht ha hc phn ng vi cc sn phm ca hot ng oxidase polyphenol v c ch s hnh thnh ca hp cht mu c sn xut ti cc bc phn ng khng men th cp dn n s hnh thnh ca hc t melanin. Kim sot s ha nu bi enzyme l mt trong nhng vn quan trng nht trong ngnh cng nghip thc phm v mu sc l mt thuc tnh quan trng ca thc phm nh hng n quyt nh ca ngi tiu dng. i vi ngi tiu dng thc phm c cc mu nu (c bit l tri cy) c xem nh l h hng.Mt s phng php c th c p dng trnh s ha nu bi enzyme l bt hot cc enzym hoc hn ch s tip xc gia oxy vi thc phm

5.1 Cac phng phap vt ly5.1.1 Phng php chn

X l nhit l phng php c s dng rng ri nht n nh cc loi thc phm v n c kh nng tiu dit cc vi sinh vt v lm bt hot cc enzym. Chn l mt trong nhng phng php c p dng c hiu qu nht ca x l nhit kim sot s ha nu bi enzyme trong tri cy v rau qu ng hp hoc ng lnh. Tuy nhin trong thc t ta khng dng phng php chn kim sot s ha nu bi enzyme trong thc phm ti sng. Ngoi ra phng php chn cng c mt s nhc im nh: Sn phm ty trng thng i hi mt bc lm mt trc khi ng bng, bc lm mt ny c thc hin bng cch ngm sn phm trong nc lnh dn n lm tn tht cht dinh dng, vitamin, hng v, mu sc, kt cu, carbohydrate v cc thnh phn ha tan trong nc khc; Phng php chn yu cu mt lng ln nc v nng lng, cng vi vn x l cht thi. Thit bi s dung: My chn hi nc nng kiu trc vt, Belzhytse, My chn hi nc nng kiu chy qua....My chn hi nc nng kiu trc vt, Belzhytse

My chn hi nc nng kiu chy qua

Nhit p dng trong vic x l nhit bng phng php chn l khc nhau i vi tng loi thc phm, ty thuc vo nhit bt hot ca cc enzyme c trong thc phm, cng nh bn cht ca sn phm thc phm. Thanh trng thng c thc hin nhit t 60 o C v 85 o C, trong khi cc k thut chn thng hot ng nhit t 70 o C v 105 o C hoc cao hn. Ni chung, tip xc ca oxidase polyphenol vi nhit trong khong 70-90 o C s lm mt hot tnh xc tc ca chng (Vamos-Vigyz, 1981).

Bng 2: nhit bt hot ca mt s enzymeEnzymenh hng n thc phmNhit bt hot ca enzyme (0C)

Lipolityc acyl hydrolaseGy mi hi~ 75

LipoxygenaseGy mi hi~ 80

PolyphenoloxidaseLm sm mu ~ 100

PeroxidaseGy h hng~ 135

Cc phng php chn:

Chn trong hi nc v nc si;Chn trong hi nc hoc chn trong nc si l mt loi x l nhit kim sot s ha nu ca enzyme trong tri cy v rau ng hp hoc ng lnh. Trng cc loi rau hoc thc phm trong nc si hoc hi nc cho mt khong thi gian ngn.Chn hi di hn chn nc si 1,5 ln. Chn trong hi nc v chn trong nc si c p dng rng ri trong vic bt hot cc enzym v to tnh n nh cho rau ng lnh, do t nh hng n hng v hay gy mt dinh dng v ri lon sc t v n l mt qu trnh tng i ngn. Chn cng ngn nga cht dip lc v carotenoid sc t tri qua qu trnh phn hy bi enzym. Thi gian v nhit phi c kim sot trong c hai chn. Thi gian bt hot nhit hon ton oxidase polyphenol l khc nhau vi cc sn phm thc phm. Chn nc si ngn chn sm mu trong khoai lang ng lnh bng cch gim ng k cc hot ng oxidase polyphenol (Ma et al. 1992). Chn bng l vi sng Chn bng l vi sng c th khng c hiu qu, v nghin cu cho thy mt s enzyme c th khng b bt hot.iu ny c th nh hng n hng v lm mt kt cu v mu sc.

5.1.2 Phng php lm lnh

Lm lnh lin quan n vic lu tr tm thi cc loi thc phm nhit cao hn nhit ng. Lnh v lm lnh c s dng ngn chn s h hng ca cc loi rau v hoa qu trong phn phi v bn l.Lm lnh c p dng thng xuyn cho bng ci xanh, qu, rau bina, u, chui, xoi, b, c chua T l phn ng ca cc enzyme xc tc c kim sot bi nhit . nhit thp, gim ng nng ca cc phn t trong cc cht phn ng s lm gim tnh di ng v "kh nng va chm " cn thit cho s hnh thnh cc phc hp enzyme-cht nn v cc sn phm ca chng. . nhit di 7 C hot ng ca enzym polyphenoloxidase b c ch, nhng cc enzyme khng bt hot.

Qu trnh lnh thng c thc hin bng hi nc, nc (hydrocooling), nc , hoc chn khng (lm mt chn khng).

5.1.3 Phng php ng lnh

T ng tip xc

Thit bi ng lnh : Bng chuyn cp ng, Bng chuyn ti ng, T ng tip xc Nh lm lnh, ng lnh c ch, nhng khng lm bt hot cc enzym.Sau khi r ng, cc hot ng ca enzyme s tip tc. ng lnh nhit -18 o C hoc thp hn thng c s dng cho vic bo qun lu di thc phm. C ch bt hot enzym nhit ng lnh c th c gii thch bi mt vi gi thuyt. Tappel (1966) xut rng cc cht ha tan, chng hn nh mui, ng, v carbohydrate khc l cc cht c ch enzyme c hiu qu nng cao. Trong trng thi bn ng lnh nng cht tan tng do s nng cao kh nng c ch cc enzyme c trong sn phm. Fennema (1975b) cho rng ng lnh c th thay i pH. Theo l thuyt ca ng tng cng tnh di ng ca cc ion hydro trong nc so vi trong nc s dn n nhng thay i trong nng m v thnh phn, gy ra nhng thay i trong pH axit Mt yu t khc lin quan n bt hot enzyme nhit ng lnh l lm nhiu lon cc nhm sulphydryl cn thit cho s hot ng ca mt s enzyme. Nhiu lon ca cc nhm sulphydryl l do xu hng tng ln ca s trao i SS-SH l kt qu ca vic tng nng ca cc nhm disulfide, nhng thay i v cht, v tng qu trnh oxy ha ca cc nhm sulphydryl do nng xy tng ln nhit ng lnh (Fennema, 1975b). Cc hi tho gn y a ra phng php loi b nh hng ca nc trong qu trnh lm ng lnh. Loi b nc trong qu trnh ng lnh gy ra nhng thay i v mi trng ca cc enzyme, mt cch tng t nh phng php lm mt nc. Nh vi bt hot nhit cao, lm bt hot nhit thp cng c nhc im ca n. ng lnh gy ra nhng thay i trong kt cu v to ra nhng tnh cht khc ca thc phm.

5.1.4 Phng php lm mt nc

Nc c nh hng rt ln i vi hot ng enzyme, n ng vai tr l mt dung mi v cht phn ng (Ashie v Simpson, 1996). Hot ca nc (aw) c nh ngha l t l p sut ring phn ca hi nc trn mt mu vi hi nc bo ha nhit tng t. Hot ca nc c th nh hng n cc phn ng trong mi trng rn hoc hn ch s di chuyn ca cc cht phn ng hoc thay i c cu hot ng ca cht nn v enzyme. Nhn chung, gim aw s dn n lm gim hot ng ca enzyme. Hot ca nc c th c kim sot bng bng cch lm kh hoc b sung cc cht lm gim hot ca nc nh cc polyol, ng v mui, tng tnh n nh v c ch s tng trng ca vi khun.

Cc phng php vt l Thng hoa ( sy chn khng ng lnh) loi b nc bng cch thng hoa (s thay i t rn thnh kh).

My sy thng hoa ( sy chn khng ng lnh) Sn phm c ng lnh v lm mt nc trong chn khng. Trong phng php ny nhit thp c p dng trong sut qu trnh c ch cc phn ng ha hc v sinh ha khng mong mun, gim thiu s mt mt ca cc hp cht thm d bay hi. Lm lnh nhanh chng trong sut qu trnh lm gim thiu s ha nu do enzyme v thng gi nguyn tnh cht cm quan ca sn phm, trong khi ng bng chm c phn km hiu qu trong vic gim thiu s ha nu do enzyme. Phng php vt l khc ca mt nc bao gm sy phun, bc x-, nng lng mt tri v l vi sng sy kh. Cc phng php ha hc: Mui c tc dng kh nc. Trong nng mui cao loi b nc t mi trng phn ng (tc l gim aw), lm cho n khng c sn cho cc tng tc nc protein, do lm gim hot ng ca enzyme. Mui cng c kh nng thay i nhit ng lc hc ca cc phn ng enzyme xc tc. Natri clorua, sucrose, v ng khc, glycerol, propylene glycol v xi-r ng bin i l mt s cht tan c s dng lm mt nc khi thc phm.

5.1.5 Phng php chiu x

Chiu x thc phm (i khi n c gi l thanh trng lnh) l mt phng php gim tn tht sau thu hoch thc phm, m bo cht lng v sinh, v to ra gi tr thng mi ln trong thc phm. Chiu x thc phm c o ch n s dng bc x ion ha ko di thi gian bo qun ca sn phm thng qua vic tiu dit cc vi sinh vt gy hi trong thc phm, c ch cc ha ng sinh l ca sn phm sau thu hoch (chn, mc mm) . Cc loi tht, hi sn, tri cy, rau, v cc loi ng cc c th c bo qun bng chiu x. Nhc im ca bc x l mt cht dinh dng v t c ngi tiu dng chp nhn, do phng php chiu x khng c s dng rng ri trong vic bo qun v ch bin thc phm Vit Nam hin nay. Tia gamma (t cobalt-60 hoc cesium-137), X-quang, v gia tc cc electron (chm electron) l nhng hnh thc ca bc x ion ha p dng trong ch bin thc phm. Chiu x thc phm cho c bo qun v ch bin c ng dng rng ri Hoa K. Nhng nh hng ca liu khc nhau ca bc x ion ha trn tri cy ti v rau qu c tm tt trong bng 4 (Kader, 1986). Bng 4. nh hng ca bc x ion ha trn tri cy ti v rau qu. Liu lng (kGy) Hiu ng quan st

0,05-0,15 c ch ny mm trong cc loi rau c, c, r; c ch s tng trng trong mng ty v nm

0,15-0,75 Dit cn trng

0,25-0,50 Chn chm tr ca mt s loi tri cy nhit i nh chui, xoi, u

> 1,75 Kim sot h hng sau thu hoch

1,00-3,00 Tng tc lm mm; pht trin hng v trong mt s mt hng

> 3.00 Lm mm qu mc; gy chn bt thng; gy ra mt s ri lon sinh l; gy hng v km

1 kilogray (kGy) = 1000Gy, l n v SI nng lng hp th (1 jun / kg) bc x ion ha. 1 Gy = 100 rad (1 rad = 100 erg / g), v 1 kGy = 100 krad

Chiu x Gamma lng thp dng cho tm ti lm gim hc t v tng ng k thi gian bo ca tm c lu tr trong ngn (Novak et al. 1967). Tuy nhin chiu x liu thp v tm sau khi tm hnh thnh hc t, dn n kh nng tng cao hn ca t l hc t. Lm gim hin tng ha nu gy ra bi enzyme trong c khoai ty v cc loi tri cy nhit i bng phng php chiu x gamma c nghin cu k bi Thomas (1984; 1986). Gamma chiu x ln n 1 kGy c ch ny mm trong c khoai ty v lm gim lng phenolic v thnh phn axit chlorogenic (Pendharkar v Nair, 1987). Mondy v Gosselin (1989) cho rng mt liu lng bc x khong 1 kGy t gy ra hin tng sm mu trong khoai ty so vi liu lng cao hn. Khi chiu x khoai ty liu lng chiu x cao hn lm v mng lipid v gii phng polyphenol oxidase t ty th gy oxy ha cht phenolic trong khng bo dn n hin tng ha nu. Do s ha nu do enzyme c th c gim thiu bng cch kim sot mc liu lng ca bc x ion ha c p dng.

5.1.6 Phng php ch bin bng p sut cao

Ch bip p sut cao cn c gi l High Pressure Processing(HPP)-ch bin cao p l mt k thut ch bin thc phm trong iu kin p sut cao (500-700 atm) tiu dit vi sinh vt v lm bt hot enzyme X l p sut cao gy ra nhng thay i nh trong thc phm.So vi x l nhit, HPP gi c hng v ti trong thc phm, v t lm thay i kt cu v dinh dng trong sn phm thc phm.X l p lc cao khng cn nhit trnh c vic lm mt hng v.Cng ngh ny l c bit c li cho cc sn phm nhy cm vi nhit, nhng vn cn rt tn km. Polyphenol oxidase l cht chu c p sut cao. ngng hot ng ca polyphenol oxidase c trong to pH 4.5 v 5.4, cn c p sut khong 5 -7 kbar (Nicoli et al. 1994). Oxidase polyphenol trong cc ngun khc nhau th cn c p sut nhit khc nhau (Bng 5). Weemaes et al. (1998) cho thy lm bt hot polyphenol oxidase t to, nho, b v l nhit phng (25 o C) cn p sut tng ng l 600, 700, 800 v 900 Mpa. Tuy nhin, polyphenol oxidase mn khng b bt hot nhit phng bng cch p sut ln n 900 Mpa.

Bng 5: n nh p sut ca PPO c ngun gc t nhiu ngun khc nhau.Ngun gc ca PPO Trung bnh p sut x l Kch hot / bt hot Ti liu tham kho

To chit xut du th (pH 4,5) chit xut du th (pH 5.4) chit xut du th (pH7) # 300 Mpa/25 o C/1min> 500 Mpa/25 o C / 1 pht # 300 Mpa/25 o C/1min> 700 Mpa/25 o C/1min # 100 Mpa/25 o C/1min kch hot ngng hot ng kch hot ngng hot ng ngng hot ng Anese et al. (1995)

B mt phn tinh khit 800 Mpa/25 o C ngng hot ng Weemaes et al. (1998)

Hnh ty enzyme tinh khit trong Tris m (pH 6,5, 0.01m) > 700 Mpa/25 o C/10 pht kch hot, l ti a mc 500 MPa Butz et al., (1994)

L trong lt mt phn tinh khit 400 Mpa/25 o C/10 pht 900 Mpa/25 o C kch hot ngng hot ng nh Asaka v Hayashi (1991) Weemaes et al. (1998)

Nho kh mt phn tinh khit 900 Mpa/25 o C khng ngng hot ng Weemaes et al. (1998)

Khoai ty trong khi 400 Mpa / NaCl > NaBr > NaI+ S c ch enzyme gy sm mu bng cch tng nng mui.+ Natri clorua c th hin l mt cht c ch PPO c hiu qu cao khi c s dng kt hp vi canxi clorua, axit ascorbic v axit citric. Vd: Hot ng oxidase Poplyphenol c quan st thy gim vi tng nng NaCl cho o (Luh v Phithakpol, 1972), c tm v b (Knapp, 1965). Mt ong: Mt ong c chng minh c ch enzyme nu.Do , vic s dng mt ong nh mt cht c ch mu nu t nhin l mi quan tm ca ngi tiu dng tuyt vi.Mt ong t ra c ch nu trong lt to, nc p nho.

Gim pH: Nhm Ionizable ca cu trc protein ca enzyme b nh hng bi pH ca mi trng thc phm.Cc nhm ny phi dng ion thch hp duy tr cu to ca cc cht hot ng, rng buc cht, hoc xc tc cc phn ng enzym (Segel, 1976).Nhng thay i trong trng thi ion ha ca cc enzym thng o ngc.Tuy nhin s bin tnh khng th o ngc c th xy ra trong iu kin pH cc oan.S n nh ca cht nn cng b nh hng bi nhng thay i trong pH, v cht c th tri qua s c ha di iu kin khc nghit ca pH Acidulants thng c p dng duy tr pH thp hn m cn thit cho hot ng xc tc ti u ca mt loi enzyme.Acidulants nh citric, malic, axit photphoric v c kh nng lm gim pH ca mt h thng, do khin polyphenol oxidase polyphenol oxidase khng hot ng Acid citric ( c trong cam, chanh v cc dng qu khc thuc chi Citrus)

N thng c p dng cc cp khc nhau, t 0,5 n 2 (phn trmw / v) phng nga nu trong tri cy v rau qu.Ngoi ra, n thng c s dng kt hp vi cc i l antibrowning khc nh ascorbic hay erythorbic axit v mui trung tnh ca h, cho thi ca prooxidants v cho ngng hot ng ca polyphenol oxidase

5.2.2 Loi b kim loiEnzyme thng c cha ion kim loi trong cu trc ca n.Loi b nhng ion c th lm cho enzyme khng hot ng. Nhng cht s dng trong cng nghip thc phm loi b ion kim loi bao gm axit sorbic, axit carboxylic (citric, malic, tartaric, oxalic, axit succinic v), polyphosphat (ATP v pyrophosphates), i phn t (porphyrin, protein), v EDTA,. EDTA (EthyleneDiamineTetraaceticAcid): l cht cng ha thng dng ( Cheating i l) Nh vo kh nng to phc bn vi ion kim loi (c lp hot tnh ion kim loi nng - chelation), ngi ta thng s dng EDTA khi s xut hin ca ion kim loi gy nh hng xu cho qu trnh sn xut Phc ca EDTA vi kim loi tan hon ton trong nc (khng phi to kt ta)

Hnh: Cu trc EDTA v phc vi kim loi EDTA thng c s dng kt hp vi phng php iu tr ha cht khc phng nga enzyme nu trong thc phm

Kojic acid

Kojic acidl mtchelationi l sn xut bi mt s loi nm, c bit lAspergillus oryzae, tn gi Nht Bn lkoji. Acid Kojic l mt sn phm ph trong qu trnh ln men ca go mch nha, s dng trong sn xut sake, ru go Nht Bn.N l mt cht c ch nh ca s hnh thnh sc t trong m thc vt v ng vt, v c s dng trong thc phm v m phm bo qun hoc thay i mu sc ca cc cht. N to phc mu vi ion st, ng Kojic acid c th c s dng trn cc loi tri cy ct ngn chnoxy ha mu nu, tronghi sn bo v mu hng v mu

Maltol+ N l mt dng bt tinh th mu trng, tan trong nc nng, chloroform v dung mi phn cc khc + N c tm thy trong v cythng rng lcy, trongthngkim, v trong rangmch nha + C cng dng tng t nh Kojic acid l in kt vicngtrung tm kim loi nh Fe3 +, Ga3 +, Al3 +

Hnh: Maltol phc vi kim loi

5.2.3 Loi b oxi Sulphiting i l: Ngn nga qu trnh oxi ha trong qu trnh sn xut Sulfit l nhng cht c ch c s dng rng ri nht ca enzyme nu.i l Sulphiting bao gm lu hunh ioxit (SO) v mt s hnh thc sulfit v c gii phng SO2theo cc iu kin s dng ca h.SO2: sulfur dioxide; SO32 -: sulfit;H SO3-: bisulphite; S2O52 -: Metabisulphite O2v mui sunfit to thnh axit cha lu hunh (H2SO3) v tn ti nh l mt hn hp ca cc loi ion, bisulphite (HSO3-) v anion sulfit (SO32 -) trong dung dch nc.Cc loi ion ch yu thay i theo pH, mi trng ion, hot ng nc, v nng ca mi.Axit dibasic tri qua ion ha theo s phn ng sau y:SO2H2O -> (H2SO3)--> HSO3-+ H+HSO3--> SO32 -+ H+ Trong ng hp tri cy, bisulfit natri c s dng ngn chn nu (gy ra bi qu trnh oxy ha) v tiu dit vi khun. Lu hunh dioxit nhanh chng phn ng vi qu trnh oxy ha cc sn phm v ngn khng cho chng gy suy gim hn na. Sulfite ngn chn nu bng cch gii phng ion sulfite sau tc dng vi oxy ngn chn s hnh thnh melanin Sunfit nh hng tiu cc tm n i vi sc khe: phn ng d ng ngi, sau khi n phi thc phm sulfit c iu tr bi bnh nhn hen nhy cm. Sau y l danh sch cc i l sulphiting v nng sut l thuyt ca h v sulphur dioxide,gii thiu mt phng php sunfit tiu th hng ngy chp nhn c 0-0,7 mg sulfur dioxide mi kg trng lng c th.Bng : Ha cht nng sut sulfur dioxide hin ang c php s dng trong thc phm nh cht bo qun (Trch t Green, 1976)Ha hcCng thcNng sut l thuyt (%)Kh nng ha tan (mg/100 ml)

Sulphur dioxideSO2100.011 20oC

Natri sunfit khanNa2SO350.828 40oC

Natri sunfit (Heptahydrate)Na2SO37H2O25.424 ti 25oC

Natri hydro sulfitNaHSO361.6300 20oC

Sodium MetabisulphiteNa2S2O567,454 20oC

Kali MetabisulphiteK2S2O557,61. oC

+ Sulfit hin ang p dng i vi s c ch hc t (blackspot) trong tm, khoai ty, nm, to, hoa qu v cc loi rau khc.Sulfit cng c p dng trong vic n nh hng v v mu sc ca ru vang.Nng sunfit cn thit kim sot enzyme nu rt khc nhau ph hp vi cc nguyn liu thc phm v thi gian cn thit c ch phn ng ha nu-L-ascorbic acid: ( vitamin C)

+ Hot ng nh mt cht chng oxy ha. xy c nhiu kh nng phn ng vi acid ascorbic, ch khng phi l vi cc hp cht phenolic trong cc loi rau qu. Mu nu khng tip tc cho n khi hu ht cc acid ascorbic c s dng trong cc phn ng.

O-diphenol + O2 O-quinone + H2O (1)O-quinone + Ascorbic acid O-diphenol + dehydro ascorbic acid (2)T (1),(2) :Ascorbic acid + O2 dehydro ascorbic acid + H2O+ Acid ascorbic c tnh axit trong t nhin, to thnh mui trung tnh vi cc cn c, v rt ha tan trong nc.L-ascorbic acid (vitamin C) v mui trung tnh khc nhau ca n v cc dn xut khc c cc cht chng oxy ha GRAS hng u s dng trn cc loi tri cy v rau qu v nc p tri cy, phng nga nu v phn ng oxy ha khc + Acid ascorbic gy ra mt mu vng ring bit khi c s dng trong cng tc phng chng hc t trong tm (Otwell v Marshall, 1986).N thng c p dng kt hp vi axit citric duy t tr mc pH c tnh axit hn.Ngoi ra, n cng c cho l c tc dng chelating trn ng nhm gi ca polyphenol oxidase (Whitaker, 1972b). Cysteine:

+ Cystein(vit tt lCysorC)[1]l mt -axit aminvicng thc ha hc HO2CCH(NH2)CH2SH . y l axit amin khng thit yu, ngha l c th ngi t tng hp c.+ Cysteine l mt cht c ch hiu qu ca enzyme nu.N c bo co l c hiu qu hn natri bisulphite nh mt tc nhn antibrowning (Kahn, 1985).Nng ca cysteine v thiol khc cn thit cho vic t c cc mc chp nhn c ca s c ch nu c chng minh l c tc ng tiu cc vo khu v5.2.4 c ch s to thnh melanin Cyclodextrins l mt nhm ca cc hp cht c to thnh t cc phn t ng lin kt vi nhau trong mt vng (cyclicoligosaccharides).

Vic s dng cc cyclodextrins cho vic loi b cc hp cht phenolic t nc p tri cy v rau sng c cp bng sng ch ti M (Hickset al. 1990).Cyclodextrins c cho l c ch hot ng oxidase polyphenol thng qua s hnh thnh ca khu phc hp bao gm polyphenol (Saperset al. 1989)Ngng hot ng i vi cc sn phm (thay i thnh phn sn phm)O-quinon, m l sn phm ca qu trnh oxy ha diphenol, c kh nng phn ng vi nhau, dn n s hnh thnh ca cht nh trng ca phenol ban u.Cc cht nh trng, trong c mtocu trc diphenolic, tri qua li qu trnh oxy ha dn n s hnh thnh ca cc oligomer ln hn cng mu khc nhau.Acid ascorbic (Hsuet al. 1988), cc hp cht thiol (Henze, 1956), Sulfit (Sayavedra-Soto v Montgomery, 1986), v cc axit amin (Kahn, 1985) tuy nhin c kh nng c ch s hnh thnh dimer v ti oxy ha bng cch gimo-quinon o-diphenols, hoc thng qua s hnh thnh ca cc sn phm b sung khng mu.

Chng 6: ng dng ca enzyme lm sm mu PPO trong thc phm v cc ngnh cng nghip khc

Trong nhng nm gn y enzyme Polyphenol oxidase thu ht c s quan tm ng k v Enzyme ny cho nng sut cao trong vic oxi ha hp cht Polyphenol. Nh tnh nng ny m polyphenol oxidase c ng dng trong mt s ngnh cng nghip nh: Cng nghip sinh hc, cng nghip thc phm, ngnh cng nghip giy v bt giy, cng nghip dt may, y hc v cng nghip mi trng.6.1 Trong ngnh cng nghip thc phmMc d polyphenol oxidase khng c li do gy phn ng ha nu trong mt s loi thc phm nh: to,b,chui,thy hi sn, nhng chng c th c p dng cho cc mc ch mang li li ch khc nhau.+ Polyphenol oxidase c s dng trong cng ngh ch bin tr, c ph, cacao hnh thnh mu sc v hng v khc nhau. +Polyphenol oxidase c th c s dng trong ch bin ung cho vic loi b cc phenolic ca bia, ru gim c ca bia, ru v tng thi gian bo qun.+S dng trong sn xut cc loi mt kh nh nho kh, mn. kh, to kh.+ Polyphenol oxidase, c bit l laccases c thm vo bt dng sn xut cc sn phm nng, to ra mt tc nhn oxy ha trn cc thnh phn bt v ci thin sc mnh ca cu trc gluten trong bt hoc sn phm nng (Rodriguez Couto v Toca Herrera 2006). 6.2 Trong ngnh cng nghip giy v bt giyTrong cng nghip giy yu cu loi b lignin t cc m ha g v ty trng bt giy. Thng thng ty trng bt giy c thc hin bng cch s dng cc tc nhn clo nhng phng php ny gy ra nhim c hi i vi mi trng.+ Cc ng dng ca laccases c tm thy thnh cng k t khi laccases lm cho bt giy ti sng hn, loi b c hm lng ln ligin t cc m ha g, m bo s ton vn ca cenllulose (Rodriguez Couto v Toca Herrera 2006) em li nng sut v hiu qu cao, tit kim nng lng. +Khi kt hp Peroxydase v laccase c tc dng tch cc trong vic x l dch lng trong qu trnh ty trng (cha cc sn phm b chlorin ha c kh nng gy nhim i vi mi trng) gim bt cc cht c hi thi ra mi trng so vi phng php s dng clo6.3 Trong cng ngh mi trngS hin din ca cc hp cht phenolic v cc dn xut ca phenolic trong nc thi cng nghip t cc nh my lc du, dt may, giy v thc phm l mt ln vn . i vi cc nc pht trin quy nh ca chnh ph ang tr nn nghim ngt hn trong vic loi b cc hp cht c hi t nc thi trc khi thi ra mi trng. +Gn y ngi ta tp trung s dng cc Polyphenol oxidase loi b phenolics t nc thi cng nghip. +Ngoi ra polyphenol oxidases c bit l Laccase c th c p dng cho phn hu cht thi nha c cc n v olefin, mt qu trnh oxy ha ca cc n v olefin c cc hp cht trung gian l laccase-ha gii(LMS), c th bt u mt phn ng dy chuyn trit , dn n s tan r ca nha. + C th c s dng loi b mi hi pht ra t nhng ni nh rc cc bi thi, cc trang tri chn nui, hoc nh my bt giy. + C th c s dng gim nng ca thuc tr su c trong t.6.4 Trong lnh vc y t+ Theo mt nghin cu gn y, Polyphenol oixdase c tm thy c ch s bm dnh ca vi khun Streptococcus sobrinus, mt loi vi khun c khoang ming hnh thnh trn b mt rng (Cowan, et al. 2000). + Hn na, Polyphenol oxidase c th c s dng iu tr bnh Parkinson. Do tc ng ca polyphenol oxidase, L-tyrosine c chuyn thnh L-DOPA ( L-3,4-dihydroxyphenylalanine) l cht c s dng b sung s lng dopamine trong vic iu tr bnh Parkinson (Asanuma, et al. 2003, Xu, et al. 1998). +Polyphenol oxidase cn c ng dng nh 1 cht c ch khi u (Seo, et al.2003). 6.5 Trong ngnh cng nghip dt may + Trong ngnh cng nghip dt may polyphenol oxidase c s dng ci thin trng ca bng. + Polyphenol oxidase lm sch loi b mi hi trn vi, b mt sofa v rm, hoc c trong cht ty ra loi b cc mi pht sinh trong vi. + C th ty mu chm trong thuc nhum vi denim mu nht hn (Rodriguez Couto v Toca Herrera 2006). 6.6 Trong cc ngnh cng nghip khc + Polyphenol oxidase c th c s dng nh mt cm bin sinh hc pht hin cc phenol v cc hp cht phenolic trong nc thi, thc phm v ung (Duran v Esposito 2000) pht hin cc morphine, codeine (Bauer et al., 1999), v catecholamin ( Lisdat v cng s, 1997;. Leite v cng s nm 2003,;. Ferry v Leech, 2005 ), Flavonoid thc vt ( Jarosz-Wilkoazka et al., 2004 ). + Trong m phm thuc nhum tc c cha laccase c th t gy kch ng hn so vi thuc nhum tc khng c laccase. + ng thi chng c tm thy trong mt s sn phm thng mi nh thuc kh mi, x phng, thuc kh trng ,thuc xt cp cu, thuc sc ming.

Cu hi

1. Laccase khc bit nh th no o-diphenol oxidase? O-diphenol oxidase l enzyme xc tc phn ng diphenol c hai nhm OH nm v tr o, cn laccase li v tr p.2. Ti sao PPO li c kh nng khng khun? Bn thn PPO v cc hp cht phenolic c tnh cht khng khun, khi enzyme PPO xc tc th phn ng trng hp to ra melanin, to mng bo v, ngn chn s xm nhp ca vi sinh vt l, ng thi Melanin cng l cht khng khun tt.3. Nhit ti u v pH ti u ca PPO: pH: 6-7: y l pH ti u ca PPO trn qu vi.

S nh hng ca nhit ln hot ng ca PPO.4. Ti sao khi ngm to vo nc mui th to khng b en? Khi ngm to trong nc mui th trc tin l ngn chn s xm nhp ca oxy khng kh vo trong lt ct, ha tan gip gim nng phenol ln PPO => Gim tc nhn phn ng. iu c bit khc na th khi ta ngm nh th, ion Na+ v Cl- trong mui lm bin tnh enzyme, c ch s xc tc phn ng.5. Ti sao oxi li u tin phn ng vi vitamin C hn hp cht phenolic? V vitamin C c tnh kh mnh hn Phenol.6. Khi PPO lm tip xc sm mu trong thc phm th ti sao ppo li c ty trng trong bng? Trong bng th c tc nhn l phenolic l nhng hp cht mu. Ta dng enzyme PPO xc tc phn ng nhanh v mnh gip cho phenolic trong giy gn nh mt hon ton=> a v di dng melanin, d tch ra khi bt giy. giy s trng v gim thiu ri ro giy s b xc tc sm mu m ta khng kim sot c.