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VIN CNG NGH SINH HC THC PHM

BO CO MN:

NHNG VN MI TRONG CNG NGH THC PHM

TI:

NG DNG CA K THUT TRNG XUNG

IN TRONG NGNH THC PHM

TP.HCM, thng 3 nm 2011

Trng i Hc Cng Nghip TP.HCM Bo co tiu lun Vin CN Sinh Hc Thc Phm Nhng vn mi trong thc phm

LI M U

Ha nhp cng vi s pht trin mnh m ca khoa hc k thut. Ngnh cng ngh

thc phm cng ang hng ti vic pht trin nhng ng dng ca k thut hin i

trong sn xut thc phm. Hin nay, c ba k thut hin i ang c ng dng

trong sn xut thc phm l: k thut trng xung in, k thut p sut cao v k

thut siu m. Trong k thut trng xung in ang c quan tm kh nhiu.

Bi nhng u im ca k thut ny hon ton ph hp vi xu hng ca th trng

ngi tiu dng thc phm.

Vy k thut trng xung in l g? N c s dng nh th no trong Ngnh thc

phm? Nhng u im ca k thut ny l g? Liu ngi tiu dng c c hng

li g t k thut ny hay khng? gii p tt c nhng cu hi chng em

tri qua thi gian nghin cu v tm hiu. Bi tiu lun ny chnh l kt qu cui

cng.

Tuy nhin, do thi gian v trnh cn hn ch nn bi cn nhiu thiu st. Mong

thy v cc bn gp thm. Chng em chn thnh cm n!

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Chng 1: TNG QUAN V K THUT TRNG XUNG IN

1.1.nh ngha

Trng xung in (PEF) l mt phng php khng s dng nhit trong bo qun

thc phm v c s dng dng in v hot ho vi sinh vt v nh hng ti thiu

hoc khng gy hi n cc thuc tnh cht lng thc phm. PEF c th c dng

ch bin cc sn phm thc n lng v na lng.

Qu trnh ch bin cng cao xung in trng (PEF) lin quan n vic p dng

cc xung in p cao (thng 20-80 kV / cm) thc phm c t gia 2 in cc.

X l PEF c thc hin nhit mi trng xung quanh hoc hi cao hn nhit

mi trng xung quanh cha ti 1s, v tn tht nng lng lm nng cc loi

thc phm c gim thiu. i vi cc thuc tnh cht lng thc phm, cng ngh

PEF c xem l tin ch hn x l nhit truyn thng vi cc loi thc phm v

n trnh hoc lm gim ng k nhng thay i bt li cc c tnh cm quan v vt

l trong cc loi thc phm (Quass 1997). Mc d mt s nghin cu kt lun rng

PEF bo tn cc thnh phn dinh dng trong thc phm, nh hng ca PEF v ha

cht v cnh dinh dng trong thc phm phi c hiu r hn trc khi n c s

dng trong ch bin thc phm (Qin v nhng ngi khc 1995b).

1.2.M t v trng xung in

PEF c th c p dng di cc hnh thc theo cp s nhn phn r, sng vung,

lng cc, hoc xung dao ng. Mt ln sng in p theo cp s nhn phn r l mt

in p mt chiu m tng ln nhanh chng n mt gi tr ti a v phn r t t v

gi tr khng. Cc mch nh trong hnh 1 c th c s dng to ra mt dng

sng phn r theo hm m. Mt ngun in DC np in cho mt t in ni tip vi

mt in tr sc (R s).. Khi mt tn hiu kch hot c p dng, in nng lu tr

trong t in chy vo trong thc n trong bung ch bin.

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Nhng dng sng xung lc hnh vung c th gy t vong v hiu qu nng lng

nhiu hn so vi xung lc phn r theo hm m. Mt dng sng vung c th thu

c bng cch s dng mt mng li hnh thnh xung lc (PFN) bao gm mt lot

cc t in v cun cm v cc thit b chuyn mch trng thi rn (Hnh 2).

Cc xung lc ph ti tc th o ngc c c trng bi mt phn electron ( + )

v mt phn electron ( - )(Hnh 3) vi rng khc nhau v cao cc nh ca peak

3


khc nhau. Chiu rng ca xung lc ph ti tc th o ngc vi s o ngc ph

ti cui xung ng th khc nhau ng k so vi mt xung lc lng cc chun.

Ti thi im sau , cc cc ca nhng xung lc c o ngc lun phin vi

thi gian ngh gia nhng xung lc. Ngay c vi mt xung lc tn s cao hn (v d,

1000 Hz), thi gian ngh ca in mi in p bng khng gia nhng sng xung

lc vung 4 s l 0,996 ms (Quass 1997). Nhng xung lc nghch o tc thi c th

lm gim mnh nhu cu nng lng thp n mc 1,3 J / ml (EPRI 1998).

Hnh 3. Mt vch in p (V) ca mt xung lc nghch o tc thi, a l chu k xung

(s), b l rng xung (s), c l thi gian (s) tng xung ng t e (kV), d l chiu

rng tng gim t bin (s), e l mt in p nh (kV), v f c mt in p tng

gim t bin (kV) (H v nhng ngi khc 1995)

Dao ng xung phn r l nhng hiu qu ti thiu, bi v chng ngn chn cc t

bo khi b lin tc tip xc vi mt trng in cng cao trong mt thi gian

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ko di, do ngn nga cc mng t bo khi s c khng thun nghch trn mt

vng ln (Jeyamkondan v nhng ngi khc 1999).

1.3.Hin trng s dng trng xung in trong ngnh thc phm

p dng cng ngh PEF c chng minh thnh cng i vi vic thanh trng

cc loi thc phm nh nc hoa qu, sa, sa chua, sp, v trng lng. p dng ca

PEF ch bin b hn ch i vi sn phm thc phm khng c bt kh v c dn

in thp. Cc kch thc ht ti a trong cht lng phi nh hn khong cch ca cc

khu vc x l trong khoang cha m bo iu tr thch hp. PEF l mt phng

php ch bin lin tc, khng ph hp cho cc sn phm thc n rn m khng c kh

nng bm c. PEF cng c p dng tng kh nng chit xut cc ng v

hm lng t bo khc t cc t bo thc vt, chng hn nh c ci ng. PEF cng

thy cc ng dng trong vic gim khi lng rn (bn) ca nc thi.

Ti Hoa K, quy m thng mi u tin h thng lin tc PEF c t ti S i

hc bang Ohio ca ca thc phm Khoa hc v Cng ngh. H thng ny PEF l mt

phn ca mt h thng x l thc phm mi kt hp bi mt phng ti tr B Quc

phng ti tr, lin minh trc tip i hc cng nghip. a dng Technologies Inc,

Bedford, MA, xy dng h thng thng mi PEF khi lng ch bin khc nhau, t

500 n 2.000 lt / gi, vi trng i hc Nh nc Ohio cung cp vin iu tr

PEF.

Cc phng tin truyn thng truyn ti cm tng rng cng ngh PEF c

hon thin ln u tin ti n v sn sng cho s dng thng mi. Ngc li

nhiu cng vic cn phi lm chun ha qu trnh ch bin cc sn phm tri cy

nhit i v thc vt ph bin trong nc. Sa c l l i tng thch hp nht p

dng hng lot cng ngh ny, nhng thc t khng c thng tin ng tin cy lin

quan n s ph hp ca n i vi mt hp cht phc tp nh protein-cht bo nh

sa. Vi bo co cho thy ng dng ca PEF i i vi vic gia nhit c th ko di

thi hn s dng ca sa ln ti 24 ngy. Hy tng tng nhng thun li cho ngi

tiu dng trung lu khi cc gi sa m mi ngy n trc nh h, c th c gi

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trong iu kin mi trng xung quanh hay thm ch trong t lnh t nht mt tun

hoc nhiu hn. y l ni m n lc ku gi n l nc sn xut sa ln nht

th gii v mt phn ln c tiu th nh sa dung dch trong hng triu ngi nh t

chc trn ton quc.

Chng 2: QUY TRNH LM VIC CA TRNG XUNG IN

2.1.Phn tch cc yu t quan trng

C ba yu t quan trng nh hng n hot ng kh vi sinh vt ca k thut trng

xung in:

-Qu trnh: cng in trng, rng xung, nhit v thi gian x l, hnh dng ca sng xung.

-Vi sinh vt: chng loi, s lng, giai on tng trng ca vi sinh vt.

-Cc yu t sn phm: pH, dn in, lc ion2.1.1.Cc yu t qu trnh

a. Cng in trng

Cng in trng l mt trong nhng yu t chnh nh hng n kh nng v

hot ha cc vi sinh vt (theo Hshelguer v Niemann 1980; Dunne v cng s 1996).

S gia tng s lng cc vi khun b v hot t l thun vi s gia tng cng in

trng ( theo Qin v cng s, nm 1998). iu ny ph hp vi l thuyt

electroporation. Trong , cc tc ng gy ra qua mng t bo l t l thun vi in

trng p dng. Mt s m hnh ton hc thc nghim c xut m t mi

quan h gia cng in trng v s v hot ca cc vi khun

rng ca xung in cng nh hng n kh nng v hot cc vi sinh vt. V d,

vi rng xung ln hn 50 s th Ec l 4,9 kV/cm, cn vi rng xung nh hn

2s th Ec l 40 kV/cm ( theo Schoenbach v nhng ngi khc 1997). b. Thi gian x l

Thi gian x l l kt qu ca s lng xung v thi gian xung, theo s gia tng

bt k ca cc yu t ny s lm tng kh nng v hot ha cc vi sinh vt (Sale v

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Hamilton 1967). Nh ni trn, chiu rng xung tng hay gim cng nh hng

n kh nng v hot ha cc vi sinh vt bng cch tc ng n cng in

trng. Tuy nhin, vic ko di thi gian xung c th lm tng nhit thc phm

mt cch khng mong mun. Do , cc iu kin ch bin ti u nn c thit lp

cc thit b xung in trng c th cho kt qu lm vic tt nht vi tc dng lm

nng thp nht. Hlsheger v cng s (1981) xut mt m hnh v hot ha lin

quan n phn sng ca vi sinh vt (S) vi thi gian x l bng PEF (t). Qua cho

thy s lng vi sinh vt ngng hot ng tng ln tng ng vi mc tng thi gian

x l.

Mc quan trng ca thi gian x l cng ph thuc vo cng in trng p

dng.

c. Hnh dng sng xung

Trng xung in c th c p dng theo hnh thc phn r, sng vung, dao

ng, lng cc. Trong , hnh thc dao ng l hiu qu nht v hot ha cc vi

sinh vt v cc sng vung th c nhiu nng lng v hiu qu lm cht tt hn so

vi cc xung phn r. Xung lng cc lm cht tt hn so vi cc xung ch c mt

cc v mt xung in trng gy ra chuyn ng ca cc phn t tch in trong cc

mng t bo ca vi sinh vt v i chiu theo hng hoc chiu phn cc ca in

trng gy ra mt s thay i tng ng theo hng ca cc phn t mang in (theo

Ho v cng s 1995; Qin cng s 1994). Vi xung lng cc, s chuyn ng ca

cc phn t tch in gy ra p lc trn mng t bo v tng kh nng ph v n.

Dng xung lng cc s thun li trong vic tit kim nng lng, gim lng ng

ca cc cht rn trn b mt in cc.

Cc xung o ngc tc th c th c m t nh l mt phn mang in vo trc

th ngay tc th mt phn khng mang in vo sau. c tnh ny ca hnh dng sng

chu nh hng bi dn in ca cc thc phm em i x l.

S khc bit gia cc xung o ngc v xung lng cc l thi gian phc hi ca

cc xung. Tc dng v hot ha ca cc xung o ngc lin tc l gy ra p lc xen

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k trn t bo vi khun l nguyn nhn lm cu trc ca chng yu i. Hiu qu ca

dng sng khi v hot ha cc vi sinh vt so vi phng php khc l c th tit kim

1/5 n 1/6 tng s nng lng v chi ph thit b. Tuy nhin, cc nghin cu su hn

l cn thit chng minh tc dng v hot ha vi sinh vt ca phng php ny.

Mt nghin cu tin hnh bi Zhang v cng s (1997) cho thy nh hng ca

sng vung, sng phn r v cc xung o ngc tc th n thi gian bo qun ca

nc cam. Ba loi dng xung c s dng l:

1. Sng vung vi in trng cao 35 kV / cm, c chiu rng xung l 37,22 s v ko

di xung mt thi gian l 60 ns.

2. Phn r theo cp s nhn vi mt sng in trng cao 62,5 kV / cm, c chiu rng

xung l 0,57 s v xung mt thi gian l 40 ns

3. Xung o ngc vi in trng cao im l 37 kV / cm, c chiu rng xung 0,96

s, v xung mt thi gian l 400 ns.

Kt qu nghin cu cho thy sng vung c hiu qu hn so vi hai sng cn li.

Qin v cng s (1994) cng nghin cu kh nng v hot ca S. Cerevisiae khi s

dng hai dng sng l hnh m phn r v sng vung, cng iu kin in trng

cao im l 12 KV/cm v 60J/xung. Kt qu ny cho thy c hai dng sng u cho

hiu qu v hot vi sinh vt, nhng vi sng vung th cho hiu qu tt nht.

d. Nhit x l

Kt qu thc nghim chng minh rng, nhit x l v nhit ch bin c nh

hng n s sng st v phc hi ca vi sinh vt.

X l bng phng php PEF nhit va phi ( t 50-60oC) c tin hnh

cho thy tc dng ca nhit n v hot ha cc vi sinh vt. Vi cng in

trng khng i, mc v hot ha tng theo s gia tng nhit . Cng in

trng l nguyn nhn lm tng nhit ca mt vi thc phm, v vy, vic lm

ngui l cn thit duy tr nhit ca thc phm xung thp hn nhng thc phm

c to ra bi thanh trng.

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nh hng ca nhit c quan st khi thy E. coli gim t 1-6,5 ln trong chu

k tng ng vi s thay i nhit t 32-55oC (Vega-Mercado v cng s, nm

1996)

2.1.2.Cc yu t v sn phm

a. Tnh dn in, pH, lc ion

Cc tnh dn in trung bnh ( n v , Siems / m) c nh ngha nh l kh nng

dn in hin hnh, l mt bin quan trng trong PEF. Dn in l nghch o ca

in tr sut, c nh ngha bi cc tnh hiu r v c o bng ohm-mt (W.m).

Thc phm c tnh dn in cao gy ra nhng im in nh hn trn bung x l, do

khng thch hp x l bng PEF (Barbosa-Cnovas v cng s, 1999). Khi v

hot ha Lactobacillus brevis bng PEF cho thy tnh dn ca cht lng tng ln, kh

nng chng n mn ca bung x l gim. Do , lm gim rng xung v gim

kh nng v hot cc vi sinh vt. Bi v tnh dn in tng dn n kt qu l lc lin

kt ion trong cht lng cng tng. Hn na, s gia tng chnh lch gia dn

in ca mt t bo v vi sinh vt s lm suy yu cu trc mng t bo do mt cht

lm tng lng ion qua mng t bo.

Vega-Mercado v cng s (1996) nghin cu tc ng ca pH v lc ion ca mi

trng trong khi x l bng PEF. T l vi sinh vt b v hot ha tng khng th nhn

bit t chu k 2,5 khi lc ion c iu chnh t 168-28mm. Dunne v cng s

(1996) bo co rng, ty thuc vo loi vi sinh vt, pH m lm tng kh nng v

hot ha cc vi sinh vt.

b. Ht thc phm

Kh hot tnh ca vi sinh vt trong h thng ht cht lng c nghin cu bi

Dunne v cng s ti (1996). Theo , E. coli, L. innocua, aureus Staphyloccocus,

Lactobacillus acidophilus b v hot trong trong h thng ht alginate c ng

knh l 2mm v nh hng ca cc bin khc trong phng php ny cng c

th nghim.

c) Kt hp cc yu t

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Nhn chung, s kt hp ca cc yu t (chng ngi) nh pH, ion v cc hp cht

khng sinh trong iu tr PEF s l mt phng tin hiu qu h tr trong vic v

hot ha cc vi sinh vt vi PEF.

2.1.3.Cc yu t vi sinh vt

a. Loi vi sinh vt

Trong s cc vi khun, cc vi khun gram dng c kh nng khng PEF cao hn so

vi nhng vi khun gram m. Nhn chung, nm men d b tc ng hn so vi vi sinh

vt do chng c kch thc ln hn, mc d cng in thp, chng c th trnh

c nhiu hn so vi cc t bo vi khun gram m (Sale and Hamilton 1967; Qin

and others 1995a). Mt so snh gia s v hot ca hai loi nm men c kch thc

khc nhau cho thy cng in trng cn thit chng ngng hot ng t l

nghch vi kch thc t bo. Nhng kt qu trn hp l nhng khng ph hp vi

kt qu ca Hlsheger v cng s (1983). V vy cc nghin cu trong lnh vc ny

cn c tip tc hiu r hn v nh hng ca loi vi sinh vt n kt qu ca

phng php PEF.

b. S lng vi sinh vt

S lng vi sinh vt c trong thc phm c th nh hng n s v hot ha chng

bng phong php PEF. Barbosa-Cnovas v cng s (1999) bo co rng mc

v hot ha E. coli trong mt h thng thc phm dng sa ultrafiltrate (SMUF)

khng b nh hng khi nng ca vi sinh vt c thay i t 103-108 cfu/ml sau

khi phi chu n 70 KV/cm, 16 xung v chiu rng xung l 2 s.

Cn trong nc to, iu kin 25 kV / cm, 1 xung, v rng xung l 25 s, nu

tng s lng S. Cerevisiae th kh nng vo hot ha s gim i. nh hng ca

nng vi sinh vt n mc v hot ha c th lin quan ti s hnh thnh nhm

cc t bo nm men hoc vi sinh vt c giu trong khu vc c in trng thp.

c) Giai on sinh trng ca vi sinh vt

Nhn chung, cc t bo giai on tng trng mnh th nhy cm hn so vi cc t

bo giai on tng trng chm hoc suy thoi. Vi sinh vt trong giai on tng

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trng mnh c c trng bi qu trnh phn chia t bo lin tc. Trong , mng

t bo nhy cm hn vi in trng p dng. Hlsheger v cng s (1983) kt lun

rng t bo t cc giai on tng trng mnh nhy cm vi PEF hn l giai on

tng trng chm v suy thoi. Nghin cu vi E. Coli cho kt qu tng t.

Gaskova v cng s (1996) bo co rng hiu qu lm cht ca PEF trong giai on

tng trng mnh l 30% ln hn trong giai on chm hoc ngng tng trng.

2.2.C ch kh hot vi sinh vt

Hai c ch c a ra nh l phng thc hot ng ca PEF trn vi sinh vt:

v electroporation.

2.2.1.Electrical breakdown

Zimmermann (1986), nh trong hnh 5 gii thch nhng g in ph hy mng t

bo. Mng ny c th c coi l mt t y vi mt cht in mi (Hnh 5a). S

khc bit l kh nng chng li bnh thng trn mng V'm l 10 mV v dn n

hnh thnh s khc bit th mng V do s tch in trn mng t bo. V l t l thun

vi cng trng E v bn knh ca t bo. S gia tng in th mng dn n

gim dy mng t bo. S ph hy mng xy ra nu im ti hn in th Vc t

c mt s gia tng hn na cng trong trng bn ngoi (Hnh 5c). Ngi ta

cho rng s ph hy gy ra s hnh thnh cc l rng trn mng (y dung dch dn

in), dn n s phng in ngay lp tc ti mng t bo v do phn hy mng t

bo. S ph hy c th hi phc nu sn phm cc l rng l nh i vi tng b mt

mng. Trn im ti hn cng trng vi thi gian tip xc di, khu vc ln hn

ca mng l b phn hy (Hnh 5d). Nu kch thc v s lng cc l chn lng tr

nn ln i vi tng b mt mng, s ph hy c th hi phc bin thnh s ph hy

khng th hi phc, l lin quan n ph hy c hc ca mng t bo.

in trng tng ng l Eti hn = V ti hn / f a, a l bn knh ca t bo v f ph

thuc vo hnh dng ca t bo (Schoenbach v nhng ngi khc 1997). i vi

mt t bo hnh cu f l 1,5; cho cc t bo hnh tr c chiu di l v bn cu c

ng knh d ti mi u, khi f = l (l - d) / 3

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Hnh 5. Biu ca s ph hy hi phc v khng th hi phc. (A) mng t

bo c tim nng V'm, (b) mng nn, (c) l rng hnh thnh vi s ph hy hi

phc, (d) din tch ca mng b ph hy khng th hi phc vi l rng ln

(Zimmermann, 1986)

2.2.2.Electroporation

Electroporation l hin tng trong mt t bo tip xc vi trng xung in cao

p dn n lm mt n nh lp mng lipid kp v cc protein ca mng t bo

Castro v nhng ngi khc 1993).

Cc mng sinh cht ca cc t bo tr nn thm qua c vi cc phn t nh sau

khi c tip xc vi mt in trng, v s thm thu sau gy ra s sng ph v

cui cng l s thng mng t bo (Hnh 6) (Vega-Mercado 1996b).

Hiu qu chnh ca mt in trng trn mt t bo vi sinh vt l tng tnh thm

mng do mng nn v poration (Vega-Mercado v nhng ngi khc 1996b).

Kinosita v Tsong (1977, 1979) chng minh rng mt in trng l 2,2 kV / cm

gy ra l rng trong hng cu ca con ngi trong khong 1 nm ng knh. L rng

ln thu c bng cch tng cng in trng v thi gian xung hoc gim

cng ion ca mi trng.

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Hnh 6. Electroporation ca mt mng t bo (Vega-Mercado, 1996b)

2.3.Mt s u nhc im ca phng php

2.3.1.u im

-K thut trng xung in v hiu ha cc vi sinh vt nhit 500C trong 3 giy, thp hn rt nhiu so vi mt thanh trng pasteur thng thng cng nhit

khong 70 n 900C, trong khong 30 n 60 giy.

-Thc phm c x l bng k thut ny vn gi nguyn c gi tr dinh dng cng nh tnh cht cm quan. V d, trong sn xut pho mt s dng sa c x l

bng PEF l mt gii php c th loi b cc tc nhn gy bnh c trong sa. Mt

v d th hai l cc loi nc tri cy sau khi x l PEF vn gi

c hng v nh tri cy ti vt.

-Ko di thi hn s dng ca thc phm hn cng l mt u im ca phng php.

-Phng php s dng in thng thng nn m bo an ton v khng gy nhim mi trng

-Mt u im na l phng php ny tiu tn t nhin liu v thi gian x l rt ngn nn gim c gi thnh ca sn phm. V gp phn tit kim nhin liu.

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2.3.2.Nhc im

Mt s nhc im quan trng nht ca k thut hin ti hoc hn ch ca cng ngh

PEF l:

-Tnh sn c ca n v thng mi, c gii hn trong mt bi PurePulse Technologies, Inc, v mt bi Thomson-CSF

- S c mt ca bong bng, c th dn n iu tr khng ng nht cng nh cc vn an ton hot ng. Khi in trng p dng vt qu sc mnh in mi ca

cc bong bng kh, phng in cc b din ra bn trong cc bong bng c th lm bay

hi cht lng v do lm tng khi lng ca cc bong bng. Cc bong bng c th

tr thnh ln thu hp khong cch gia 2 in cc v c th to ra mt tia la.

V vy, bong bng khng kh trong thc phm phi c loi b, c bit vi cc h

thng hng lot.

-Gii hn ca ng dng, l gii hn cho cc sn phm thc phm c th chu c in trng cao. Cc thuc tnh in mi ca thc phm l lin quan cht ch

n cu trc vt l ca n v thnh phn ha hc. Cht lng ng nht vi tnh dn

in thp, cung cp iu kin l tng iu tr lin tc vi cc phng php PEF.

Sn phm thc phm khng c thm cc mui c dn in trong khong 0,1-0,5

S / m. Cc sn phm c tnh dn in cao lm gim in tr ca cc phng v do

i hi nhiu nng lng hn t c mt in trng c th. V vy, khi ch

bin cc sn phm mui cao, mui s c thm vo sau khi ch bin.

-Cc kch thc ht ca cc thc phm lng trong c hai ch iu tr dng chy v tnh. Cc kch thc ht ti a trong cht lng phi nh hn khong cch ca cc

khu vc x l trong bung duy tr hot ng x l thch hp.

-Vic thiu cc phng php o chnh xc cng sut x l. S lng v s a dng trong thit b, cc gii hn hiu lc ca kt lun c th c rt ra v hiu qu

ca qu trnh iu kin c th. Mt phng php o lng cng sut x l s ngn

14


chn kt qu khng ph hp do cc bin th trong h thng PEF. Nhng phng php

khng c sn

Chng 3: NG DNG TRONG CNG NGH THC PHM

n nay, trng xung in ch yu c p dng bo qun cht lng, tng thi

hn s dng thc phm chng hn nh sa, nc cam, nc to, trng v ru.

3.1.ng dng cng ngh ch bin ru vang

-Ho v Mittal(1996) p dng trng xung in hi phc hoc o ngc mng t bo cht ca t bo Eukaryote v Prokaryote

-Heinz v cng s (2001) cng bt hot vi khun, lm tng an ton, n nh thc phm m khng nh hng cm quan v c im dinh dng ca thc phm.

-Trong vi nm qua, ngi ta cc ng dng ca cng ngh ny trong sn xut ru vang cho ngng hot ng ca vi sinh vt h hng v hn ch nguy c bin i

ca ru do vi sinh vt gy ra, ci thin hng v ru trong qu trnh ngm.

-Kh nng ca trng xung in bt hot cc vi sinh vt nhit m khng gy ra bt k tc hi v hng v, mu sc, hoc gi tr dinh dng ca ru vang

m ra cc ng dng rt th v ca cng ngh ny vo qu trnh sn xut ru vang

15


X l in trng 29 kV/cm lm gim s lng cc vi sinh vt h hng

(Purtolas nm 2009). Ngoi ra c th to thun li cho s pht trin ca nm men

ru vang kh m bo cho qu trnh ln men ru v ti sn xut ln men. Ngng

hot ng ca h vi sinh vt h hng trong qu trnh ln men trong ru vang c hiu

qu trnh s nhim ca b mt v kim sot s thay i sut qu trnh lo ha trong

thng v lu tr trong chai ca ru vang.

Trong nhng nm gn y, c mt s quan tm c bit trong cc loi ru vang

rt giu cc hp cht phenolic khng nhng c th gip ngn nga bnh nhi mu

c tim m cn l mt cht chng xy ha rt mnh, c kh nng ngn nga ung th

hu hiu, n nh mu sc ca ru trong qu trnh lo ha. Tuy nhin cc loi

ru c c nng phenolic cao cn ko di thi gian ngm, thc t ny i hi

phi tng s lng vi khun ln men trong sn xut ru, iu ny dn n kh khn

kim sot nhit ln men dch nho. p dng phng php trng xung in cho

php ci thin vic nng cc hp cht phenolic trong thi gian ngm, tng hm

lng phenolic v cng mu ca ru vang (10-45%) v gim thi gian ngm (t

nht l 48 gi) (Purtoals 2010)

3.2.ng dng trong cng nghip nc qu

3.2.1.Ch bin nc to

Simpson v nhng cng tc vin (1995) bo co: nc

to sau khi x l bng phng php trng xung in

in trng l 50 kV/cm, 10 xung mi xung in c chiu

rng 2 s, nhit x l ti a l 45C ko di thi hn

s dng 28 ngy so vi 21 ngy thi hn s dng ca nc

to p ti. Sau khi phn tch v kim tra, kt qu cho thy

khng c s thay i vt l, ha hc no (v d acid

ascorbic hay cc loi ng) trong nc to s dng

16


phng php trng xung in v nh gi cm quan cng khng tm thy s khc

bit ng k no so vi nc to p ti

Vega Mercado v nhng ngi khc (1997) cng bo co bng phng php

trng xung in ko di hn s dng ti nhit 22-25C ca nc to ti v

nc p to t 32 n 56 ngy, khng thy c s thay i trong ha l v cc c tnh

cm quan ca n

3.2.2.Ch bin nc cam

Sitzmann (1995) bo co hiu qu ca vic bo qun

nc cam vt bng phng php trng xung in

gim mt lng vi sinh vt in trng p dng l

15 kV/cm m khng nh hng ng k n cht

lng ca n.

Zhang (1997) tng hn s dng nc cam hon

nguyn c c x l bng trng xung in 32

kV/cm. Ngoi ra, ng cn bo co l tng s vi sinh

vt hiu kh gim 3 ln so vi nc cam khng x l v khi bo qun nc cam

4oC th vitamin C tn tht thp, vn gi c mu sc, v tng thi gian bo qun ln

n 90 ngy ( nhit 4-22C) hoc 15 ngy ( nhit 37C).

3.3.ng dng trong cng nghip ch bin sa

Dunn v Pearlman (1987) tin hnh mt th nghim vi sa nhim vi khun

Salmonella x l vi in trng 36,7 kV/cm v 40 xung, Salmonella khng c

pht hin sau khi sa x l phng php trng xung in. Vi nhit lu tr

7-9C trong 8 ngy cc vi khun trong sa tng ln

17


n 107 cfu/ml, trong khi sa c s dng phng php trng xung in cho

thy khong 4x102 cfu/ml.

Fernandez-Molina (1999) nghin cu thi hn s dng ca sa tch kem ti (0,2%

cht bo sa), x l bng phng php trng xung in 40 kV / cm, 30 xung, thi

gian 2 s, thi hn s dng ca sa l 2 tun 4oC. Tuy nhin vi phng php

trng xung in trong 6 giy, 30 kV/cm, 30 xung, mi xung c chiu rng 2 s,

sa tch kem ti c hn s dng ln n 22 ngy, vi tng s vi sinh vt hiu kh

gim v coliform khng tm thy. Lu nhit x l khng vt qu 28 C trong

khi s dng phng php trng xung in ca nguyn sa tch kem.

3.4. ng dng trong mt s sn phm khc

3.4.1.Ch bin trng

Cc nghin cu khc trn trng c x l bng trng xung in thc hin bi Tan

- cc cng s (1995) v Ma (1997) cho thy x l bng trng xung in gim

nht nhng tng mu sc ca trng. Sau khi nh gi cm quan cho thy khng c s

khc bit gia sn phm trng ch bin t trng ti v trng qua x l xung in.

Ngoi ra phn tch mu sc ca sn phm trng, Ma v nhng ngi khc (1997)

nh gi ti v ch s protein c kh nng to bt ca trng c x l bng

trng xung in. Cc phn tch thng k ca cc nh gi cm quan cho thy khng

c s khc bit gia cc loi bnh ch bin t trng ti v trng qua x l trng

xung in.

3.4.2.Bo qun thc phm thc n nh

Thc phm thc n nh ang tm kim gii php ngn chn s pht trin ca vi

sinh vt m khng lm gim cht lng ban u ca sn phm, ng ch nht l bo

qun thc phm x l theo phng php vt l nhit thp hn so vi nhng yu

cu tit trng Pasteur m vn gi c cht lng ban u, cc sn phm khng cn

18


b nh hng bi nhit. X l trng xung in l mt phng php bo qun thay

th cho tit trng Pasteur, ng dng trn nhiu loi thc phm.

Vega-Mercado (1996) x l vi sp u xanh bng trng xung in 16 xung ti

35 kV/cm v lu ngn chn s gia tng nhit vt qu 55 C trong khi x l.

Thi hn s dng nhit lnh vt qu 4 tun v khng c thay i cc tnh cht

ha l hay cm quan ca sp u sau khi x l bng trng xung in

3.4.3.Ci thin ti ca tri cy v rau qu

Thng thng mt nc ca tri cy v rau qu nh hng n tnh trng sinh ha

dn n co rt, thay i kt cu, mu sc v hng v v cht lng. Th trng tiu

dng ngy cng tng i vi tri cy v rau qu, trnh tnh trng mt nc cc nh

nghin cu nghin cu cc phng php kt hp k thut bo qun. Trng xung

in l mt trong nhng phng php bo qun y ha hn gi c ti ca

thc phm m khng gy nh hng n cht lng ca n.

19


TI LIU

1. www.ichaus.de/MagneticEncoder

2. http://www.freepatentsonline.com/6746613.html

3. http://fst.osu.edu/PEFfactsheet.pdf

4. U. S. Food and Drug Administration

Center for Food Safety and Applied Nutrition

June 2, 2000

http://altered-states.net/barry/rife/pulsedelectricflds.htm

5. Barbosa-Cnovas, GV, Gongora-Nieto, MM, Pothakamury, UR, Swanson, BG

1999. Preservation of foods with pulsed electric fields. 1-9, 76-107, 108-155.

Academic Press Ltd. London.

20


6. Calderon-Miranda, ML 1998. Inactivation of listeria inocua by pulsed electric

fields and nisin. Pullman, WA. Washington State University.

7. Jeyamkondan, S., Jayas, D. S. and Holley, R. A. 1999. Pulsed electric field

processing of foods: a review. J Food Protect. 62(9):1088-1096

8. Keith, W. D., Harris, L. J., Hudson, L. and Griffiths, M. 1997. Pulsed electric

fields as a processing alternative for microbial reduction in spice. Food Res Int.

30(3/4):185-191

MC LC

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