CC H VI SINH VT TRONG HP Cc h vi sinh vt tn ti trong hp nguy him
nht l cc loi vi khun, sau mi n nm men v nm mc. Vi khun Cc loi vi
khun ph bin nht thng thy trong hp. a. Loi hiu kh + Bacillus
mesentericus : c nha bo, khng c, trong nc v trn b mt rau. Nha bo b
ph hy 1100C trong 1 gi. Loi ny c trong tt c cc loi hp, pht trin
nhanh nhit quanh 370C. + Bacillus subtilis : c nha bo khng gy bnh.
Nha bo chu 1000C trong 1 gi, 1150C trong 6 pht. Loi ny c trong hp
c, rau, tht. Khng gy mi v l, pht trin rt mnh 25 - 350C. b. Loi k kh
+ Clostridium sporogenes: c nh trng thi t nhin ca mi mi trng. N phn
hy protid thnh mui ca NH3, ri thi NH3,, sn sinh ra H2S, H2 v CO2.
Nha bo ca n chu ng c trong nc si trn 1 gi. Clostridium sporogenes c
c t, song b ph hy nu un si lu. Loi ny c trong mi hp, pht trin rt
mnh 27 - 580C. Nhit ti thch l 370C. + Clostridium putrificum: l loi
vi khun ng rut, c nha bo, khng gy bnh. Cc loi nguyn liu thc vt khng
mnh vi Clostridium putrificum v c phitonxit. Loi ny c trong mi hp,
nhit ti thch l 370C. c. Loi va hiu kh va k kh + Bacillus
thermophillus: c trong t, phn gia sc, khng gy bnh, c nha bo. Tuy c
rt t trong hp nhng kh loi tr. Nhit ti thch l 60 - 70oC. +
Staphylococcus pyrogenes aureus : c trong bi v nc, khng c nha bo.
Thnh thong gy bnh v sinh ra c t, d b ph hy 60 - 70oC. Pht trin
nhanh nhit thng. d. Loi gy bnh, gy ra ng c do ni c t + Bacillus
botulinus : cn c tn l Clostridium botulinum. Triu chng gy bi lit rt
c trng : lm c s iu tit ca mt, ri lm lit cc c iu khin bi thn kinh s,
sau ton thn b lit. Ngi b ng c sau 4 - 8 ngy th cht. Loi ny ch b
nhim khi khng tun theo nguyn tc v sinh v thanh trng ti thiu. Nha bo
c kh nng khng mnh: 100oC l 330 pht, 115oC l 10 pht, 120oC l 4 pht.
c t b ph hy hon ton khi un nng 80oC trong 30 pht. + Salmonella:
thuc nhm vi khun gy bnh, hiu kh, a m, khng c nha bo nhng c c t. 2.
Nm men, nm mc + Nm men: ch yu l Saccharomyces ellipsoides, hin din
rng khp trong thin nhin. Nm men thng thy trong hp c cha ng. Bo t ca
nm men khng c kh nng chu ng c nhit cao, chng c th cht nhanh nhit
60oC. + Nm mc : t thy trong hp. Ni chung men, mc d b tiu dit nhit
thp v d loi tr bng cch thc hin v sinh cng nghip tt. PHNG PHP THANH
TRNG VT L Thanh trng bng tia ion ha Nguyn l
Tc dng dit trng ca cc tia ion ha l thay i cu trc ca mt s phn t
protein ca t bo vi sinh vt v lm ion ha dung mi. Hiu qu thanh trng
ca tia ion ha ph thuc vo thi gian x l, chiu dy ca thc phm v lng vi
sinh vt nhim vo thc phm. Cc tia ion ha Cn c vo tn s dao ng in t,
ngi ta chia tia sng lm cc loi : Bng 4.1. Tn s dao ng in t ca cc tia
ion ha Tia Tn s dao ng in t (Hz) 1012 - 101410151016 - 1017 1018
Tia hng ngoiTia sng trng thyTia t 10201021 - 1022 ngoiTia XTia
Rongel cng, tia Bng 1 (Nguyn Vn Tip. 2000) Cc tia c tn s dao ng cao
th c lc m xuyn l cc tia ion ha u c tc dng dit trng. Liu lng s cao.
Tia X, tia dng ty thuc vo bn cht tng loi vi sinh vt. Chiu dy ti a
ca thc phm em chiu tia X v tia m cc l 127mm (nu chiu c 2 mt). Tia
hng ngoi v tia t ngoi l cc tia bc x. Tc dng ca tia hng ngoi l lm
nng sn phm dit vi sinh vt. Tia t ngoi c tc dng st trng l lm ng t
protid v ph hy h thng men ca vi sinh vt. Thanh trng bng sng siu m
Di tc dng ca siu m, mi trng lng truyn m b x y, b p v to chn khng
lin tip, sinh ra nhiu khong trng. Lc , cc cht ha tan v hi ca cht
lng lp tc dn vo khong trng y, gy ra tc dng c hc lm cht vi sinh vt
trong mi trng. Mt khc trong qu trnh y, mt phn cht kh ha tan b ion
ha to ra nc oxy gi (H2O2), Nitrogen oxy (NO) l nhng cht c i vi vi
sinh vt. Trong cc loi vi sinh vt th vi khun d b siu m tc dng nht.
Thanh trng bng dng in cao tn Thanh trng bng cch t sn phm trong in
trng ca dng in xoay chiu (c tn s cao) Cc phn t tch in trong sn phm
(ion, in t) s dao ng do tc dng ca in nng, chuyn in nng c hp thu
thnh nhit nng lm cht vi sinh vt. Kh nng hp thu in nng ty thuc vo:
kch thc bao b ng thc phm, in p tn s ca dng in. Tn s ca dng in cng
ln hay bc sng cng ngn th qu trnh thanh trng cng nhanh (Tn s thch hp
nht l 3.108 - 3.107 Hz). Thi gian thanh trng ch trong vi mi giy n
vi pht. Thanh trng bng s dng p sut cao p lc 300 - 600MPa c kh nng v
hat cc vi sinh vt khng hnh thnh bo t. Trong khi v hat cc vi khun
sinh bo t cn p lc rt cao (1800MPa) Tuy nhin, ti p sut thp 200 -
400MPa cng lm gim s sn sinh bo t. Thanh trng bng xung in t Trng
xung in (p dng cho cc lai thc phm lng, thi gian x l t vi micro ti
mili giy) c th tiu dit vi sinh vt v to xp mng t bo. Lc in trng i hi
v hat vi sinh vt thay i m. t 0,1 - 2,5 V/
Lc Thanh trng Sn phm lng, nh nc qu trong c th loi tr vi sinh vt
bng cch lc. Bn lc, thng l cc mng s xp, c nhng l nh ch cho sn phm
qua, cn gi li vi sinh vt. Sau khi lc, sn phm c rt vo bao b st trng,
ri ghp kn ngay. Qu trnh ny phi tin hnh trong iu kin v sinh cao. Bng
phng php ny, sn phm hon ton gi c tnh cht t nhin. THANH TRNG BNG TC
DNG CA NHIT Thanh trng bng nhit cao ca nc nng v hi nc nng l phng
php thanh trng ph bin nht trong sn xut hp. Khi nng nhit ca mi trng
qu nhit ti thch ca vi sinh vt th hot ng ca vi sinh vt b chm li.
nhit cao, protid ca cht nguyn sinh ca vi sinh vt b ng t lm cho vi
sinh vt b cht. Qu trnh ng t protid ny khng thun nghch, nn hot ng ca
vi sinh vt khng phc hi sau khi h nhit. ng hc ca qu trnh tiu dit vi
sinh vt bng nhit T thc nghim ch s tiu dit vi sinh vt c th hin bi
phng trnh: (1)dN dt =kT.Nn Trong : N : lng vi sinh vt trong sn phm
sau thi gian t (cfu/ml). kT: h s vn tc tiu dit vi sinh vt nhit T,
ty theo loi vi sinh vt v tnh cht ca hp m tr s k thay i. t : Thi
gian x l (pht) n : Bc phn ng Trong hu ht trng hp, bc phn ng bng 1,
tin trnh v hot bc nht c th vit nh sau: (2)dN dt =kT.N Hay dN N
=kT.dt (3) Vi phng trnh vi phn (3) c th c ly tch phn theo cc iu kin
thi im ban u t = 0 th N = No thi im t = t th N = N N N0 dN N
= t 0 kT.dt (4) Khi thc hin tiu dit vi sinh vt nhit khng i, kT =
hng s (qu trnh ng nhit) Phng trnh (4) c th vit nh sau: (5) N N0 dN
N =kT t 0 dt ln (N) ln (No) = - kT. t(6) ln N N0 =kT.t (7) Hoc (8)T
ta c c : N = No e -kt Trong N : lng vi sinh vt trong sn phm thi im
t (cfu/ml) No: lng vi sinh vt ban u (cfu/ml) kT : h s vn tc tiu dit
vi sinh vt nhit T t : Thi gian gia nhit (pht) nhit tiu dit vi sinh
vt khng i, lng vi sinh vt gim theo hm s m theo thi gian. iu ny c
ngha tng s vi sinh vt khng th gim n 0. V vy, khng th m bo tuyt i
rng tt c vi sinh vt s b tiu dit bi mt qu trnh no . Nu v ng biu din
v mc tiu dit vi sinh vt theo thi gian bi phng trnh (8) ta c th theo
hnh 4.1
Hnh 1 Hnh 4.1. S tiu dit vi sinh vt bng nhit theo thi gian Cng c
th vit : lg N N0 = k 2,303 t (9) Nu biu din theo hm logarite thp
phn phng trnh (9) th l mt k 2,303 ng thng, c h s gc biu th qua hnh
4.2 ng l thuytng thc nghim
Hnh 2 Hnh 4.2. Thi gian tiu dit vi sinh vt theo mi quan h
logarite Vi gi tr D l thi gian cn thit ti mt nhit xc nh tiu dit 90%
lng vi sinh vt ban u. c gi l thi gian tiu dit thp phn. Theo hnh 4.2
v phng trnh (9), ta xy dng c mi quan h gia h s vn tc k v thi gian D
: 1 D = k 2,303 Phng trnh (9) c th vit : (10) lg N N0 = 1 D t Vy
thi gian tiu dit vi sinh vt t=Dlg N0 N (11) Tnh ton nh hng ca qu
trnh x l nhit (Gi tr thanh trng F) xc nh mc tiu dit vi sinh vt, cn
phi bit tr s D v z biu th cho loi vi sinh vt cn tiu dit. (ng hiu
chnh)(ng thc nghim)
Hnh 3 Thi gian tit trngNh ta bit ng thi gian cht nhit ca vi sinh
vt trong qu trnh x l nhit l mt ng thng, ta v th biu din (hnh 4.3)
Hnh 4.3. Biu din thi gian cht nhit ca vi sinh vt - F : thi gian cn
thit (tnh bng pht) tiu dit vi sinh vt, ti mt nhit nht nh. - z :
khong nhit cn thit cho ng thi gian cht nhit thc hin mt chu trnh
logarite (i vi mi loi vi sinh vt v thc phm khc nhau, c gi tr D v z
khc nhau) Bng 4.2. S khng nhit ca vi sinh vt trong qu trnh x l nhit
Nhm vi khun D (pht) z (OC) Sn phm khng chua v t chua(pH > 4,5)-
Vi khun chu 2,0 - 5,0 (1)0,1 - 8 - 128 nhit (bo t) - Vi khun khng
chu nhit (bo t) 1,5 (1) 10 Sn phm chua (pH 4,0 - 4,5)- Vi khun chu
nhit (bo t)- Vi 0,01 - 0,07 8 - 107 khun khng chu nhit (bo t)
(1)0,1 - 0,5 (2) 10 Sn phm rt chua (pH < 4,0)Vi sinh vt khng chu
nhit (vi 0,5 - 1,0 (3) 5-7 khun khng sinh bo t, nm men, nm mc) Bng
2 (Carla,1992) Ghi ch (1): x l 121,1OC (2): x l 100OC (3): x l 65OC
Bng 4.3. S v hot vi sinh vt (bo t) trong qu trnh tit tng LOI VI
SINH VT(Type of microorganism)MI TRNG(Medium)z-value (oC)D121,1
(min)Bacillus stearothermophilusGeneral7,6-10,31,8-4,7Bacillus
subtilis 5230General7,4-130,3-0,76Bacillus
coagulanssolution8,2-9,00,2-2,5Bacillus
cereusGeneral9,70,0065Bacillus megateriumGeneral8,80,04Clostridium
perfringensGeneral10,0/Clostridium
sporogenesGeneral8,0-12,00,48-1,4Clostridium
botulinumGeneral9,90,21(Carla.1992) Bng 4.4. S v hot vi sinh vt (T
bo sinh dng) trong qu trnh thanh trng LOI VI SINH VT(Type of
microorganism)MI TRNG(Medium)z-value (oC)DT (min)Escherichia
coli/4,94,5 (56oC)Pseudomonas fluoresens/7,53,2
(60oC)Streptococcus
faecalisFish6,715,7 (60oC)Staphylococcus aureusPea soup4,610,4
(60oC)Salmonella senftenbergPea soup5,710,6 (60oC)Lactobacillus
plantarumTomato soup12,511,0 (70oC)Listeria
monocytogenesCarrots6,70,27 (70oC)Closstridium
botulinumNonproteolytic type BNon-proteolytic type EBuffer pH
7,0Water9,79,432,3 (82oC)3,3 (80oC)Bacillus cereusBuffer pH
7,010,58,0 (100oC)Bacillus subtilisBuffer pH 6,89,80,57
(121oC)(Carla.1992) Bng 4.5. S khng nhit ca cc enzyme trong qu trnh
x l nhit Enzyme D (pht) z (OC) 232 (1)20 (1)0,82
PeroxydasePolygalacturonaseO(1)0,09 286,85,58,58,3262
diphenoloxydaseLipoxygenaseCatalaseLipaseProtease (1)0,02 8 (1)25
(2)300 (2) Bng 3 (Carla.1992) Ghi ch (1): x l 80OC (2): x l 120OC
Bng 4.6. Gi tr Z i vi s v hot enzyme v cc nhn t cht lng ca mt s thc
phm GA TR Z ENZYME (oC) Lipoxygenase (peas) 8,7 Lipoxygenase
(soybean) 6,9 Polyphenoloxidase (mushroom) 6,5 Polyphenoloxidase
(plum) 17,6 Chlorophyllase (spinach) 12,2 Peroxidase (potato) 35,0
NHN T CHT LNG Thiamine (milk) 29,4 31,4 Thiamine (meat, vegetables)
25,0 31,3 Cht lng chung (peas) 28,3 Cht lng chung (green beans)28,8
Cht lng chung (bp) 31,6 Bng 4 (Carla.1992) Bng 4.7. Ga tr Z ca cc
nhn t thc phm (tng qut) NHN T GA TR Z (oC) Bo t vi khun 7 12 T bo
sinh dng 48 Vitamins 25 30 Proteins 15 37 Enzymes 5 50 Cht lng cm
quan chung25 45 Cu trc 17 47 Mu sc 17 - 57
Bng 5 (Carla.1992) Theo hnh 4.3, ta c th vit: dc ca ng thng
lgtlgF 121,1T = 1 Z = lgtlgF= 121,1T Z Hay c th vit li lg F t =
T121,1 Z F=t.10 T121,1 z Mt cch tng qut, ga tr F c biu th :
FTrefz=t.10 TTref z Tref : nhit tham chiu tng ng vi qu trnh x l
nhit (v d i vi qu trnh tit trng th nhit l 121,1oC, i vi qu trnh
thanh trng th nhit l 100oC...) T : Nhit x l nhit (oC) z : ty thuc
vo loi vi sinh vt cn tiu dit v tnh cht ca sn phm. Ni chung, ngi ta
chn loi sinh bo t Clostridium botulinum l mc tiu ca qu trnh thanh
trng v i din cho loi chu nhit, c z = 10oC FTrefz= 10 T(t)Tref z
.dtTrong trng hp nhit thay i theo thi gian, ngi ta ghi nhn T(t),
khi gi tr F c tnh nh sau :
N c ngha l tnh trn tng thi gian nh hng tc thi, m c biu th bi ga
tr 10 (T - Tref)/z c gi l yu t Bigelow. Cng thc Bigelow cho ta tnh
c s ph hy cc bo t bi nhit trong trng hp x l nhit khng c nh. Mc tiu
ca qu trnh tit trng Bo t ym kh Clostridium botulinum l mc tiu chnh
trong qu trnh ch bin nhit v : - C th sn sinh ra c t lm cht ngi d
liu lng rt thp. - C kh nng thnh lp bo t, rt bn nhit - Clostridium
botulinum c th tm thy bt c ni u, v vy hu ht nguyn liu u nhim vi
sinh vt ny, nn chng quan h mt thit ti lnh vc an ton thc phm Chnh v
nhng l do trn, Clostridium botulinum c xem l nguyn nhn gy ng c thc
phm. trnh s "bng n" v ng c, cc nh ch bin thc phm cn : - Gim mt s bo
t Clostridium botulinum n mc c th chp nhn c trong thc phm - Ngn cn
s pht trin ca Clostridium botulinum (bo t) v qu trnh sn sinh c t
Trong thc t rt kh v hot bo t Clostridium botulinum, v vy trnh h hng
i hi phi x l nhit cao, y l nguyn nhn dn n vic gim tnh cht dinh dng,
cm quan ca cc thc phm, khng p ng c i hi ca ngi tiu dng. Chnh v th,
vic ngn cn h hng thc phm thng l hn ch s pht trin nhanh ca bo t
Clostridium botulinum hn l v hot. Vic x l nhit thnh cng ph hy bo t
Clostridium botulinum l kt hp vi nhiu yu t (yu t bn trong v bn
ngoi) nh pH, nhit , oxy, hot ng ca nc, ph gia bo qun hoc kt hp vi
nhm vi sinh vt cnh tranh Bng 4.8. Cc ni v ngoi tc nhn gp phn ngn
chn s pht trin ca clostridium botulinum Yu t bn trong- aw : 0,93
(theo FDA, aw < 0,85)- pH < 4,6- Ph gia : Nitrit : 0,1
0,2g/kg, Mui : < 100g/kg Yu t bn ngoi- Nhit bo qunT < 10oC :
Clostridium botulinum dng A, B; enzyme phn gii proteinT < 3,3oC
: Clostridium botulinum dng B, E, F; khng phn gii protein Bng 6
(Carla.1992) Thng thng bo t Clostridium botulinum khng hnh thnh v
pht trin trong thc phm c pH < 4,6. V vy, pH : 4,6 c chn l ranh
gii phn chia gia thc phm acid v t acid. - Trong thc phm acid (pH
< 4,6) bo t Clostridium botulinum c th hin din, khng c du hiu
lin quan n s pht trin nhanh, c th p dng x l nhit trung bnh ph hy
chng (thanh trng) - Trong thc phm t acid (pH > 4,6) x l nhit mc
tng i c th s dng vi mc ch tiu dit bo t Clostridium botulinum, nhng
phi kt hp vi qu trnh bo qun mt. Trong trng hp ny, qu trnh tit trng
thng c p dng hn. Xc nh im kt thc ca qu trnh tit trng Tri s gi tr
tit trng F cn c xc nh cho mi loi h hng do vi sinh vt. Mt tr s ca qu
trnh ny c tnh ton da vo z = 10oC v nhit qui c l 121,1oC,
c k hiu l F0. Nhiu nm trong thc t ng hp cho php kt lun i vi qu
trnh tit trng nhit m, tr s F10121,1 (Clostridium botulinum) tc l F0
= 3 pht, ti tm ca sn phm ng hp s cho kt qu an ton theo quan im an
ton v mt sc khe. Nhng bo t ca vi sinh vt chu nhit c th cn sng i vi
qu trinh nhit c thit lp git bo t Clostridium botulinum v c th gy h
hng cho sn phm, nhng khng sinh ra c t trong khi bo qun thc phm. V
vy, vic thit lp qu trnh nhit ti thiu l hng n vic tiu dit cc bo t ca
cc ging Clostridium botulinum phn gii protein da vo nhng thng s z
(khong nhit cn thit thc hin 1 chu trnh logarit tiu dit vi sinh vt)
v nhit thc hin qu trnh tiu dit vi sinh vt. im kt thc ca qu trnh
thanh trng thng c xc nh theo Xc sut ca mt vi sinh vt cn sng st
(PNSU: Probability of a Non-Sterile Unit) Tr s thc nghim ca
F10121,1 i vi : 1. Sc khe cng ng Bo t Clostridium botulinum N0 =
103 D121,1 = 0,2 pht PNSU = 10-9 F0 = 3 pht 2. Ngn nga h hng - Bo t
chu nhit trung bnh N0 = 104 D121,1= 0,5 pht PNSU = 10-6 F0 = 5 pht
D121,1= 0,7 pht F0 = 7 pht - Bo t chu nhit Phn b nhit < 30oC N0
= 102 D121,1= 1,5 pht PNSU = 10-2 F0 = 6 pht Phn b nhit > 30oC
N0 = 102 D121,1= 1,5 pht PNSU = 10-6 F0 = 12 pht D121,1= 2,5 pht F0
= 20 pht Chn ch thanh trng Ta phi chn c mt ch thanh trng hp l, c
ngha l m bo c yu cu tiu dit cc vi sinh vt c hi trong hp , ng thi cc
cht dinh dng t b tn tht nht, phm cht sn phm tt nht. a. Chn nhit
thanh trng Tt c cc loi thc phm em ng hp u l mi trng sng ca cc loi
vi sinh vt. Mc d c rt nhiu yu t nh hng n kh nng hot ng ca vi sinh
vt, trong acid nh hng rt ln, nn acid l yu t quan trng trong vic chn
nhit thanh trng. Ngi ta chia sn phm hp thnh 2 nhm theo acid hot ng
ca sn phm, lm c s cho vic chn nhit thanh trng : >- Nhm sn phm hp
khng chua v t chua c pH 4,6 4,6t chua, tc l c mi trng pH rau.): vi
sinh vt pht trin mnh trong mi trng ny u l cc vi sinh vt chu nhit.
Trong loi nguy him hn c, c hi n sc khe ngi s dng l nhng bo t ca loi
vi khun Clostridium botulinum c kh nng phn gii protein, l loi vi
sinh vt chu nhit nguy him nht, c cc nc trn th gii coi l i tng ch yu
phi loi tr, v tiu dit nha bo ca n c coi l tiu chun thanh trng ti
thiu. Mc d n khng phi l i din a nng nht ca nhm vi
sinh vt ln men thi. Trong hp tht, c, ta cn c th gp cc loi vi
khun ym kh gy thi hng hp nh Clostridium sporogenes bn vi nhit hn c
Clostridium botulinum. Ngoi ra cc loi hp c acid hot ng khng cao lm,
cng thng c cc loi vi khun bn vi nhit nh Clostridium
thermosaccharolyticum thuc nhm ym kh a nhit, c tc dng phn hy
glucid. V loi hiu kh a nhit nh loi Bacillus stearothermophillus, l
loi vi sinh vt lm hng hp. 4,6>Do i vi cc loi hp c mi trng pH cn
phi c nhit thanh trng cao mi tiu dit c cc loi vi sinh vt a nhit gy
h hng hp. Nhit vo khong 105oC - 121oC, c gi l qu trnh tit trng. + i
vi cc loi hp thuc nhm chua, tc l c 4,6 (nh hp qu, c chua, rau mui
chua): cc vi khun chu
