Cng ngh Bo qun Lnh ng Tht B

GVHD: TS Nguyn Tin Lc

Page

Mc lc

tht b............................................................................................................................................... 1

Li ni u ........................................................................................................................................... 4

1.Tng quan v nguyn liu tht b: ............................................................................................ 5

1.1.Cu trc tht b: .................................................................................................................. 8

1.1.1.Cu trc m c ............................................................................................................. 8

1.1.2.Cu trc ca m m .................................................................................................... 9

1.1.3.Cu trc m lin kt .................................................................................................... 9

1.2.Tnh cht vt l - ha l c bn ca tht b: .................................................................. 10

1.2.1.Khi lng ring ........................................................................................................ 10

1.2.2.Nhit dung ring......................................................................................................... 10

1.2.4.Tnh dn nhit ............................................................................................................ 11

1.2.5.pH ................................................................................................................................ 11

1.3.Mt s tnh cht cm quan ca tht b:........................................................................... 12

1.3.1.Mu sc tht b ........................................................................................................... 12

1.3.2.Mi v ca tht b ....................................................................................................... 12

1.3.3. mm ca tht: ........................................................................................................ 13

1.4.Thnh phn ha hc ca tht b: ..................................................................................... 14

2.C s khoa hc v lnh ng .................................................................................................. 15

2.1.i nt v k thut lnh .................................................................................................... 15

2.2.Bn cht ca qu trnh lnh ng ................................................................................... 16

2.3.Phng php thc hin..................................................................................................... 20

2.3.1.Mi trng lm lnh.................................................................................................. 20

2.3.2.Lm ng bng t ng tip xc .............................................................................. 25

2.3.3.Lm ng bng kh ha lng..................................................................................... 26

3.Quy trnh cng ngh v gii thch quy trnh: ........................................................................ 27

3.1.Git m: .............................................................................................................................. 28

3.1.1.Tm ra: ..................................................................................................................... 28

3.1.2.Gy chong:................................................................................................................ 29

3.1.3.Ct tit: ....................................................................................................................... 29

3.1.4.Ly ni tng: .............................................................................................................. 29

3.1.5.X na:........................................................................................................................ 30

3.1.6.Pha lc tht: b na con c pha lc v phn loi theo hnh di y: ................... 30

3.1.7.Nhng bin i ca tht sau khi git m: ................................................................. 31

3.2.Quy trnh lnh ng: ........................................................................................................ 39

3.2.1.Lm lnh s b:.......................................................................................................... 39

3.2.2.Cp ng:.................................................................................................................... 40

3.2.3.M bng: ..................................................................................................................... 47

3.2.4.Bao gi: ....................................................................................................................... 48

4.Sn phm: ................................................................................................................................. 49

4.1.Cc ch tiu nh gi cht lng tht lnh ng: theo TCVN 7047:2002 ..................... 49

4.1.1.Yu cu cm quan ...................................................................................................... 49

4.1.2.Cc ch tiu l ha ...................................................................................................... 49

4.1.3.D lng cc kim loi nng ...................................................................................... 49

4.1.4.Cc ch tiu vi sinh vt............................................................................................... 50

4.1.5.D lng thuc bo v thc vt................................................................................ 50

4.1.6.D lng thuc th y ................................................................................................. 50

4.1.7.c t nm mc .......................................................................................................... 51

4.1.8.D lng hoocmon ..................................................................................................... 51

4.2.Qu trnh bo qun:.......................................................................................................... 51

4.2.1 Bo qun sn phm............................................................................................................. 51

5.Kt lun: ................................................................................................................................... 53

Li ni u

Trong cuc sng hin i, thc phm ng lnh l nhng sn phm i lin vi i sng hng ngy ca mi gia nh. Tit kim thi gian v tin bc chnh l nhng yu t u tin ngi tiu dng la chn thc phm ng lnh cho thc n ba n gia nh. Th trng thc phm ng lnh ca Vit Nam vi nm gn y ang c tc pht trin t 20-

40% mi nm.

K thut lnh l nhu cu thit yu pht trin cng nghip thc phm: Lnh cn cho cng nghip thc phm nh in v hi nc cn cho cng nghip nng vy. in v hi nc y cng nghip nng tin ti, th lnh s lm cho cng nghip thc phm pht trin vt bc (Micoiang - 1935).

Qu trnh lm lnh khng th thiu trong ngnh nh bt thy sn, cng nghip ch bin tht, rau qu, ru bia, sa tm li trong hu ht cc ngnh cng nghip ch bin nguyn liu ti c ngun gc thc vt v ng vt u cn n lnh.

Trong bi bo co ny, chng ti xin gii thiu v quy trnh cng ngh lnh ng tht b. Bi bo co gm 5 mc:

1. Tng quan v nguyn liu tht b: Phn ny gii thiu i cng v cu trc, tnh cht cm quan v thnh phn dinh dng ca nguyn liu tht b.

2. C s k thut lnh ng: Phn ny trnh by nhng nguyn l v phng php c bn ca qu trnh lnh ng.

3. Quy trnh cng ngh: y l phn quan trng, s cung cp cho cc bn kin thc v cc bc ca quy trnh git m, pha lc tht v tin hnh lnh ng to ra sn phm.

4. Sn phm: nh gi v cc gi tr cm quan, ch tiu vi sinh, phng php bo qun v r ng tht b ng lnh.

5. Kt lun: Tng qut li v m rng thm v ngha thc t ca bi bo co.

Bi bo co chc chn khng th trnh khi nhng thiu st v ni dung v cch trnh by. Chng ti rt mong nhn c s gp b sung v hon chnh hn.

1. Tng quan v nguyn liu tht b:

B tht hay b ly tht, b nui ly tht l mt loi b nh c chn nui ch yu phc ph cho mc ch ly tht b khc vi b sa chuyn phc ph cho mc ch ly sa hoc cc ging b nh khc phc v cho mc ch cy ko, vn chuyn.... c im ni bt ca ging b chuyn dng tht l to con, con ci trng thnh nng t 500-800kg, con c trng thnh nng t 900-1.400kg. T l tht x t t 60-65%, thch nghi vi nui chn th v v bo.

B tht c chn nui phc v cho nhu cu tiu th tht b ngy cng tng trn th gii. Theo mt thng k, bnh qun nhu cu tiu th tht b/ngi/nm ca th gii l 9 kg/ngi/nm, cc nc pht trin t l tht b chim 25 30% tng lng tht tiu th bnh qun u ngi, ring Vit Nam l 1,9 kg (nm 2006), t l tht b/tng lng tht hi tiu th l 5,19% (tng ng 0,85 kg tht x/ngi/nm).

Mt s ging b ly tht:

-Ging b tht nhit i

B Brahman

B Red Sindhi

B Sahiwal

B vng

C lu i ti Vit Nam, c chn lc, nhn ging t b c u n v khng u Trung Quc.

Ging b H'mng (b Mo) ti Vit Nam

-Nhm b tht n i

B Drought Master

B Lymousine

B Crymousine

B Red Angus

1.1.Cu trc tht b:

Tht c cu trc rt phc tp nhng v c bn thnh phn tht b c th bao gm cc m: m c, m m, m lin kt, mu, m thn kinh. Trong m c, m m v m lin kt theo th t l nhng thnh phn c gi tr dinh dng cao nht v c nghin cu nhiu nht.

T l thnh phn ca cc m trong cc loi tht khc nhau

1.1.1. Cu trc m c

M c l mt b phn quan trng ca tht b n chim khong 57- 62% khi lng ca tht v chim khong 35% trng lng ca con vt.

M c ca cc loi ng vt khng ch khc nhau v ging loi, gii tnh, tui m cn ph thuc nhiu vo ch chm sc v trng thi ca ng vt sau trc khi git m. M c thng c

mu thm hoc nht, m c ca cc ng vt c, trng thnh v lao ng nhiu c mu thm hn so vi nhng loi ng vt ci, cn non hoc ch nui ly tht.

M c l cu trc c gi tr dinh dng cao nht ca tht, hm lng cc cht trong m c tht b dao ng nh sau:Nc: 72- 75%, protein: 18.5- 22%, lipid v lipoid: 2- 3, cht ngm ra: 2- 2.8%, 0.3-0.8% glycogen,khong: 1- 1.4%, ch yu gm Fe, cc hp cht P, Ca, Mg, Zn,..v vitamin: thiamin, vitamin B6, vitamin E, vitamin A,..

1.1.2. Cu trc ca m m

M m c to thnh t cc m lin kt hnh li xp mm ha v cc t bo cht bo. Trong tht b hm lng m m dao ng trong khong kh rng t 2- 40% v t l nghch vi hm lng nc trong cu trc c tht.Lng cht bo vi mt t l nht nh s lm tng gi tr cm quan v gi tr dinh dng ca tht.

Lng m m, v tri tch ly, thnh phn ,mu sc, mi v v cc tnh cht khc ca m m ph thuc nhiu vo ging loi, tui, gii tnh, mc bo ca vt nui v iu kin nui dng.

Thnh phn ha hc ca m m ch yu l lipid v cc dn xut(chim 70- 90%). Ngoi ra cn c cha protein(chim 0.5- 7.2%), nc(chim 2- 21%), sc t, enzyme v cc vitamin tan trong du.

1.1.3. Cu trc m lin kt

Trong c th, m lin kt c phn b rng ri, c tc dng lin kt cc b phn li vi nhau, tham gia vo qu trnh trao i cht v thc hin nhim v bo v c th. M lin kt c cu thnh t ba phn: cht nn, cu trc hnh si v dch m.

M lin kt c hnh thnh trn c s t cc si colagen v si eslatin, trong si colagen l cu trc quan trng nht.

Hm lng m lin kt ph thuc vo ging loi, mc bo, tui, gii tnh, b phn c quan nhng thng khng vt qu 12% khi lng ca sc tht.

Thnh phn ha hc trung bnh ca m lin kt c th hin nh sau:Nc: 62-

74%, protein: 21- 35%, lipid v lipoid: 1- 3.3% v cc thnh phn khc.

Tm ti, m lin kt v m m tuy c gi tr dinh dng v hm lng trong tht b thp hn so vi m c nhng cng c s dng nhiu trong cc sn xut cc sn phm nh: xc xch, pate, ch, nem chua, vy kt hp s dng m c, m m v m lin kt lm tng khi lng sn phm, to ra gi tr cm quan tt cho sn phm, tng tnh to nh, to gel ph hp vi yu cu mt s sn phm, tn dng c nhiu sn phm khc nhau ca tht do hiu qu s dng v gi tr kinh t s tng ln.

1.2.Tnh cht vt l - ha l c bn ca tht b:

Tnh cht vt l ca tht b khc nhau theo tng ging loi, tui, gii tnh, ch chm sc, ch dinh dng. Tnh cht vt l ca tht cng l mt trong nhng tiu chun nh gi cht lng ca tht, nghin cu r v tnh cht vt l-ha l ca tht gip ta c nhng c s b ch trong vic tnh ton cc qu trnh bo qun nh nhit, lnh,....Mt s tnh cht vt l quan trng c xt nh sau:

1.2.1. Khi lng ring

Khi lng ring ca tht b thay i theo rt nhiu yu t nh ging loi, gii tnh,

tui,...nhng quan trng nht l hm lng cht bo trong tht v v tr ca sc tht.

Khi lng ring trung bnh 150C ca tht b kh m l 1.02- 1.07kg/l, ca cht bo l 0.95-0.97kg/l v ca xng l 1.13- 1.3kg/l.

1.2.2. Nhit dung ring

Nhit dung ring ca tht khc nhau theo t chc hc v thnh phn ha hc ca n.

Nhit dung ring ca mt s loi sc tht ca tht b.

Mt lu khi tnh nhit dung ring ca cc loi thc phm l phi tnh nhit dung ring ca n trn im bng v di im bng.

Khitnhtonnhit dung ring cho tht b ta cn ch n nhit dung ring trn v di im bng, do nhng nhit dung ny la khc nhau, v vyqu trnh lm lnh (ng bng) hoc sy nhit s c nhng gi tr dung ring khc nhau v vic iu

chnh cc thng s sao cho ph hp s khc nhau. Nguyn nhn: c ch truyn nng lng, truyn nhit khc nhau trong tht trn im bng v di im bng l khc nhau. Khi ng bng cc tinh th hnh thnh nn ch truyn nhit theo dn nhit.

1.2.4. Tnh dn nhit

Nghin cu nh hng ca cu trc c tht n h s dn nhit ca tht cho thy rng:

khi cc si c ca tht xp vung gc vi nhau th tht c h s dn nhit cao nht khong

1kcal/m.gi.0C; khi cc si c xp song song th h s dn nhit gim xung t khong

0.8- 0.9kcal/m.gi.0C; c bit khi c tht c nhiu m th h s dn nhit cng b gim xung.

H s dn nhit ca tht ng cao hn so vi so vi tht cha ng v nhit ng c cng thp th h s dn nhit ca tht cng cao. H s dn nhit ca tht sau khi gii ng ln hn so vi trc khi cp ng; ca tht b ti trung bnh khong

0.43kcal/m.gi.0C; ca tht b ti p nc trung bnh khong 1.2kcal/m.gi.0C; ca

tht cp ng nhit -10- -200C l 1.3kcal/m.gi.0C.

1.2.5. pH

pH l mt trong nhng ch tiu quan trng trong vic nh gi cht lng ca tht ti. pH tng loi vt nui thay i theo tng ging loi, tui, gii tnh, ch dinh dng, v tr tng sc tht ca vt nui.

pH trung bnh ca tht b ti c tnh acid yu t khong 6.5- 6.9.

Cc yu t nh hng n pH ca tht cng nh s thay i pH ca tht trong sut qu trnh bo qun s c nghin cu nhiu hn trong cc phn sau ny.

1.3.Mt s tnh cht cm quan ca tht b:

1.3.1. Mu sc tht b

Mu sc ca tht ti do cu trc, thnh phn ca c tht v hm lng cht bo trong quyt nh. Mu sc ca tht khng ch do ging loi, tui tc, gii tnh, v tr sc tht quy nh m cn ph thuc nhiu vo cch thc chn nui v loi thc n m b s dng.Mu ca m b gy ra bi s c mt ca cc sc t caroten c nhiu trong m ca b, do vy n thng c mu vng c trng.

Mu sc ca t chc c tht do lng hemoglobin v myoglobin ca t chc c tht quyt nh. Tuy nhin Hb ch yu c trong mu, v sau khi qu trnh git m ta x mu do vy, lng Hb trong tt b l khng ng k, do vy

mu sc ca c tht ch yu do Mb, ba dng Mb, oxyMb, v MetMb.

Mu sc tht ca b trng thnh thng m hn so vi b cn non. Mu sc ca tht cn chu nh hng ca sc t thc vt trong thc n ca chng, b n loi thc vt c mu no th tht thng c mu . Tht b c c mu hng ti trong khi tht b ci li c mu hng sm. B lm vic, vn ng cng nhiu th tht cng c mu sm hn.

1.3.2. Mi v ca tht b

Mi v ca tht b ph thuc rt nhiu vo cht ngm ra, l nhng cht rt d bay hi, rt chit hay trch ly ra ngoi, y chnh l tc nhn chnh gy ra hng v, mi c trng cho cc loi tht.

Thnh phn ca cc hp cht d bay hi c trong tht b nguyn liu thng gm: acetaldehyde, aceton, methylethylceton, lng nh ru ethylic, methylic, methyl- dimethyl v ethylmercaptan,...

Mi v ca tht b ph thuc vo ging vt nui, mc cht bo, gii tnh, la tui v tnh hnh chn nui ca cc loi ng vt. Mi v ca tht b cn ph thuc vo chung tri chn nui v c loi thc n m b n. Chung tri c mi hoc thc n ca chng c mi c trng th tht ca chng cng c mi tng t nh vy. c bit khi b s dng khng sinh nu khng c thi gian cch ly th tht ca chng vn cn tn ti khng sinh v c mi nay.Tht ca b c, trng thnh thng c mi v nng hn, c trng hn so vi b ci hoc cha trng thnh.

Do mi v ch yu do nhng acid bo, cht bo d bay hi gy ra nhng nu lu tht c mi c trng ngoi khng kh hoc ni thong gi th mi ny c th gim hoc b mt i.

1.3.3. mm ca tht:

mm ca tht ph thuc vo cc nhn t ca ng vt khi cn sng v c khi cht.

+ Khi cn sng: mm ca tht ph thuc vo ging loi, gii tnh, la tui, cch thc lin kt ca m c,..

+ Khi cht: mm ca tht ph thuc vo cch thc git m, gy ngt, cch thc m tht,...

Ngi ta cng thy rng, mm ca tht cng l mt yu t c th di truyn, tnh cht ny c di truyn qua con c v kh nng di truyn b t khong 65- 70%.

mm ca tht cng ph thuc vo gi tr pH ca tht, pH cng gn im ng in th cu trc ca c tht cng bn cht v mm ca n cng gim. Ngoi ra cc cht ph gia cng c nh hng khc nhau n mm ca tht m ta s c kho st trong nhng phn sau.

Ta c th ci thin mm mm ca tht b bng mt s cch c bn:

+ Dng Marbling: c tc dng bi trn lm d nhai, ng thi n s lm gim

mm biu kin v lm cho cu trc ca tht t dy dc hn

+ Ci thin mm bng chn hay kch thch in

+ Ci thin bng bin php c hc: massage, xy, xm tht, dng enzyme loi protease,...

1.4.Thnh phn ha hc ca tht b:

Tht b l mt trong nhng loi tht c gi tr dinh dng kh cao, gi tr dinh dng ca tht b ch yu quyt nh bi hm lng, thnh phn cc protein ca tht b, ngoi ra tht b cn cha lng lipid, vitamin v khong cht cn thit cho c th con ngi.

Thnh phn ha hc ca tht b thay i theo ging loi, tui, gii tnh, cch nui, ch dinh dng, v tr sc tht...Bng sau y cho ta ci nhn tng quan v thnh phn

ha hc ca mt loi tht b:

Thnh phn tht b

Hm lng trong 150g

Hm lng trong 100g

Nng lng

793kJ (189kcal)

529kJ (126kcal)

Cht m

34.1g

22.7g

Cht bo

5.8g

3.9g

Cht bo bo ho

2.4g

1.6g

Axit trans

0.2g

0.1g

Cht bo khng bo ho a

0.6g

0.4g

EPA (omega 3)

38mg

25mg

DHA (omega 3)

8mg

5mg

Cht bo khng bo ho n

2.6g

1.7g

Carbohydrate

0g

0g

Cht ng

0g

0g

Natri

77mg

52mg

Vitamin B12

1.63mcg (81%RDI)

1.08mcg

St

2.94mg (25%RDI)

1.96mg

Km

6.23mg (52%RDI)

4.15mg

Trong thnh phn ha hc ca tht b ta ch n cht ngm ra. y l nhng cht rt d rt chit hay trch ly ra khi m c, chim khong 1.5- 2.3% m c, c ngha quan trng to nn hng v, mi thm c trng ca tht b. Thnh phn cc cht ngm ra

thng gp l: methylethylceton, lng nh ru ethylic, methylic, methyl- dimethyl v ethylmercaptan,...Cht ngm ra gm c hai loi:

Cht ngm ra cha N: chim 1.2- 1.6%

Cht ngm ra khng cha N: chim mt t l nh

Cht ngm ra l thnh phn quan trng nht gp phn to nn mi v dc trng cho

sn phm.

2. C s khoa hc v lnh ng

2.1.i nt v k thut lnh

Con ngi bit lm lnh v s dng lnh cch y rt lu:

-Cc tranh v trn tng trong cc kim t thp Ai Cp cch y khong 2500 nm m

t cnh n l qut cc bnh gm xp cho nc bay hi lm mt khng kh.

-Cch y khong 2000 nm ngi n v Trung Quc bit trn mui vo nc hoc tuyt to nhit thp hn. Nhng k thut lnh hin i bt u phi k t khi gio s Black tm ra n nhit ha hi v n nhit nng chy vo nm 1761 - 1764.

- cui th k XVIII t pht hin u tin l trong iu kin chn khng nc bay hi nhit thp. Vo nm 1834 bc s Perkins (Anh) xy dng c my lnh u tin vi tc nhn lnh l ete etylen lm vic p sut thp hn p sut kh quyn.

-Cui th k XIX c hng lot cc pht minh ra my lnh vi nhng tc nhn c p sut

trong chu trnh kn cao hn p sut kh quyn:

Nm 1871 Tellier xy dng my lnh vi tc nhn ete metylen.

Nm 1872 Boil pht minh nguyn l my lnh NH3.

Nm 1874 k s Linde (c) thit k c my lnh NH3, lc ny vic ch to my lnh nn hi mi thc s pht trin rng ri trong hu ht cc ngnh kinh t.

-Mc quan trng trong k thut lnh l vic sn xut v ng dng cc freon M vo nm 1930. Cc loi rau, tri cy, hi sn v tht ng lnh c bn cho cng chng ln u tin vo nm 1930 ti Springfield, Massachusetts, di thng hiu Birds Eye Frosted Foods.

-Ngy nay k thut hin i ang i vo nhng nh cao ca khoa hc k thut hin i.

Phm vi nhit ca k thut lnh ngy nay c m rng rt nhiu v k thut ang

tin dn n nhit khng tuyt i.

-Ring k thut lnh l nhu cu thit yu pht trin cng nghip thc phm: Lnh cn cho cng nghip thc phm nh in v hi nc cn cho cng nghip nng vy. in v hi nc y cng nghip nng tin ti, th lnh s lm cho cng nghip thc phm pht trin vt bc (Micoiang - 1935).

-Ngy nay, ngi ta thng dng nit lng lm ng thc phm, thc phm cng

nhanh ng s cng t ng tuyt.

-Lm lnh ng c thc hin trong cc ngnh khai thc ch bin v bo qun thc phm. Qu trnh lm lnh khng th thiu trong ngnh nh bt thy sn, cng nghip ch bin rau qu, ru bia, sa tm li trong hu ht cc ngnh cng nghip ch bin nguyn liu ti c ngun gc thc vt v ng vt u cn n lnh.

2.2.Bn cht ca qu trnh lnh ng

-Lnh ng l qu trnh h nhit ca vt liu xung thp hn nhit ban u (Tc < Tmt) v thp hn nhit ng bng.

Lnh ng thng: Tc > -100oC

Lnh ng su: Tc < -100oC

-Lm m v tan gi l qu trnh ngc li ca lnh ng.

-Hn ch ca phng php lnh ng l:

Cu trc ca sn phm c th b thay i. Trong qu trnh lnh ng cc bin i v cu trc ca sn phm l cc bin i khng thun nghch. V vy, sau khi r ng cu trc ca sn phm khng tr li nh trc khi lnh ng na.

Qu trnh lnh ng cn phi c cung cp nhiu nng lng. Nng lng ny p ng 2 mc ch: thc hin qu trnh lnh ng v bo qun sn phm lnh ng.

2.2.1. Qu trnh kt tinh nc

Qu trnh kt tinh nc l qu trnh to mm tinh th v lm tng kch thc ca chng, qu trnh gim nhit tc l lm gim nng lng, gim s chuyn ng t do v nhit ca cc phn t cht lng n mt mc no lc lin kt c th c nh chng li ti nhng v tr xc nh, to thnh tinh th nc .

C ch

-Trong nc thng lun tn ti nhng phn t rn vi kch thc rt nh, nhit gn

0oC, nhng phn t ny s ngng chuyn ng nhit, lc lin kt ca chng ln hn lc lin kt gia cc phn t nc vi nhau. V vy, cc phn t nc s lin kt vi cc phn t rn hnh thnh mm tinh th. Do , xu hng l cc mm tinh th ht cc phn t nc tng kch thc mm tinh th v t xu hng l tng s lng mm tinh th.

Cc s hnh thnh tinh th

-Trong cu trc thc phm, nc chu nhiu tc ng ca cc cht tan, cht khng tan, nhng v tr khc nhau trng thi ca chng cng khc nhau, v vy nhit kt tinh ca nc trong cc sn phm khc nhau l khc nhau.

2.2.2. Nhng yu t nh hng n s kt tinh nc

Nng cht ban u

-Khi tng nng cht tan nhit kt tinh ca nc gim. V cc cht ha tan s ko theo cc pn t nc lm ngn cn chng kt hp vi nhau.

Phng trnh th hin s mi quan h ca nhit kt tinh v nng cht tan:

t = -1.84. n

Trong :

t: gim nhit kt tinh.

n: s phn t gam cht tan.

Nhit kt tinh

-Khi nhit kt tinh ca nc trong thc phm cng gim th tinh th hnh thnh

cng nh, di. Do mc nh hng ti cu trc thc phm gim.

nhit khong (-20 -10)oC cc tinh th to thnh c kch thc ln,

khng u.

nhit khong (-22 -20)oC cc tinh th to thnh c kch thc nh v

u.

Nu nhit thp hn na th tinh th to thnh c kch thc rt nh v lng tinh th ln.

-Khi ng lnh cn phi xc nh nhit cp ng ti u, ng vi nhit cp ng ti u th lng nc t do v nc lin kt ha l trong thc phm phi kt ng hon ton, ng thi vi sinh vt cht hoc ngng hot ng hon ton.

Thi gian lnh ng:

-Thi gian thc hin qu trnh lnh ng ph thuc vo bn cht nguyn liu (hnh dng, kch thc, cu trc, thnh phn ha hc ca thc phm), nhit v phng php thc hin qu trnh lnh ng.

-Ngi ta thng s dng m hnh ton ca Plank xc nh thi gian lnh ng vi cc iu kin gi nh (qu trnh lnh ng din ra vi ton b nc trong thc phm; iu kin truyn nhit n nh; hnh dng, kch thc, t trng ca nguyn liu khng

thay i; nhit dung ring v dn nhit l hng s):

[ ( ) ]

Trong :

tf [s]: thi gian lnh ng.

h [W/m2.K]: h s truyn nhit b mt.

f []: im lnh ng

a []:nhit mi trng

[J/kg]: nng lng gii phng trong qu trnh kt tinh.

[kg/m3]: khi lng ring ca nguyn liu.

x[m]: dy ca nguyn liu. k1[W/m.K]: dn nhit ca bao gi. k2[W/m.K]: dn nhit ca mi trng

6, 24: l h s c trng cho tng hnh dng ca nguyn liu (dng cu)

Tc lm ng

-Tc lm ng c th c o bng chuyn dch ca vch phn cch gia min nc kt tinh v min nc cha kt tinh.

-Qu trnh lnh ng c 2 dng c bn:

Lnh ng 1 pha: sau khi git m xong tht s c lnh ng ngay lp tc, lm gim nhit xung 8oC. Lnh ng 1 pha c u im hn so vi lnh ng 2 pha v gim c thi gian lm lnh ng, gim tn hao khi lng sn phm, gim chi ph lnh v din tch phng lnh.

Lnh ng 2 pha: gm 2 giai on. Giai on u tht nng c lm lnh

h nhit xung 4oC, v sau c a vo thit b lnh ng.

-Tc lnh ng l t s gia chiu dy lp thc phm v thi gian lm ng thc phm :

Vf = X/ [m/h]

-Da theo tc lm ng, qu trnh lnh ng chia lm 3 loi:

Lnh ng chm: S gim nhit din ra chm qu trnh kt tinh nc c iu kin ht cc phn t nc xung quanh s lng tinh th t, th tch v kch thc tinh th nc ln nh hng nhiu n cu trc thc phm.

Lnh ng nhanh: S trao di nhit ln, nhit thc phm gim nhanh

Mc di chuyn ca nc trong qu trnh kt tinh t hnh thnh cc tinh

th nc nh, s lng tinh th nhiu t nh hng n cu trc ca thc phm.

Lnh ng cc nhanh (tc thi): Chuyn nc v trng thi rn ngay v tr tn ti ban u ca n, vi nhit kt tinh thp cc tinh th c hnh thnh vi kch thc rt nh hu nh khng nh hng n cu trc v cht lng thc phm.

2.3.Phng php thc hin

2.3.1. Mi trng lm lnh

Trong ngnh cng ngh ch bin thc phm, trong thc t thng thng mi trng lm lnh ba dng sau:

Mi trng lm lnh

u im

Nhc im

Kh (khng kh lnh

i lu)

Mi trng t nhin c th

gim nhit xung rt thp ph hp vi mi hnh dng, kch thc phc tp ca thc phm

Kh nng trao i nhit

km, d lm bay hi nc t b mt thc phm, oxy ca khng kh c th gy nn nhng phn ng ha hc lm bin i mu sc, cht lng thc phm.

Lng (nc, cc dung

mi hu c)

Thch hp cho nhiu thc

phm nc gii kht nh: bia, nc ngt v mt s nc gii kht khc.

Tn km nhiu v chi ph

u t thit b, chi ph sn xut, cn phi c h thng lnh lm lnh cht ti lnh trung gian (dm hu c).

Rn (nc , nc

xay phi trn vi mui)

Khi nc nng chy

mc tip xc vi thc phm tng ln, kh nng trao i nhit ln, thi gian lm lnh gim, hn ch s mt nc.

D thc hin, c bit trong iukinsnxutkh khn.

Hao ph lnh ln do nhng

dngnhittruynvo trong qu trnh sn xut, vn chuyn, bo qun v s dng nc .

Nc d lm h hng thc phm do va chm c hc.

2.3.2. Lm ng bng mi trng khng kh

u nh c i m

u im

Nhc im

Ph hp vi thc phm c ngun

gc trn cn

m bo v sinh

Vn hnh n gin

Ph hp vi mi hnh dng, kch

thc ca thc phm

D mt nc

Kh nng trao i nhit chm

Nh ng i u ki n

Nhit thc phm: l nhit trung bnh v th tch ca chng cui qu trnh cp ng, ph thuc vo c im tnh cht ca thc phm v yu cu thi gian bo qun.

Nhit mi trng lnh: mi trng lnh ng phi c nhit thp hn nhiu so vi nhit lm ng thc phm m bo tc lm ng nhanh.

Vn tc dng kh: v vn tc nh hng n kh nng trao i nhit, mc mt nc ca thc phm, chi ph sn xut nn ta cn phi xc nh gi tr ti u ca vn tc dng kh.

Nu nhit mi trng trong khong (-45 -35)0C th vn tc ti u

Vopt=(510)m/s

Cch ti n hnh

Cc thit b lm ng bng khng kh c cc vch c cch nhit v cch m, trong khng kh i lu cng bc tun hon gia b mt sn phm v b mt ca dn lnh.

M hnh 1 thit b tunnel (freezing tunnel) lnh ng bng khng kh cng bc

2.3.1.1.H thng cp ng IQF dng xon: h thng cp ng nhanh cc sn phm ri

H thng cp ng IQF dng xon c u im:

Cng sut lnh tng i ln

Thi gian ng lnh ngn

Thng s dng phng php cp dch bng bm

Nguyn l chung: cc sn phm c t ln cc bng chuyn, chuyn ng vi tc chm, trong qu trnh n tip xc vi khng kh lnh nhit thp v nhit h xung rt nhanh.

Cu to:

Bung dng khi hp, cc tm vch l tm cch nhit polyurethan, 2 mt inox, bn trong b tr 1 bng ti dng xon l xo t di ln trn.

Bung cn c ba lm rung chng sn phm dnh vo nhau v vo bng ti

Dn lnh c qut kiu hng trc, s dng mi cht NH3

S nguyn l:

2.3.1.2.H thng cp ng IQF dng thng

Dn lnh b tr ln trn cc bng ti, thi gi lnh ln b mt sn phm trn bng

chuyn, ton b bng chuyn tri di theo mt ng thng.

Sn phm cp ng a vo mt u v ra bng u kia.

2.3.1.3.H thng cp ng IQF dng siu tc

Cu to cng gn ging vi h thng cp ng IQF dng thng, bn trong c 1 hoc 2

bng ti c kh nng iu chnh tc v cp.

Cc dn lnh xp thnh 2 dy 2 bn bng ti, qut gi kiu ly tm.

Nguyn l lm vic

Khi sn phm di chuyn trn bng chuyn qua bung cp ng, hng ngn tia kh lnh vi tc cao hng trc tip v lin tc vo 2 b mt ca sn phm, thi hi nng bao bc quanh sn phm y nhanh qu trnh trao i nhit.

Khi cc tia kh lnh thi ln b mt sn phm th nhanh chng to ra mt lp bng mng bao quanh sn phm do lm gim s mt nc v sn phm vn gi c hnh dng, kch thc ban u.

2.3.2. Lm ng bng t ng tip xc

u nh c i m

u im

Nhc im

Cht lng thc phm c m bo

iu chnh c nng sut lnh

Hot ng khng lin tc

Thi t b: T n g ti p xc

Cu to bn ngoi:

C dng hnh hp ch nht.

V t gm 3 lp:

Lp ngoi cng v lp trong cng l lp cch inox

Lp gia l lp cch nhit v cch m lm bng polyurethan

Cu to bn trong:

Gm nhiu tm lc (lm bng hp kim nhm) c dng hnh hp ch nht lp t song

song theo phng nm ngang ca y t v c iu chnh ln xung bng ben thy lc.

Khong trng bn trong tm lc chia lm 5 khoang ghp ni tip thng qua ng gp 2

u, mi khoang c 8 rnh dn mi cht lnh i vo.

Khong cch gia 2 tm lc l khng gian cho sn phm cp ng vo.

Nguyn l lm vic:

Hnh: M hnh 1 thit b lnh ng tip xc

Thc phm c t vo khong gia 2 tm lc, lc ny ben thy lc p tm lc xung lm cho 2 b mt sn phm tip xc vi tm lc.

T trong cc rnh mi cht s nhn nhit ca sn phm cn lm ng thng qua b mt tm lc v bc hi, sn phm lin tc truyn nhit cho mi cht v nhit ca n gim dn.

Mi cht lnh vo v ra c cc lc nh cc ng gp c ni vi 1 ng gp cao su, ng cao su ny ni vi ng dn mi cht lnh t bnh cha thp p v tm lc ng thi dn hi mi cht sau khi bay hi v li bnh cha thp p.

2.3.3. Lm ng bng kh ha lng

u nh c i m

u im

Nhc im

m bo c cht lng thc phm

Thit b n gin, an ton, d vn chuyn

p dng vi thc phm c kch thc nh

Cht kh ha lng c gi thnh cao

Nguyn l lm ng

Cho cc cht lng c nhit ha hi thp (iu kin p sut kh quyn) tip xc vi b mt thc phm, cht lng s thu nhit t thc phm ha hi, cht kh to thnh c nhit thp s c s dng lm lnh thc phm trc khi nc ng bng v cn bng nhit trong thc phm khi nc kt tinh.

Mt s cht kh ha lng thng c ng dng:

Tn cht

Nhit si (pkq=1at)

N2

-195,8oC

O2

-182,97oC

Ar

-185,87oC

Ne

-246,1oC

H2

-252,76oC

Thit b:

Thi t b kn

Cht kh ha lng tun hon trong h thng kn, sau mi chu trnh cht kh sinh ra

c loi i tp cht v ha lng tr li.

Tit kim cht kh ha lng, tn dng c nng sut lnh.

H thng thit b cng knh, phc tp.

Gy nhim mi trng v nh hng gi tr sn phm.

Thi t b h

Thit b dng hnh tr nm ngang, khong trng bn trong chia lm 4 ngn c kch thc khc nhau, gia trc thit b c bng chuyn li dng vn chuyn thc phm:

Ngn lm lnh: s trao i nhit din ra nh i lu cng bc ca cht kh v pha

ngn lm ng, lm tng kh nng thu hi nng sut lnh.

Ngn lm ng: cht lng c phun ln b mt theo nhiu hng khc nhau, phn

cha kp ha hi c bm a tr li vi phun.

Ngn cn bng nhit: s trao i nhit ch yu xy ra gia cc lp bn trong v bn ngoi ca thc phm nn mi trng kh ch c tc dng gi cho nhit b mt thc phm n nh.

3. Quy trnh cng ngh v gii thch quy trnh:

Nhn b

Kim tra

Tm sch

Pha lc tht

Gy chong

Phn loi

Ct tit

Lm lnh s b

Chuyn ln bng ti

Lnh ng

Ct b c quan sinh

M bng

Lt da

Bao gi

Ct u

Ly ni tng

Sn phm tht b lnh ng

Ra

X na

3.1.Git m:

Trc khi git m b phi c kim dch ca cc c quan th y c thm quyn, b phi khng mc bnh, c nht khong 24 gi.

3.1.1. Tm ra:

B trc khi git m phi c tm ra, ngh ngi nhm m bo cht lng tht sau khi git m.

B c la vo v tr c vi phun nc c p lc mnh tm ra sch, cho gia sc di chuyn trong phvi h p chng c st vo nhau nhm tng hiu qu qu trnh ra . Mc ch ca cng on ny l loi i cht bn trn da (t, phn, vi sinh v ...).

3.1.2. Gy chong:

L lm cho con vt mt kh nng nhn bit nhng h h hp v tun hon vn hot ng bnh thng .ngha ca vic gy chong l lm cho con vt khng b hong s , cng thng khi git m , m bo an ton cho ngi git m .

C nhiu phng php gy chong nh: Dng ba, dng sng, ph hnh ty, dn g kh CO2,... Hin nay thit b gy chong da vo hin tng git in xoay chiu tc ng ln h thn kinh ca con vt lm cho con vt b ngt xu, khng ku, khng giy gia trong thi gian ngn tin hnh qu trnh chc tit. Dng in ca thit b g y chong l dng in xoay chiu khng c trung tnh trn c hai u dy ra, do rt an ton cho ngi s dng, s khng c hin tng b in git nu chm mt dy trong hai dy ca thit b.

Ch : Bt k phng php gy chong no cng l yu t gy stress nghim trng cho con vt. Do vy khi gy chong cn lu khng con vt giy nhiu, thi gian gy chong nhanh chnh xc v hiu qu, m bo con vt b hn m tuyt i.

3.1.3. Ct tit:

Mc ch ca vic ly tit l lm cht con vt v duy tr cht lng tht sau khi git m. Vic ly tit phai c thc hin ngay sau khi lm chong, thi gian t lc lm chong n khi ly tit khng c qu mt pht.

Cch lm: dng dao chuyn dng ct t mch mu chnh, mu t c th con vt ra dng c cha. Lc u ta s b i mt t, sau s ly mu n mt mc no ri ngng v mu sau cng thng l mu en. Thi gian ly tit khong 4 -6 pht.

3.1.4. Ly ni tng:

Vic ly ni tng cn phi tin hnh cn thn, vt ct phi bng nhn, gi nguyn cu trc ca ni tng. Thi gian ly ni tng khng nn ko di do tht c th v nh hng mi t cc cht bay hi c mi hi trong ni tng.

Cn trnh lm v ni tng v s lm nhim vi sinh vo tht. Sau khi ly ni tng, tht cn c ra qua mt ln nc lm sch mu trong khoang ngc v bng. Dn treo v mc c thit k sao cho khi treo b ln hai chn sau m rng d m ly cc b phn

ni tng, ng thi dn cng lm gi di chuyn mng tht sau khi m ti ni bo

qun.

3.1.5. X na:

C th x bng phng php th cng hay my.

X bng phng php th cng: ngi cng nhn dng dao di, ln x dc xng sng. X tht phi m bo m quan ca vt x, mnh tht v vy yu cu cng nhn phi c tay ngh cao.

X bng my: my x tht c li dao to t thng ng theo chiu treo tht. Khi x

tht, ngi cng nhn s cm cn dao a vo x tht. X bng my th vt x tht t b sai phm

3.1.6. Pha lc tht: b na con c pha lc v phn loi theo hnh di y:

Cch chia v phn loi tht b

3.1.7. Nhng bin i ca tht sau khi git m: Qu trnh co cng:

-nh ngha

T cng sau khi cht l qu trnh m khi cc cu trc ca c tht tp hp, lin kt li vi nhau lm cho tht tr nn rn chc hn di tc ng ca nhiu yu t ni ti bn trong v nhng yu t mi trng bn ngoi khc.

S t cng l kt ca cc qu trnh bin i ha sinh mt cch phc tp do enzyme gy ra v ph thuc vo nhiu yu t.

-Cch thc nh gi: nh gi thng qua trng thi cm quan ca tht:

Cu trc: sau qu trnh c cng cc si c c xu hng co ngn li, si c tr nn cng hn, mc hydrat ha gim nhanh, tht khng cn n hi nh ban u.

Mi v: sau khi ch bin nhit, tht khng cn mi v c trng, nc luc c mu

c do c s tit dch c ra.

Mu sc nht hn so vi tht nng: s mt nc, cu trc c co li nh hng n s phn x nh sng dn n s thay i mu sc.

Thng qua cc thng s khc: pH, nhit lng ta ra

Trong qu trnh co cng xy ra s phn hy glycogen sinh ra acid lactic v acid phosphoric v gii phng mt lng nhit kh ln nn ta c th da vo nhng ch tiu ny nh gi mc co cng.

-Din bin

Thy phn glycogen

Sau khi cht, s h hp b ngng tr, oxy khng cung cp c vo t bo, trao i nng lng hiu kh gim dn v bt du xy ra s phn gii glycogen vi s tham gia ca ATP.

u tin, glycogen b phn hy theo con ng phosphoril ha to thnh acid lactic, mt phn gii phng acid phosphoric v gii phng nng lng. Trung bnh khi to thnh 1g acid lactic th gii phng c 280cal nhit, nhit ny gi l nhit ha cng.

Cng vi s phn gii glycogen theo con ng phosphoril ha cng xy ra s phn gii glycogen theo con ng amilo ha to thnh cc snh phm ng n gin c tnh kh nh: glucose, maltose v cc polysaccharide kh khng ln men.

Thy phn ATP, cretinphosphat

ATP v creatinphosphat l nhng hp cht quan trng nht tham gia ti nng lng cho cc phn ng oxy ha trong qu trnh trao i cht.

S chuyn ha ATP xy ra theo 2 hng:

+ Chuyn ha gc phospho bo ha nng lng sang phn t khc.

+ ATP thy phn thnh ADP, AMP v cc phosphat t do, gii phng nng lng cho s co rt ca c.

ATP trong c th thng c duy tr mc cn bng, mt phn ATP c to ra trong qu trnh glyco phn, mt phn mt i do s phn hy ca myosin. V vy khi lng d tr glycogen nhiu th ATP khng b phn hy hon ton v thi gian co cng ca c s c ko di.

To actomyosin

Lc mi cht ATP cn y , actin trng thi hnh cu khng lin kt vi myosin, khi si c suy yu myosin to phc cht vi K+, Ca++, glycogen v ATP. Mi phn t actin c nhng v tr c hiu lin kt vi myosin, trong iu kin thng mt s protein nh troponin v tropomyosin s che ph li v tr ny.

Khi pH gim v s phn hy ATP xy ra mnh m lm gii phng Ca2+, Ca2+ hnh

thnh lin kt vi troponin v tropomyosin l v tr lin kt v s hnh thnh actomyosin bt u.

Khi cc si c trng thi ngh, hai u ca si actin chui vo khong gia cc si myosin.

Khi co c cc si actin v myosin khng c ngn li m chng trt ln nhau, si actin chui vo gia cc si myosin.

S hnh thnh actomyosin v co ch co c

-S tc ng

mm

Tht sau khi b git m c cha mt lng nc nht nh nn cu trc ca m tht tng i mm v n hi, nhng sau s bin i xy ra nhanh chng ph thuc ch yu vo mc hydrat ha ca cc protein. mm ca tht trong sut qu trnh co cng gim do hai nguyn nhn chnh:

+ S thay i pH n gn vi gi tr pH ng in ca protein c

+ S hnh thnh phc cht actomyosin lm gim s trung tm, s lin kt a nc c

protein lm cho kh nng hydrat ha ca protein si c gim ng k.

Tnh cht

Bin i

rn

cn ct

m

Tng 25%

Tng 2 ln

t cc tiu, thp hn 25% (2h)

pH

Trong qu trnh co cng sau khi git m, pH ca tht gim nhanh chng do s to thnh ca cc acid. S thay i pH mt mt thc y qu trnh qu trnh co cng xy ra lm cho tht rn hn, mt khc to iu kin hot ng cho cc enzyme trong qu trnh t chn sau ny v vic lm gim pH s c ch tp nhim, h hng do vi sinh vt gy ra.

Thi gian (h)

pH

Hm lng (mg%)

Glycogen

Glucose

A. lactic

1

6.12

633.7

159.7

319.2

12

5.94

462

171.2

609.16

24

5.56

274.9

202.5

700.6

48

5.68

183.1

222.6

692.6

S tng nhit khi tht

Do qu trnh phn hy glycogen c sinh ra nng lng nn trong qu trnh co cng nhit khi tht c tng ln t 0.5- 20C, s gia tng nhit s gp phn lm tng hot ng ca cc enzyme v vi sinh vt sau ny, lm cho qu trnh bo qun kh khn hn.

-Cc yu t nh hng qu trnh co cng

Ccyutvbnthn nguyn liu:

Ging loi, gii tnh, la tui, cu

trc m c, loi m c,

Loi vt c cu trc c lng lo, loi ci hoc cn non, t vn ng, ch yu nui ly tht th qu trnh co cng xy ra sm hn loi cu to c chc, ging c, loi trng thnh, c vn ng nhiu.

Cc loi ng vt

Thi gian sau khi cht n lc t cng (h)

Th

G mi Ln Cu ci B

1.5- 4

2- 4

12- 18

24

18- 24

Da vo nhng s liu trn ta thy rng tht b c qu trnh co cng xy ra tng i

chm v ko di, cc c thng xuyn vn ng th qu trnh co cng cng lu xy ra.

V trng thi khi cht

i vi b mi vn chuyn v trn qung ng di, b stress khi git m, hoc ch gy ngt, phng php git m khng hp l s lm cho qu trnh co cng din ra nhanh hn, nh hng nhiu n cht lng ca tht.

Qu trnh t chin:

-nh ngha

L qu trnh t phn gii cc thnh phn cu trc ca c tht nh vo h enzyme c sn, m ch yu l s phn gii protein v lipid to nn nhng bin i su sc v mt vt l, ha l v ha hc cho sn phm.

Qu trnh t phn thng lm cho tht c nhng biu hin tt v mi v; tht tr nn mm mi, d tiu ha hn. y l giai on tht t gi tr tt v cht lng thch hp cho cho mc ch s dng, sn xut.

-Cch thc nh gi: Qu trnh t chn ca tht cng c th c nh gi da trn

cc c trng v:Trng thi cm quan ca tht:

Cu trc: tht trong qu trnh t chn mm tr li, kh nng lin kt nc, to nh,

to gel tng ln, nhng tht khng n hi.

Mi v c trng: mi v tht c ci thin nh vo s hnh thnh nhiu cht to mi trong qu trnh t chn, mi v ca tht c th hin r trong qu trnh ch bin nhit.

S ci thin mu sc ca tht: tht c mu hng, sng.

-Din bin ca qu trnh t phn

u tin s gim pH lm ph v mng t bo phng thch ra cc enzyme tiu ha sn c trong nguyn liu m i din l cc protease v lipase.

Actomyosin phn hy tr li

S gim bt mc lin kt cng vi s xm nhp ca dch tng mang mi trng acid tc ng vo cc thnh phn, cu trc ca m c thc y qu trnh thy phn cc cu t m c xy ra.

S thy phn cc cu trc ca m c trong ch yu l protein v lipid.

Cui giai on ny pH ca tht bt u

tng ln, thm vo l s to thnh nhng hp cht ha hc n gin m vi sinh vt d hp th do to iu kin thun li cho s sinh trng, pht trin ca vi sinh vt.

-S tc ng ca qu trnh t chn

mm: trong qu trnh t chn tht s bt u mm tr li do

o S phn hy actomyosin

oS thy phn ca cc enzyme c sn trong bn thn nguyn liu, ch yu l hot ng ca cathepsin lm mm ha cu trc ca m tht, lm cho tht mm hn.

o Qu trnh mm ha lm tng gi tr cm quan v gi tr dinh dng ca tht do to thnh cc acid amin lm cho qu trnh tiu ha din ra d dng hn.

S to thnh hng v c trng cho sn phm: ngi ta thy rng tht trong giai on t chn th hin r mi v c trng cho sn phm, tht tr nn thm ngon hn:

o S thay i cu trc tht, tht tr nn mm hn, cc lin kt bt cht ch hn to iu kin cho s thot mi ra khi cu trc sn phm to nn hng thm cho sn phm.

o S hnh thnh nhng hp cht to mi cho sn phm: acid inozinic, inozinin v hypoxanthin, nhng cht ny l sn phm ca qu trnh phn hy ATP trong cu trc ca c tht.

o Ngoi ra s hnh thnh ca to acid glutamic do s kh amin ha ca glutamin; s hnh thnhmui glutamate; s phn hy cc base purine to thnh acid inozinic, cc hp cht hypoxanthyl cng gp phn to nn mi v ca sn phm.

o ng thi s thy phn lipid cng to thnh mt s hp cht gy mi, nhng cht thm.

o Ngi ta thy rng trong tht b c khong 250 cht khc nhau gp phn to nn hng v cho sn phm, hm lng ca nhng cht ny t cao nht trong giai on chnh sinh ha. Mt s cht tiu biu gp phn to nn hng v ca tht b: acetaldehyde, aceton, methylethyl cetone, rc ethylic, methylic, methyl, dimethyl, ethyl- mercaptan, acid inozinic, acid glutamic, mui glutamate,

Cc yu t nh hng n qu trnh t chn

o Cc yu t v bn thn ngun nguyn liu

o Mc ca qu trnh co cng trc

o Nhit : i vi tht b nhit ti thch cho s hot ng ca cc enzyme thng l 25- 300C

o pH: 4- 4.5.

o Bng di y cho ta mt s tnh cht ca tht nng, tht co cng v tht chn sinh

ha. Ty theo mc ch s dng, sn xut m ta s chn loi tht ph hp:

Thuc tnh

Tht nng

Co cng

T chn

Ph

7- 7.2

5.4

5.5- 6

Protein c

Actin

Myosin

Phc A-M

Thy phn

Hp th nc

Ln nht

Nh nht

Tng

Ngm mui

Km

Tt

Tt nht

Kt cu

Mm, n hi

Cng

Mm, khng n hi

Mu

sm

Hng ngc

mm

Tng i

Cng, dai

Mm

Qu trnh thi ra:

-nh ngha

L qu trnh bin i phc tp xy ra di tc dng ca vi sinh vt, din ra nhng s bin i su sc c th lm h hng thc phm. Qu trnh ny c c trng bng s ph hy ton din cu trc, tnh cht, cht lng ca tht c trng bng s ph hy protein v mt phn lipid.

-Cch thc nh gi:

nh gi qu trnh qu trnh thi ra thng qua cc gi tr cm quan:

o Cu trc: Ty theo tng mc nhim vi sinh vt m cu trc sn phm thay i khc nhau. Nhng c im chung khi tht b trong giai

on ny l cu trc b thay i nghim trng, tht b mm, nhn, mt tnh chc rn chc ban u ca tht

oMu: tht b mt mu, i mu, mu b nht hn so vi tht nng, tht c th xut hin cc mu l nh xanh, xm, en.

o Tit cht nhy: tht trong qu trnh thi ra kh nng ht nc, gi nc gim dn n s tit dch nhy mnh m, b mt tht b bao bc bi mt lp nhy, c mu c.

nh gi thng qua nhng thng s khc:

o pH: trong giai on ny pH tht tng nhanh do hot ng phn hy ca vi sinh vt to ra nhiu sn phm c tnh kim.

o Ngoi ra ta cng c th nh gi trc tip s lng ca cc loi vi sinh vt c trong tht, thng dng nhng ch tiu: tng s vi sinh vt hiu kh, k kh, tng mm men, mm mc, v mt s loi vi sinh vt gy bnh cho c th.

-Din bin qu trnh phn hy

pH tng dn cui giai on t chn to iu kin cho vi sinh vt pht trin, nu trn tht c sn mt lng vi sinh vt th chng s sinh trng v pht trin nhanh chng.

Phn hy hiu kh: do nhng vi khun hiu kh thc hin. u tin qu trnh phn hy bt u t b mt sau lan su dn vo bn trong, ch yu l m lin kt, cui cng lan rng ra ton b c.

Phn hy k kh: thng bt u gn m lin kt, km theo sinh kh. Kh to thnh ph hy cu trc lin kt lm cho tht xp, bin i mu mnh m. S phn hy k kh xy ra ng b trong chiu dy ca tht v lan rng rt nhanh.

u tin protein b thy phn di tc dng enzyme ca vi sinh vt to thnh cc acid amin. Tip theo l qu trnh oxy ha kh acid amin to NH3, acid (acid acetic, propyoic, butyric), H2S, mecaptan, indol, skatol to mi thi c trng. Cui cng cc cht hu c tip tc b oxy ha thnh nhng cht v c CO2,H2O, H2S, H3 PO4 ,NH3,v tht b thay i hon ton.

-S tc ng ca qu trnh thi ra

Thi ra tht

S nhy ha b mt

S ha mu tht

S hnh thnh mi thi

Mc

-Cc yu t nh hng

Bn thn nguyn liu

o Qu trnh thi ra chu nh hng ca ging loi, gii tnh, tui, cu trc

m c, s lng vi sinh vt c trong nguyn liu,

o Cu trc ca m c cng bn vng qu trnh thi ra xy ra cng chm, i vi tht b bn vng vi qu trnh thi ra tng dn theo chiu m mu, m lin kt, m c, m m, m lin kt v m sn.

o S lng vi sinh vt ban u trn tht cng nhiu thi ra xy ra cng nhanh.

Nhit

Hu ht cc vi sinh vt trn tht b ch yu thuc loi a m, nhit tng va phi di 400C s lm cho chng sinh trng v pht trin nhanh hn.- Hnh bn cho ta thy s ph thuc gia nhit v thi gian bo qun ca mt s vi sinh vt ph bin trn tht b. Trong khong di 350C nhit t l thun vi s pht trin ca vi sinh vt v vi qu trnh thi ra.

Cc yu t khc nh pH, hot nc

Nhn chung i vi nhng loi vi sinh vt ph bin trn tht b s hot ng tt trong khong pH 6.5- 7.5 v m trn 80%.

ng:

3.2.Quy trnh lnh

3.2.1.Lm lnh s b:

Trong trng hp lnh ng bng N2 lng, kh ha lng c phun ln sn phm thi ngang qua bng ti ang chuyn ng. Kh N2 i ngc chiu vi bng ti. V vy tht b nn c lm lnh s b trc khi a n phun N2 lng trnh cho sn phm b nc ra do qu trnh lm lnh xung qu nhanh (tc thi).

Gim nhit tm khi tht xung 4 80C

Tht b c lm lnh ti kho lnh s b: Dng lm lnh s b hay bo qun tm thi thc phm ti cc nh my ch bin trc khi chuyn sang mt khu ch bin khc.

3.2.2. Cp ng:

-Mc ch:

Gim thiu s thay i v tnh cht vt l, sinh hc, vi sinh, nh hng n cht lng tht trong qu trnh lu tr bo qun. Ko di thi gian bo qun nhiu hn so vi phng php lm lnh thng thng.C th tiu dit mt s vi sinh vt trong qu trnh lnh ng.

-Phng php thc hin:

Thc phm c di chuyn trn cc bng chuyn v c phun lm lnh bng ni t lng c nhit bay hi rt thp -196oC. V th thi gian lm lnh ng cc nhanh t 510 pht. Hin nay cc nc pht trin ng dng rng ri phng php ny.

Trong bi bo co ny, chng ti chn phng php lnh ng nhanh v nhng u

im sau:

Thi gian v khng gian c tit kim

Gim s lng cng nhn v chi ph u t xy dng nh xng.

Gi c phm cht tht tt hn.

nh tr c s pht trin ca vi sinh vt trn b mt tht

Gim hao ht trng lng, dinh dng tht

Tng gi tr cm quan hn so vi phng php lm lnh khc

Phng php ny th kch thc tinh th to ra nh hn, ch yu c to thnh trong t bo, gim c s thot nc ra ngoi.

-Thit b cp ng IQF

S bin i ca tht b trong qu trnh cp ng

-Bin i v nhit vt l

S bin i nhit

Trong qu trnh lnh ng nhit ca nguyn liu s gim t nhit mi trng

n nhit lnh cn thit. S bin thin nhit khi lm lnh ng xy ra nh sau:

Nguyn liu c lm lnh xung nhit thp hn im ng bng, nhng nc vn duy tr trng thi lng. Hin tng ny gi l hin tng qu lnh. V nhit qu lnh ca thc phm thng khng ln, i vi nc dch t tht gia sc -5oC.

Sau khi t c nhit qu lnh cc tinh th bt u hnh thnh, ta ra nhiu n nhit ng bng lm tng nhit sn phm n im ng bng. Lc ny, nhit c duy tr hon thnh c bn qu trnh ng bng.

Khi nc trong sn phm ng bng lm thay i nng cht ha tan trong dch thc phm. Do , nhit ng bng ca phn dch bo cn li s tip tc h thp. Tip tc h nhit n mt lc ton b nc trong dung dch b ng bng, ng vi nhit lc ny gi l nhit eutectic.

Cui cng, nhit ca sn phm s gim ti nhit ca thit b lnh ng.

Trong qu trnh lnh ng s to thnh 1 lp bng trn b mt sn phm nn c s

bin mu do hiu ng quang hc nh tinh th khc x nh sng (bin mu gi to).

S bin i v th tch

Khi lnh ng th tch ca nguyn liu s tng ln (8-10%) do th tch ca nc tng

v mc tng ph thuc vo:

o Hm lng m trong nguyn liu: hm lng cng cao, mc thay i cng ln.

o Trt t sp xp cc t bo (nguyn liu thc vt): trong t bo thc vt c cc khng gian bo, nn khi lnh ng cc tinh th s chim ch ca cc khng gian bo. V vy, th tch ca nguyn liu c th thay i khng ng k.

o Nng cht ha tan c trong nguyn liu: hm lng cht ha tan

trong nc cng cao th mc tng th tch cng gim.

o Cc thnh phn to tinh th khc: mt s thnh phn khc cng c th kt tinh (cht bo, cc cht ha tan) v lm gim th tch ca nguyn liu.

S bin i v khi lng

Khi lng m thay i dn n khi lng t nhin ca sn phm gim do qu trnh bc hi nc khi lm lnh.

Khi lm lnh ng tht b khi lng tng thm 0,01% mi ngy. Cn khi bo qun lnh ng t = -18oC trong 6 thng, tn hao khi lng khong 0,50,8%. Tuy tn hao khng ng k, nhng khi bo qun vi khi lng ln th s gy tn tht v kinh t cho doanh nghip.

Bin php gim thiu s hao ht khi lng: lm lnh ng theo kiu gin tip (sn phm c bao gi sn) hoc sau khi lnh ng sn phm c m bng trnh tip xc vi khng kh, lnh ng cc nhanh, lnh ng 1 pha, tr ng nhit thp

S bin i cu trc.

Trong qu trnh lnh ng cc tinh th s lm bin i cu trc ca nguyn liu, mc bin i ph thuc vo kch thc tinh th v tc ca qu trnh lnh ng.

i vi tht ng vt c cu trc protein dng si nn khi lnh ng cc si ny c xu hng tch ri nhau. Nu bo qun trong gian thi di s lm cho sn phm kh, xp nh hng n cht lng cm quan ca sn phm.

V vy, khi tan gi th cng, n hi, tnh cht ch ca cu trc thc phm gim.

S kt tinh ca nc:

Trong qu trnh cp ng nc tch ra v ng thnh cc tinh th, lm cho sn phm tr nn rn, tng th tch mt t.

Khi nc trong thc phm kt tinh to thnh mng tinh th xen k gia cc thnh phn khc to ra cu trc vng chc, nhng khi lm tan bng, phc hi trng thi

ban u th cu trc thc phm b mm yu hn, km n hi hn do cc tinh th lm rch cu trc lin kt t bo thc phm.

Bin i mu sc:

ng thi vi qu trnh trn mu sc thc phm cng bin i do hiu ng quang hc do tinh th khc x nh sng. Mu sc thc phm khi nc ng bng ph thuc tnh cht quang nh sng ca cc tinh th nc .

Bay hi nc:

Trong qu trnh lm lnh ng c hin tng mt nc, gim trng lng sn phm. l s bay hi nc vo khng kh t b mt thc phm,do chnh lch mt gia khng kh st b mt v khng kh xung quanh. Hi m bc ln t b mt sn phm vo khng kh xung quanh, nu sn phm nhp c b mt cn t th khi cp ng chng s ng li, sau din ra qu trnh thng hoa. Nu chnh lch nhit b mt sn phmv khng kh trong bung cp ng cng ln th m bc cng mnh, gy hao ht khi lng.

Khuych tn nc:

Khi cp ng xy ra hin tng khuych tn nc trong cu trc thc phm,

nc khuych tn l do cc nguyn nhn:

o S chnh lch nhit gy nn do chnh lch mt .

o S ln ln ca tinh th nc lun thu ht nc t nhng v tr cha kt tinh dn n, lm cho nc t ni c nng cht tan thp chuyn n ni c nng cht tan cao. S di chuyn ca nc thc hin nh tnh bm thm v mao dn ca cu trc thc phm. ng lc ca qu trnh khuych tn, lmcho nc di chuyn t trong t bo ra gian bo v t trong ra ngoi,t v tr lin kt ra t do.

Khi nc khuych tn cu trc t bo co rt, mt s cht tan bin tnh.

Cc thng s nhit vt l thay i

o Bin i nhit dung:

Nhit dung sn phm thay i l do nc trong thc phm c ng bng.

Nhit dung khi c tnh:

Csp= Cck(1-W) + C..W + Cn.(1-).W ; kJ/kg.K

Vi:Csp, Cck, C, Cn Nhit dung ring ca sn phm, cht kh, nc v

ca nc, kJ/kg.K;

- T l nc ng bng nhit tb

W Hm lng nc trong sn phm. Nhit dung ring sn phm trc khi ng bng

Co= Cck(1-W) + Cn.W ; kJ/kg.K

Do

Csp= Co- (Cn- C)..W = Co 2,096..W ; kJ/kg.K

C th xc nh nhit dung ring sn phm theo cng thc thc nghim nh sau:

Ac, Bc L cc hng s thc nghim

o Bin i h s dn nhit:

H s dn nhit ca sn phm cng thay i th hin cng thc di y:

sp, o H s dn nhit ca sn phm lnh ng v nhit kt tinh ( nhng

sn phm cha kt tinh), W/m.K; A, B- Hng sthc nghim

t, tkt Nhit sn phm cp ng v nhit kt tinh (khng k du m),

o Bin i h s dn nhit

H s dn nhit ca sn phm cng thay i v c tnh theo cng thc sau

y:

Asp, ao H s dn nhit ca sn phm lnh ng v nhit kt tinh (

nhng sn phm cha kt tinh), m2/s; Aa, Ba- Hng s thc nghim.

t, tkt Nhit sn phm cp ng v nhit kt tinh (khng k du m)

Di y l bng cc thng s ca mt s sn phm

Bng: Cc hng s thc nghim ca tht b:

-Bin i v ha sinh.

Trong khi lm lnh ng cc phn ng ha hc, sinh hc s gim dn v tin ti

khng i.

Bnh thng cht bo, glucose, protein ha tan v cc loi mui to thnh dung dch.

Nhng khi hnh thnh tinh th , nc s tch khi protein lm protein bin i cu trc.

Cc hp cht mu lin kt vi nc v protein, khi nc ng bng n s tch ra lm hp cht mu b bin i dn n s thay i v mu sc.

Cc cht bo khi ng lnh d b oxy ha, d b chua do lipid thy phn lm hm lng acid bo tng, v cc vitamin cng b thay i nht l nhng vitamin tan trong cht bo (vitamin A, D, E, K)

Nu nhit ng lnh qu su, thi gian lm ng ko di s dn n hin tng chy lnh lm protein b bin tnh gy bin i v cht lng thc phm.

Cc hot ng ca enzyme trong tht s b c ch nhng khng nh ch hn c nh men lipaza khng mt hot tnh -35oC, v phn ng phn hy glucogen vn din ra vi tc ng k. Nhiu loi men khng b mt hot tnh khi lm lnh ng, c khi cn lm tng hot tnh sau khi tan gi.

Bin i v vi sinh vt

Hu ht cc vi sinh vt u b tiu dit. Nc trong c th vi sinh vt chim 90% nn khi lm lnh ng nc s ng bng, th tch nc tng lm cho cu trc t bo vi sinh vt v ra lm cho vi sinh vt cht. y l c s ko di thi gian bo qun nguyn liu.

Khi lm ng protein b bin tnh ph v ton b c quan trao i cht v trao i nng lng, lm cho s sng ca vi sinh vt ngng hot ng.

Tuy nhin mt s loi vi sinh vt vn cn tn ti s sng nhng khng c kh nng

hot ng do c th to bo t.

Bin i cm quan

Bn thn qu trnh lm lnh ng t dn ti nhng bin i ln v mu, mi, v ca sn phm nhng trong qu trnh bo qun c th dn ti s thay i gi tr cm quan ca thc phm. i vi cc sn phm tht, c th qu trnh bo qun lnh lm thay i mu, mi v, trng thi (mi v xu, trng thi kh, xc)

Bin i ho hc

Bn cht qu trnh bin i ho hc ca thc phm khi lm lnh l s phn gii ca cc cht d tr nng lng do tc ng ca cc enzim c sn trong thc phm.

Mc bin i ho hc ph thuc vo trng thi ban u ca thc phm v phng php lm lnh. Ni chung do nhit gim nhanh thi gian lm lnh ngn nn cc bin i ho hc din ra vi tc rt chm, t h hng, cht lng thc phm c m bo.

Cc bin i ch yu l do s xi ho cc sc t lm bin mu thc phm. S

xi ho ph thuc mc tip xc vi khng kh ca thc phm v cht lng ban

u.

gim s xi ho c th loi b cc sc t trc khi lm lnh, hn ch bt cc hot tnh ca cc enzim, hn ch tip xc vi khng kh, lm tng tc lm lnh.

3.2.3. M bng:

- nghia ca vic m bng

B mt sn phm sau khi m bng c tc dng hn ch s tip xc ca khng kh vi cu trc bn trong v b mt sn phm, ng thi lm tng v p ca sn phm nh lm mt i nhng nhc im v hnh thc bn ngoi ca n trong qu trnh cp ng.

Tuy nhin, do s trao i nhit gia mi trng m bng v thc phm m nhit

ca thc phm tng ln.

-Cch tin hnh

Nhng sn phm sau khi cp ng vo thng nc c nhit thp (0 5)OC trong thi gian (1 2) giy.

Sau trong khng kh v ch lp nc b mt sn phm ng bng, nhng

nhiu ln n khi t yu cu ca cng ngh t ra.

-C ch

Sn phm sau khi c cp ng c nhit b mt nh hn -30oC, khi c nhng vo b nc (c nhit khong 0 - 5oC) b mt ca n dnh t mt lp nc mng, thc phm s trao i nhit lp nc trn b mt sau khi nhng, lm cho nhit sn phm tng ln v lp nc ny ng bng.

Qu trnh kt tinh ca nc lun c xu hng cc phn t lng lin kt vi cc tinh th nc c b mt thc phm lm tng kch thc ca n. B dy ca lp m bng khng ph thuc vo thi gian nhng sn phm trong nc, mun b dy ca lp m bng phi m bng nhiu ln, nhng qu trnh nhng sn phm vo mi trng nc m bng s xy ra qu trnh trao i nhit gia nc v sn phm, iu ny nh hng rt ln n nhit ca sn phm. V vy, phi hn ch thi gian tip xc ca sn phm vi mi trng nc m bng.

Hn na, qu trnh trao i nhit cn c xu hng lm cho b mt nc hnh thnh mt lp bng mng, lp bng ny s bm vo b mt sn phm v cn tr s lin kt lp m bng vi sn phm. Do phi lin tc cung cp nhit lng cho nc m bng c nhit n nh, c th dng mt s ha cht chng oxy ha, cho vo nc m bng lm tng kh nng bo v i vi thc phm.

-Yu cu sn phm sau m bng

Lp m bng bo v cho thc phm phi lin kt chc chn vi b mt thc phm, nc m bng phi m bo yu cu v sinh v c nhit gn bng 0oC nhng tt nht l khng thp hn 0oC.

Tuy nhin khi m bng cc sn phm cng phi t yu cu v khi lng ca lp m bng mc cho php, i vi tht b l