Cng ngh sy lnh thc phmNhm 3

Mc LcLi m u3Chng 1.TNG QUAN V CNG NGH SY LNH41.1. Mt s nghin cu tiu biu trong lnh vc sy lnh thc phm41.2. Gii thiu phng php sy lnh61.2.1. H thng bm nhit trong sy lnh61.2.2. Phng php sy lnh71.3. S nguyn l, c im truyn nhit v truyn cht ca h thng sy lnh71.3.1. Nguyn l ca h thng sy lnh81.3.2. c im ca qu trnh truyn nhit v truyn cht ca h thng sy91.4. Phn loi h thng sy lnh101.4.1. H thng sy lnh nhit nh hn 0oc101.4.2.H thng sy lnh nhit ln hn 0oc111.5. Thi b sy lnh131.6. So snh phng php sy lnh vi phng php sy nng141.7. ng dng cng ngh sy lnh ti vit nam v cc ti nghin cu18Chng 2. NGUYN LIU SY LNH PHNG PHP SY RAU QU V CC YU T NH HNG202.1. Nguyn liu sy lnh202.2. Hnh nh mt s nguyn liu ng dng cng ngh sy lnh212.3. Phng php sy rau qu222.3.1. Quy trnh x l trc khi sy222.3.2. S quy trnh sy rau qu232.4. Mt s phng php sy rau qu252.5. nh hng ca qu trnh sy n cht lng sn phm262.6. Cc yu t nh hng n qu trnh sy29Chng 3. QA TRNH SY LNH S DNG BM NHIT V NG DNG TRN C C RT313.1. Gii thiu chung313.2. Xy dng quy trnh cng ngh sy C rt313.2.1. Gii thiu nguyn liu sy313.2.1. Xy dng quy trnh cng ngh sy C rt323.3. Xc nh cc thng s u vo ca vt liu34Chng 4. THIT B V SN PHM SY LNH354.1. Thit b sy lnh354.2. Mt s yu t nh hng n cht lng sn phm sy364.3. Sn phm sy lnh384.4. ng dng cng ngh sy lnh vo bo qun thc phm39TI LIU THAM KHO40

Li m u Vit Nam l mt nc nhit i c nhiu iu kin pht trin ngnh trng trt v ch bin rau qu. Tuy nhin, t l tn tht sau thu hoch l rt ln 25-30%. Nguyn nhn chnh l do cng ngh ch bin v bo qun ca chng ta cn lc hu nn lm cho rau qu ca Vit Nam c gi tr thp trong th trng trong nc cng nh xut khu, iu ny nh hng trc tip n i sng ca ngi nng dn, v vy vic nghin cu a ra cc quy trnh cng ngh cng nh ng dng trin khai chuyn giao cc kt qu nghin cu, cc quy trnh cng ngh bo qun, ch bin rau qu, ng vai tr ht sc quan trng trong chin lc pht trin ngnh rau qu. Rau qu hin nay ch yu c s dng dng ti, nh bit rau qu l loi sn phm c tnh thi v, thi gian thu hoch ngn, kh nng vn chuyn v bo qun hn ch, trong khi k thut bo qun rau qu ti vn ch da vo cc kinh nghin c truyn, mang tnh th cng chp v. Cng ngh sy ng dng trong ch bin rau qu kh c tin hnh t kh lu nhng cho n nay vn bc l nhiu hn ch v cng ngh cha khc phc c cht lng u ra ca sn phm, cha p ng c cc yu cu v c tnh ha l, mi, mu, thnh phn dinh dng nn kh p ng cho nhu cu tiu th v xut khu trong v ngoi nc. Vic u t nghin cu mt quy trnh cng ngh mi gii quyt nhng vn ny l thc s cn thit. Cng ngh sy lnh c xem l mt cng ngh mi, ra i t yu cu cp thit . u im ca cng ngh sy lnh l c th xy dng c tng quy trnh cng ngh sy hp l i vi tng loi rau, c, qu. Sn phm sy gi c nguyn mu sc, mi v, hn ch ti a tht thot dinh dng (khong 5%) [20], t tiu chun v sinh an ton thc phm ca Vit Nam v cc ch tiu k thut, cht lng sn phm tng ng mt s nc khc trn th gii. Vic pht trin cng ngh sy lnh c nhiu thnh tu. Tuy nhin, c mt quy trnh cng ngh hon chnh, ti u vi cc thng s ph hp nht i hi chng ta phi tin hnh nghin cu su rng hn.

CHNG ITNG QUAN V CNG NGH SY LNH

1.1. Mt s nghin cu tiu biu v cng ngh sy lnh. Macio N. Kohayakawa v cc cng s tin hnh nghin cu nh hng ca cc yu t nh: vn tc gi Var, chiu dy ca vt liu L n h s khuch tn qu trnh sy Def trong h thng sy xoi bng bm nhit. Mi cht lnh s dng trong h thng l R22. H thng sy xoi s dng hai dn ngng trong gia nhit cho khng kh. Nhit khng kh trong qu trnh th nghim thay i t 40oC n 56oC. Vn tc gi thay i t 1,6 m/s n 4,4 m/s, chiu dy vt liu sy thay i t 5,8 mm n 14,2 mm. Khi lng vt liu sy mi m l 300g, thi gian sy l 8h/m. Da vo cc quan h l thuyt tnh ton h s khuch tn, s dng phng php quy hoch trc giao v kt hp vi s liu thc nghim, cc tc gi xy dng c phng trnh hi qui xc nh h s khuch tn Def nh sau: Def=4,2625 - 0,61922.Var + 0,380538.Var2 + 1,012517.L 0,90343.Var.L (1.1) Phng trnh (1.1) cho thy rng nh hng ng thi ca hai thng s cng nh mc nh hng ca chng n h s khuch tn Def. y, nh hng ca tc gi Var l ln nht, sau n chiu dy ca vt liu sy. Phng trnh (1.1) cng cho bit nh hng ln nhau gia hai thng s thng qua mi lin h cho nhau gia chng. Tuy nhin, phng trnh ny khng cp n nh hng ca nhit , m sy mc d nh hng ca chng l ln n h s khuch tn. iu ny cng c chnh tc gi khng nh trong nghin cu ca mnh. Do vy, cn c nhng nghin cu nh gi v nh hng ca cc yu t ny. Phani K.Adapa, Greg J.Schoenau v Shahab Sokhansanj tin hnh nghin cu l thuyt v thc nghim qu trnh sy bng bm nhit i vi cc vt liu c bit. Cc tc gi tin hnh thit lp cc quan h tnh ton l thuyt qu trnh sy lp mng. Cc tc gi thit lp phng trnh cn bng nng lng, cn bng cht, truyn nhit v truyn m gia vt liu v khng kh cho mt phn t th tch vt liu sy nh sau: Phng trnh truyn m

(1.2)Trong : M - m cn bng ca vt liu sy ti thi im tMe - m cn bng ca vt liu sy, c xc nh bng thc nghimt - thi gian sy, s

k - hng s sy [1/s], c xc nh nh sau: (1.3)Gii phng trnh (1.2) ta xc nh c m ca vt liu khi sy ti thi im t nh sau:

(1.4)Vi M0 : m ca v liu sy ti thi im t0 = 0

Phng trnh cn bng cht

(1.5) Vi: W - cha hi ca khng kh x - chiu dy ca vt liu sy Gp - lu lng vt liu sy chuyn ng qua bng ti, kg/m.s Ga - lu lng khng kh chuyn ng qua bng ti, kg/m2.s y - qung ng dch chuyn ca vt liu sy, mGii phng trnh (1.5), thu c cng thc xc nh s thay i ca cha hi W theo chiu dy vt liu sy (gi thit tnh cht ca vt liu sy l ng u theo phng dch chuyn y):

(1.6) Phng trnh cn bng nng lng

(1.7)Trong : Ta - nhit ca khng kh sy, 0CTg - nhit ca vt liu sy, 0Chcv - h s truyn nhit th tch, kJ/m3.ph.KCpa - nhit dung ring ca khng kh kh, kJ/kgKCpw - nhit dung ring ca hi nc, kJ/kgKGii phng trnh (1.12), xc nh c nhit khng kh ti u ra:

Trong :

Ta0 - Nhit khng kh ti v tr ban u x0 = 0, 0C

1.2. Gii thiu phng php sy lnh1.2.1. H thng bm nhit trong sy lnh. Bm nhit c qu trnh pht trin lu di, bt u t khi Nicholas Carnot xut nhng khi nim u tin. Mt dng nhit thng thng di chuyn t mt vng nng n mt vng lnh, Carnot a ra lp lun rng mt thit b c th c s dng o ngc qu trnh l bm nhit. u nhng nm 1850, Lord Kelvin pht trin cc l thuyt v bm nhit bng lp lun, cc thit b lm lnh c th c s dng gia nhit. Sn phm bm nhit u tin c bn vo nm 1952. T khi xy ra cuc khng hong nng lng vo u thp k 70, bm nhit li bc vo mt bc tin nhy vt mi. Hng lot bm nhit mi kch c cho cc ng dng khc nhau c nghin cu ch to, hon thin v bn rng ri trn th trng. Ngy nay, bm nhit tr nn rt quen thuc trong cc lnh vc iu ha khng kh, sy, ht m, un nc

Hnh 1-1. S nguyn l h thng bm nhit

1.2.2. Phng php sy lnh Trong phng php sy lnh, ngi ta ra chnh lch phn p sut hi nc gia vt liu sy v tc nhn sy bng cch gim phn p sut trong tc nhn sy nh gim lng cha m. phng php sy lnh, nhit b mt ngoi nh hn nhit bn trong vt, ng thi do tip xc vi khng kh c m v phn p sut hi nc nh nn lp b mt cng c phn p sut hi nc nh hn pha bn trong vt. Ni khc i, y gradient nhit v gradient p sut c cng du nn gradient nhit khng km hm qu trnh dch chuyn m nh khi sy nng m ngc li, n c tc dng tng cng qu trnh dch chuyn m trong lng vt ra ngoi bay hi lm kh vt. Khi , m trong vt liu dch chuyn ra b mt v t b mt vo mi trng c th ln hn hay nh hn nhit mi trng hoc cng c th nh hn 0o. Qu trnh truyn nhit thc hin c thng qua s thay i pha lm vic ca mi cht lnh. Mi cht lnh trong gin bay hi hp th nhit v bay hi nhit thp v p sut thp. Khi hi mi cht lnh ngng t nhit cao, p sut cao ti dn ngng t, n thi nhit p sut cao hn. Khi s dng trong qu trnh sy, h thng sy s dng bm nhit lm lnh khng kh ca qu trnh n im bo ha, v sau ngng t nc (kh m), do lm tng kh nng sy ca khng kh. Trong qu trnh ny ch tun hon mc nhit thp (nhit hin v nhit n) t khng kh.

1.3. S nguyn l, c im truyn nhit v truyn cht ca h thng sy lnh1.3.1. Nguyn l lm vic ca h thng sy lnh Khc vi phng php sy nng, trong phng php sy lnh, ngi ta to ra chnh phn p sut hi nc gia vt liu sy v tc nhn sy bng cch gim phn p sut trong tc nhn sy nh gim lng cha m. phng php sy lnh, nhit b mt ngoi ca vt nh hn nhit bn trong vt, ng thi do tip xc vi khng kh c m v phn p sut hi nc nh nn b mt cng c phn p sut hi nc nh hn pha bn trong vt. Ni khc i, y gradient nhit v gradient p sut c cng du nn gradient nhit khng km hm qu trnh dch chuyn m nh khi sy nng m ngc li, n c tc dng tng cng qu trnh dch chuyn m trong lng vt ra ngoi bay hi lm kh vt. Khi m trong vt liu dch chuyn ra b mt v t b mt vo mi trng c th ln hn hoc nh hn nhit mi trng hoc cng c th nh hn 0oC. Hnh1-4. S h thng sy lnh

1.3.2. c im qu trnh truyn nhit v truyn cht Trong k thut sy lnh, th sy ca khng kh tng nh qu trnh tch m dn bc hi v qu trnh gia nhit bng chnh dn ngng t trong cc my lnh. Yu t c tnh quyt nh y l qu trnh lm lnh khng kh trong dn lnh, t y s nhn c khng kh c nhit v cha hi (d) nh m bo cho qu trnh truyn nhit, truyn cht gia vt sy v tc nhn sy trong bung sy xy ra iu kin gradient nhit v gradient p sut cng chiu, khng c giai on no xy ra hiu ng Luikov A.V. cn tr qu trnh sy nh trong phng php sy nng. V vy, ngoi vic tnh ton, thit k h thng ni chung th iu ti cn thit l ch lm vic ca dn lnh hay ni cch khc l kh nng ti u nht ca dn lnh c tm quan trng c bit. Trong k thut sy lnh, tng cng tch m cho h thng, khng kh sy tri qua giai on tch m dn lnh, v th m trong khng kh c th tn ti ba dng hi, lng v rn, vi dung m dng hi dh, dng lng dl v dng rn dr, entanpi H ca khng kh m:H= tb + (2500+1,93tb)dh + 4,18d1tb + (-335+2,1 tb)dr , kJ/kgkk (1.8)

Trong qu trnh kh m dn lnh, chiu di ng i ca dng khng kh l yu t c tnh quyt nh, theo m lu lng th tch khng kh cng nh cng sut nhit - trao i s thay i, khng kh c lm lnh n nhit im sng ts. Trn mt n v di quan h truyn nhit, truyn cht ny c th biu din di dng:

Trong c - nhit dung ring th tch ca khng kh m nhit kh quyn (c =1,23 kJ/m3K). r - Nhit ngng t (r=2500 kJ/kg i vi hi nc 00C).

- l nc ngng theo ng (ng vi 1m3 khng kh m khi nhit gim i 1K) v thay i nhanh qua nhit theo biu thc:

(1.9)Trong : Ph- p sut hi bo ha ca hi nc tng ng vi nhit ca khng kh m. Hng s R i vi hi nc trong khng kh m: R=8314/18=861,89 J/kgKMt khc c th tnh nhit lng do khng kh truyn cho mi cht lnh tng ng vi mi n v di ca thit b bay hi bm nhit:

Vi K1 l h s truyn nhit ca thit b bay hi [W/mK].T cc c s trn ta c quan h:

(1.5) vi L thng s c trng cho cng sut ca thit b bc hi ca bm nhit (thng khong 1kJ/m3K), X[m] l chiu su ca thit b bc hi, X0 [m] l khong cch t u thit b vo thit b bc hi n im xut hin qu trnh ngng ng m, Ts l nhit ng sng, cc ch s 1 v 2 l k hiu u vo v ra ca khng kh qua thit b bc hi.1.4.Phn loi h thng sy lnh1.4.1. H thng sy lnh nhit nh hn 00Ca. H thng sy thng hoa Sy thng hoa l qu trnh tch m khi vt liu sy trc tip t trng thi rn bin thnh trng thi hi nh qu trnh thng hoa. to ra qu trnh thng hoa, vt liu sy c lm lnh di im ba th, ngha l nhit ca vt liu t < 00C, p sut tc nhn sy bao quanh vt P 610 Pa. Khi nhn c nhit lng, cc phn t nc trong vt liu sy th rn s chuyn sang th lng, sau mi chuyn sang th hi v i vo mi trng. u im: Phng php ny gi c cht lng sn phm, m bo iu kin v sinh. Nhc im: H thng c chi ph u t ln, vn hnh phc tp. Phng php sy chn khng thng ch sy cc loi vt liu sy l cc sn phm qu, d bin cht. Do tnh phc tp v khng kinh t nn cc h thng sy thng hoa v h thng sy chn khng ch dng sy nhng vt liu qu him, khng chu c nhit cao. V vy, cc h thng sy ny l nhng h thng sy chuyn dng, khng ph bin.1.4.2. H thng sy lnh nhit ln hn 00Ca) Phng php s dng my ht m chuyn dng kt hp vi my lnhPhng php ny s dng my ht m kt hp vi my lnh, to ra mi trng sy c nhit kh thp, c th bng hoc b hn nhit mi trng t 5 n 150C. u im Nng sut ht m ca phng php ny kh ln. Kh nng gi cht lng, hm lng dinh dng sn phm cng kh tt (ph thuc vo nhit sy). Nhc im Chi ph u t ban u kh ln do phi s dng c my ht m chuyn dng v my lnh Cht ht m phi thay th theo nh k Vn hnh kh phc tp nn chi ph vn hnh ln in nng tiu tn ln do cn chy my lnh v t nng dy in tr hon nguyn cht hp th. Lp t phc tp, kh iu chnh cc thng s ph hp vi cng ngh Trong mi trng c bi, cn dng my v sinh cht hp th, tui th thit b gim.b. Phng php dng bm nhit nhit thpTrong phng php ny, ngi ta ch dng mt h thng bm nhit to ra mi trng sy. Nhit mi trng sy c th iu chnh trong gii hn kh rng t nhit xp x mi trng n nhit m, ty thuc yu cu ca vt liu sy. Khc vi cc thit b nhit lnh khc, khi s dng bm nhit sy kh v ht m th c dn nng v dn lnh u c s dng hu ch nn nng sut tiu th y c th c tn dng n mc cao nht m nhit khng kh li c th ch cn duy tr mc nhit mi trng hoc thp hn. u im: Kh nng gi mu sc, mi v v vitamin u tt Tit kim nng lng nh s dng c nng lng dn nng v dn lnh, hiu qu s dng nhit cao Bo v mi trng, vn hnh an ton. C kh nng iu chnh nhit tc nhn sy ty thuc vo yu cu v kh nng chu nhit ca tng loi sn phm nh thay i cng sut nhit ca dn ngng trong Cng sut kh ln Chi ph u t h thng thp hn so vi cc phng php sy lnh khc Vn hnh n gin. Nhc im Thi gian sy thng kh lu do chnh phn p sut hi nc gia vt liu sy v tc nhn sy khng ln. Phi c gii php x bng sau mt thi gian lm vic.1.5. Cc thit b trong h thng sy lnhBm nhit l mt thit b dng bm mt dng nhit t mc nhit thp ln mc nhit cao hn, ph hp vi nhu cu cp nhit. My lnh cng l mt loi bm nhit v c chung mt nguyn l hot ng,cc thit b ca chng v c bn l ging nhau. ch phn bit my lnh vi bm nhit mc ch s dng. My lnh gn vi vic s dng ngun lnh thit b bay hi cn bm nhit gn vi vic s dng ngun nhit thit b ngng t. Do s dng ngun nhit nn bm nhit hot ng cp nhit cao hn.a) Mi cht v cp mi cht:Mi cht v cp mi cht ca bm nhit c yu cu nh my lnh. Mt vi yu cu c bit hn xut pht t nhit si v ngng t cao hn, gn ging nh ch nhit cao ca iu ha khng kh, ngha l cho n nay ngi ta vn s dng cc loi mi cht nh: R12, R22, R502 v MR cho my tuabin. Gn y ngi ta ch n vic s dng cc mi cht mi cho bm nhit nhm nng cao nhit dn ngng nh: R22, R113, R114, R12B1, R142b) My nn lnhCng nh my nn lnh, my nn l b phn quan trng nht ca bm nhit. Tt c cc dng my nn ca my lnh u c ng dng trong bm nhit. c bit quan trng l my nn piston trt, my nn trc vt v my nn tuabin. Mt my nn bm nhit cn phi chc chn, tui th cao, chy m v cn phi c hiu sut cao trong iu kin thiu hoc ti.c) Cc thit b trao i nhitCc thit b trao i nhit c bn trong bm nhit l thit b bay hi v thit b ngng t. My lnh hp th c thm thit b sinh hi v hp th. Ging nh my lnh, thit b ngng t v bay hi ca bm nhit cng bao gm cc dng: ng chm, ng lng ngc dng, ng ng v ng kiu tm. Cc phng php tnh ton cng ging nh cc ch iu ho nhit .d) Thit b ph ca bm nhitTt c cc thit b ph ca bm nhit ging nh thit b ph ca my lnh. Xut pht t yu cu nhit cao hn nn i hi v tin cy, cng ngh gia cng thit b cao hn. y cng l vn t ra i vi du bi trn v m kn cc loi trong h thng.Do bm nhit phi hot ng ch p sut v nhit gn st vi gii hn ti a nn cc thit b t ng rt cn thit v phi hot ng vi tin cy cao phng nga h hng cc thit b khi ch lm vic vt qu gii hn cho php.i vi van tit lu, bm nhit c ch lm vic khc my lnh nn cng cn c van tit lu ph hp.e) Thit b ngoi vi ca bm nhitThit b ngoi vi ca bm nhit l nhng thit b h tr cho bm nhit ph hp vi tng phng n s dng ca n. Thit b ngoi vi ca bm nhit gm mt s loi sau: Cc phng n ng lc ca my nn nh: ng c in, ng c gas, ng c diesel hoc ng c givv Cc phng n s dng nhit thu dn ngng t. Nu l si m th c th s dng dn ngng trc tip hoc gin tip qua mt vng tun hon cht ti nhit, c th s dng sy, nu n, ht mMi phng n i hi nhng thit b h tr khc nhau. Cc phng n cp nhit cho dn bay hi. Trng hp s dng dn lnh ng thi vi nng th pha dn bay hi c th l bung lnh hoc cht ti lnh. Ngoi ra cng c th s dng dn bay hi t ngoi khng kh, dn bay hi s dng nc ging l mi trng cp nhit. Cng c nhng phng n nh dn bay hi t di nc, t di t hoc s dng nng lng mt tri. Cc thit b iu khin, kim tra t ng s hot ng ca bm nhit v cc thit b htr. y l nhng thit b t ng iu khin cc thit b ph tr ngoi bm nhit ph hp vi hot ng ca bm nhit1.6. So snh phng php sy lnh vi phng php sy nngSy l qu trnh tch nc v hi nc ra khi vt. Tuy nhin, sy l mt qu trnh cng ngh i hi sau khi sy vt liu phi m bo cht lng cao, tiu tn nng lng t v chi ph vn hnh thp. C hai phng php sy:a) Phng php sy nngTrong phng php sy nng, tc nhn sy v vt liu sy c t nng. Do tc nhn sy c t nng nn m tng i gim dn n phn p sut hi nc Pam trong tc nhn sy gim. Mt khc do nhit ca vt liu sy tng ln nn mt hi trong cc mao qun tng v phn p sut hi nc trn b mt vt cng tng .Nh vy trong h thng sy nng c hai cch to ra chnh phn p sut hi nc gia vt liu sy v mi trng: Gim phn p sut ca hi nc trong tc nhn sy bng cch t nng. Tng phn p sut hi nc trong vt liu sy.Tm li, nh t nng c tc nhn sy v vt liu sy hoc ch t nng vt liu sy m hiu s gia phn p sut hi nc trn b mt vt Phb v phn p sut hi nc trong tc nhn sy Ph tng ln dn n qu trnh dch chuyn m t trong lng vt liu sy ra b mt v i vo mi trng.Do , h thng sy nng thng c phn loi theo phng php cung cp nhit: H thng sy i luVt liu sy nhn nhit bng i lu t mt dch th nng m thng thng l khng kh nng hoc khi l. H thng sy i lu gm: h thng sy bung, h thng sy hm, h thng sy kh ng. H thng sy tip xcVt liu sy nhn nhit t mt b mt nng. Nh vy trong h thng sy tip xc, ngi ta to ra chnh lch p sut nh tng phn p sut hi nc trn b mt vt liu sy. H thng sy tip xc gm: h thng sy l, h thng sy tang H thng sy bc xVt liu sy nhn nhit t mt ngun bc x dn m dch chuyn t lng vt liu sy ra b mt v t b mt vo mi trng. y ngi ta to ra chnh phn p sut hi nc gia vt liu sy v mi trng bng cch t nng vt. H thng sy dng dng in cao tn hoc dng nng lng in t trngKhi vt liu sy t trong mi trng in t th trong vt xut hin cc dng in v chnh dng in ny s t nng vt. u im ca phng php sy nng Thi gian sy bng cc phng php sy nng ngn hn so vi phng php sy lnh. Nng sut cao v chi ph ban u thp. Ngun nng lng s dng cho phng php sy nng c th l khi thi, hi nc nng, hay cc ngun nhit t du m, than , rc thi,...cho n in nng. Thi gian lm vic ca h thng cng rt cao. Nhc im Ch sy c cc vt sy khng cn c cc yu cu c bit v nhit . Sn phm sy thng hay b bin mu v cht lng khng cao.b) Phng php sy lnhTrong phng php sy lnh, ngi ta to ra chnh p sut hi nc gia vt liu sy v tc nhn sy bng cch gim phn p sut hi nc trong tc nhn sy Ph nh gim cha m d. Mi quan h c th hin theo cng thc:

Ph = (1.10)Trong B - p sut mi trng (p sut kh tri).Khi , m trong vt liu dch chuyn ra b mt v t b mt vo mi trng c th trn di nhit mi trng (t > 0 oC) v cng c th nh hn 0 oC.c) So snh phng php sy lnh v phng php sy nng Di y l bng so snh cc phng php sy khc nhau vi phng php sy lnh s dng bm nhit nhit ca Vin Cng Ngh Thc Phm, s Cng Nghip H Ni da trn cc tiu ch v cht lng sn phm, gi thnh sn phm, thi gian sy, chi ph u t, chi ph vn hnh v bo v mi trng, phm vi ng dng, vv

Bng1-1 nh gi so snh cht lng sn phm sy bng bm nhit sy lnh vi phng php sy nng truyn thng v sy hng ngoi [Vin Cng Ngh Thc Phm, s Cng Nghip H Ni]Th tPhng Php sy

Ch tiu so snhSy nngSy thng hoa v chn khngSy lnh s dng my ht m kt hp my lnh

1Cht lng sn phm (mu sc, mi v, vitamin)Km hn rt nhiuTt hnBng nhau

2Gi thnh sn phmThp hnt hn nhiut hn

3Thi gian syNgn hnNgn hnLn hn hoc bng

4Chi ph u t ban uThng thp hnCao hn nhiuCao hn

5Chi ph vn hnh, bo dngThng r hnt hn nhiut hn

6Kh nng iu chnh nhit tc nhn sy theo yu cu cng nghKh hnKh hnKh hn

7V sinh an ton thc phmThng km hnTt hnBng nhau

8Bo v mi trngThng km hnNh nhauKm hn

9Phm vi ng dngRng hnHp hnHp hn

1.7.ng dng cng ngh sy lnh ti vit nam v cc ti nghin cu. Tc gi Phm Vn Ty v cc cng s tin hnh nghin cu v ng dng thnh cng h thng bm nhit sy lnh ko Jelly, ko Chew, Caramel, ko Cng ti cng ty bnh ko Hi H . Nm 1997, 1998 cc tc gi thit k ln lt hai h thng lnh theo nguyn l bm nhit nhit thp kiu mun. sy ko Jelly vi nng sut 1100 kg/ngy v 1400 kg/ngy hin nay vn cn c s dng cho phng sy lnh s 2 v s 3 Nh my thc phm Vit Tr- Cng ty c phn bnh ko Hi H. Thng s nhit khng kh bung sy 22-280C, m 30-40%. H thng my lnh DSL - P - V - 01

Hin nay, my sy lnh ti Vit Nam ch yu c nhp t nc ngoi vi gi cao. c th ch ng sn xut trong nc, thay th sn phm nhp ngoi, cc nh khoa hc thuc Khoa Cng ngh ha hc v thc phm - Trng i hc s phm k thut TP H Ch Minh nghin cu, ch to thnh cng h thng my lnh DSL - P - V - 01 dng Pilot vi nhiu u im nh: nng sut sy ti a: (56) kg nguyn liu/m; nhit mi trng sy: (30 40)0C; nhit ti calorifer: (40 60)0C, kh ca khng kh v h chn khng t gn tuyt i; nhit ngng t tch m t tc nhn sy: (-12 10)0C; thi gian sy: (8 14) h/m; m sn phm c th t: (4 8)%; h thng t ng iu khin PLC. c bit, my c gi ch bng 1/4 so vi my nhp ngoi cng cng sut.

Chng2NGUYN LIU SY LNH PHNG PHP SY RAU QU V CC YU T NH HNG

2.1.Nguyn liu trong sy lnh Tt c cc sn phm u chu bin i trong qu trnh sy v bo qun sau . Yu cu t ra i vi qu trnh sy l bo v ti mc tt nht cht lng, hn ch nhng h hi trong qu trnh sy, bo qun ng thi nng cao hiu qu kinh t mt cch ti u nht. Xt v c bn nhng thay i trong qu trnh sy c th chia ra: Nhng thay i l hc: st m, gy, v, Nhng thay i ha l: trng thi tnh cht ca nhng keo cao phn t b thay i. Nhng thay i ha sinh: do s oxi ha ca cht bo, phn ng sm mu phi enzim, phn ng enzim, Nhng thay i do vi sinh vt Nhng thay i lm thay i cu trc mu sc mi v, gi tr dinh dng v c nh hng n tnh hi nguyn ca sn phm sau khi sy. Cc phng php sy khc nhau c nhng u im v nhc im trong qu trnh sy cc sn phm rau qu. Trong , phng php sy nng p ng c cc yu cu v nng sut, thi gian sy nhng li khng p ng tt cc i hi v cht lng sn phm. Ngc li, i vi cc sn phm sy yu cu nhit thp i hi phi c quy trnh sy ph hp hn. Cng ngh sy lnh l mt cng ngh mi c dng gii quyt cc vn khng th gii quyt i vi cng ngh sy nng. T nghin cu thc nghim chng minh nhng u im vt tri ca cng ngh sy lnh trong qu trnh xy dng quy trnh sy i vi cc loi rau, c, qu, nm c gi tr kinh t, cc dc phm trong y hc. Ngoi ra, cng ngh sy lnh cn ng dng trong ngnh cng nghip sn xut ko Jelly, ko Chew, Caramel, ko Cng

2.2. Hnh nh mt s nguyn liu ng dng cng ngh sy lnh.

2.3. Phng php sy rau qu2.3.1. Quy trnh x l trc khi sySy rau qu thng thng c thc hin 3 dng ch yu: dng nguyn (hoc ming); dng bn mng v dng bt hoc nh tng. Tu theo dng sn phm, cng ngh sy rau qu c s chung nh sau: Rau qu ti sau khi ra sch c loi b phn khng tiu chun, c phn c theo kch thc, lm sch, ct ming. Sau rau qu c chn (hp), x l ho cht. Tip theo, cc hnh thc sn phm khc nhau c ch bin theo cc s khc nhau. Trong khi chn (hp), do tc dng ca nhit v m nn tnh cht ho l ca nguyn liu b bin i c li cho s thot nc khi sy. ng thi vi sinh vt b tiu dit v h thng enzim trong nguyn liu b mt hot tnh, hn ch ti a kh nng bin mu trong khi sy rau qu v rt ngn thi gian sy. Ngoi ra qu trnh chn lm gim ht m ca rau qu kh. Trong cng nghip sy rau qu, ngn nga qu trnh oxy ho lm bin mu rau qu khi sy, ngi ta s dng cc cht chng oxy ho nh axit sunfur, axit ascobic, axit xitric v cc mui natri ca axit Sunfur (nh sunfit, bisunfit, metabisunfit, ...) x l ho cht cho rau qu trc khi sy.

2.3.2. S cng ngh sy rau quRau qu (phi thch hp cho qu trnh sy)Lm sch (kh, t)La chn phn loi (theo kch thc)Gt saCt, thi (ty theo yu cu)Chn, hp (ty theo yu cu)X l ha hc (nu cn)

ChCh pSySyC cLm nguiLm nguiC cSyPhn loiPhn loiPhn loip bnhNghin nhng ging ging giSn phmSn phm dngSn phm dng nguynbn mngdng bt

Hnh 2-1. S cng ngh sy rau qu

2.4. Mt s phng php sy rau qua) Phng php sy bng khng kh Cng vic ny c tin hnh bng cch tri rau qu ln cc loi b mt ngoi tri nhn nh sang mt tri trc tip. Tuy nhin, sn phm c cht lng km do kh kim sot c vn v sinh, iu chnh m, nhit v tc sy. Ngi ta ch to my sy dung nng lng mt tri nhm khc phc nhng nhcim trn. Thit b ny s dng mt c cu rt n gin c tc dng tng cng nhit t mt tri v bo v sn phm. Cn ch phn bit gia sy trc tip v sy gin tip bng nng lng mt tri. i vi sy trc tip, sn phm c t dinh nng mt tri v kt qu l s thay i v mu sc, thnh phm vitamin. i vi sy gin tip, nguyn liu nyc bo v khinh sng trc tip t mt tri. phng php ny, ngi ta s dng mt phng ring thu nhn nhit lng t mt tri v ti, khng khc cp nhit ri thi qua phng cha sn phm. My sy c hc dng nhin liu t nng khng k mt cch trc tip, thc phm c sy bng kh t, hoc mt cch gin tip thc phm c sy bng khng kh nng do kh t. Hai hnh thc ny u c kh nng kim sot tt hn so vi sy bng mt tri v c th tin hnh c ngy ln m, khng ph thuc vo thi tit. Tuy nhin, chi ph u t v vn hnh cho thit b ny kh cao. i vi cc sn phm c la chn phn loi tt t nguyn liu ban u, cng on ra v x l cng quan trng nh cng on sy.b) Phng php sy lt Phng php ny tin hnh sy mt hoc hn hp nhiu loi rau qu (c x l bng dioxyt sunfua nhm hn ch mt mu v vi sinh vt pht trin) dng lt mng. Loi ny thng c dng nh thc phm n nh, c th tng ngt bng cch b sung ng vo nguyn liu ban u hoc thay i thnh phn nh thm hnh nhn, da no hay bt gia v.c) Phng php sy b sung V d nh chui c sy trc nhm loi b lp ng dnh tip tcc sy b sung. Vic ng gi v bo qun sn phm sy khi hi nhiu yu cu. Sn phm sau khi sy cn c bo qun trnhnh sng mt tri, m v nhit nhm ngn nga s gim hng v v h hng. Ngi ta thng dng dng c cha bng gm, thy tinh, kim loi hay nha cho ti khi chng cng hp. Gii php r nht l s dng ti mng mng PE vi iu kin phic ghp mng bng. Ni bo qun cn thong mt, trnh xa nhsng mt tri, cn trngv loi gm nhm. a s, sn phm sy un nh cht lng trong nhiu tun.

2.5. nh hng ca qu trnh sy n cht lng sn phma) nh hng n cu trc Thay i v cu trc ca cc vt liu l mt trong nhng nguyn nhn quan trng lm gim cht lng sn phm. Bn cht v mc ca cc bin php x l rau qu trc khi sy u c nh hng n cu trc ca cc sn phm sau khi hi nguyn. Nguyn nhn l do s h ha ca tinh bt, s kt tinh ca xenluloza v s hnh thnh cc sc cng bn trong do khc bit v m cc v tr khc nhau. Kt qu la s to thnh cc vt nt gy, cc t bo b nn p vn vo vnh vin, lm cho sn phm c b ngoi b co ngt, nhn nheo. Trong qu trnh lm t tr li sn phm ht nc chm, khng th ly li hnh dng nh ban u. Cc sn phm khc nhau c s dao ng v mc co ngt v kh nng hp th nc tr li. Sy nhanh nhit cao lm cho cu trc b thay i nhiu hn so vi sy vi tc va phi nhit thp. Trong qu trnh sy, cc cht ha tan di chuyn theo nc t bn trong ra b mt ngoi ca sn phm. Qu trnh bay hi lm c c cc cht tan b mt, kt hp vi nhit khng kh (c bit khi sy tri cy, c, tht,) gy ra cc phn ng l ha phc tp ca cc cht tan b mt ngoi nn lp v cng khng thm c. Hin tng ny gi l hin tng cng v (case hardening), lm gim tc sy v lm cho sn phm c b mt kh, nhng bn trong th m. V vy cn kim sot nhit sy trnh chnh lch m qu cao gia bn trong v b mt sn phm. i vi k thut sy lnh hon ton c th gii quyt c vn ny. H thng sy lnh c nhit tng i thp cho nn qu trnh kh ca b mt vt liu s chm hn trong khi m c ly ra nhiu bng s chnh lch phn p sut hi ngoi b mt v bn trong vt liu sy.b) nh hng n mi v Nhit lm tht thot cc thnh phn d bay hi ra khi sn phm v vy phn ln cc sn phm sy b gim mi v. Mc tht thot ph thuc vo nhit v m ca vt liu sy, p sut hi nc v ha tan ca cc cht bay hi trong nc. Nhng sn phm c gi tr kinh t cao nh vo c tnh mi v (nh gia v) cn c sy nhit thp. Mt s sn phm c kt cu xp to iu kin cho oxi khng kh d dng tip xc vi sn phm, gy ra cc phn ng oxi ha cht tan v cht bo trong qu trnh bo qun lm thay i mi v ca sn phm. Tc ca qu trnh gy h hng ph thuc vo nhit bo qun v hot ca nc. Phn ln rau qu ch cha mt lng nh lipit. Tuy nhin, s oxi ha cc cht bo khng no to ra cc hydroperoxit tham gia vo cc phn ng polime ha, phn ng tch nc hoc oxi ha to thnh aldehit, Kenton v cc axit gy mi i thui kh chu.c) nh hng n mu scC nhiu nguyn nhn gy ra s mt mu hay thay i mu trong sn phm sy, nh l: S thay i cc c trng b mt ca sn phm gy ra s thay i phn x nh sng v mu sc. Nhit v s oxi ha trong qu trnh sy gy ra nhng bin i ha hc i vi carotenoit v clorophyl, cng nh hot ng ca enzim polyphenoloxidaza gy nn s sm mu trong qu trnh bo qun cc sn phm rau qu.C th ngn nga c nhng thay i ny bng cc phng php chn hp hoc x l tri cy bng axit ascorbic hoc SO2.d) nh hng n gi tr dinh dng Cc s liu v s tht thot cc cht dinh dng ca cc tc gi thng khng thng nht, c th do s khc bit ng k trong cc qu trnh chun b sy, nhit v thi gian sy, cng nh iu kin bo qun. rau qu, tht thot dinh dng trong qu trnh chun b thng vt xa qu trnh sy. V d, tht thot vitamin C trong qu trnh chun b to sy (dng khi) l 8% do qu trnh ct gt, 62% do chn hp, 10% do qu trnh nghin pu r v 5% do qu trnh sy. Vitamin c ha tan trong nc khc nhau v khi qu trnh sy din ra, mt vi loi (v d: vitamin B2 riboflavin) t trng thi bo ha v kt ta khi dung dch, nh vy chng t b tn thng. Mt s khc, v d: axit ascorbic, ha tan ngay c khi m ca sn phm h xung n mc rt thp, chng phn ng vi cc cht tan vi tc cng lc cng cao hn trong qu trnh sy. Vitamin C cng rt nhy cm vi nhit v oxy ha. V th trnh nhng tht thot ln cn sy trong thi gian ngn, nhit thp, bo qun m thp v nng kh oxi thp. Thiamin (Vit B1) cng nhy cm vi nhit, tuy nhin cc vitamin khc ha tan trong nc bn vi nhit v oxy ha hn v tn tht qu trnh sy him khi vt qu 5-10%, ngoi tr tht thot do qu trnh chn hp. S tn tht cc vitamin c th hn ch ng k hoc ngn nga hon ton khi s dng cc phng php sy nhanh v n ha (nh sy phun), c bit bng phng php sy thng hoa i vi cc nguyn liu nghin nt, nguyn cht dng ct nh. Cc cht dinh dng nh cht bo (v d: cc axit bo khng thay th c v cc vitamin A, D, E, K) phn ln cha trong phn cht rn ca sn phm v chng khng b c c trong khi sy. Tuy nhin nc l dung mi ca cc kim loi nng, l nhng cht xc tc ca qu trnh oxy ha cc cht dinh dng khng no. Khi nc b mt, cht xc tc tr nn hot ng hn v lm tng tc oxy ha. Cc vitamin tan trong cht bo b bin i mt i khi tip xc vi peroxit c sinh ra do s oxy ha cht bo. gim tht thot trong qu trnh bo qun ngi ta h thp nng oxy, nhit bo qun v loi tr nh sang tip xc vi sn phm.e) nh hng n s hi nguyn sn phm (rehydration) Sn phm sau khi sy khng th tr li tnh trng ban u khi lm t tr li. Sau khi sy, t bo b mt p sut thm thu, tnh thm thu ca t bo b thay i, cc cht tan di chuyn, polysacarit kt tinh v protein t bo b ng t, tt c gp phn vo s thay i cu trc, lm tht thot cc cht d bay hi v y u l nhng qu trnh khng thun nghch. Nhit trong qu trnh sy lm gim kh nng hydrat ha tinh bt v tnh n hi ca thnh t bo, lm bin tnh protein, gim kh nng gi nc ca chng. Tc v mc thm nc tr li c th c dng nh ch s nh gi cht lng sn phm sy. Nhng sn phm sy trong nhng iu kin ti u, t h hi hn s thm t tr li nhanh hn, hon ton hn.2.6. Cc yu t nh hng n qu trnh sya) Nhit syYu t nh hng nhiu n cht lng sn phm rau qu kh l nhit sy. Nu nhit sn phm trong qu trnh sy cao hn 60 oC th prtin b bin tnh. Nu loi rau qu t thnh phn protin th nhit t nng sn phm c th ln n 80-90 oC. Nu tip xc nhit trong thi gian ngn nh sy phun th nhit sy c th ln n 150 oC. i vi sn phm khng chn nh chui, u th c th sy nhit cao, giai on u 90-100oC, sau gim dn xung.Qu trnh sy cn ph thuc vo tc tng nhit ca vt liu sy. Nu tc tng nhit qu nhanh th b mt mt qu b rn li v ngn qu trnh thot m. Ngc li, nu tc tng chm th cng thot m yu.b) m khng khMun nng cao kh nng ht m ca khng kh th phi gim m tng i ca n xung. C 2 cch lm gim m tng i ca khng kh [19] Tng nhit khng kh bng cch dngcalorife. Gim nhit khng kh bng cch dng my ht m.Thng thng khi vo l sy, khng kh c m 10 - 13%. Nu m ca khng kh qu thp s lm rau qu nt hoc to ra lp v kh trn b mt, lm nh hng xu n qu trnh thot hi m tip theo. Nhng nu m qu cao s lm tc sy gim.Khi ra khi l sy, khng kh mang theo hi m ca rau qu ti nn m tng ln (thng thng khong 40 - 60%). Nu khng kh i ra c m qu thp th s tn nng lng; ngc li, nu qu cao s d b ng sng, lm h hng sn phm sy. Ngi ta iu chnh m ca khng kh ra bng cch iu chnh tc lu thng ca n v lng rau qu ti cha trong l sy.c) Lu thng ca khng khTrong qu trnh sy, khng kh c th lu thng t nhin hoc cng bc. Trong cc l sy, khng kh lu thng t nhin vi tc nh (nh hn 0,4m/s), do vy thi gian sy thng ko di, lm cht lng sn phm sy khng cao. khc phc nhc im ny, ngi ta phi dng qut thng gi cng bc vi tc trong khong 0,4 - 4,0 m/s trong cc thit b sy. Nu tc gi qu ln (trn 4,0 m/s) s gy tn tht nhit lng.[20]d) dy ca lp sy dy ca lp rau qu sy cng nh hng n qu trnh sy. Lp nguyn liu cng mng th qu trnh sy cng nhanh v ng u, nhng nu qu mng s lm gim nng sut ca l sy. Ngc li, nu qu dy th s lm gim s lu thng ca khng kh, dn n sn phm b " m hi" do hi m ng li. Thng thng nn xp lp hoa qu trn cc khay sy vi khi lng 5 8 kg/m2 l ph hp.[20]

Chng3QU TRNH SY LNH S DNG BM NHIT V THC NGHIM SY LNH C RT

3.1. Gii thiu chung Cc loi rau qu rt nhy cm vi nhit cao, c bit l cc loi vitamin v khong cht, nhit trn 600C cc cht ny bt u phn hy, dn n lm gim gi tr dinh dng cng nh gi thnh ca sn phm [20]. i vi cc phng php sy nng, vic ly m t vt liu ch thc hin c bng vic t nng vt liu hoc tc nhn sy ln n nhit cao, s khng p ng c cc yu cu v cht lng. gii quyt vn ny, my sy lnh s dng bm nhit ra i, l phng php sy m vic ly m t vt liu sy c thc hin bng cch to ra s chnh p gia tc nhn sy v vt liu sy cho nn khng i hi phi gia nhit tc nhn sy ln nhit qu cao. Cng cng nguyn l dch chuyn m t bn trong nhn ra ngoi b mt vt liu sy nhng c th d dng nhn thy rng, i vi phng php sy nng tc nhn sy nhit cao s lm kh b mt vt liu nhanh hn do s cn tr qu trnh dch chuyn m. Hn na, cc vt liu sy khc nhau c cu trc t bo v thnh phn ha l khc nhau, vic s dng phng php sy lnh chng ta c th xy dng quy trnh cng ngh i vi cc loi rau qu khc nhau. Bi ton thit k m hnh my sy lnh s dng bm nhit sy C rt c thc hin xc nh cc thng s qu trnh t thc nghim.3.2. Xy dng quy trnh cng ngh sy C rt3.2.1. Gii thiu v nguyn liu syC rt - Daucus carota L., ssp sativus Hayek., thuc h Hoa tn - Apiaceae. M t nguyn liucy C rt l loi tho sng 2 nm. L ct thnh bn hp. Hoa tp hp thnh tn kp; trong mi tn, hoa chnh gia th khng sinh sn v mu ta, cn cc hoa sinh sn chung quanh th mu trng hay hng. Ht C rt c v g v lp lng cng che ph. B phn dngC v qu - Radix et Fructus Carotae. Ni sng v thu hiC rt l mt trong nhng loi rau trng rng ri nht v lu i nht trn th gii. C rt cng c trng nhiu nc ta. Hin nay, cc vng rau ca ta ang trng ph bin hai loi C rt: mt loi c c mu ti, mt loi c c mu ng sang mu da cam. Loi v (C rt ) c nhp trng t lu, nay nng dn ta t gi ging; loi c rt ny c c to nh khng u, li to, nhiu x, hay phn nhnh, km ngt. Loi v mu ng sang mu da cam l c rt nhp ca Php (C rt Tim tm) sinh trng nhanh hn loi trn; t l c trn 80%, da nhn, li nh, t b phn nhnh nhng c hi ngn, mp hn, n ngon, c th trng a chung. Thnh phn ha hcC rt l mt trong nhng loi rau c nh gi cao v gi tr dinh dng v cha bnh i vi con ngi. C rt giulng ng v cc loi vitamin cng nh nng lng. Cc dng ng tp trung lp v v tht ca c; phn li rt t. V vy c c rt c lp v dy, li nh mi l c tt.Trong 100g n c ca C rt, theo t l % c: nc 88,5; protid 1,5; glucid 8,8; cellulose 1,2; cht tro 0,8. Mui khong c trong C rt nh kalium, calcium, st, phosphor, ng, bor, brom, mangan, magnesium, molipden... 3.2.2. Xy dng quy trnh cng ngh sy C rt C rt phi chn mu , c to v li nh. Sau khi ra sch chn trong nc si nhit 87-880C trong thi gian 6-8 pht. Ra li loi b v v sunfit ha bng dung dch SO2 c nng 0,2-1%. C rt c sunfit ha thi mng thnh lt, tri u trn khay sy m bo sao cho qu trnh trao i nhit i lu ti u nht. C rt l loi rau c nhiu vitamin v cht dinh dng nn khng th tin hnh sy nhit cao. Thng thng khong nhit thch hp sy C rt trong khong 30 -700C [3].Ta c s cng ngh sy c rt nh sau:

C rt ti u vo ( m 88,7%)

Ra sch, ct gt

Chn trong nc si nhit (87-880C) trong thi gian 6-8 pht

Ra li trong dung dch SO2 (0,2-1%)Loi b v

Thi mng, xp vo khay sy

Sy ( nhit 30-50oC) theo phng php sy lnh

n m yu cu (12-14%)ng gi bo qun

Hnh 3-2. S cng ngh sy C rt3.3. Xc nh cc thng s u vo ca vt liu a) Thnh phn dinh dng ca vt liu syC rt sy kh rt giu vitamin: C, B1, B2, PP v c bit l tin vitamin A. Thnh phn ha hc ca C rt sy kh bao gm: 13% nc, 9,2% protit, 1,5% lipit, 48% ng, 10,4% tinh bt, 9,6% xenluloza, 2% axit, 6,3 % tro. [20]b) Xc nh kch thc vt liuS dng thc kp c chnh xc l 0,05mm c thang o t 0,05100mm. Kch thc ban u l kch thc ln nht ca cc ming C rt thi trn. Kch thc ngang (ng knh) o gn gia ming C rt. Tin hnh o th nghim 10 ln v thu c kt qu trung bnh ca ming C rt.c) Xc nh m ca vt liu sym l mt thng s k thut quan trng v lm c s cho qu trnh sy. Cn c vo m u v cui m chng ti c th tnh c thi gian sy l thuyt cng nh thi gian bo qun.m u ca C rt c xc nh bng phng php t sy. d) Phng php xc nh mu, miBng cch nh gi cm quan ca nhiu ngi v mu sc ca nguyn liu u vo v sn phm.e) La chn ch syi vi rau qu ni chung cng nh C rt ni ring nhit sy yu cu khng qu cao. Thng thng i vi cc loi rau qu nhit sy khng qu 60C, v nu cao hn c th lm tn thng cc thnh phn vitamin, cht dinh dng v mu sc trong sn phm dn n lm gim gi thnh sn phm. y ta tnh ton theo hai ch sy khc nhau, mt l ch sy hi lu hon ton tc nhn sy v ch thi b tc nhn sy.

Chng 4THIT B V SN PHM SY LNH4.1. Thit b sy lnh

Hnh 4-1 Thit b sy lnh s dng bm nhit.

Hnh 4-2 T sy lnh

4.2. Mt s yu t nh hng n cht lng sn phm sya) Nhit syYu t nh hng nhiu n cht lng sn phm rau qu kh l nhit sy. Nu nhit sn phm trong qu trnh sy cao hn 60 oC th prtin b bin tnh. Nu trn 90 oC th fruetoza bt u b caramen ho, cc phn ng to ra mebanoizin, polime ho hp cht cao phn t ... xy ra mnh v nhit cao hn na rau qu c th b chy. Rau qu i hi c ch sy n ho (nhit thp). Nu loi rau qu t thnh phn protin th nhit t nng sn phm c th ln n 80-90 oC. i vi sn phm khng chn nh chui, u th c th sy nhit cao, sau gim dn xung.Qu trnh sy cn ph thuc vo tc tng nhit ca vt liu sy. Nu tc tng nhit qu nhanh th b mt mt qu b rn li v ngn qu trnh thot m. Ngc li, nu tc tng chm th cng thot m yu.b) m khng khMun nng cao kh nng ht m ca khng kh th phi gim m tng i ca n xung. C 2 cch lm gim m tng i ca khng kh: Tng nhit khng kh bng cch dngcalorife. Gim nhit khng kh bng cch dng my ht m.Thng thng khi vo l sy, khng kh c m 10-13%. Nu m ca khng kh qu thp s lm rau qu nt hoc to ra lp v kh trn b mt, lm nh hng xu n qu trnh thot hi m tip theo. Nhng nu m qu cao s lm tc sy gim.Khi ra khi l sy, khng kh mang theo hi m ca rau qu ti nn m tng ln (thng thng khong 40 - 60%). Nu khng kh i ra c m qu thp th s tn nng lng; ngc li, nu qu cao s d b ng sng, lm h hng sn phm sy. Ngi ta iu chnh m ca khng kh ra bng cch iu chnh tc lu thng ca n v lng rau qu ti cha trong l sy.c) Lu thng ca khng kh.Trong qu trnh sy, khng kh c th lu thng t nhin hoc cng bc. Trong cc l sy, khng kh lu thng t nhin vi tc nh (nh hn 0,4m/s), do vy thi gian sy thng ko di, lm cht lng sn phm sy khng cao. khc phc nhc im ny, ngi ta phi dng qut thng gi cng bc vi tc trong khong 0,4 - 4,0 m/s trong cc thit b sy. Nu tc gi qu ln (trn 4,0 m/s) s gy tn tht nhit lng.d) ca lp sy dy ca lp rau qu sy cng nh hng n qu trnh sy. Lp nguyn liu cng mng th qu trnh sy cng nhanh v ng u, nhng nu qu mng s lm gim nng sut ca l sy. Ngc li, nu qu dy th s lm gim s lu thng ca khng kh, dn n sn phm b " m hi" do hi m ng li.Thng thng nn xp lp hoa qu trn cc khay sy vi khi lng 5 8 kg/m2 l ph hp.

4.3. Sn phm sy lnh Mt s hnh nh

Hnh 4-1.Carot sy lnh

Hnh 4-2. Cafe ha tan ng dng cng ngh sy lnh

Hnh 4-3. Chui ng vua sy lnh

4.4. ng dng cng ngh sy lnh bo qun thc phm

Nng sn c bo qun bng cng ngh sy lnh s gi nguyn c mu sc, mi v. Phng php ny c thc hin bng cch gim m tng i trong khng kh to ra s chnh lch p sut gia hi nc trong khng kh v hi nc trong nng sn, thc phm. Bng cch ny m s tch ra khi nng sn, thc phm, v i vo khng kh. Khi lm lnh khng kh trong thit b trao i nhit xung thp hn nhit ng sng, khng kh bo ho m s ngng ng v tch ra khi khng kh. Khng kh sau i qua dn nng s sy kh nng sn, thc phm.

u im ca cng ngh ny sy lnh l c th xy dng c tng quy trnh cng ngh sy hp l i vi tng loi rau, c, qu. Sau khi sy, nng sn, thc phm gi c nguyn mu sc, mi v, thnh phn dinh dng tht thot khng ng k (khong 5%), t tiu chun v sinh an ton thc phm ca Vit Nam v cc ch tiu k thut, cht lng sn phm tng ng ca Thi Lan v mt s nc khc trn th gii.

TI LIU THAM KHO1. http://www.say.vn/cong-nghe-say( Internet)1. Quy trnh cng ngh sn xut cc sn phm rau qu lnh ng v rau qu sy kh - (T Internet)1. PGS.TS V Ch Chnh (2000) Gio trnh iu Ho Khng Kh NXB Khoa Hc v K Thut.1. Nguyn Vn May (2005) - Bm Qut My Nn NXB Khoa Hc v K Thut.1. Nguyn c Li, Phm Vn Ty (1994) - K thut lnh c s Nh xut bn Gio Dc.1. Phm Vn Ty, Thi Sn, V Khuy Hu, Nguyn Thanh Lim, Dng Vn Vng, Nguyn c Tuyn -Nghin Cu Cng Ngh Ht m V Sy Lnh Nng Sn Thc Phm Bo co tng kt ti NCKH cp B B2001-28-30, H Ni 7/2003. 1. Phm Vn Ty, Thi Sn, Nguyn Lun - Hiu qu s dng bm nhit sy lnh cng ty Bnh ko Hi H Tp Ch KH&CN Nhit No2 (1999).1. Gio n k thut sy nng sn thc phm- Nguyn Vn La, NXB Khoa Hc K Thut, 2003.

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