Luận án tiến sĩ Hóa học Nghiên cứu chế tạo và tính chất của màng polyme ứng dụng để bảo quản quả

B GIO DC V O TO VIN KHOA HC V CễNG NGH VIT NAM VIN HO HC PHM TH THU H NGHIấN CU CH TO V TNH CHT CA MNG POLYME NG DNG BO QUN QU Chuyờn ngnh: Hoỏ Hu c Mó s: 62.44.27.01 LUN N TIN S HO HC NGI HNG DN KHOA HC: GS.TS Nguyn Vn Khụi PGS.TS Thỏi Hong H NI - 2012 B GIO DC V O TO VIN KHOA HC V CễNG NGH VIT NAM VIN HO HC PHM TH THU H NGHIấN CU CH TO V TNH CHT CA MNG POLYME NG DNG BO QUN QU LUN N TIN S HO HC H Ni - 2012 M U Hoa qu sau thu hoch l nhng t to sng v tip tc cỏc hot ng hụ hp v trao i cht thụng qua mt s quỏ trỡnh bin i Chớnh nhng bin i ny lm cho qu nhanh chớn, nhanh gi, nhn dn ti hng nu khụng ỏp dng bin phỏp c bit lm chm quỏ trỡnh ny Trc nhu cu bc thit v cụng ngh bo qun sau thu hoch, t lõu ó cú nhiu cụng trỡnh nghiờn cu nc nhm tỡm cỏch thc bo qun rau qu cú hiu qu phự hp vi iu kin Vit Nam Mt s qui trỡnh bo qun s b ó c cụng b nh phng phỏp kt hp trựng nh cho mt s loi rau qu Ngoi cũn cú mt s phng phỏp khỏc nh x lý nhit, hoỏ cht, bo qun mt s loi bao bỡ Cỏc phng phỏp ny cú th kộo di thi hn bo qun ca hoa qu nhng khụng nhiu, mt khỏc li khụng gi c giỏ tr cm quan bờn ngoi cho hoa qu nờn vic ỏp dng thc t cha c rng rói Hin nay, cú cụng ngh bo qun hoa qu ang c nghiờn cu v s dng khỏ ph bin l bo qun bng lp ph n c v bo qun bng mng bao gúi khớ quyn bin i (MAP) Lp ph n c ỏp dng trc tip trờn b mt qu bng cỏch nhỳng, phun hay quột to mt khớ quyn bin i Lp mng bỏn thm to thnh trờn b mt hoa qu s gim bt quỏ trỡnh hụ hp v kim soỏt s mt m, nh ú trỡ cht lng v kộo di thi hn s dng ca qu ti Cỏc loi rau qu c chn bo qun cng rt a dng nh c chua, cam, bi, vi, nhón, da, hng, xoi Hu ht cỏc nghiờn cu u cho kt qu kh quan Cụng ngh th hai l bo qun bng mng bao gúi khớ quyn bin i õy l phng phỏp bo qun m qu c ng tỳi mng mng cú tớnh thm thu chn lc hoc ng st cú lút mng bao gúi Thm qu cũn c ng container ln c lút bng vt liu tng hp cú tớnh thm thu chn lc i vi cỏc loi khớ Vit Nam, vic nghiờn cu bo qun qu bng mng polyme gn õy bt u c quan tõm nghiờn cu Tuy nhiờn, nhng cụng trỡnh ó cụng b cho thy cỏc nghiờn cu u trung vo vic s dng mng MAP v dung dch to lp ph n c nhp ngoi bo qun qu m cha cú cụng trỡnh no cp ch to cỏc vt liu ny Vi mong mun gúp phn gii quyt nhng nhu cu cp thit m thc t t ra, ti Nghiờn cu ch to v tớnh cht ca mng polyme ng dng bo qun qu nhm nghiờn cu v ch to vt liu cú th ỏp ng nhu cu bo qun rau qu sau thu hoch, gúp phn tng hiu qu kinh t Vi mc tiờu ú, nhng nhim v m lun ỏn phi thc hin l: a) Nghiờn cu ch to vt liu dng dung dch t shellac - To mng v xỏc nh tớnh cht ca mng shellac vi cht húa (hỡnh thỏi hc, tớnh cht c lý, tớnh cht nhit ca mng) b) Nghiờn cu ch to vt liu bo qun qu dng nh tng polyvinyl axetat (PVAc) - Nghiờn cu quỏ trỡnh tng hp PVAc bng phng phỏp trựng hp nh - S dng cỏc phng phỏp phõn tớch ỏnh giỏ chuyn húa, bn nh, tng; trng lng phõn t trung bỡnh (TLPTTB), hỡnh thỏi hc b mt, cu trỳc, tớnh cht nhit ca sn phm c) Nghiờn cu cụng ngh ch to mng bao gúi khớ quyn bin i (MAP) trờn c s polyethylen (PE) vi cỏc ph gia vụ c - Nghiờn cu quỏ trỡnh trn v ct ht nha, phõn tớch kh nng trn v phõn tỏn ph gia ng thi s dng mt s phng phỏp phõn tớch ỏnh giỏ - Nghiờn cu quỏ trỡnh thi mng v ỏnh giỏ cỏc tớnh cht ca mng MAP (chiu dy mng, hỡnh thỏi hc b mt, tớnh cht c lý, bn mi hn) d) Nghiờn cu v th nghim vt liu bo qun cho loi qu (vi v mn), ỏnh giỏ cỏc tớnh cht ca qu quỏ trỡnh bo qun: hao ht lng, t l h hng, hm lng ng, cng CHNG TNG QUAN 1.1 Cỏc phng phỏp bo qun rau, qu ti sau thu hoch Hu ht quỏ trỡnh suy gim lng v cht lng ca hoa qu ti u din giai on t thu hoch n tiờu th c tớnh t l tn tht hoa qu sau thu hoch h hng cú th lờn ti 20-80% [1] Nguyờn nhõn l hoa qu sau thu hoch l nhng t bo sng v tip tc cỏc hot ng hụ hp v trao i cht thụng qua mt s quỏ trỡnh bin i Chớnh nhng bin i ny lm cho hoa qu nhanh chớn, nhanh gi, nhn dn ti hng nu khụng ỏp dng bin phỏp c bit lm chm cỏc quỏ trỡnh ny [2] Rau qu sau thu hoch thng tri qua mt s bin i nh: bin i sinh hoỏ, bin i vt lý v bin i hoỏ hc Hiu rừ c tớnh hụ hp ca qu ti cng nh c ch ca nhng bin i trờn cú th kộo di thi hn bo qun ca chỳng 1.1.1 Trao i cht sau thu hoch v bo qun cỏc sn phm ti 1.1.1.1 Quỏ trỡnh chớn v thi hn s dng Quỏ trỡnh chớn l mt quỏ trỡnh thoỏi húa c iu chnh ni sinh dn n hng v thi khụng th dng li nhng ch cú th lm chm li Trong h hng v thi gúp phn quan trng lm tn tht sau thu hoch, thỡ quỏ trỡnh chớn gõy tn tht thm cũn cao hn Trong quỏ trỡnh chớn, sn phm d b tn thng nm tn cụng Tt c cỏc hoocmụn t thc vt chớnh bao gm auxin, giberela, cytokinin, abscisic axit v c bit l etylen, u gõy nh hng ti mt cỏc quỏ trỡnh chớn v lóo húa [3] Tuy nhiờn, lóo húa i kốm vi quỏ trỡnh chớn ca qu Khỏi nim v phõn bit gia hin tng ny l khỏ khú khn v ụi cũn gõy nhm ln Quỏ trỡnh lóo húa l mt quỏ trỡnh t nhiờn v thoỏi húa liờn quan n s gi húa c trng ca quỏ trỡnh lóo húa i vi sn phm ti sau thu hoch cú th c mụ t bi nhng thay i nh lm gim clorophyl, thoỏi húa mng t bo, gim hm lng RNA v protein, lm bin i cu trỳc (cú th dn n lm mm v gõy cỏc nh hng tiờu cc) [4] 1.1.1.2 Hụ hp Hụ hp l quỏ trỡnh trao i cht quan trng nht din bt k t bo sng no Hụ hp c mụ t l s phõn hy oxy húa ca cỏc cht nn phc cú t bo, chng hn nh cacbohydrat, protein v cht bộo thnh nhng phõn t n gin hn (CO2 v H2O) vi vic sn sinh nng lng v cỏc phõn t khỏc c s dng bi t bo cho cỏc phn ng tng hp Mc ớch chớnh ca hụ hp l cung cp nng lng v cỏc cht giỳp t bo thc hin cỏc phn ng trao i cht cn thit cho vic trỡ t chc t bo [5] Hụ hp cú th xy iu kin hiu khớ hoc k khớ, tựy thuc vo s sn cú ca oxy i vi rau, qu sau thu hoch, phn ln nng lng c cung cp bi hụ hp hiu khớ, ch yu liờn quan n ba ng trao i cht: chuyn húa glucozit, chu k tricacboxylic axit (TCA) v chuyn electron Tuy nhiờn, iu kin mc nng oxy thp (thng nh hn 1-2% i vi thc vt), hụ hp k khớ (lờn men) c bt u, ú pyruvat ch yu b chuyn húa thnh etanol v axetalehyt [6] Hụ hp cng l mt ch s tuyt vi ca trao i cht; nú cng cú th c dựng nh mt tiờu chun hu ớch cho vic bo qun sn phm ti Mc dự mi liờn h chớnh xỏc gia hụ hp v thi hn s dng ó khụng c c th phm vi nht nh, t l h hng ca sn phm liờn quan n tc hụ hp ca chỳng Sn phm cú tc hụ hp thp (tỏo, hnh tõy, khoai tõy, c rt ) cú th bo qun di hn sn phm hụ hp nhanh, nh dõu tõy v nm cú thi hn bo qun ngn Nh vy, sn phm trng trt cú th c phõn loi vo nhúm khỏc v kh nng bo qun tc hụ hp ca chỳng [7] Do tc hụ hp l mt ch s quan trng ca quỏ trỡnh trao i cht ca sn phm sau thu hoch, cỏc yu t nh hng n tc ny s c xem xột chớnh quỏ trỡnh bo qun rau qu ti sau thu hoch Nhiu cụng ngh bo qun sn phm ti liờn quan n hụ hp nh iu khin iu kin mụi trng (vớ d nh nhit thp v khớ quyn bin i O2 thp v CO2 cao) [8, 9] 1.1.1.3 Hao ht thoỏt hi nc Mt nc cú th gõy nhng thay i khụng mong mun v ngoi quan nh hộo v qut, lm mm t bo, ht trng lng v lm thay i hng v Nú cng gõy mt nc, lm tng tc quỏ trỡnh lóo húa Hu ht rau qu khụng cũn kh nng thng mi húa chỳng b mt i 5-10% trng lng ti Nc mt ch yu l s thoỏt hi ca sn phm ti [10] ng lc ca quỏ trỡnh chuyn m l gradient ỏp sut hi t b mt sn phm n mụi trng bo qun Tr ỏp sut hi nc khớ quyn bo qun cõn bng ỏp sut trờn b mt sn phm, cũn li thỡ hm lng m s liờn tc bay hi v sn phm Nh vy, cỏc c im ca sn phm nh cu trỳc b mt ca lp biu bỡ v din tớch b mt riờng ca qu tip xỳc vi khụng khớ nh hng trc tip n tc bay hi p sut hi nc trờn b mt sn phm thng gn bng ỏp sut hi nc bóo hũa ti nhit nht nh, trong khụng khớ bo qun ỏp sut hi nc s thp hn so vi hi bóo hũa Vỡ nhiu yu t cú liờn quan n thoỏt hi, mt thut ng tng quỏt c gi l "h s thoỏt hi" c s dng thc t nh lng quỏ trỡnh thoỏt hi nc [11] Trao i cht, tc thoỏt hi cng cú liờn quan vi quỏ trỡnh trao i cht hụ hp Tc sn sinh nc liờn quan trc tip n t l hp th O2 v sinh nhit Ngi ta c tớnh rng ch cú 42% lng nhit cú th c s dng cho cỏc phn ng tng hp, phn nhit cũn li ny c s dng cho bay hi Bt k phng phỏp no lm gim tc hụ hp u cú th gúp phn gim thoỏt hi Tuy nhiờn, rt ớt bit v thoỏt hi iu kin khớ quyn bin i Mc dự khụng th ngn nga s thoỏt hi, nhng mt s bin phỏp cú th lm gim hao ht thoỏt hi, chng hn nh vic bo qun m cao, bao phim tng sn phm, v nhit thp, cú th lm tng m tng i lung bo qun sn phm [12-14] 1.1.1.4 Cỏc yu t gõy suy gim cht lng Ri lon sinh lý: Sn phm ti thng b cỏc ri lon sinh lý khỏc cú ngun gc t vic tip xỳc vi nhit khụng mong mun, C2H4, O2 thp ( 12%) v s mt cõn bng dinh dng Trong s cỏc iu kin mụi trng bt li gõy ri lon sinh lý, bo qun nhit quỏ thp thng hay gp nht Cỏc loi qu cú ngun gc nhit i v cn nhit i, nhit di im ti hn (10-120C), thng cú s phỏ v hy sinh lý, c gi l tn thng úng ỏ [15] Cỏc triu chng ca tn thng úng ỏ chung quan sỏt c l r, tht qu b thõm, chớn bt thng v tng kh nng h hng Nhng tn thng ny c th hin sn phm c chuyn t nhit úng ỏ n nhit thng Mt hu qu khỏc ca tn thng úng ỏ l vic to mựi khụng mong mun Cỏc phng phỏp thụng thng ngn nga tn thng úng ỏ liờn quan ch yu n vic gii hn nhit bo qun v x lý trờn mt ngng nht nh [16] Cỏc phn ng sinh húa: ngoi quỏ trỡnh trao i cht s cp, cỏc phn ng sinh húa th cp xy t bo thc vt cú th gúp phn tng hp mt s hp cht mong mun cng nh suy gim v cht lng Chỳng bao gm s suy gim cht dip lc (mt mu xanh lỏ cõy), to sc t tng hp carotenoit v phenylpropanoit, gim axit (decacboxyl húa), tng v ngt (thy phõn tinh bt), to hng thm (tng hp ru v este tng hp thụng qua s phỏ v enzym oxy húa ca cht bộo khụng no), lm mm t bo (hot tớnh cỏc enzym pectinaza v xenluloza), gõy thõm enzym (phenolaza) v quỏ trỡnh oxy húa cht bộo v thy phõn cht bộo (lipaza, lipidoxygenaza v peroxidaza) [17] Nhim khun v bnh: Nm v vi khun cú tm quan trng nht nh cỏc bnh sau thu hoch ca sn phm ti Nhim nm l mt yu t hn ch ch yu vic kộo di thi gian bo qun cỏc loi rau qu ti Núi chung, hu ht cỏc sn phm thu hoch u cú kh nng khỏng nm giai on u sau thu hoch Tuy nhiờn, bt u chớn v lóo húa, chỳng tr nờn d b nhim Tn tht sau thu hoch ch yu ca rau qu ti b gõy bi cỏc loi nm Botrytis, Alternaria, Rhizopus v Pseudomonas spp Núi chung, mm gõy bnh sau thu hoch l cỏc ký sinh trựng yu ch xõm nhp vo cỏc t bo b h hng [18-21] Tn tht sau thu hoch lõy nhim cú th hn ch bng cỏch gim thiu cỏc tn thng c hc, nh trỡ cỏc sn phm giai on u ca qu chớn hoc quỏ trỡnh lóo húa, bo qun chỳng iu kin ti u v x lý sn phm vi cỏc tỏc nhõn khỏng khun Tn thng c hc Tn thng c hc i vi sn phm ti cú th hn ch kh nng thng mi húa Thm va p nh cng cú th gõy v thỳc y s suy gim cht lng gia tng hụ hp v to etylen, lm thỳc y cỏc phn ng sinh húa khụng mong mun v lm cho cỏc sn phm d b nhim khun Hao ht x lý rau qu ti cú th xy quỏ trỡnh thu hoch, chuyn, úng gúi v bo qun sau thu hoch Cỏc vt thõm cú th xy vic ct, lốn lc v va p kim soỏt thit hi x lý sau thu hoch, quy trỡnh x lý cng nh bao gúi phự hp bo v chng va p v rung lc l rt cn thit [22] 1.1.2 Cỏc phng phỏp bo qun rau qu 1.1.2.1 Nhit thp, m tng i (RH) cao Phng phỏp ph bin nht trỡ cht lng v kim soỏt s h hng ca hoa qu l lm lnh nhanh vi m tng i (RH) cao Tuy nhiờn, phng phỏp ny li gõy nờn s h hng lnh hoa qu v vic kim soỏt nhit mt cỏch hiu qu l rt khú nờn mt s phng phỏp bo qun khỏc ang c nghiờn cu [23] 1.1.2.2 Bo qun bng húa cht S dng mt s loi hoỏ cht nhng liu lng khỏc kộo di thi gian bo qun ca hoa qu ch yu da vo kh nng tiờu dit vi sinh vt ca nhng hoỏ cht ny Hoỏ cht c s dng bo qun hoa qu ti cn ỏp ng mt s yờu cu nh: dit c vi sinh vt liu lng thp di mc nguy him cho ngi, khụng tỏc dng vi cỏc thnh phn qu dn ti bin i mu sc, mựi v lm gim cht lng hoa qu, khụng tỏc dng vi vt liu lm bao bỡ hoc dng c, thit b cụng ngh, d tỏch sn phm cn s dng Tuy nhiờn, ớt cú loi hoỏ cht no cú th tho tt c cỏc yờu cu trờn, cho nờn s dng phi chn la cho phự hp nhm m bo ng thi cht lng bo qun v an ton thc phm Phng phỏp bo qun bng hoỏ cht cng bc l mt s nhc im nh: hoỏ cht cú th lm bin i phn no cht lng ca hoa qu, to mựi v khụng tt, gõy hi cho sc kho ngi, cú th gõy ng c tc khc hoc lõu di Vỡ vy cn thn trng s dng hoỏ cht bo qun hoa qu [24] 1.1.2.3 Bo qun bng tia bc x Nguyờn lý ca phng phỏp ny: chiu bc x vo sn phm thỡ mt mt vi sinh vt s b tiờu dit, mt khỏc vi rau qu ti quỏ trỡnh sinh lý, sinh húa cú th b c ch, nh vy kộo di thi hn bo qun 10 [40] Bai J and others, Alternatives to shellac coatings provide comparable gloss, internal gas modification, and quality for Delicious apple fruit, HortScience, 2002, 37, p.559-563 [41] Bai J and others, Coating selection for Delicious and other 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London, 1996 [115] Krzytof P., James N., Thermal degradation of polymeric materials, Rapra Technology, ISBN: 1-85957-498-X, 2005 [116] Behjat T., Thermal properties of low density polyethylene filled kenaf cellulose composites, European Journal of scientific research, 2009, Vol 32(2), p 223-230 168 DANH MC HèNH Hỡnh 1.1 Cụng thc cu to gn ỳng ca nha shellac 15 Hỡnh 1.2 n v cu trỳc c bn ca zeolit 31 Hỡnh 1.3 S minh s hỡnh thnh cu trỳc zeolit 31 Hỡnh 1.4 Cỏc dng cu trỳc ca vt liu MQTB 34 Hỡnh 1.5 C ch n lp .34 Hỡnh 1.6 C ch chuyn pha t dng lp sang dng lc lng 35 Hỡnh 1.7 S khụng gian mng li cu trỳc ca montmorillonit .36 Hỡnh 1.8 S nguyờn lý mỏy ựn .38 Hỡnh 2.1 S nguyờn lý ca h thng trn, ct ht 63 Hỡnh 2.2 Cu trỳc mỏy ựn .64 Hỡnh 2.3 S nguyờn lý h thng ựn thi mng 65 Hỡnh 2.4 S thớ nghim xỏc nh thm hi nc qua mng 66 Hỡnh 3.1 Cu trỳc hoỏ hc ca shellac [113] 73 Hỡnh 3.2 nh SEM ca mng SH (a,b), SH cú 10% glyxerin (c,d) 74 Hỡnh 3.3 Gin DSC ca: (a) mng SH v (b) SH cha 10% glyxerin 76 Hỡnh 3.4 nh hng ca nhit v thi gian ti quỏ trỡnh trựng hp 79 Hỡnh 3.5 C ch gi thit phn ng trựng hp nh tng VAc vi cht mo APS v cht nh húa Emulgel 220 82 Hỡnh 3.6 Ph hng ngoi ca PVAc 84 Hỡnh 3.7 Gin TGA ca cỏc mu PVAc cú TLPT khỏc 85 Hỡnh 3.8 Gin DSC ca cỏc mu PVAc cú TLPT khỏc 87 Hỡnh 3.9 B mt nh tng PVAc di hớnh hin vi in t 87 Hỡnh 3.10 nh SEM mng PVAc cỏc phúng i 20000 (a) v 30000 (b) .88 Hỡnh 3.11 nh chp masterbatch (MB) vi cỏc ph gia khỏc 90 Hỡnh 3.12 nh SEM ca mng MAP vi 5% zeolit c phõn tỏn bng phng phỏp trn trc tip 94 Hỡnh 3.13 nh SEM ca mng MAP vi ph gia zeolit hm lng (3a, 3b), (5a, 5b) v 7% (7a, 7b) c ựn thi t MB 95 Hỡnh 3.14 nh SEM ca mng MAP vi ph gia bentonit hm lng (3a, 3b), (5a, 5b) v 7% (7a, 7b) c ựn thi t MB 96 Hỡnh 3.15 nh SEM ca mng MAP vi ph gia silica hm lng 5% c ựn thi t MB 97 Hỡnh 3.16 nh chp kớnh hin vi quang hc ca mng LDPE khụng cha ph gia 98 Hỡnh 3.17 nh chp kớnh hin vi quang hc ca mng MAP vi ph gia zeolit hm lng (3a, 3b), (5a, 5b) v 7% (7a, 7b) c ựn thi t MB .99 Hỡnh 3.18 nh chp kớnh hin vi quang hc ca mng MAP vi ph gia bentonit hm lng (3a, 3b), (5a, 5b) v 7% (7a, 7b) c ựn thi t MB 100 Hỡnh 3.19 nh chp kớnh hin vi quang hc ca mng MAP vi ph gia silica hm lng 5% c ựn thi t MB .101 Hỡnh 3.20 nh SEM ca mng MAP vi ph gia zeolit hm lng (5a, 5b) v 7% (7a, 7b) c ựn thi t CP .102 Hỡnh 3.21 nh SEM ca mng MAP vi ph gia bentonit hm lng (5a, 5b) v 7% (7a, 7b) c ựn thi t CP .103 Hỡnh 3.22 nh SEM ca mng MAP vi ph gia silica hm lng (5a, 5b) v 7% (7a, 169 7b) c ựn thi t CP .103 Hỡnh 3.23 nh chp kớnh hin vi quang hc ca mng MAP vi ph gia zeolit hm lng (5a, 5b) v 7% (7a, 7b) c ựn thi t CP .104 Hỡnh 3.24 nh chp kớnh hin vi quang hc ca mng MAP vi ph gia bentonit hm lng 5% (5a, 5b) v 7% (7a, 7b) c ựn thi t CP 105 Hỡnh 3.25 nh chp kớnh hin vi quang hc ca mng MAP vi ph gia silica hm lng 5% (5a, 5b) v 7% (7a, 7b) c ựn thi t CP 105 Hỡnh 3.26 nh SEM ca mng CE44 106 Hỡnh 3.27 nh chp kớnh hin vi quang hc ca mng CE44 106 Hỡnh 3.28 Gin TGA ca cỏc loi mng MAP 111 Hỡnh 3.29 Gin DSC ca cỏc loi mng MAP 113 Hỡnh 3.30 Nng CO2 bờn bao gúi 136 Hỡnh 3.31 Nng O2 bờn bao gúi 136 Hỡnh 3.32 Nng CO2 bờn bao gúi 146 Hỡnh 3.33 Nng O2 bờn bao gúi 147 170 DANH MC BNG Bng 1.1 Mt s tớnh cht vt lý ca PVAc 18 Bng 1.2 iu kin MA v chn lc cn thit cho bao gúi khớ quyn bin i i vi cỏc loi qu 22 Bng 1.3 iu kin MA v chn lc cn thit cho bao gúi khớ quyn bin i i vi cỏc loi rau qu 23 Bng 1.4 Kh nng thm khớ v chn lc ca mt s loi polyme ti 40C 24 Bng 1.5 Phõn loi cỏc loi nha PE .28 Bng 2.1 Thụng s cụng ngh quỏ trỡnh trn ct ht nha .64 Bng 3.1 Tớnh cht c lý ca mng shellac .75 Bng 3.2 thm hi nc ca mng shellac .75 Bng 3.3 Kt qu la chn cht nh húa 77 Bng 3.4 nh hng ca nng cht nh húa ti bn nh .78 Bng 3.5 nh hng ca nhit n KLPT v bn nh 80 Bng 3.6 nh hng ca nng cht mo n quỏ trỡnh trựng hp .80 Bng 3.7 nh hng ca nng monome 81 Bng 3.8 nh hng ca cht chuyn mch ti TLPT ca sn phm .82 Bng 3.9 thm hi nc ca mng PVAc 88 Bng 3.10 Kt qu quan sỏt ht nha cha ph gia 91 quỏ trỡnh trn hp to MB 91 Bng 3.11 Thụng s k thut ht nha MB v CP 92 Bng 3.12 nh hng ca cỏc thụng s k thut n chiu dy mng 107 Bng 3.13 Tớnh cht c lý ca mng MAP 108 Bng 3.14 D liu phõn tớch nhit trng lng ca cỏc loi mng MAP 111 Bng 3.15 D liu nhit vi sai quột ca cỏc loi mng MAP 114 Bng 3.16 thm hi nc ca mng MAP cỏc nhit d khỏc 115 Bng 3.17 T l h hng ca qu mn quỏ trỡnh bo qun (%) 117 Bng 3.18 Hao ht lng ca qu mn quỏ trỡnh bo qun (%) 118 Bng 3.19 cng qu mn quỏ trỡnh bo qun (kg/cm2) 120 Bng 3.20 Ch s mu (a+) v qu mn 121 Bng 3.21 S bin i hm lng cht rn ho tan qu mn quỏ trỡnh bo qun (0Brix) 122 Bng 3.22 S thay i hm lng axit ca mn quỏ trỡnh bo qun (%) .122 Bng 3.23 T l h hng ca qu mn quỏ trỡnh bo qun (%) 123 Bng 3.24 Hao ht lng ca qu mn quỏ trỡnh bo qun (%) 124 Bng 3.25 cng v qu mn quỏ trỡnh bo qun (kg/cm2) .126 Bng 3.26 Ch s mu (a+) v qu mn 127 Bng 3.27 S bin i hm lng cht rn ho tan qu mn quỏ trỡnh bo qun (0Brix) 127 Bng 3.28 S thay i hm lng axit ca mn quỏ trỡnh bo qun (%) .127 Bng 3.29 T l h hng ca qu mn quỏ trỡnh bo qun (%) 128 Bng 3.30 cng qu mn (kg/cm2) 134 Bng 3.31 Ch s mu v qu mn 135 Bng 3.32 S thay i hm lng cht rn ho tan ca qu mn quỏ trỡnh bo qun (0Brix) 137 171 Bng 3.33 S thay i hm lng axit ca mn quỏ trỡnh bo qun (%) .138 Bng 3.34 T l h hng ca qu vi quỏ trỡnh bo qun (%) .139 Bng 3.35 cng qu vi quỏ trỡnh bo qun (kg/cm2) 145 Bng 3.36 Ch s mu ca qu vi 145 Bng 3.37 S bin i hm lng cht rn ho tan ca qu vi quỏ trỡnh bo qun (0Brix) 148 Bng 3.38 S thay i hm lng axit ca qu vi quỏ trỡnh bo qun .148 172 MC LC CHNG TNG QUAN 1.1 Cỏc phng phỏp bo qun rau, qu ti sau thu hoch 1.1.1 Trao i cht sau thu hoch v bo qun cỏc sn phm ti 1.1.1.1 Quỏ trỡnh chớn v thi hn s dng 1.1.1.2 Hụ hp .7 1.1.1.3 Hao ht thoỏt hi nc 1.1.1.4 Cỏc yu t gõy suy gim cht lng 1.1.2 Cỏc phng phỏp bo qun rau qu .10 1.1.2.1 Nhit thp, m tng i (RH) cao .10 1.1.2.2 Bo qun bng húa cht 10 1.1.2.3 Bo qun bng tia bc x .11 1.1.2.4 Bo qun mụi trng khớ quyn iu khin CA 11 1.1.2.5 Bo qun mụi trng khớ quyn bin i MA .11 1.2 Bo qun bng lp ph n c .12 1.2.1 Lp ph trờn c s polysaccarit 12 1.2.2 Lp ph trờn c s protein .13 1.2.3 Lp ph trờn c s lipit 13 1.2.4 Lp ph trờn c s shellac t cỏnh kin 14 1.2.5 Lp ph trờn c s polyvinyl axetat 16 1.3 Bo qun rau qu bng bao gúi khớ quyn bin i 20 1.3.1 Thit k v la chn vt liu 20 1.3.1.1 thm thu ca mng bao gúi v thụng lng trao i khớ ca h bao gúi 21 1.3.1.2 Thit k bao gúi bin i khớ quyn .25 1.3.1.3 Vt liu ch to MAP 26 1.3.2 Cụng ngh ch to bao gúi MAP 36 1.3.3 Phng phỏp iu chnh thm khớ qua mng MAP 39 1.3.3.1 iu chnh dy mng 39 1.3.3.2 Phng phỏp c l .39 1.3.3.3 B sung ph gia iu chnh thm thu khớ 40 1.3.4 ng dng bao gúi MAP bo qun rau qu ti sau thu hoch 42 1.3.4.1 S lc tỡnh hỡnh bo qun hoa qu bng MAP .42 1.3.4.2 Cụng ngh bo qun hoa qu ti Vit Nam 45 1.3.4.3 Cỏc nghiờn cu bo qun loi qu c cp .47 1.4 Tỡnh hỡnh nghiờn cu rau, qu sau thu hoch Vit Nam .51 1.4.1 Gii thiu v qu vi 53 1.4.2 Gii thiu v qu mn 54 CHNG THC NGHIM 57 2.1 Nguyờn vt liu v hoỏ cht 57 2.2 Dng c v thit b 58 2.2.1 Dng c 58 2.2.2 Thit b s dng 58 173 2.3 Phng phỏp thc nghim, tng hp, gia cụng 59 2.3.1 Nghiờn cu ch to vt liu bo qun qu dng dung dch t shellac .59 2.3.1.1 Xỏc nh tớnh cht ca nguyờn liu shellac .59 2.3.1.2 To mng v xỏc nh tớnh cht ca mng shellac cha cht hoỏ .60 2.3.2 Nghiờn cu ch to vt liu bo qun qu dng nh tng PVAc 60 2.3.2.1 Nghiờn cu quỏ trỡnh tng hp PVAc bng phng phỏp trựng hp nh tng 60 2.3.2.2 To mng t nh tng PVAc cha cht hoỏ 62 2.3.2.3 Cỏc phng phỏp phõn tớch, ỏnh giỏ .62 2.3.3 Ch to mng bao gúi khớ quyn bin i .62 2.3.3.1 Trn v ct ht nha to masterbatch (MB) v compound (CP) .62 2.3.3.2 Thi mng v ỏnh giỏ cỏc tớnh cht ca mng MAP .65 2.3.4 Xỏc nh thm hi nc ca mng MAP v cỏc lp ph 66 2.3.5 Th nghim vt liu bo qun cho cỏc loi qu 67 2.3.5.1 Nguyờn liu 67 2.3.5.2 Bo qun mn bng lp ph shellac .68 2.3.5.3 Bo qun mn bng lp ph PVAc 69 2.3.5.4 Bo qun mn bng mng MAP .70 2.3.5.5 Bo qun vi bng mng MAP 70 2.3.5.6 Cỏc phng phỏp o c, ỏnh giỏ 71 CHNG KT QU V THO LUN 73 3.1 Nghiờn cu ch to vt liu bo qun qu dng dung dch t shellac .73 3.1.1 To mng v xỏc nh tớnh cht ca mng shellac cha cht hoỏ 74 3.1.1.1 Hỡnh thỏi hc b mt ca mng 74 3.1.1.2 Tớnh cht c lý ca mng shellac .74 3.1.1.3 thm hi nc ca mng shellac 75 3.1.1.4 Tớnh cht nhit ca mng shellac .76 3.2 Nghiờn cu ch to vt liu bo qun qu dng nh tng PVAc 77 3.2.1 Nghiờn cu quỏ trỡnh tng hp PVAc bng phng phỏp trựng hp nh tng 77 3.2.1.1 La chn cht nh húa 77 3.2.1.2 nh hng ca nhit v thi gian 79 3.2.1.3 nh hng ca nng cht mo 80 3.2.1.4 nh hng ca nng monome 81 3.2.1.5 nh hng ca cht chuyn mch 81 3.2.2 Mt s c trng lý hoỏ v tớnh cht ca mng trờn c s PVAc 83 3.3 Nghiờn cu cụng ngh ch to mng bao gúi khớ quyn bin i 89 3.3.1 Nghiờn cu quỏ trỡnh trn v ct ht nha .89 3.3.2 Nghiờn cu quỏ trỡnh thi mng .93 3.3.2.1 nh hng ca phng phỏp ựn thi n s phõn tỏn ph gia mng 93 3.3.2.2 nh hng ca cỏc thụng s cụng ngh ti chiu dy mng MAP 107 3.3.3 Mt s tớnh cht v c trng lý hoỏ ca mng MAP 108 174 3.3.3.1 Tớnh cht c lý ca mng MAP 108 3.3.3.2 Tớnh cht nhit ca mng MAP 109 3.3.3.3 thm hi nc ca mng MAP .114 3.4 ng dng cỏc loi vt liu bo qun vi v mn .116 3.4.1 Nghiờn cu bo qun mn bng cỏc ch phm to mng ph .117 3.4.1.1 Bo qun mn bng lp ph shellac .117 3.4.1.2 Bo qun mn bng lp ph PVAc 123 3.4.2 Nghiờn cu bo qun vi v mn bng mng bao gúi khớ quyn bin i (MAP) 128 3.4.2.1 Bo qun mn bng mng MAP 128 3.4.2.2 Bo qun vi bng mng MAP 138 KT LUN CHUNG 150 I CC KT QU CHNH CA LUN N 150 II NHNG IM MI V ểNG GểP CA LUN N 151 DANH MC CC CễNG TRèNH KHOA HC .152 LIấN QUAN N LUN N C CễNG B .152 TI LIU THAM KHO 153 175