Luận án tiến sĩ Hóa học Nghiên cứu chế tạo và tính chất của màng polyme

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 tng; - S dng cỏc phng phỏp phõn tớch ỏnh giỏ chuyn húa, bn nh, 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 O 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, C 2H4, 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 Cỏc loi tia bc x c s dng bo qun thc phm gm: tia õm cc v tia , tia Rngen (X) v tia Do yờu cu cn phi u vit, tin li v mi mt nh: cú xuyờn thu cao, cú ngun thu nhn d dng, n nh, r nờn hin tia ang c s dng nhiu nht [25] 1.1.2.4 Bo qun mụi trng khớ quyn iu khin CA (Controlled Atmosphere) 10 p.185251 [19] Littlefield N.A., Wankier B.N., Salunkhe D.K., McGill J.N., Fungistatic effects of controlled atmospheres, Appl Microbiol., 1996, Vol 14(4), p.579-81 [20] Chiesa A., Moccia S., Frezza D., Filippini de Delfino S., Influence of potassic fertilization on the postharvest quality of tomato fruits, Agric Tropi Subtropi., 1998, Vol 31, p 7181 [21] Jacxsens L., Devlieghere F., Falcato P., DeBevere J., Behavior of Listeria monocytogenes and Aeromonas spp on fresh-cut produce packaged under equilibrium modified atmosphere, J Food Prot., 1999, Vol 62(10), p 1128-1135 [22] Ferguson I., Volz R., Woolf A., Cavalieri R.P., Preharvest factors affecting physiological disorders of fruit, Postharvest Biol Technol., 1999, Vol 15, p 255262 [23] LeBlanc D.I., Stark R., MacNeil B., Goguen B., Beaulieu C., Perishable food temperatures in retail stores, In: New Developments in Refrigeration for Food Safety and Quality, Refrigeration Science and Technology Proceedings of the Meeting of Commission C2, with Commissions B2, D1, and D2-3; 1999, p 42-51 [24] Senesi E., Prinzivalli C., Sala M., Gennari M., Physicochemical and microbiological changes in fresh-cut green bell peppers as affected by packaging and storage, Ital J Food Sci., 2000 Vol 12, p 5564 187 [25] Hsu B.L., Weng Y.M., Liao Y.H., Chen W., Structural investigation of edible zein films/coatings and directly determining their thickness by FT-Raman spectroscopy, J Agric Food Chem., 2005, Vol 53, p 50895095 [26] Bennik M.H.J., Vorstman W., Smid E.J., Gorris L.G.M., The influence of oxygen and carbon dioxide on the growth of prevalent Enterobacteriaceae and Pseudomonas species isolated from fresh and controlled-atmosphere-stored vegetables, Food Microbiol, 1998, Vol 15, 459-469 [27] Bidawid S., Farber J.M., Sattar S.A., Survival of hepatitis A virus on modified atmosphere packaged (MAP) lettuce, Food Microbiol, 2001, Vol 18(1), p.95-102 [28] Molin G., Modified atmospheres, In: Lund B.M., Baird-Parker T.C., Gould G.W., editors The microbiological safety and quality of food Gaithersburg M.A, Aspen Publishers, 2000, p 214-34 [29] Phillips C.A Review: modified atmosphere packaging and its effects on the microbiological quality and safety of produce, Intl J Food Sci Technol., 1996, Vol 31, p 463-479 [30] Peris E., Dvir O., Feygenberg O., Arie R.B., Ackerman M., Lichter A., "Production of acetaldehyde and ethanol during maturation and modified atmosphere storage of litchi fruit", Postharvest Biology and Technology, 2002, 26, p 157-165 [31] Sivakumar D., Korsten L., "Influence of modified atmosphere packaging and postharvest treatments on quality retention of litchi cv Mauritius", 188 Postharvest Biology and Technology, 2006, Vol 41, p 145-142 [32] Tien C.L., Vachon C., Mateescu M.A and Lacroix, Milk protein coatings prevent oxidative browning of apples and potatoes, Journal of Food Science, 2001, 66(4), p.512 [33] Gennadiois A., Hanna M.A., Kurth B., Application of edible coatings on meats, poultry and seafood: a review, Lebens Wissen Technol, 1997, Vol 30, p.337-350 [34] Vi thiu, http://vi.wikipedia.org/wiki/V%E1%BA%A3i_thi%E1%BB%81u [35] Baldwin E.A., Baker R.A., Use of proteins in edible coatings for whole and minimally processed fruits and vegetables, In: Gennadios A., editor Protein based films and coatings, CRC Press, 2002 [36] Lim L.T., Mine Y., Britt I.J., Tung M.A., Formation and properties of egg white protein films and coatings, In: Gennadios A., editor Protein based films and coatings Boca Raton, Fla.: CRC Press, 2002, p 233-252 [37] Sothornvit R and Krochta J.M., Whey protein molecular weight effect on film oxygen permeability and mechanical properties, http://trc.ucdavis.edu/pftf2000/w2/sothornvit/syllabus.htm [38] Sothornvit R and Krochta J.M., Plasticizer affect on oxygen permeability of b-lactoglobulin films, J Agric Food Chem., 2000, Vol 48, p 6298-6302 189 [39] Morillon V and others, Factors affecting the moisture permeability of lipid based edible films: a review, Crit Rev Food Sci Nutr., 2002, Vol 42, p.67-89 [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 apples, Postharvest Biology and Technology, 2003, 28, p.381-390 [42] Da-Mota W.F 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