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Tp ch Khoa hc 2011:19b 209-218

Trng i hc Cn Th

NH HNG CA MT S NM MEN, CHT KH HA TAN V PH CA DCH LN MEN N CHT LNG RU VANG THT NTNguyn Minh Thy1, Nguyn Th M Tuyn, Nguyn Ph Cng, Dng Kim Thanh, L Vn Boi, L Thanh Trng, Hunh Th Chnh v Phan Thanh Nhn

ABSTRACTThe present study was conducted to evaluate the fermentation efficiency of isolated locally identified yeast strains against the commercial yeast preparations in the case of palm wine. The impact of isolated yeast cell number varied from 101-106 CFU/ml, soluble solid contents and pH values ranged 20-24oBx and 3.5 to 4.5 (respectively) were studied. The quality of fermented wine produced from isolated was compared to wine fermented from the commercial yeast. After fermentation for 12 days, isolated Saccharomyces had all of the desired properties for the purpose of this study and fermented alcohol better than commercial wine yeasts. The highest of 13.67% (v/v) and lower 12.33% (v/v) alcohol concentrations with corresponding residual sugar concentrations of 2.57% (w/v) and 3.42% (w/v) were produced from palm wine (pH 4.0 and 24oBrix) with isolated yeast strain (103 CFU/ml) and commercial yeast, respectively. The chemical properties of wine (volatile acid, ester, sulfur dioxide and methanol content) were less than permitted levels of Vietnamese standard. Keywords: palm wine, isolated yeast, commercial yeast, fermentation, quality Title: Effect of isolated yeast cell number, total soluble solid and pH value to palm wine quality

TM TTNghin cu c thc hin nhm nh gi hiu qu ln men ca dng nm men Saccharomyces c phn lp v tuyn chn t nc tht nt so vi nm men thng mi trong qu trnh sn xut ru vang tht nt. nh hng ca s lng t bo nm men phn lp (101106 CFU/ml), hm lng cht kh ho tan (2024oBx), pH (3,54,5) cng vi qu trnh ln men t 2 dng nm men c kho st. Sau 12 ngy ln men, kt qu cho thy dng nm men thun chng Saccharomyces c tt c cc c tnh mong mun cho mc ch nghin cu ny v ru ln men tt hn so vi nm men thng mi. Hm lng ethanol cao (13,67% v/v) v hm lng ng st thp (2,57%) th hin vi qu trnh ln men t dng nm men thun chng (vi dch ln men c s lng t bo nm men 103 CFU/ml, hm lng cht kh ho tan 24oBx v pH 4,0). Hm lng ethanol thp hn (12,33%) v hm lng ng st cao hn (3,42%) th hin vi ru ln men t nm men thng mi. Cc ch tiu ha hc khc ca ru (acid bay hi, ester, SO2 v methanol) u thp hn mc cho php ca tiu chun Vit Nam (7045:2009). T kha: Ru vang tht nt, nm men phn lp, nm men thng mi, ln men, cht lng

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Khoa NN & SHD, Trng i hc Cn Th

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1 T VN nc ta, cy tht nt mc v c trng cc tnh khu vc Nam B gip vi Campuchia. Ring vng Tht Sn-An Giang, ngi dn trng v khai thc tht nt nhm mang li thu nhp hng ngy. Cy tht nt c xem l cy cho hiu qu kinh t cao, d trng v c thi gian khai thc di. Sau khi thu hoch, nc tht nt thng ch c bn nh nc gii kht dng ti hoc dng sn xut ng. Tuy nhin nc tht nt sau thu hoch thng nhanh chng hng do qu trnh ln men, lm gim gi tr dinh dng ca sn phm v cn lm cho sn phm khng cn kh nng s dng c (Nguyn Minh Thy et al., 2006). nh hng s dng nguyn liu ny cho qu trnh sn xut a dng s gip nng cao gi tr ca c sn tnh An Giang, a dng ha sn phm t cy tht nt v nng cao thu nhp cho ngi trng. Sn xut ru vang cng l phng cch s dng hiu qu ngun nguyn liu. Tuy nhin kim sot tin trnh ln men (t cc yu t tc ng) vi dng nm men tuyn chn l bin php k thut tt qun l cht lng sn phm. Do vy, mc tiu nghin cu nhm chn la iu kin ti u cho qu trnh sn xut ru vang tht nt cht lng cao t ngun nm men thun chng v so snh cht lng ru vang ln men t nm men thng mi vi quy trnh c kim sot. 2 PHNG TIN V PHNG PHP NGHIN CU 2.1 Nguyn vt liu Nc tht nt: thu hoch trc tip trn cy ci (bng s cho tri) ti huyn Tnh Bin, tnh An Giang vo bui sng (t ng thu nc tht nt t bui chiu hm trc n sng hm sau). Vn chuyn nc (trong iu kin lnh) v phng th nghim B mn CNTP, Trng i hc Cn Th. Ging nm men: nm men thuc ging Saccharomyces c phn lp v tuyn chn t nc tht nt thu hoch bui sng, x l sodium metabisulfite (khong 0,5 g/l). Ging c gi trn mi trng Sabouraud trong cc ng thch nghing, bo qun 4-10oC (Bi Th Thy Ngn, 2010). nh k cy chuyn 2 thng/1 ln. Nui cy nhn ging nm men: Trc khi s dng nm men cho qu trnh ln men ru, qu trnh nui cy c thc hin bng cch s dng nc tht nt c pH 4.5, 12-14oBrix, thanh trng nhit 121oC trong 15 pht, nui cy nhit 30-32oC trn my lc (140 RPM). Kim sot cht lng nm men thng qua s lng t bo/ml mi trng 120-149.106, s lng t bo ny chi 10-15%, lng t bo cht khng qu 2-4% (thc hin theo phng php lm tiu bn nhum t bo cht bng dung dch Xanh methylene vi pH 4,6, m s lng men cht v tng s bung m - Lng c Phm, 2006). 2.2 Phng php th nghim 2.2.1 B tr th nghim Th nghim c b tr ngu nhin ban u vi vic chn la t l nm men phn lp (10106 CFU/ml) cho qu trnh sn xut ru. T kt qu t c, cc th nghim c tip tc b tr theo khi hon ton ngu nhin vi 2 nhn t: Brix (2024oBrix) v gi tr pH (3,54,5) ca dch ln men. Cc th nghim c lp li 3 ln.210

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2.2.2 Ln men B sung nm men vi cc mt s 10106 CFU/ml. Thc hin qu trnh ln men (th tch khong 50 lt) nhit phng (28-30oC) trong iu kin ym kh (Hnh 1). Nhit bn ln men c kim sot bng phn mm Logger Lite (version 1.4) v kim sot tin trnh ln men trong khong 10 n 14 ngy. Thc hin gii nhit bn ln men (trong trng hp cn thit) bng nc (t khi bt u qu trnh ln men cho n khong 72 gi sau ln men). Thc hin ng thi qu trnh ln men ru vang tht nt t dng nm men hin c trn th trng (Lesaffre 59703 Marcq, France) v so snh cht lng thnh phm ru vang c ln men t hai dng nm men ny.

Hnh 1: H thng ln men ru vang tht nt: Bnh ln men chnh; : Bnh ln men ph; : Bnh ln men ph; : Van chit chai; : p sut k; : Van x kh; : H thng kim sot nhit sut qu trnh ln men ru

2.2.3 Cc ch tiu phn tch Hm lng ethanol (%v/v), ng st (%), acid bay hi (g/l), ester (g/l), SO2 (mg/l), methanol (g/l) (L Thanh Mai, 2007). 2.3 X l s liu S dng phn mm Excel v Statgraphics 4.0 tnh ton, thng k s liu, v th. 3 KT QU THO LUN 3.1 nh hng ca mt s nm men n cht lng ru vang tht nt 3.1.1 nh hng ca mt s nm men n hm lng ethanol v hm lng ng st trong sn phm ru vang tht nt Kt qu kho st nh hng ca mt s nm men phn lp n hm lng ethanol sinh ra v hm lng ng st trong ru vang tht nt c th hin bng 1. Kt qu thng k cho thy mt s nm men b sung ban u c nh hng n hm lng ru sinh ra. Khi s dng mt s nm men t 103-106 CFU/ml cho ru vang c cn cao (t 13,13 n 13,88%). Trong khi , cc mu ru ln men vi mt s nm men thp hn (101-102 CFU/ml) cho hm lng ethanol thp (11,88-12,63% v/v). Nh vy mt s nm men thp hn 103 CFU/ml hu nh qu trnh ln men khng trit . Theo Lng c Phm (2006) khi s dng nm men211

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nng thp th kh nng ny chi tip v thi gian t c nh mc l rt di s nh hng n hot ng v trao i cht ca nm men. Nhng m ln men ny thng cho hiu qu km v cht lng thnh phm xu. Tng ng vi ru to thnh cao hn th hm lng ng st cc mu ru s dng nm men t l 104-106 CFU/ml th hin thp hn (khong 1,071,32%) so vi cc mu ru ln men vi mt s nm men 101-103 CFU/ml (khong 2,2 n 2,37%).Bng 1: Hm lng ethanol sinh ra v hm lng ng st trong ru vang tht nt (sau 12 ngy ln men) theo mt s nm men phn lp (dch ln men c hm lng cht kh ha tan 22oBrix v pH 4,0)

Mt s nm men (CFU/ml) 10 102 103 104 105 106

Hm lng ethanol (% v/v) 11,88a 12,63b 13,38cd 13,63cd 13,88d 13,13bc

Hm lng ng st (% w/v) 2,20bc 2,37c 1,92b 1,32a 1,34a 1,07a

Ghi ch: Cc trung bnh nghim thc i km vi cc ch ging nhau trong cng mt ct th hin s khc bit khng ngha (mc ngha 5%).

Ngoi ra, khi t l nm men b sung cng cao th tc ln men thi gian u cng nhanh v c th cn tr qu trnh ln men tip theo (Lng c Phm, 2006). V vy, vi cc t l nm men cao (106 CFU/ml) th cn sinh ra khng khc bit ngha so vi cc mu ru s dng mt s nm men 103-105 CFU/ml. Hm lng ng st thp do ng c s dng nhiu t giai on ln men ban u. Hn na s dng nm men vi mt s cao th cn thi gian nhn ging di v tn km hn. 3.1.2 nh hng ca mt s nm men n cc ch tiu cht lng khc ca ru vang tht nt Kt qu thng k cho thy mt s nm men phn lp khng nh hng nhiu n hm lng acid bay hi v hm lng methanol trong ru vang tht nt (bng 2). Trong sn phm ny hm lng acid bay hi v hm lng methanol dao ng mc thp v di mc cho php ca tiu chun Vit Nam. Hm lng ester tng s trong ru vang tht nt kh cao (t 500-700 mg/l) v thay i khng theo quy lut no. Mu ru ln men vi mt s nm men 102, 103, 105 v 106 CFU/ml cho hm lng ester tng ng nhau v cao hn cc mu khc. Hp cht ester l cht mi v c vai tr quan trng to nn mi hng c trng ca sn phm (Lng c Phm, 2006). Nghin cu ca Wondra v Berovi (2001) v cht to mi trong ru vang nho Chardonnay ca M cho thy hm lng ester trong ru cng dao ng trong khong 450-790 mg/l. Khi thay i mt s nm men phn lp th hm lng SO2 sinh ra cng thay i ng k (khong 159,57-522,24 mg/l), hm lng ny thp hn trong ru khi s212

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dng t l nm men cao (104-106 CFU/ml). Theo nhiu nghin cu cng cho thy nm men sinh ra SO2 trong sut qu trnh ln men (Lonvaud-Funel et al., 1988; Henick-Klink v Park, 1994). Khi s dng nm men vi t l thp (10102CFU/ml) th thi gian nhn mt s ca nm men ko di v c th trong thi gian ny, nm men sinh ra nhiu SO2 hn. Mt khc, vi t l nm men 104-106 CFU/ml tc ln men cao v hm lng CO2 to ra v c gii phng nhiu hn nn mt phn SO2 c th bay hi v lm gim hm lng sulfite trong thnh phm.Bng 2: Cht lng ru vang tht nt ln men theo mt s nm men phn lp (sau 12 ngy ln men-dch ln men c hm lng cht kh ha tan 22oBrix v pH 4,0)

Mt s nm men (CFU/ml) 10 102 103 104 105 106

Hm lng acid bay hi (g/l) 0,158a 0,149a 0,161a 0,151a 0,158a 0,156a

Hm lng methanol (g/lit cn 100o) 0,416a 0,402a 0,390a 0,489a 0,459a 0,450a

Hm lng ester tng s (mg/l) 576,4ab 756,8c 719,4bc 512,4a 631,4abc 607,2abc

Hm lng SO2 (mg/l) 490,88b 490,88b 501,12b 227,2a 230,4a 229,8a

Ghi ch: Cc trung bnh nghim thc i km vi cc ch ging nhau trong cng mt ct th hin s khc bit khng ngha (mc ngha 5%).

3.2 nh hng ca hm lng cht kh ha tan v pH dch ln men n cht lng ru va