KHAO SAT HE VI SINH VAT TRONG QUA TRJNH LEN MEN CHE VANG SAN TUY^T THEO PHl/ONG PHAP
LEN MEN CHE PHO
NHTDao Thj Vidt Ha\ Khult HQ-u Thanh^ Nguyin Duy ThjiiH*
^Tnrbng Cao dang Cdng nghigp thirc pliim Vigt Tri
* Vign Cdng ngh^ sinh hge - Cdng nghg thuv phim, Trwbng Dai hge Bich khoa Hi Ndi;
Tom tat
Qud trinh len men Id budc quan trpng trong viec hinh thdnh chdt lupng che theo phuang phdp len nfen che Phd Nhi. Trong nghien ci^i ndy chiing tdi mong mudn xdc dinh qudn thi vi sinh vgt trong qud trinh len men theo phuang phdp len men che Phd Nht dp dyng cho giong che Vdng Shan Tuyit, Hd Giang, Viet Nam. Kit qud nghien ciiu da xdc dinh dupc he vi sinh vdt trong qud trinh len men che gdm: Aspergillus, Penicilium, Rhizopus, Saccharomyces, Bacterium. Trong dd, Aspergillus niger Id chiing chiim ty le ldn han 80%, tiip din. Id chiing Aspergillus glaucus, Penicillium citrinum, Rhizopus oryzae. Ket qud ndy cho thdy vai trd quan trpng ciia chimg ndpi mdc Aspergillus niger tdi qud trinh len men che theo phucmg phdp lin men che Phd Nhi. Kit qud md ra hudng nghien cieu sdu hon, nfydm l^ea chpn dieu kiin tdi uu cho qud truth len men bdi chung^
Aspergillus niger hhdm ndng cao chdt lupng che len men.
\ 1
I. OAT VAN Bt
: Ch^ cd khd ndng bdo ve sftc khde, cd tac dung gidm beo, gi-dm md mdu, gidtn dudng hoylt vdimpt sd tinh chdt d§c bipt khae (Barbosa, 2007; Petersona va cs, 2005), do vdy nhu cdu sft dyng ngdy cdng cao. Cdng ngh? sdn xuat che den ludn gdn liin voi qud trinh len men, bdn chdt Id cdc phdn ftng oxy hda hgp chdt polyphenol catechin dudi tac dung cfta cdc enzym oxy hda, ddc bi?t Id polyphenoloxxydaza (PPO) tao thdnh cdc hgp chat quan trpng nhu theaflavin (TF) vd thearubigin (TR) cd tac dung quyit dinh din chat lupmg cua che.
G ^ day, chung ta biit din chd Phd Nh? Id mdt sdn pham cd xudt xft tft V&i Nam Trung (Juoc dd sft dimg vi sinh vat trong qua trinh len men che. Nf uyfen Ii?u 6k, sdn xudt che Phd Nhi Id che vdng, qua qua trinh ft ddng va ddo trdn md thuc chat la qua trinh len men tu nhien kit hgp vdi qua trinh hodn thien da tao ra san phdm ddc ddo ndy. Len rtien Id giai 4dan quan trpng trong vi^c hinh thanh chat lupmg cua che Phd NhT. Qua trinh len men tao ra hang loat cdc biln ddi hda hoc ldm cho v} chat giam, ham lugng dudng va cdc chat hda tan trong nguyen lieu tatig, mui vi nong chdt cua pguyen lieu chuyin hda thdnh huang vi d$tn da eta sdn' phdm. Qua trinh len men ty nhi6n, cd su tham gia cfta iihilu loai vi sinh v|t cd nguon gde tft nguyen lipu ban dau vd tft moi trtidng khdng khf.
Hd Giang cung Id vung sdn xuat che vdng ndi tieng.cua Viet Nam ma nhieu nam trudc ddy, cdc thuong Idi Trung Quoc da mua vl dh lam nguyen lieu sdn xudt che Phd Nhi. Trong thdi gian gin ddy, chftng tdi da tiln hdnh nghien cftu toan dien cdng nghe san xudt che len men vd da tao ra dugc sdn phdm che Idn men dang khd vd dugc ep bdnh nhu dang banh che J»hd ;^Ihl cua Van, Nam Trung Qudc. Trong nghien cftu ndy, chftng tdi sS tiln hdnh xdc dinh he vi sinh vdt tham gia qud trinh 16n men chd v^gnhdm tftng budc Idm sdng td vai trd cua nhiing vi sinh vat chinh, Idm tiln de cho vipc chu dOng nudi ciy vi smh vat phuc vu cho cdng righe sdn xiiit che Idn men, khdc phye tinh tr^ng len men tv nhien nhu hi?n nay.
II. 0 6 l TU'gNG VA PHU'aNG P H A P NGHIEN CLFU 2.1.061 tu'O'ng
Che len men dugc san xudt qua 2 giai ddan chinh.
Giai dogn I: Tft la che tuai sdn xudt ra che vang.« Chung tdi sft dimg nguyen lieu dugc thu hdi tft gidng che Shan Tuyet, Ha Giang gdm nhung dgt che cd mdt bup va ba hodc bdn Id. Chiing tdi da nghien cftu cdng nghe san xudt che vang va thu dugc che vang de Idm nguyen lieu san xuat che len men.
Giai dogn 2: Tft che vang sdn xuat che len men. Chung tdi tiep tuc nghien cftu cdng nghe sdn xudt che len men do vi sinh vdt. Qud trinh u len men tu nhien dugc diln ra d nhiet dp moi trudng 25°C± 2°C tuomg ung vdi dieu kien nhiet dp tu nhien cua vung Ha Giang, dp dm cua che khi len men dugc dieu chinh den 35% ± 2%, khdi lupmg u la 50 kg che vang.
2.2. Bd tri thi nghiem
Nham xdc dinh su bien ddi cua qudn the vi sinh vat trong qua trinh ft len men theo phuong phdp len men che Phd NhT, chung tdi tien hanh Idy mdu thi nghiem theo thdi gian ft, cft 7 ngay lay mdu mdt lan, thdi diem lay mau la thdi diem trudc khi tien hanh dao rii. Qua trinh len men keo ddi den ngdy thft 56 do vay tdng sd Ian lay mau la 9 Ian.
2.3. Phu'O'ng phap nghien CLPU
2.3.1. Phan lap vi sinh vat va xae dinh dac diem hinh thai khuan lac
Cdc mau thi nghiem dugc tien hdnh phan lap va xdc dinh tdng sd vi'sinh vdt hilu khi bdng each pha loang vdi dung dich NaCI 9 g/l tren mdi trudng PCA. Phdn lap ndm sgi tren mdi ftudng thach PDA vd Czapeck (Nguyen va cs, 1976), phdn lap ndm men tren mdi trudng thach Hansen (Trdn, 2003), phdn lap vi khudn tren mdi trudng thach LB (Nguyen va cs, 1976). Dac dilm hinh thdi cfta cdc chiing ndm mdc phan lap dugc xae dinh vd so sanh theo Samson vd cs 1995.
III. K^T QUA NGHIEN CU'U
3.1. Xae djnh chung vi sinh vat c6 trong qua trinh len men 3.1.1. Bien doi quan the vi sinh vat trong giai doan u
Qudn the va chung loai vi sinh vat trong qua trinh len men che duac xdc dinh va ftinh bay d bdng 1. Tft so lieu trong bang cd thl thay a tftng thdi dilm len men, sir xudt hien cdc lo^ vi sinh vdt cd su khdc nhau: d mdu 1 (nguyen lieu) vd cac mau 2, 3, 4 thdy sir cd mat cfta 3 Io?i vi sinh vdt. Nhu vdy sudt trong thdi gian Idn men 21 ngdy, sd chung vi sinh vat khdng thay dii, c6 nghia Id nhftng chung vi sinh vat cd trong nguyen lieu dd phdt biln va duy tri, do la vi khuio, ndm men va ndm mdc. Khi thdi gian len men tilp tuc sang ngdy thft 28 va din ngay 35, sd chiing vi sinh vdt tang them 1, tdng cdng la 4. Chung vi sinh vat mai xuat hien la xa khudn. Day Id lo?i vi sinh vat thudng gap frong dat. Cd thl giai thich cho su xuat hien cua xa khudn bdi khi thdi gian len men keo ddi, nhiet do khoi che tang cao len tren 50°C la dilu kien de xa khudn phit trien. Len men tiep tuc den ngay thft 42 va keo ddi din ngay thft 56, sd lugng chung VSV chi cdn ndm mdc, ndm men va vi khudn. Xa khudn da bi tieu didt do su phat triln manh cua cdc VSV khdc. Mdt khdc sd lugng xa khudn cd mat d cac giai doan len men Id rdt nhd nen tren thuc tl xa khudn khdng cd vai trd gi dang kl trong viec tao ra cac chi tidu chdt lugng cua che.
Sang 1. Chung lo^i va sd luHT-ng vi sinh v^t trong giai do;in u ehe
ST 1 2 3 4 5 6 7 8
Tdn m l u 1 2 3 4 5 6 7 8
Thd'i d i l m ISy m l u B i t dau u chd (nguyen lidu) Sau khi u 7 ngay (dao ru lan 1) Sau khi u 14 ngay (dao ru lan 2) Sau khi u 21 ngay (dao ru lan 3) Sau khi u 28 ngay (dao ru l l n 4) Sau khi u 35 ngay (dao ru l l n 5) Sau khi u 42 ngay (dao ru lan 6) Sau khi u 56 ngay (dao ru lan 8)
Sd lo?i VSV 3 3 3 3 4 4 3 3
T d n g s d V S V / i g m l u (Td bao/g che)
1.4x10"
2,0x10"
7,0x10*
1,8x10^
2,0x10®
1,3x10®
1,1x10®
5,0x10*
Theo ddi so lugng VSV, chung tdi thay cung cd su thay doi rat rd ret. Tdng sd VSV ban dau trong nguyen lieu la 1,4x10^* Nhu vdy, ngay tft ban dau, trong nguyen lieu cung da cd sir hien dien cua vi sinh vdt va tang ddn theo thai gian u len men. Mat dp vi sinh vat dat cao nhdt tdi 2x10^ sau 28 ngay u va bdt dau giam dan sd lugng. Dilu nay cd thl giai thich bdi sir canh tranh dinh dudng gifta cdc chung VSV cung nhu do su tang nhiet dp va sir giam dp dm cua khdi che la nhung dilu kien bat lgi dan tdi su giam qudn thl vi sinh vat khi thdi gian u ddng keo dai.
3.1.2. Khao sat ty le cac loai vi sinh vat trong qua trinh u che len men
Tft kit qua nghien cuu tren cho thay trong qua trinh u che cd su tham gia cua nhilu nhdm vi sinh vat: ndm mdc, ndm men, vi khudn va xa khudn. Sir xuat hien cua cdc nhdm vi_sinh vat d cac giai doan khae nhau cd vai trd khdc nhau trong qua trinh u che vi vdy cdn tim hieu sdu bom tdi su biln ddi cua cac nhdm vi sinh vat nay trong qua trinh len men. Chiing tdi tien hanh nghien ciiu ty le cac nhdm vi sinh vat trong qua trinh len men, de cd cai nhin rd han ve vai trd ciia tung nhom, kit qua dugc trinh bay trong bang 2.
Bang 2. Ty \g cac lo?i vi sinh v^t trong qud trinh u len men che
TT
1 2 3 4 5 6 7 8
Ten m l u
1 2 3 4 5 6 7 8
Thd'i diem l l y m l u
Bat d l u u che (nguyen li#u) Sau khi u 7 ngay (dao ru lan 1) Sau khi u 14 ngay (dao ru lan 2) Sau khi u 21 ngay (dao ru lan 3) Sau khi ii 28 ngay (dao ru lan 4) Sau khi u 35 ngay (dao ru l l n 5) Sau khi u 42 ngSy (dao ru l l n 6) Sau khi u 56 ngay (dao ru l l n 8)
Ty \g cac \og N i m S9'i Den
20 22 53 71 66 87 88 87
Vang 16,5 9 31 16 7 7 6 6
Xanh 3 2 2 0 0 0 1 2
i vi sinh v^it (%) N i m
men 1 1 1,5
2 15
3 3 3
Vi k h u i n
59,5 66 12,5
11 10 2 2 2
X?
khuan 0 0 0 0 2 1 0 0
Tft sd lieu d bang cho thdy sir bien ddi cac loai vi sinh v|it theo thdri gian ft len men. d mau nguyen lieu (bdt ddu len men) vd cdc mdu trong thdri gian ddu ciia qua trinh len men, ty le vi khudn vd ndm sgi la rat cao va 90 su xudt hien cfta nam men nhupg khdng cd x^ khuan. Cdc loai ndm sgi d day chiem chft yeu Id cdc loai ndm sgi den va vang the hien sir cd mat cua hai gidng la Aspergillus va Rhizopus day la hai loai nam sgi thuomg gap trong cdc vung cd khi hau nhiet doi dm. Dilu nay cho thdy cdc loai ndm sgi cd thl nhiem vdo nguyen lieu tft mdi trudng khdng khi trong qua trinh chudn bi u vd trong thai gian u len men. Ngodi ra cdn cd ty le nhd ndm sgi xanh dai dien cho gidng Penicillium. Dilu ndy cd thl gidi thich bdi Penicil^tim thudng phdt triln tit trong dilu kien nhiet do thdp, nhung trong qua trinh len men che vdi nhiet do tang cao, dan tdi loai nam sgi nay khdng the phat trien dugc. Cd the nhdn thdy ndm sgi xanh chi xuat hien d giai doan dau va cudi qua trinh len men. Ty Id ndm sgi tang len va vi khudn gidm xudng khi thdi gian u keo ddi. Ty 1? cd 3 loai ndm sgi chiem tdi 95%, vi khudn chi cdn 5% sau 42 ngdy ft len men.
3.1.3. Dac diem hinh thai khuan lac cua cac loai nam soi trong qua trinh u che len men Chung tdi da tien hanh nghien cuu ve dac diem hinh thai, kich thuac cua khuan lac nhdHi budc ddu cd the xdc dinh dugc chiing ndm sgi trong qua trinh len men. Thi nghiem dugc thuc hien tren mdi trudng ddc trung cho cac loai nam mdc Id PDA. Ngodi ra, cdc loai ndm sgi nay con dugc nudi cdy tren cdc mdi trudng khdc nhu: Nudc chiet malt, Sapezk, Sabouraud nhdm so sanh xdc dinh ddc diem hinh thdi vd budc ddu cd the xdc djnh dugc ten gidng ndm sgi. CdC chung ndm sgi dugc tien hdnh nudi cay d nhiet do 30°C va sau 48 h nudi cay, ket qua trinh bay d bdng 3.
TT
1
2
3
4
Ky h i f u
Dl 1
O2
Vi
Xi
Bing 3. D|c diem hinh thai cac chiing n i m sqt'i trong m l u che len men ' , .
.1(1 •
Lo?i VSV
N i m s^i mau den
vang Nim sgi mau den
Nim sgi mau vang
N i m sp-i mau xanh
Mdta Hinh thai
khuan \gc Trdn, cd nhan, vien
trang Toa trdn
Toa trdn, cd nhan Toa trdn
,>3 in.
Mau sac
Oen vang, xung quanh khuIn lac la hg s^i n i m cd mau tring
Nim SQ'i sinh bao Xiy nen a gifta khuan t^c cd mau den dnh, he sg\ nam lan toa
Vang tu'oi
Nam bit dau sinh bao tir nen ft giira khuIn l^c cd mau xanh Igc, xung quanh khuIn l^c cd mdu trang, a ngoai cung khuan l^c cd dac SQ'i nam khdng mau
Bd m|lt Hd SQ'i lan toa
rdng
Giua hoi loi, nhan giira
Hoi loi
Loi ft tam, t^o thanh khia
Kich , thirpv ' (mm) 15
17
20
25
Tft kit qud nghien cftu tren vd so sdnh vai dac dilm hinh thdi khudn lac theo Samson va cs 1995, cd the sa bd xdc dinh dugc cac gidng ndm sgi cd mat trong che thudc cdc giong Aspergillus niger, Aspergillus glaucus, Penicillium citrinum, Rhizopus oryzae. Vdi ddc diem hinh thai khudn lac chung tdi da sa bd djnh dugc ten vdi cdc loai ndm sgi nay va kit qua cung dd budc ddu dugc khdng dinh khi sft dung ky thuat sinh hge phdn tu vdi trinh t\r doan 18S rRNA, va vung ITS chfta trinh tu 5,8S. Trinh tu cdc doan gen dugc xdc dinh bdi hang Macrogen (Han Qudc). So sdnh bdng chuang trinh BLAST/NCBI da xdc dinh dugc ten cua cac chiing vi sinh vat: Chung Di cd phan tram tuang ddng vdi Rhizopus oryzae 98%, chung E^ tuong ddng 99%
vdi Aspergillus niger, I8S ribosomal RNA gene (GU295947.1), chung Xi tuomg ddng 95% v6i Penicillium citrinum, ITSl, 5,8S rRNA gene va ITS2, strain MASA2 (AM745115.1), Chung V, tuang ddng 99% vdi Aspergillus glaucus CMM-2007, 18S ribosomal RNA gene, chfta trinh tv
1,5.8S ribosomal RNA gene (EF624000.I).
IV. T H A O LUAN
l i t ' ' • '
' Tft ket qua nghidn cuu cho thdy cdc chung vi sinh vd!t nhu Aspergilliis niger, Penicillium, Rhizopus, Aspergillus glaucus, ndm men vd vi khuan tdn tai trong sudt qua trinh len men che Phd NhT. Cdc lojii ndin sgi ludn chiim uu thl trong qua h-inh len men, dac biet Aspergillus niger ehilm tren 80% tdng lugng vi sinh v|t. v^ cung phu hgp vdi mdt sd nghien cftu cua cdc tde gid nudc ngodi (Jeng vd cs, 2007; Abe vd cs, 2008). Hoat ddng trao ddi chdt cua chung ndm sgi nay sinh 'tdng hgp cac enzym thuy phdn khdc nhau nhu glucoamylase, cellulose, pectinase (Jayaraman va cs, 2002) gay nen su biln ddi thdnh phdn hda bgc cua che, hang loat cdc phdn ftng hda hpc xdy ra Iam vi ddng chat gidm, tinh boa tan cua dudng vd cdc chdt hda tan trong nguyen Ii?u tdng, mui vi ndng cua nguyen lieu chuyin hda thanh huomg vi dam da cua sdn ph&n' (Xiao Wei Xiang, 1986). Day chinh la ngudn gde tao nen chdt lugng cua che Phd NhT.
Chung tdi cftng da so sanh sd lieu thuc nghiem cua minh vdi sd lieu cfta cdc nhd nghien cftu vl che Phd NhT cua Trung Qudc va di din nhdn xet nhu sau: trong qud trinh len men che vdng Shan Tuyet, Hd Gidng, tdng lupmg vi sinh vdt ldn ban rdt nhilu so vdi che len men Phd NhT vimg Vdn Nam, Trung Qudc. Dilu nay cho thdy d cac dilu kien khi hdu vd mdi trudng ft khdc nhau ddn tdi sd lugng cac chung lodi vi sinh vdt cung rat khdc nhau. Theo Chan Ying Can (2006), trong qua trinh ft che Vdn Nam, Trung Qudc, Aspergillus niger ehilm uu thl vd chiing Aspergillus glaucus cd ty I? rat nhd, tuy nhien vdi ket qud nghien cftu che vdng Shan Tuyet, Hd Giang thi chiing ndm Aspergillus glaucus phdt trien sd lirgng khd ldn (4,9x10^ bdo tft/g) gay dnh hudng khdtig'tdt den chat lupmg che len men, trong khi dp che len men Phd NhT, Vdn Nam, Tmng Qudc chung ndm nay chi chiem 14,92 bao tft/g (Chan Ying Can, 2006). Vi vdy cdn cd nhihig nghidn cuu tilp theonhdm han che sir phdt triln cfta chiing ndm mdc ndy trong qud trinh len men.
Trong qua trinh len men che, ngodi cdc chung vi sinh v§t ke tren cdn cd su cd mat cfta Aspergillus terreus, Aspergillus candidus, mdt lupmg nhd tl bdo nam men va vi khuan rat khd xdc djnh. Kit hgp cdc phuang phdp phdn tich, xft Iy khdc nhau, cdc yi sinh vdt chft ylu trong qud trinh ien men vd phdn tich su biln ddi chdt lupmg cho thdy: su biln doi cdc chung vi sinh vdt trong qud trinh len men che Id phftc tap, mdt vdi chung tft dau den cudi qua trinh len men cd vai trd tich cue trong sir hinh thdrih chat lupmg sdn phdm, mdt vdi chiing lai phdt huy tai mdt giai doan ndo dd trong sir hinh thanh chat lugng dac tnmg cfta sdn phdm, mdt vdi chiing khdc lai cd tde dyng ngugc lai, gay bdt lgi trong su hinh thanh chdt lugng sdn pham.
.-. Trong fl[ua trinh sdn xuat che Shan Tuylt len men, sd lugng Aspergillus niger ludn chiim uu thl, ddy Id chiing cd khd ndng sdn sinh ra cac enzym ndi bao vd-enzym ngoai bao cao. Trong dd cd khoang 20 lo^ enzym thuy phdn nhu glucoamylase, cellulose, pectinase cd kha ndng phdn gidi pdc ch4t hda tan va Ididng hda tan. San phdn; cua qud trinh thfty phdn do enzym da so Id cac
^dng don, amino axit, pectin hda tan vd cdc hgp chat carbohydrate cd khd ndng hda tan, Iam cho cdc chdt ben trong la che de dang thdm thdu, khuich tdn, vd hinh thdnh nen nhimg phdm chdt CO ban cua chp len men, lam tang huomg vi vd do nggt diu cua sdn phdm. Cd the ndi, trong qua teinh len men che, thdng qua qua trinh trao ddi chdt, Aspergillus niger da san sinh ra cdc axit him CO vd cdc enzym, cd tac dung quan trgng trong viec hinh thanh chat lupmg che.
V4n dl dugc ddt ra la moi quan he giua lugng vi sinh vdt, cu thl Id Aspergillus niger tdi khd ndng oxy hda cdc hgp chdt polyphenol cd trong che, hay la khd ndng sinh tdng hgp cdc enzym PPO cfta chiing Aspergillus niger Idm tang hieu qua cua qud trinh len men bdi cdc enzym oxy hda trong che. Dieu nay can dugc lam rd trong nhimg nghien cftu tiep theo.
V. K^T LUAN
Tft nhftng kit qua nghien cftu cd thl thdy su biln ddi cua cdc lo^i vi sinh v$t brong qua trinh len men vd khdng dinh vai trd cua ndm sgi, ddc biet Id Aspergillus niger, trong qud trinh len men che theo phuang phdp len men che Phd NhT cd tinh quyit dinh tdi chdt lupmg cua sdn phdm.
Nghien cftu cung da budc ddu dinh ten cac loai ndm sgi chinh trong qua trinh left men gdm co Aspergillus niger, Penicillium citrinum, Rhizopus oryzae. Nghien cuu ciing da md / a hudng nghien cftu sdu hom tdi mdi quan he giua he enzym cua nam sgi tdri kha ndng oxy hda cac hpp chdt polyphenol dnh hudng tdi chat lupmg che len men.
TAI LIEU THAM KHAO
1. Nguyen Lan Dung, Nguyin Dang Dftc, Dang Hdng Mien, Nguyin VTnh Phudc, Nguyin Dinh Quyln, Nguyin Phung Tiln, Pham Van Ty. 1976. Mdt so phuang phdp nghien cieu vi sinh vdt hoc, NXB Khoa hpc va Ky thuat.
2. Trdn Linh Thuac. 2003. Phuang phdp phdn tich vi sinh vdt trong nudc, thirc phdm vd my phdm, NXB Giao due.
3. Abe M., Takaoka N., Tdemoto Y., Takagi C, Imai T., Nakasaki K. 2008. Characteristic fungi observed in the fermentation process for Puer tea. Int J Food Microbiol 124(2), 199-203.
4. Barbosa D.S. 2007. Green Tea Polyphenolic Compounds and Human Health. Joumal fiir Verbraucherschutz undLebensmittelsicherheit 2(4), 407-413.
5. Chan Ying Can. 2006. Thao luan ve ca che len men che Phi NhT, Tap chi Thong tin kinh tl che 1,36 - 37.
6. Jayaraman A., Muthusarny P., Subbaiyan M., Krishnasamy S. 2002. Improvement of tea leaves fermentation with Aspergillus spp pectinase. JBiosci Bioeng 94(4), 299-303.
7. Jeng K. C, Chen C.S., Fang Y.P. 2007. Effect of Microbial Fermentation on Content of Statin, GABA, and Polyphenols in Pu-Erh Tea. J Agric Food Chem 55(21), 8787-8792.
8. Petersona J., Dwyera J., Bhagwat S., Major. 2005. Flavonoids in dry tea. J Food Comp Anal 18, 487- 501.
9. Samson R.A., Hoekstra E.S., Frlsvad J.C, Fiitenborg O. 1995. In R.A. Samson and E.S. van Reenen-Hoekstra (eds.). Introduction to food-borne fungi. 4th ed., Centraalbureau voor Schimmeicuitures, CBS, Baam, The Netherlands, 322p.
10. Xiao Wei Xiarg. 1986. Nghien ciru tiin trinh ca chi sinh hda qua trinh len men che. Tap chi che Phuc Kiln 2, 4 - 5 .
Summary
DETERMINATION OF MICROORGANISMS POPULATIONS DURING FERMENTATION OF THE SHAN TUYET TEA COLLECTED IN HA GIANG PROVINCE OF VIET NAM
Fermentation is an important critical step in shaping the quality of tea. In this study we try to determine the micro-organisms populations during the fermentatioti of tea of Shan Tuyet, Ha Giang, Viet Nam. We used the isolation method and molecular techniques to identify the names of the micro-organisms in the fermentation process. The investigation on micro-organisms during the fermentation process of tea shows that the main micro-organisms are Aspergillus, Penicilium, Rhizopus, Saccharomyces, Bacterium. The number of Aspergillus niger is the most among them about 80%, the next is Aspergillus glaucus, Penicillium citrinum, Rhizopus oryzae. This result shows the important role of the Aspergillus niger strain to the fermentation process. On further research, we try to select optimal conditions for fermentation by Aspergillus niger.
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