Changing Regularity Of Microflora During The Fermentation Of Chinese Leaf Mustard(Brassica Juncea Coss) And Preparation Of Its Microbial Starter Culture

As a traditionally processing technology of vegetable, pickle is highly popular among the public. Fermented Chinese leaf mustard as a Hunan region characteristic of food is an important component of Sauce packet in instant noodle. So it is in great demand. Cultivation of Chinese leaf mustard is seasonal, so great challenge is posed on its continual supply. In order to realize the goal of its standard industrial production, the paper chose suitable strains for preparation of its microbial starter culture on the base of research on changing regularity of mircoflora during the fermentation of Chinese leaf mustard. The following conclusions were got:1. In different time during process of Chinese leaf mustard fermentation, the Chinese leaf mustard was used to analyze microflora change of advantage microbial and change of pH. The result showed:It is better to choose combination bacteria for starter culture, and Lactococcus lactis and Lactobacillus is good choice.2.45strains of acid-producing bacteria were isolated from fermented Chinese leaf mustard. Then six strains of lactic acid bacteria were got by test of gram stain, catalase and screening of acid-production rate. They are L14#、 LA、LT8、 R8、 R2、 R6. After analysis of16SrDNA sequence, the results were that:L14#is Weissella koreensis%LA、 LT8、 R8are Lactobacillus plantarum; R2is Leuconostoc mesenteroides, R6is Pediococcus pentosaceus。3. Employing Plackett-Burman and orthogonal experimental design, high-density culture of A+6(combination of LA and R6) and R2were optimized in two aspects, one is ingredients of culture medium, another is culture conditions. Optimal formula of A+6was3%glucose(w/v),1.5%beef extract(w/v),0.5%ammonium sulfate(w/v) and1%tryptone(w/v); The optimal culture conditions for it was pH6.0, inoculum volume3%,21h culture time in33℃. The optimal formula of R2was4%whey powder(w/v),1.5%ammonium sulfate(w/v),0.5%peptone(w/v),2%yeast extract(w/v). The optimal culture conditions for it was pH6.0, inoculum volume3%,21h culture time in29℃.4.Comparing the bacteria count before and after lyophilization, two group of starter culture with higher survival rate were obtained. Under same fermenting condition, flavor, nitrite and pH were compared between naturally fermented Chinese leaf mustard and the two kinds of inoculated fermented ones. The results showed that: inoculated fermentation was in accord with natural fermentation in flavor. But pH and content of nitrite in inoculated fermentation were lower than the natural fermentation.Summarizing the experiment results:The starter culture of Chinese leaf mustard should choose Lactococcus lactis and Lactobacillus as strains. And co-fermentation of Lactococcus lactis, Lactobacillus and Leuconostoc mesenteroides consistent with natural fermentation in flavor. Such co-fermentation can reduce content of nitrite in m fermented Chinese leaf mustard. The starter culture has a market potential.