Studies On The Symbiotic Relationship Between Lactic Acid Bacteria And Yeast In Koumiss

In this paper, the symbiotic relationship among lactobacillus casei MLS5, lactococcus lactics WLB5 and kluyveromyces marxianus WWMJ1 were studied. The main results were as follows:(1) The single factor experiment and response surface methodology were conducted to optimize the fermentation conditions of koumiss. The optimal fermentation conditions of koumis were inoculation size of 6%(V/V), fermentation temperature of 32℃, fermentation time of 48 h. Under the optimal conditions, the viable count of lactic acid bacteria in koumiss was up to(4.72±0.08)×108 CFU/mL.(2) The interaction among Lactobacillus casei MLS5, Lactococcus lactics WLB5 and Kluyveromyces marxianus WWMJ1 were studied in the optimal fermentation conditions. The results indicated that the growth of Lactobacillus casei MLS5 during fermentation was significantly promoted by Kluyveromyces marxianus. The K. marxianus WWMJ1 was significantly inhibited by Lactobacillus casei MLS5, but was significantly enhanced by Lactococcus lactis WLB5.(3) The reducing sugar metabolism and organic acid metabolism in koumiss fermented by different strain combinatons were studied in the optimal fermentation conditions. The results indicated that the lactose metabolism was promoted by Kluyveromyces marxianus WWMJ1. Two lactic acid bacteria species consumed succinic acid, however, the utilization of succinic acid was inhibited by Kluyveromyces marxianus WWMJ1. Lactobacillus casei MLS5 and Kluyveromyces marxianus WWMJ1 could produce amounts of citric acid. The production of lactic acid and formic acid by Lactococcus lactis WLB5 was signicantly promoted by Kluyveromyces marxians WWMJ1, however, the production of lactic acid by acetic acid and formic and acetic acid by Lactobacillus casei MLS5 were inhibited by Kluyveromyces marxians WWMJ1.(4) The volatile flavor compounds in koumiss fermented by different strain combinations were studied in the optimal fermentation conditions. The results indicated that 45 kinds of volatile flavor compounds were identified by SPME-GC-MS, including alcohol, esters, aldehydes, acids, hydrocarbon and heterocyclic compounds. 6 types of volatile flavor compounds in these koumiss sample were further analyzed by PCA. The results of PCA showed that the accumulative contribution rate of the former 3 principal components was up to 90.575%, which meaned 3 principal components could reflect most of infamation of volatile flavor compouns in koumiss. The effects of 6 types of volatile compounds on the koumiss flavor were aldehydes, acids and hydrocarbon, esters, alcohol, heterocyclic compounds.(5) The single factor experiment and response surface methodology were conducted to optimize the growth of lactic acid bacteria in koumiss. The results indicated that the optimal additions of 3 oligosaccharides were galactooligosaccharides of 1.30%(W/V), isomalto-oligosaccharide of 0.80%(W/V) and xylooligosaccharide of 0.40%(W/V). Under the optimal conditions, the viable counts of lactic acid bacteria in koumiss was up(5.97±0.16)×108 CFU/mL, which revealed an increase by 70.57%, compared with the original koumiss.(6) 3 kinds of freeze-drying protective agents were screened by two level fractional factorial design, and the central point of response surface experiment was confirmed by the steepest ascent experiment. The optimal additions of 3 freeze-drying protective agents were 2.30%(W/V) of maltodextrin, 3.50%(W/V) of trehalose and 3.10%(W/V) of α-cyclodextrin. Under the optimal conditions, the viable count of lactic acid bacteria in koumiss powder was up to(8.78±0.10)×108 CFU/g.