The Fermentation Process Optimization And Research On The Related Metabolism

1.22bacteria were isolated from traditional dairy.2Leuconostoc pseudomesenteroides and5Leuconostoc mesenteroides were identified according to the16S rRNA gene.11Kluyveromycesmarxianus and4Kazachstania unispora were identified based on the26S rRNA gene. All the identifiedbacteria were stored at-80℃in order to study in the future.2. The optimum process conditions such as strains inoculating proportion inoculationamount，fermentation temperature and fermentation time was determined by using single factorand response surface experiment. According to the changes of the pH and the acidity along withthe texture, the sensory score and the viable count of the fermented milk after ripening24h，theoptimum process conditions were as follows:lactobacillus （Lactobacillusbulgaricus:Leuconostoc mesenteroides=1:1）: Kluyveromyces Marxianus=15.3:1, inoculationamount3.09%, fermentation temperature34.6℃, fermentation time9.2h. In the optimumprocess conditions the sensory score of fermented milk reached82.37points, and firmness,consistency,cohesiveness and viscosity were144.900g,3803.842g s,-74.917g and-153.145g s， respectively and the acidity and viable count also reached107.29°T and2.8×108cfu/mLafter ripening24h. The optimum technological parameters were revealed to be reliable，and hadpractical significance.3. The changes in the volatile profile of this fermented milk were determined by themethod of solid-phase micro-extraction-gas chromatography-mass spectrometry(SPME-GC-MS) during maturation. A total of24compoounds were detected:5acids,8alcohols,3esters,1ketone and8conpounds which could not be classified in these groups.Thecontent of volatile compounds was significantly modified during ripening. The relative totalamounts of acids, esters, alcohols and ketone increased during the first two weeks.4. Proteolytic activity, which occurs during the storage period of three kinds of fermentedmilk (①LB+ST, including Lactobacillus bulgaricus and Streptococcus thermophiles;②LB+LM, Lactobacillus bulgaricus and Leuconostoc mesenteroides;③LB+LM+M,Lactobacillus bulgaricus, Leuconostoc mesenteroides and Kluyveromyces Marxianus), wasdetermined. Peptide fractions obtained from fermented milk were investigated and the effect ofproteolysis on peptide release during storage was determined. The antioxidant activity of peptides released from water-soluble extracts (WSE) were determined by2,2’ azino-bis(3-ethylbenzothiazoline-6-sulfonic acid)(ABTS) method. In analysis by the ABTS method,mean values increased from2.79~3.22mM Trolox/g in LB+ST, from3.16~4.33mM Trolox/g inLB+LM and from2.27~4.30mM Trolox/g.