The Influence Of Kluyveromyces Marxianus On Fermented Milk Proteins Metabolism

Kluyveromyces marxianus(Km) is one of the inevitable in the fermented milk of yeast that get widely research in this field. With the developing of this research, Km has proven to be a valuable function, for example, it could change the fermented milk flavor and the typic structure and so on. In order to study the effect of Km in fermented milk protein metabolism. On the basis of Streptococcus thermophilus( St) and Lactobacillus bulgaricus( Lb) fermentation reconstituted milk, this study mix up the Km with the lactobacillus on a pro-rate basis. This research aims to know how yeast affects the fermented milk pH and the quality and structure change tendency. The milk starter cultures in the relationship, and the effect of milk protein metabolism and through the in vitro cell experiment on fermented milk whey powder effects on cells. Results are as follows:1. After adding yeast, the pH drop speed in fermented milk and milk curd time reduced; The hardness, consistency, cohesiveness, viscosity coefficient of the mixed fermented milk was higher than lactobacillus fermentation(p<0.01); in the process of ripening, fermented milk quality and structure features continue to rise, mixed fermentation higher than lactobacillus fermentation(p<0.05), after 7 days, it will be reach to the highest point with a slight decline.2. To determine the number of living bacterium in the fermented milk, fermentation strains showed a raise tendency in the fermentation process, St content is significantly higher than Lb, Km play an important role for the growth of lactic acid bacteria. Lactobacillus promotes the Km at first and consequent reduction. In the process of ripening, St and Lb levels drop rate increase while adding the Km, it showed that lactobacillus has a promoting effect on Km.3. Using SDS-PAGE to study the different time fermented milk, it stated that: Add Km in fermentation process could promote the degradation of Bovine serum albumin, α-casein, β-whey protein and inhibit the degradation of κ-casein predominate. In the process of ripening, α-casein, β-whey protein content in mixed fermented milk is lower than lactobacillus fermentation means Km promote the α-casein, β-whey protein degradation. 7 days later, degradation become steady and kinds of proteins’ contents to maintain relatively stable state.4. Extraction the fermentation terminal fermented milk protein precede 2-DE, the result indicated that: Mixed fermentation impact on the metabolism of αS2-Casein and bovine serum albumin is higher than lactobacillus fermentation. For αS1-Casein and β-Casein, mixed fermentation is similar to lactobacillus fermentation. The metabolism of κ- Casein is very rarely.5. Using TCA sediment the protein in the milk, extract the polypeptide to do LC-MS/MS test, the result stated that: polypeptide first rise after falling in the fermentation process. In the process of ripening, polypeptide variety rise gradually, and up to balance at 7 days, mixed fermentation polypeptide type is higher than the lactobacillus fermentation. After adding Km, it reflect the polypeptide molecular weight ratio and increase the small molecule substance content. Some literature indicated that lactobacillus fermented milk content 21 biological active peptide; the mixed include 22 kinds, at the end of the fermented milk fermentation, put it in 4℃ refrigerator. On account of the temperature change abruptly, produce a large number of bioactive peptides, and the content is higher gradually, after 7 days, it reach the stable state to dynamic balance; adding Km has a promoting effect on most of the bioactive peptides, and give big impact on RPKHPIKH tendency; Also produce lactobacillus fermentation without bioactive substances, such as MAIPPKKNQDK antithrombotic peptides.6. Fermented milk conduct with high speed centrifugation, using 3KDa for whey ultrafiltration after adjusting the pH and tested the samples derived after using UPLC to amino acid, the result indicated that there are different change of the amino acid content is variable. In the fermentation process, Km give smaller contribution to amino acids and total free amino acid content in the ripening process gradually rise, after adding yeast, Ala/Met, Glu, Phe, Pro, Ser, and total free amino acid content bacterium fermentation was increased, different ripening time significantly difference(p<0.05); While Arg, ihs, Ile, Leu, Thr content is declined.7. The fermented milk using TCA precipitation to be purification, make use of HLB column and use the vacuum freeze drier get whey powder, adopt the method of in vitro cultured cells, set up the matched group and the sample group, optimization results show that the sample of Caco-2 all have a role in promoting the growth of the two cells. Compared with the injury group, the sample group of cell survival rate increased with the extension of incubation time, and LDH release a quantity to reduce MDA content(p<0.01), the antioxidant enzyme activity in cells and cultures of increased(p<0.01); cultivate after 48 hours mixed bacteria fermented with lactobacillus fermentation group significant difference(p<0.01).