Interaction Between Debaryomyces Hansenii Yarrowia Lipolytica And Lactococcus Lactis And The Influence In Cheese Ripen

Yeasts used to lead dairy deterioration, which were considered harmful to dairy productionin past time, with more research found that yeast play an important role in cheese mature, andplays an irreplaceable role in the formation of cheese flavor.Two common dairy yeasts--Debaryomyces hansenii and Yarrowia lipolytica were taken bythis experiment. Their acidity tolerance, salinity tolerance and basic fermentation capacity(including the fermentation capacity of lactose, lactate, citrate, protein and fat) were determined, tojudge whether there is potential to ripen cheese. Debaryomyces hansenii has the ability tometabolism lactose,lactate and protein, can normally growth at pH=4.0, salt concentration at8%,Yarrowia lipolytica has the ability to metabolism citrate, lactate and protein, can normally growthat pH=4.5, salt concentration up to6%, it is determined that two yeasts have potential as a cheesefermentation agent.Two yeasts and cheddar cheese starter culture--Lactococcus lactis will be co-cultured insterilized milk, comparing the number of strains, acidity, autolysised and protease activity withcultured alone. The sample which three strains co-cultured, the number of strains, strain autolysisand protease activity has significantly increased (p <0.05), illustrate strains can promote thegrowth and accelerate the metabolism. And two yeasts co-cultured also showed the increase in thenumber of strains. Then added cell-free supernatant of Lactococcus lactis to yeasts and cell-freesupernatant of yeast to Lactococcus lactis, the results show that the two yeasts cell-freesupernatant accelerated the growth of Lactococcus lactis (p <0.05), the Lactococcus lactis number(�'10cfu/g) from7.26to7.82,8.87respectively. Result indicated that metabolites of yeast playeda positive role in growth of Lactococcus lactis. Co-cultured strains under TEM also found that thelactic acid bacteria and yeasts closely grew together, also proved the metabolites of yeast indeedcan be utilized by lactic acid bacteria, this specific component need further study. Illustrate twoyeasts the experiments selected and Lactococcus lactis are commensalism.Two yeasts growth state under different inoculation ratio were studied, make a preliminarydetermination of the filter paper method at first, the results show that two yeasts with differentmixed concentration directly affect the growth activity of the strains. Then set the proportion ofdifferent inoculation, co-cultured in YEPD medium, then determined strain concentration, to findthe sample with maximum strain concentration in medium after cultured, that Debaryomyces hansenii and Yarrowia lipolytica inoculate with ratio of1:4.The influence of added yeast in cheese to starter culture--Lactococcus lactis and ripening ofchaddler cheese was studied. Designed different ways of adding yeast, the number of two yeast andLactococcus lactis, cheese acidity, proteolysis (electrophoresis analysis, pH4.6–SN,12%TCA-SN), texture and sensory evaluation were determined, comprehensive evaluated the additionof yeast to cheese mature. Yeast addition in cheese made the number of Lactococcus lactis increase,accelerate proteolysis and enhance cheese flavor, but there is a bad influence to the cheese texture,make the cheese soften, individual became crunchy. Sample4(two yeasts1:4inoculation, afterco-cultured added to the cheese) the yeast and Lactococcus lactis have a better growth, proteolysissignificantly faster than other samples; sample2(two yeasts1:4mixed addition) the number ofstrain and other indicators are not prominent, but sample3(two yeasts1:1mixed addition) thenumber of strain and proteolysis only lower than samples4. Proved that the optimumconcentration proportion for two yeasts to the growth in YEPD medium cannot be realized incheese, the optimum proportion varies with growth environment.There is great potential for yeasts to be used in nonstarter culture of cheddar cheese, inparticular after Debaryomyces hansenii and Yarrowia lipolytica co-cultured used in cheese there isa more obvious effect in accelerating proteolysis and increasing the number of Lactococcus lactis.The further study should make sure the optimum addition amount of yeasts in the cheese andproportion of two yeasts, to improve the stability of the mixed culture.