Studies On Characteristics Of Yogurt Enriched With Conjugated Linoleic Acid

Conjugated linoleic acid(CLA), a mixture of positional and geometric isomers of octadecadienoic acids with conjugated double bonds, is believed to have many important physiological functions, such as oxidation resistance, anti-mutation,anti-microbial, distinct reduction of cancer risk, protection against arteriosclerosis,enhances the immune system; enhances bone density and prevention diabetes risk.Similarly, many other health effects have been attributed to yogurt, including improve the intestinal flora, reduction of cancer risk, improve digestion, anti-aging and prevent against diseases. Many researches showed that some strains of Lactobacillus are able to biosynthesize CLA from linoleic acid, they have also been shown non-toxic; innocuity and easy to cultivate. The isomers of CLA in Lactobacillus fermentation is single. The composition of isomers are similar to that of natural food. In this paper, linoleic acid was added to the skim milk and fermented by lactobacillus plantarum R6, which can form CLA from linoleic acid. The fermentation character of the mixed strains, lactobacillus plantarum R6,Streptococcus thermophilus and Lactobacillus delbrueckii subsp. Bulgaricus was also studied. The optimized fermentation conditions were established for high quality yogurt enriched with CLA. The experimental results were showed as follows:Lactobacillus plantarum R6 was chosen to single strain fermentation, the best technological parameters were obtained through single factor experiment and the response surface analysis. They are as follows: the content of linoleic acid,fermentation time, concentration of skim milk and fermentation temperature were0.1%, 40.47 h, 11.65% and 37℃, respectively,The conversion ratio is 92%.After fermentation, the viscosity, acidity, water retention, number of viable count and the content of CLA were 100 o T, 3000 m Pa.s, 54%, 1×109 cfu/mL and 0.918 mg/mL,respectively.Lactobacillus plantarum R6, Streptococcus thermophilus and Lactobacillus delbrueckii subsp. Bulgaricus were chosen for mixed strains fermentation. The best fermentation parameters were obtained by single factor experiment and the response surface analysis. They are as follows: the inoculation proportion of three strains, the content of linoleic acid, fermentation time, concentration of skim milk and fermentation temperature were 1:1:1, 0.11%, 40.77 h, 11.5% and 37℃, respectively.After fermentation, the viscosity, acidity, water retention, number of viable count andthe content of CLA were 100 oT, 3400 m Pa.s, 56%, 2×109 cfu/mL and 1.03 mg/mL,respectively. The conversion of LA to CLA is 94%. This yogurt product can meet the quality requirements of National Food Safety Standard. Furthermore, the nutrition of yogurt and healthy functions of CLA were obtained from this product. It can satisfy the consumer’s demands for new type and healthy functions of yogurt.PCR-DGGE was chosen to analyze the relationship between the change of flora and the synthesis of CLA, the results showed that the mixed strains grew well and had no inhibitory effect between each other, so not only the quality of yogurt was ensured, but the synthesis of CLA was also ensured. When the fermentation time came to 40 h, the synthesis of CLA increased from 0.68mg/mL to 0.9mg/m L, the result showed that the synthesis of CLA in yogurt is a accumulative process.