Study On The Effect Of Lactic Acid Bacteria On Goat - Eating Of Yogurt Yoghurt

Goat milk is nutritious, and it has unique flavor, so its yogurt product is creamy and has better quality than cow milk yogurt product, but the goat milk has goaty flavor, limiting the use of goat milk and its products. Goaty flavor of goat milk is mainly generated from low volatile fatty acids, especially the free fatty acids (FFA),which is related with its lipase activity.under the function of lipase, milk fat is degraded and forming FFA makes goat’s milk has goaty flavor. Fermentation is one of the most effective way to remove the goaty flavor, in which lactic acid bacteria fermentation process is to break down the lactose to the lactic acid and some flavoring substances which can cover the flavor of goat milk to a certain extent. But in the production process of goat’s milk yogurt, because of different kinds of lactic acid bacteria starter, the goat’s milk yogurt product is still has some goaty flavor. Therefore, this study based on lactic acid bacteria to explore the impact on goat milk yogurt, laying the foundation for further study of improving the quality of milk yogurt.The paper is mainiy divided into four parts, including the influence of different starter cultures on de-odoring effect of goat milk yogurt, screening the low-goaty flavor fermentation strains for goat milk yogurt, the effect of lactobacillus on goaty flavor of goat milk yogurt and the effect of post-fermentation on goaty flavor of goat milk yogurt.The first part was the influence of different starter cultures on de-odoring effect of goat milk yogurt. The influence of categories and amounts of starter cultures, fermentation temperature and time, post-fermentation on goaty flavor were researched. The results showed that choosing YO-MIX 187 as starter culture in addition of 2%, when fermentation temperature is 40℃ and fermentation for 4 h, and post-fermentation time is 24 h at 5℃, goat milk yogurt has lower goaty flavor.The second part was screening low-goaty flavor fermentation strains for goat milk yogurt. The lipase activity, FFA content and goaty flavor were evaluated with 6 Lactobacillus bulgaricus strains and 6 Streptococcus thermophilus strains from the commercial starter cultures in fermented goat milk. The results showed that using a single strain, Lactobacillus bulgaricus L.b-883 strain and L.b-211 strain, Streptococcus thermophilus S.t-187 strain and S.t-300 strain had lower lipase activity, FFA content and goaty flavor in fermented goat milk.The third part was the effect of lactobacillus on goaty flavor of goat yogurt. This part studied the effects of the proportion of lactic acid bacteria, the amount of bacteria, fermentation temperature and fermentation time on goat yogurt lipase activity, FFA content and the goaty flavor of goat yogurt. The results showed that with combination of Lactobacillus bulgaricus and Streptococcus thermophilus, L.b-211 strain and S.t-187 strain with the ratio of 1:2 had lowest lipase activity (11.62 μmoL/mL·min) and FFA content (3.28 μequ/mL) and goat yogurt almost has no goaty flavor.The forth part was the effect of post-fermentation on goaty flavor of goat milk yogurt. The main research studied the effect of post-fermentation temperature and time on the goat’s milk yogurt lipase activity, FFA content and goaty flavor. The results showed that when post-fermentation condition was 5℃ for 24h, goat milk yogurt’s lipase activity (18.71 μmoL/mL-min) and FFA content (7.96 μequ/mL). under the condition, the organization state uniform of goat milk yogurt was fine, it had good taste and flavor, and almost had no goaty flavor.