Preparation And Application Of Functional Direct-Vat-Set(DVS) Kefir Starter Cultures For Goat Milk

Kefir is an ancient fermented milk with unique flavor and special aroma originating from the North Caucasus Mountains in Russia,having many functions such as improving immune function and regulating the intestines.As "champagne in fermented dairy products",kefir is very popular worldwide.It is kefir grains that used as starter cultures during kefir production at present.However,the proliferation of kefir grains is slow and and the microbial composition is unstable,which make the large-scale and large-scale production of kefir restricted.Therefore,it is necessary to prepare DVS kefir starter cultures.The effects of different kefir grains on the fermentation and biological activity of goat milk kefir were studied first to screen kefir grain suitable for the goat milk fermentation,and fermentation conditions were optimized.Kefir flora was separated,screened and identified then.The dominant strains were prepared by freeze-drying.The functional DVS kefir starter cultures capable of fermenting goat milk with antioxidant peptides and ACE inhibitory peptides was prepared by optimizing the proportion of strains powder.Finally,goat milk kefir was prepareted by DVS kefir starter cultures and its storage stability was studied.The following results were obtained:1.Using degree of protein hydrolysis(DH),ACE inhibition rete and sensory evaluation as responses,the kefir grain K1 was screened for goat milk fermentation among 5 kefir grains from different regions.With 2% as inoculum size and fermentation at 25 oC for 22 h,the DH and ACE inhibition rate of goat milk kefir were 67.02% and 73.83%,respectively,and the value of sensory evaluation reached to 75.83%.2.The optimized fermentation conditions for kefir grain K1 were determined by single factor test and response surface methodology(RSM),which were fermentation at 24 oC for 23 h with a inoculum size of 2.5%.Under the optimum conditions,ACE inhibition rate and sensory evaluation of kefir were 85.97±0.62% and 84.65±0.76,which were 12.25% and 8.82 higher compared to the control,respectively.There was no significant difference between the validation and the predicte,indicating that RSM was feasible to optimize the fermentation conditions of goat milk kefir.3.The effects of L.plantarum Lp69,producing antioxident peptides,and L.plantarum L60,producing ACE inhibitory peptides,on the fermentation of goat milk kefir were studied.The results showed that DPPH free radical scavenging activity and ACE inhibition rate of the experimental tended to be stable,and there was no significant difference between pH and acidity compared to the control after adding different Lactobacillus and incubating second generation.After four generations of inoculation,the DPPH free radical scavenging activity for goat milk kefir of adding L.plantarum Lp69,L.plantarum L60 and two Lactobacillus were increased by 9.96%,16.11% and 13.77%,respectively,and the ACE inhibition rate decreased by 6.47%,13.16% and 9.92%,compared to the control.It indicated that L.plantarum Lp69 and L.plantarum L60 could colonize on kefir grain and change its fermentation performance.4.Using 5 selective media,36 strains were isolated from kefir grain K1 fermented goat milk by plat streaking method.5 strains,KM1,KM2,M3,MC3 and Y5,with better fermentation characteristics were screened using the parameters of DH,lactose content and water holding capacity as indicators.The strains were identified by 16 S rDNA as Lactobacillus helveticus,Enterococcus faecium,Lactobacillus fermentum,L.plantarum and Kluyveromyces lactis,respectively.5.The optimum formula of functional DVS kefir starter cultures for goat milk was determined by mixing experiment: L.helveticus KM1 10%,L.fermentum M3 25.8%,Kluyveromyces lactis Y5 23.4%,L.plantarum Lp69 18.4% and Lactobacillus casei L61 22.4%.the DPPH free radical scavenging activity of goat milk fermented by DVS kefir starter cultures was 79.76±0.65%,the ACE inhibition rate was 78.52±0.52%,and the value of sensory evaluation was 65.75±0.77.6.The storage test showed that the DPPH free radical scavenging activity of the two kinds of goat milk kefir fermented by DVS kefir starter cultures and kefir grain changed steadily,and the ACE inhibition rate decreased first and then increased,reaching 82.94% and 72.05% finally,respectively.The pH showed a decreasing trend,and the acidity gradually increased.After 14 d,it stabilized at 91.73 °T and 96.84 °T.Sensory evaluation values increased continuously,reaching maximum of 86.34 and 85.93 after 14 d of refrigeration.In this study,kefir grain K1,which is suitable for goat milk fermentation,was screened,and the strains in kefir goat milk were screened and identified.The functional DVS kefir starter cultures for goat milk with high antioxidant activity and ACE inhibitory activity was preparated,which provides technical support for the development of subsequent kefir goat milk products.