Study On Fermentation Technology Of Functional Goat Yogurt

Yogurt is characterized by unique flavor, plentiful nutrition and benefit forhealth, so it is well welcomed by most of consumers. Recently, the goat milk isdeveloped in different products all over the world. However, goat's milkprocessing in China is mostly in powder and liquid. Hence, the study on thechanging quality of probiotic and synbiotic yogurts when them were producedand stored is important to utilize the goat resources in China.The study determined the growth curve of Lactobacillus acidophilus (LA₆),Bifidobacterium longum (BL) and L. rhamnosus (LR) in goat milk. Based on theprophase study of common yogurt fermentation technology, three fermentationtechnology of probiotic yogurts were optimized via single-factor experiment andresponse surface methodology. As starter for common yogurt, the proportion of L.bulgaricus (LB) and Streptococcus thermophilus (ST) was2:1, which was LS forshort. Effects of xylo-oligosaccharide (XOS), fructo-oligosaccharide (FOS),galaeto-oligosaccharide (GOS), isomalto-oligosaccharide (IMO), inulin andstachyose on growth of LA₆, BL and LR in goat milk were studied. Synbioticgoat yogurt was produced by adding stachyose as prebiotic, and HPLC-ELSDwas used to examine the content of stachyose. Meanwhile, the pH, acidity,texture, bacterial counts and stachyose content changing of the varied yogurtquality during storage at4℃was studied. The results were as follows.The best incubation time of LA₆, BL and LR was18.0h at37℃inreconstituted goat milk. At that time, the viable count of mentioned reached thepeak, which was0.98×10⁹cfu/mL,1.38×10⁹cfu/mL and3.16×10⁹cfu/mLrespectively.Optimal conditions for goat AB-yogurt were7.0%of LA₆,5.0%of BL,namely the proportion of LA₆, BL and LS was7:5:3,7.0%of total content,41℃for4.0h. Under this condition, the viable counts of LA₆and BL reached2.08×10⁸cfu/mL and4.82×10⁸cfu/mL respectively, the total bacteria numberreached1.06×10⁹cfu/mL. AR-yogurt's optimal conditions were9.0%of LA₆, 8.5%of LR, namely the proportion of LA₆, LR and LS was9:8.5:3,7.0%of totalcontent,42℃for3.5h. Under this condition, the viable counts of LA₆and LRreached1.75×10⁸cfu/mL and2.45×10⁸cfu/mL respectively, the total bacterianumber reached1.84×10⁹cfu/mL. Optimal conditions of BR-yogurt's were3.0%of BL,5.0%of LR, namely the proportion of BL, LR and LS was3:5:3,9.0%oftotal content,42℃for4.0h. Under this condition, the viable counts of BL andLR reached4.88×10⁸cfu/mL and5.87×10⁸cfu/mL respectively, and the totalbacteria number reached1.44×10⁹cfu/mL. The sensory evaluation of the sampleswas pleasant and acceptable.Adding prebiotics had no significant differences on pH and acidity ofprobiotics in goat milk. At low concentration, IMO, inulin and stachyose couldimprove the growth of LA₆obviously, but GOS inhibited the growth of them.XOS, FOS and IMO could promote the growth of BL, while XOS and GOS hadobvious increased effect on growth of LR. Considering the economic benefitsand advantage of Shaanxi province resources, we selected the stachyose asprebiotic for follow-up studies.HPLC-ELSD was used to determine the stachyose content in goat yogurts.The optimal stachyose concentration of goat AB-yogurt, AR-yogurt andBR-yogurt was1.0%,0.6%and0.8%, respectively. At that time, the enumerationof total bacteria and pobiotics were higher, and the utilization of stachyose waslower.The changing situation of pH, acidity, texture, the viable count andstachyose content of yogurts was studied, which prepared with differenttechnology during the storage time at4℃. With time goes by, pH decreased andacidity increased gradually. Firmness, consistensy, cohesiveness and consistencyincreased firstly and then decreased. The enumeration of total bacteria andpobiotics were above10⁸cfu/mL, and both of them reached the peak at1-7d, andthen decreased gradually. The effect of adding stachyose was not obvious, andthe utilization of stachyose was lower. Probiotic and synbiotic goat yogurts werepleasant during14d of storage at4℃.The probiotic and synbiotic goat yogurts prepared by the researchtechniques have the best sensory evaluation, higher nutritional and hygienicvalue, which storage time was14d at4℃. It provides reliable technical support for the production of goat yogurt, and also can supply theoretical basis to safestore and control of yogurt quality.