【作者】 季丽媛；

【导师】 陈合； 舒国伟；

【作者基本信息】 陕西科技大学 ， 发酵工程， 2012， 硕士

【摘要】 酸乳以其特有的风味、丰富的营养，良好的保健功效，深受广大消费者的青睐。目前，国际上羊奶产品研究开发较为广泛，而我国羊奶加工以奶粉及液态奶居多。因此，研究开发益生菌及合生元酸羊乳及冷藏过程中品质变化，对于充分利用我国山羊奶资源，推动奶山羊产业的发展意义重大。本研究测定了嗜酸乳杆菌（LA₆）、长双歧杆菌（BL）和鼠李糖乳杆菌（LR）的生长曲线。在课题组前期获得的普通酸羊乳发酵工艺（发酵剂为保加利亚乳杆菌与嗜热链球菌菌种比例LS=2:1）基础上，通过单因素试验和响应面试验设计，优化了益生菌酸羊乳的发酵工艺，确定了益生菌酸羊乳的最佳工艺条件，开发了3种益生菌酸羊乳。研究了低聚木糖、低聚果糖、水苏糖、低聚半乳糖、低聚异麦芽糖和菊糖6种益生元对LA₆、BL和LR3种益生菌在羊乳中生长的影响，确定了水苏糖作为益生元，并开发出了3种合生元酸羊乳。采用高效液相色谱-蒸发激光散射检测法（HPLC-ELSD）对合生元酸羊乳中的水苏糖含量变化进行了检测；研究了益生菌及合生元酸羊乳在4℃条件下冷藏过程中pH值、酸度、感官、质构、活菌数以及水苏糖含量等的变化情况，获得以下结论：LA₆、BL和LR在山羊乳中37℃条件下培养18.0h活菌数最高，分别达到了0.98×10⁹cfu/mL、1.38×10⁹cfu/mL和3.16×10⁹cfu/mL。嗜酸-长双歧（AB）酸羊乳的最佳工艺条件：LA₆接种量7.0%、BL接种量5.0%，即菌种配比LA₆:BL:LS=7:5:3；总接种量7.0%、41℃发酵4.0h，成品中嗜酸乳杆菌数达2.08×10⁸cfu/mL，长双歧杆菌数4.82×10⁸cfu/mL，总菌数达1.06×10⁹cfu/mL。嗜酸-鼠李糖（AR）酸羊乳最佳工艺条件：LA₆接种量9.0%、LR接种量8.5%，即菌种配比LA₆: LR:LS=9:8.5:3；总接种量7.0%、42℃发酵3.5h，成品中嗜酸乳杆菌数达1.75×10⁸cfu/mL，鼠李糖乳杆菌数2.45×10⁸cfu/mL，总菌数达1.84×10⁹cfu/mL。长双歧-鼠李糖（BR）酸羊乳最佳工艺条件：BL接种量3.0%、LR接种量5.0%，即菌种配比BL:LR:LS=3:5:3；总接种量9.0%、42℃发酵4.0h，成品中长双歧杆菌数达4.88×10⁸cfu/mL，鼠李糖乳杆菌数5.87×10⁸cfu/mL，总菌数达1.44×10⁹cfu/mL。三种益生菌酸羊乳感官品质良好。添加益生元对LA₆、BL和LR生长过程中环境的pH值和酸度变化影响不明显。低浓度时，低聚异麦芽糖、菊糖和水苏糖能明显促进LA₆的生长，低聚半乳糖则抑制其生长。低聚木糖、低聚果糖和低聚异麦芽糖对BL的生长有促进作用。低聚木糖和低聚半乳糖可明显促进LR的生长。综合考虑选择水苏糖作为益生元。HPLC-ELSD法测定酸羊乳中水苏糖含量，确定了益生菌酸羊乳中水苏糖的最佳添加量。AB酸羊乳、AR酸羊乳及BR酸羊乳中水苏糖最佳添加量分别为1.0%、0.6%和0.8%。酸羊乳中益生菌数和总菌数均较高，且水苏糖有少量消耗。随着冷藏时间的延长，酸羊乳的pH值逐渐降低，酸度逐渐增大；硬度、稠度、粘聚性与黏度先增大后减小；总菌数和益生菌数在1-7d达到最大值，之后逐渐减小，总菌数和益生菌数均在10⁸cfu/mL左右。添加水苏糖对pH值、酸度、质构、活菌数等影响不显著；水苏糖有少量消耗；4℃条件下，益生菌及合生元酸羊乳冷藏期均可达14d。采用本研究工艺制备的益生菌及合生元酸羊乳，感官评价良好，具有较高营养价值及保健作用，冷藏期可达14d，为酸羊乳生产提供了较为可靠的技术支持，对酸羊乳的安全冷藏及质量控制提供了理论依据。更多还原

【Abstract】 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.更多还原