西藏牦牛奶渣优良乳酸菌筛选及混合发酵优化

摘要

对从西藏牦牛奶渣中分离出的113株乳酸菌,以牛乳为基质经遗传稳定性、凝乳时间、凝乳酸度、后发酵酸度及组织状态等指标综合评价筛选出5株优良乳酸菌,得到4株乳酸杆菌(B、C、D、E)和1株乳球菌(A).将4株杆菌与球菌复配,进行组合发酵优化试验.通过发酵乳增菌规律、产酸性能、pH值、产香能力等综合指标加权比较,确定最优组合,为工业化应用提供参考.结果表明:①5株优势菌单株发酵凝乳时间均在4～6h之间,凝乳酸度在62.57 ～ 70.40°T之间,后发酵酸度在96.24～ 109.20°T;②以活菌数增菌性能和产酸性能为指标进行组合优化,显示AB和AC具有共生关系,在脱脂牛乳中37℃发酵8h,AB组合活菌数最高,达6.46× 109 mL-1,AC组合酸度最高,达91.87°T.AB、AC组合发酵性能均优于各单菌株,差异显著(P＜0.05),而AD和AE组合与各单菌株间发酵性能无显著性差异(P＞0.05).③最优菌种组合为AB(1∶1)复配,凝乳时活菌数为4.57× 109 mL-1,凝乳酸度为71.54°T,后发酵酸度为115.30°T,发酵乳产品中乙醛质量浓度为36.91 μg/mL、丁二酮质量浓度为13.82 μg/mL,产品质构良好.%A total of 113 strains of Lactic acid bacteria (LAB) were isolated from yak milk dreg in Tibet.Five LAB strains showing better fermentation performance were obtained through preliminary selection by genetic stability,coagulation time,titratable acidity and sensory evaluation.There were 4 strains of Lactobacillus (B、C、D、E) and one strain of Staphylococcus(A).They were used in combination to fermented dairy flavor.Optimal fermentation strain combination was obtained throughgrowth and acidic performance,pH,the composite ratio of strains and the content of acetaldehyde and diacetyl.The results showing that:① The curd time and titratable acidity of the 5 strains were 4 to 6 h and 62.57 to 70.40 °T;After refrigeration 24 h,titratable acidity were 96.24 to 109.20 °T;②The number of live bacteria enrichment performance and acid production performance index of combinatorial optimization,showed that AB and AC have a good symbiotic relationship.After fermentation of 8 h in skim milk,AB of the highest number of viable cells was 6.46× 109 mL-1,AC combination of curd acidity was highest.The performance of AC and AB combinations were superior to those of single strains,and the difference was significant (P＜0.05).While there was no significant difference in the fermentation performance between AD and AE (P＞0.05);③The optimal strain combination was AB(1 ∶ 1).The number of live bacteria was up to 4.57× 109mL-1,curd acidity and after fermentation acidity were 71.54 °T,115.30 °T.The acetaldehyde content of fermented milk products was 36.91 μg/mL and the content ofbutanedione was 13.82 μg/mL.