益生菌干酪乳杆菌Zhang和乳双歧杆菌V9发酵乳胞外多糖含量对流变学特性、质构和稳定性的影响

Effects of Extracellular Polysaccharide in Yogurt Produced by the Probiotic Bacteria,Lactobacillus casei Zhang and Bifidobacterium animalis subsp.lactis V9 on Rheological Properties,Texture and Stability

干酪乳杆菌Zhang和乳双歧杆菌V9是我国自主开发具有良好益生特性的益生菌,发酵乳是益生菌的最优载体之一。本研究以2株益生菌应用于发酵乳为研究对象,采用多频扩散波谱法研究发酵过程中的流变学特性,通过稠度、硬度、内聚性和黏度指数测定分析发酵乳的质构特性,并分析贮藏期间活菌数和稳定性,胞外多糖(EPS)含量。结果表明,干酪乳杆菌Zhang、乳双歧杆菌V9和二者复配的发酵乳中EPS含量从贮藏期起始的(546.3±31.5),(361.1±20.1),(515.2±17.5)mg/L至贮藏期末增至(1165.4±37.8),(903.6±33.9),(1103.8±45.6)mg/L,显著高于对照组(P<0.05)。在发酵过程中,干酪乳杆菌Zhang组表现出较高弹性因子和低固液平衡值的流变学特性,显示形成紧密的凝胶结构。后熟后,干酪乳杆菌Zhang(包括单一和复配)发酵乳的稠度、硬度、内聚性和黏度指数显著较高,乳双歧杆菌V9发酵乳硬度和黏度指数显著较高,前者的黏度和持水性显著高于对照组,后者的黏度显著高于对照组(P<0.05)。各组发酵乳贮藏期间的后酸化程度没有显著差异(P>0.05),表明益生菌及其代谢产生的EPS对发酵乳流变学特性、质构特性及贮藏稳定性具有积极影响,且干酪乳杆菌Zhang作用较为突出。此外,干酪乳杆菌Zhang和乳双歧杆菌V9在贮藏期间活菌数在10~8CFU/mL以上,可有效保证益生菌发挥其促进健康的作用。综上,在发酵乳中添加益生菌干酪乳杆菌Zhang和/或乳双歧杆菌V9,不仅能够赋予发酵乳益生功效,而且能够改善质构特性和贮藏稳定性。本研究为实际生产、推广应用提供技术依据,同时为益生菌发酵乳的发酵及贮藏特性评价提供研究思路和方法。

Lactobacillus casei Zhang(L.casei Zhang)and Bifidobacterium animalis subsp.lactis V9(Bifidobacterium lactis V9,B.lactis V9)are probiotics that were isolated and developed in China,and they exhibited desirable properties.Yogurt is one of the best carriers for probiotics.This study characterized the content of extracellular polysaccharide(EPS)in yogurt fermented by L.casei Zhang and/or B.lactis V9 for the first time.The rheological properties of yogurt were studied by multi-frequency diffusion spectroscopy.The texture parameters of yogurt,like firmness,cohesiveness,consistency,and viscosity index,were measured.The viable counts of the probiotic strains and their stability during storage were analyzed.The results showed that the increase in EPS content was significantly higher for the probiotic groups compared with the control group,increased from(546.3±31.5),(361.1±20.1),(515.2±17.5)mg/L to(1165.4±37.8),(903.6±33.9),(1103.8±45.6)mg/L for groups containing B.lactis Zhang alone,B.lactis V9 alone,and a combination of both bacteria,respectively,contrasting to an increase from(64.4±5.4)mg/L at the beginning to(351.6±5.4)mg/L at the end of storage(P<0.05 for the control group).The application of L.casei Zhang group resulted in high elastic index and low solid liquid balance rheological properties,enhancing the strength of the gel structure.The levels of firmness and viscosity index were associated with the EPS content in yogurt.Adding L.casei Zhang(including single and compound)significantly increased the consistency,firmness,cohesiveness,and viscosity index of yogurt.Adding B.lactis V9 only increased the firmness and viscosity index.In addition,there was no difference in the degree of acidification of yogurt between different groups(P>0.05).Furthermore,L.casei Zhang and B.lactis V9 were stable during storage with>108 CFU/mL,which ensures the probiotic effect of yogurt.In conclusion,adding probiotic L.casei Zhang and/or B.lactis V9 to yogurt does not only maintain the probiotic effect of the yogurt,but also improve the texture characteristics and storage stability.Data provided by this work will serve as technical references for production and industrialization of these products.This study also provides insights into methodology development and evaluation for fermentation and storage of probiotic yogurt.