Study On Stablility Of Embedding Of Lactobacillus Casei Zhang

Lactic acid bacteria (LAB) is of great development and application for probiotic potential. However, LAB always encounter several stressful conditions which would greatly affect its viability. In these cases, it has been a focus on exerting probiotic effect including improving the shelf life of the LAB product and obtaining a higher general survival rate in severe environment of human gastrointestinal tract. In this paper, a probiotic Lactobacillus casei Zhang(L. casei Zhang) was choosen as original culture to prepare starter culture from optimized aspects of the enzyme entrapped temperature, pH, coagulation time, moisture content and water activity of freeze-dried powder, heat resistance, vitality, gastrointestinal fluid tolerance, stability of storage and so on. On the basis of these preliminary tests, the direct embedding of fermentation broth was carried out. The main results were as follows:By observation of the curd state, the optimal condition of embedding bacterial sludge was under37℃bath at pH7.0. The effect of embedding by transglutaminase was better than rennet. The moisture and water activity of freeze-dried powder by transglutaminase embedding were significantly lower than control group and rennet group (4.30%and0.14, P<0.05), Above50%survival of L. casei Zhang in transglutaminase embedding powder was observed undergo a simulating gastrointestinal fluid. Heat resistance of freeze-dried powder by transglutaminase was significantly higher than control group and rennet group (P<0.01) and transglutaminase embedding bacterial powder could resist a heating at80℃for2min with a survival rate upto1.90%o. The transglutaminase embedding bacterial powder activity and storage stablility was better than rennet embedding group and control group. The viable counts of transglutaminase embedding bacterial powder under a storage at25℃for120d were more than1010CFU/g with a loss of1order of magnitude, while storaging at37℃for120d were more than107CFU/g with a loss of4order of magnitude.Furthermore, the protein-derived protective agents in L. casei Zhang embedding were optimized. The optimal protective agent included12%skim milk powder,1%casein,1%soy protein isolate,1%lactalbumin80,2.5%lactose,4%trehalose,0.5%glucose and1%soy peptone. By adding this protective agent, the survival rate was24.99%and viable counts could reach above1010CFU/g at37℃within storage of21days.Finally, the embedding of fermentation liquid of L. casei Zhang was investigated. The survival rate was14.35%and viable counts could above109CFU/g at37℃within a storage of21days.