Schoug Asa, Fischer Janett, Heipieper Hermann J, Schnürer Johan, Håkansson Sebastian
Department of Microbiology, Swedish University of Agricultural Sciences, Uppsala, Sweden.
J Ind Microbiol Biotechnol. 2008 Mar;35(3):175-81. doi: 10.1007/s10295-007-0281-x. Epub 2007 Dec 5.
During the industrial stabilization process, lactic acid bacteria are subjected to several stressful conditions. Tolerance to dehydration differs among lactic acid bacteria and the determining factors remain largely unknown. Lactobacillus coryniformis Si3 prevents spoilage by mold due to production of acids and specific antifungal compounds. This strain could be added as a biopreservative in feed systems, e.g. silage. We studied the survival of Lb. coryniformis Si3 after freeze-drying in a 10% skim milk and 5% sucrose formulation following different fermentation pH values and temperatures. Initially, a response surface methodology was employed to optimize final cell density and growth rate. At optimal pH and temperature (pH 5.5 and 34 degrees C), the freeze-drying survival of Lb. coryniformis Si3 was 67% (+/-6%). The influence of temperature or pH stress in late logarithmic phase was dependent upon the nature of the stress applied. Heat stress (42 degrees C) did not influence freeze-drying survival, whereas mild cold- (26 degrees C), base- (pH 6.5), and acid- (pH 4.5) stress significantly reduced survival. Freeze-drying survival rates varied fourfold, with the lowest survival following mild cold stress (26 degrees C) prior to freeze-drying and the highest survival after optimal growth or after mild heat (42 degrees C) stress. Levels of different membrane fatty acids were analyzed to determine the adaptive response in this strain. Fatty acids changed with altered fermentation conditions and the degree of membrane lipid saturation decreased when the cells were subjected to stress. This study shows the importance of selecting appropriate fermentation conditions to maximize freeze-drying viability of Lb. coryniformis as well as the effects of various unfavorable conditions during growth on freeze-drying survival.
在工业稳定化过程中，乳酸菌会面临多种应激条件。不同乳酸菌对脱水的耐受性存在差异，其决定因素在很大程度上仍不明确。棒状乳杆菌Si3通过产生酸和特定的抗真菌化合物来防止霉菌腐败。该菌株可作为生物防腐剂添加到饲料系统中，如青贮饲料。我们研究了在不同发酵pH值和温度下，棒状乳杆菌Si3在10%脱脂乳和5%蔗糖配方中冻干后的存活率。最初，采用响应面法优化最终细胞密度和生长速率。在最佳pH值和温度（pH 5.5和34℃）下，棒状乳杆菌Si3的冻干存活率为67%（±6%）。对数后期温度或pH应激的影响取决于所施加应激的性质。热应激（42℃）不影响冻干存活率，而轻度冷应激（26℃）、碱应激（pH 6.5）和酸应激（pH 4.5）显著降低存活率。冻干存活率变化了四倍，冻干前轻度冷应激（26℃）后的存活率最低，最佳生长后或轻度热应激（42℃）后的存活率最高。分析了不同膜脂肪酸的水平，以确定该菌株的适应性反应。脂肪酸随发酵条件的改变而变化，当细胞受到应激时，膜脂饱和度降低。本研究表明选择合适的发酵条件以最大化棒状乳杆菌冻干活力的重要性，以及生长过程中各种不利条件对冻干存活率的影响。
