Pardo Silvina, Galvagno Miguel Angel, Cerrutti Patricia
Laboratorio de Microbiología Industrial, Departamento de Ingeniería Química, Facultad de Ingeniería, Universidad de Buenos Aires, Buenos Aires, Argentina.
Rev Iberoam Micol. 2009 Jun 30;26(2):155-60. doi: 10.1016/S1130-1406(09)70028-2.
The aim of this study was to evaluate the vitality and viability of the probiotic yeast Saccharomyces boulardii after freezing/thawing and the physiological preconditioning effect on these properties. The results indicate that the specific growth rate (0.3/h(-1)) and biomass (2-3 x10(8)cells/ml) of S. boulardii obtained in flasks shaken at 28 degrees C and at 37 degrees C were similar. Batch cultures of the yeast in bioreactors using glucose or sugar-cane molasses as carbon sources, reached yields of 0.28 g biomass/g sugar consumed, after 10h incubation at 28 degrees C; the same results were obtained in fed batch fermentations. On the other hand, in batch cultures, the vitality of cells recovered during the exponential growth phase was greater than the vitality of cells from the stationary phase of growth. Vitality of cells from fed-batch fermentations was similar to that of stationary growing cells from batch fermentations. Survival to freezing at -20 degrees C and subsequent thawing of cells from batch cultures was 0.31% for cells in exponential phase of growth and 11.5% for cells in stationary phase. Pre-treatment of this yeast in media with water activity (a(w)) 0.98 increased the survival to freezing of S. boulardii cells stored at -20 degrees C for 2 months by 10 fold. Exposure of the yeast to media of reduced a(w) and/or freezing/thawing process negatively affected cell vitality. It was concluded that stress conditions studied herein decrease vitality of S. boulardii. Besides, the yeast strain studied presented good tolerance to bile salts even at low pH values.
本研究的目的是评估益生菌酵母布拉氏酵母菌在冻融后的活力和生存能力，以及对这些特性的生理预处理效果。结果表明，在28℃和37℃振荡培养瓶中获得的布拉氏酵母菌的比生长速率（0.3/h-1）和生物量（2-3×108个细胞/ml）相似。使用葡萄糖或甘蔗 molasses 作为碳源在生物反应器中对酵母进行分批培养，在28℃孵育10小时后，每消耗1g糖的生物量产量达到0.28g；补料分批发酵也得到了相同的结果。另一方面，在分批培养中，指数生长期恢复的细胞活力大于稳定生长期的细胞活力。补料分批发酵细胞的活力与分批发酵稳定生长细胞的活力相似。分批培养处于指数生长期的细胞在-20℃冷冻并随后解冻后的存活率为0.31%，处于稳定期的细胞存活率为11.5%。将该酵母在水分活度（aw）为0.98的培养基中进行预处理，可使在-20℃储存2个月的布拉氏酵母菌细胞的冷冻存活率提高10倍。将酵母暴露于水分活度降低的培养基和/或冻融过程会对细胞活力产生负面影响。得出的结论是，本文研究的应激条件会降低布拉氏酵母菌的活力。此外，所研究的酵母菌株即使在低pH值下也对胆盐具有良好的耐受性。
