Brocklehurst T F, Mitchell G A, Pleass W, Smith A C
Institute of Food Research, Norwich Laboratory, Colney, UK.
J Appl Bacteriol. 1995 May;78(5):495-500. doi: 10.1111/j.1365-2672.1995.tb03091.x.
Water activity is a method of preservation that can affect microbial growth in foods and that may fluctuate during their processing, distribution and storage. Sucrose has been used to change the water activity of microbiological culture media. Suspensions of Salmonella typhimurium LT2 in the exponential phase of growth have been subjected to step changes in sucrose concentration at 20 degrees C. The changes in the numbers of viable bacteria were measured with time and the experimental growth curves compared with predictions based on growth data obtained at constant sucrose concentrations. Steps down in sucrose concentration showed some apparent loss of viability after the step followed by growth at a rate close to the expected value. Steps up in sucrose concentration resulted in a greater apparent loss of viability after the step and either growth or the inducement of lag, depending on the final concentration of sucrose. A series of small steps up in sucrose concentration to 45% (w/v) was able to sustain growth where it was not possible by inoculation directly into this concentration. Improved recovery of bacteria subject to osmotic stress was possible with a medium containing sodium chloride.
水分活度是一种保存方法，它会影响食品中的微生物生长，并且在食品加工、分销和储存过程中可能会发生波动。蔗糖已被用于改变微生物培养基的水分活度。在20摄氏度下，处于生长指数期的鼠伤寒沙门氏菌LT2悬浮液经历了蔗糖浓度的阶跃变化。随时间测量活菌数量的变化，并将实验生长曲线与基于在恒定蔗糖浓度下获得的生长数据的预测结果进行比较。蔗糖浓度下降时，阶跃后显示出一些明显的活力损失，随后以接近预期值的速率生长。蔗糖浓度上升时，阶跃后导致更大的明显活力损失，并且根据蔗糖的最终浓度，要么生长要么诱导延迟。一系列小幅蔗糖浓度上升至45%（w/v）能够维持生长，而直接接种到该浓度则无法实现生长。使用含有氯化钠的培养基可以提高遭受渗透胁迫细菌的回收率。
