Department of Food Science and Nutrition, University of Minnesota, Minneapolis, Minnesota, USA.
Drug Dev Ind Pharm. 2009 Aug;35(8):1003-8. doi: 10.1080/03639040902755197.
Creatine degradation to creatinine, which has no biological activity, in combinations of glycerol and pH 4.0 buffer solutions followed first-order kinetics up to a point where degradation started to level off, generally beyond the first half-life. Practical data are reported for a wide range of water activity (a(w)) values (0.31-0.983) at 4 degrees C, 23 degrees C, and 35 degrees C. Creatine degradation did not exhibit a dilution effect, that is a decrease in rate about an a(w) of 0.7, as is found for both microbiological growth and chemical reactions in semisolid food matrix systems. The temperature dependence obeyed the Arrhenius relationship with an energy of activation of about 20 kcal/mol at a(w) >or= 0.68 increasing to 23 kcal/mole below that a(w). In addition, a semilog plot of half-life as a function of a(w) at each temperature follows a predicted straight line. The pH and assumed liquid viscosity increase through increased glycerol concentration were not able to completely explain the decrease in rate of degradation as a function of a(w). Furthermore, we confirmed that creatine stability in the crystal form is very high as long as it does not reach the deliquescence state.
肌酸降解为肌酐，肌酐没有生物活性，在甘油和 pH 值为 4.0 的缓冲溶液的组合中，遵循一级动力学，直到降解开始趋于平稳的程度，通常超过半衰期的一半。在 4°C、23°C 和 35°C 下，报告了广泛的水活度（a(w)）值（0.31-0.983）的实际数据。肌酸降解没有表现出稀释效应，即速率随着 a(w)的降低而降低约 0.7，这在半固态食品基质系统中的微生物生长和化学反应中都有发现。温度依赖性遵循阿仑尼乌斯关系，在 a(w)≥0.68 时的活化能约为 20 千卡/摩尔，低于该 a(w)时增加到 23 千卡/摩尔。此外，在每个温度下，半衰期的半对数图作为 a(w)的函数遵循预测的直线。pH 值和假设的液体粘度随着甘油浓度的增加而增加，但不能完全解释降解速率随 a(w)的降低。此外，我们证实只要肌酸晶体不达到潮解状态，其稳定性就非常高。
