Chen Y H, Aull J L, Bell L N
Department of Nutrition and Food Science, Auburn University, Alabama 36849, USA.
J Agric Food Chem. 1999 Feb;47(2):504-9. doi: 10.1021/jf9807216.
Research continues to differentiate the impact of water activity (a(W)) and the glass transition temperature (T(g)) on chemical reactions. Invertase with and without sucrose was incorporated into low and high molecular weight poly(vinylpyrrolidone) model systems (PVP-LMW and PVP-K30, respectively). Invertase activity and sucrose hydrolysis were monitored during storage at a(W) = 0.32-0.75 and 30 degrees C. Pseudo-first-order rate constants for activity loss in PVP-K30 were not different, regardless of the system being glassy or rubbery. In PVP-LMW, invertase stability decreased with increasing a(W). An a(W) > 0.62 was required for sucrose hydrolysis to occur in PVP-LMW. PVP molecular weight appeared to affect invertase stability and reactivity. No dramatic change around T(g) was found in either invertase stability or sucrose hydrolysis, suggesting that T(g)-dictated mobility has a minimal effect on these reactions in amorphous solids.
研究仍在继续区分水分活度（a(W)）和玻璃化转变温度（T(g)）对化学反应的影响。将添加和未添加蔗糖的转化酶分别加入低分子量和高分子量的聚乙烯吡咯烷酮模型体系（分别为PVP-LMW和PVP-K30）中。在a(W) = 0.32 - 0.75及30℃储存期间监测转化酶活性和蔗糖水解情况。PVP-K30中活性损失的伪一级速率常数并无差异，无论体系是玻璃态还是橡胶态。在PVP-LMW中，转化酶稳定性随a(W)升高而降低。PVP-LMW中蔗糖水解发生需要a(W) > 0.62。PVP分子量似乎会影响转化酶稳定性和反应活性。在转化酶稳定性或蔗糖水解方面，未发现T(g)附近有显著变化，这表明T(g)决定的流动性对非晶态固体中的这些反应影响极小。
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