旋光法研究L-半胱氨酸在食品加工条件下的稳定性

The stability of L-Cysteine in room temperature and processing determined by polarimetry

为明确L-半胱氨酸(L-Cys)在食品加工条件下的稳定性,测定其溶液在不同酸度、不同食品添加剂等食品加工条件下的旋光度值,进而探讨L-Cys在加工条件下的变化规律。结果表明:在室温下、pH 3.0～8.0内,L-Cys的氧化反应为零级反应,其氧化速率常数在pH值3.0时最小,在pH值4.0和pH值8.0时最大。溶液含氧会影响L-Cys的起始浓度,但不影响其氧化速率常数。H2O2、NaHSO3氧化L-Cys的速率常数分别为:9×10-6mol/(dm3h)和2×10-6mol/(dm3.h),NaHSO3不能作为保护L-Cys的抗氧化剂。L-Cys具有热不稳定性,加热至60℃和100℃时其溶液旋光度无规律性变化。

To discover the change pattern of L-Cysteine （L-Cys） in food processing, the optical rotation of L-Cys and L-Cystine （L-Cys-Cys） solution were determined under different pH and environment （H202 and NaHSO3 ）. The results showed that, at room temperature and pH = 3.0 - 8.0, the oxidation reaction of L-Cys followed zero order re- action and the rate constant was the smallest at pH 3.0, and the biggest at pH 4.0 and 8.0. Whether the solution is aerobic or not influenced the initial concentration of L-Cys, but would not have impact on its rate constant. H202 and NaHSO3 , which are used as pro-oxygenic agent in L-Cys solution, could increase the oxidation reaction rate constant, to 9 ×10-6 mol/（dm3 · h） and 2 × 10-6 mol/（ dm3 · h） , respectively. So NaHSO3 could not be antioxidant for pro- tecting L-Cys. L-Cys was thermal instability when heated above 60 ℃.