介电离子调控射频钝化米糠脂肪酶的特性及机制研究

Lipases (LA) present in rice bran (RB) splited the triglycerides into glycerol and free fatty acids are originated responsible for the quality deterioration of RB, which restricts the utilization of RB. Studies have confirmed that the inactivation of LA using radio frequency (RF) heating or dielectric ion inhibitor is effective to improve the stability of RB. While the inactivation temperature of RF heating is higher and the activity of LA can be active again during storage, dielectric ions only result in partially inhibition of LA. To overcome the shortage of RF inactivation or dielectric ion inhibition of LA, this study will conduct the research on the dielectric ion regulation of RF inactivation of RB LA, focusing on the two key scientific matters in RB processing, that is relationship between the structural characteristics of RB LA and its catalytic property, and the correlation between the catalytic property and activity of oil-water interfaces, which is the catalytic site of LA. The relationship between RB LA activity and molecular conformational changes under dielectric ion regulation of RF heating will be studied by circular dichroism, fluorescence spectroscopy, transmission electronic microscopy, and dynamic light scattering to elucidate the mechanism of the regulatory inactivation based on molecular structure of LA. The oil-water interface model of LA will be constructed with decane as the oil-phase and phosphate buffer as the water-phase, and the relationship between the RB LA activity and the changes of interfacial tension and elastic modulus will be determined by using the interface rheometer under the dielectric ion regulation of RF heating to elucidate the mechanism of the regulatory inactivation based on catalytic characteristic of LA. This project will provide reliable support of new theory and new technology for the inactivation of LA in RB.

脂肪酶引发的油脂水解是米糠品质劣变的根源，制约着米糠的开发利用。射频钝酶效果显著，但钝酶温度高，易发生米糠油脂自动氧化及脂肪酶复性；介电离子抑酶条件温和，但脂肪酶不能完全失活。为了解决射频钝酶或介电离子抑酶的不足，本项目基于米糠脂肪酶结构特征与其催化特性以及脂肪酶催化特性--油水界面活性与其催化性能的关系两个关键科学问题，开展介电离子调控射频钝化米糠脂肪酶的特性与机制研究。采用圆二色光谱、荧光光谱、透射电镜和纳米粒度电位仪分析研究介电离子调控射频加热下，米糠脂肪酶活性与分子构象变化的关系，基于脂肪酶的结构特征揭示调控钝酶机制；以癸烷为油相磷酸盐缓冲液为水相构建脂肪酶的界面模型，采用界面流变仪分析研究介电离子调控射频加热下，米糠脂肪酶活性与界面张力及弹性模量变化的关系，基于脂肪酶的催化特性揭示调控钝酶机制。本项目研究结果将为米糠脂肪酶的钝化处理提供新的技术与理论支持。

内源酶引发的油脂水解是米糠品质劣变的根源，制约着米糠的开发利用。射频波与微波类似，同为非电离辐射，但其穿透力更强，在针对体积较大的物料热处理时具有潜在应用前景，因此本研究基于射频加热钝酶开展米糠的稳定化效果与机理研究，主要研究内容与结果如下：（1）系统归纳了射频加热技术在粮食采后加工中的应用研究进展，特别是射频加热技术在控制粮食加工副产物发生油脂酸败方面的研究进行了详细综述，并展望了其未来发展方向；（2）初步探明了米糠在射频电磁场中的介电行为以及射频波对米糠的穿透深度，明确了米糠的射频加热模式即存在边角集中加热效应。同时，发现NaCl、1%的KCl、2%的Na6O18P6等三种金属盐会显著增加米糠的介电损耗，提高射频加热时的升温速率；（3）优化出射频协同热风加热钝化米糠内源酶的最优工艺参数为米糠经射频加热至100°C并用热风保温15min，米糠品质指标未受到显著影响；35 °C储藏条件下可安全贮藏60天；（4）探明了射频钝酶作用对米糠分离蛋白结构与功能特性的影响，发现米糠经射频加热至100-120 °C保温5min，分离蛋白的产率、纯度、起泡特性和溶解性均降低，但吸附特性和乳化特性提高。分离蛋白的一级结构未受影响，但二级结构与三级结构发生改变。通过上述三方面研究，初步探明了米糠在射频电磁场中的介电行为以及射频波对米糠的穿透深度，实现了米糠的小规模射频快速均匀加热，在达到有效钝化米糠脂肪酶延长储藏期的同时可以保持米糠品质不受损失，使得射频钝酶效率与产品品质整体优于传统蒸汽稳定化处理，基于上述研究成果共发表高水平科研论文4篇，申请专利1件，获批榆林市科技计划项目与陕西省重点研发一般项目各一项。