Variation of structures of ingredients of desiccated coconut during hydrolysis by hydrochloric acid at low temperature

Abstract Owing to the high content of lignocellulose, desiccated coconut become a healthy material for dietary fiber supplementation. In this study, the changes in solubility of the fibers of desiccated coconut were evaluated. The changes of the pHs and weight losses were studied. Furthermore, variations of the ingredient structures of desiccated coconut by hydrolysis by hydrochloric acid were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and scanning electron microscopy (SEM). After hydrolysis 30 s, the pHs of all systems increased, while six hours later, the pH of only system with initial pH = 1.00 decreased. The decline of pH only existed in hydrolysis systems with initial pH = 1.00, there is no relevant with the quantities of desiccated coconut. The lower initial pH of hydrolysis system was, the less the intrinsic viscosity of the desiccated coconut after hydrolysis was, the small the crystallinity was. After hydrolysis, the microstructure of the desiccated coconut become looser, and the secondary structure of the coconut protein became more stable and ordered. The results suggest that the hydrolysis of desiccated coconut mainly occurred in the branched chain and the non-crystalline region of lignocellulose, which transforms some insoluble dietary fiber into soluble dietary fiber. This improves the nutritional value of desiccated coconut.

摘要 鉴于木质纤维素含量较高，干燥椰蓉（desiccated coconut）可作为膳食纤维补充的优质原料。本研究对干燥椰蓉纤维的溶解度变化进行了考察，同时分析了体系pH值与质量损失的演变规律。此外，本研究采用傅里叶变换红外光谱（Fourier transform infrared spectroscopy, FTIR）、X射线衍射（X-ray diffraction, XRD）以及扫描电子显微镜（scanning electron microscopy, SEM）对盐酸水解过程中干燥椰蓉的成分结构变化进行了表征。水解30秒后，所有体系的pH值均有所上升；而水解6小时后，仅初始pH=1.00的体系pH值出现下降。pH值下降仅发生在初始pH为1.00的水解体系中，与干燥椰蓉的添加量无关。水解体系的初始pH值越低，水解后干燥椰蓉的特性黏度越低，结晶度也越小。水解完成后，干燥椰蓉的微观结构变得更为疏松，椰蛋白的二级结构也更加稳定且有序。研究结果表明，干燥椰蓉的水解主要发生在木质纤维素的支链与非结晶区域，该过程可将部分不溶性膳食纤维转化为可溶性膳食纤维，从而提升干燥椰蓉的营养价值。