Physicochemical properties of layered starch of japonica rice

Objective: This study aimed to improve the high-value utilization of japonica starch and the comprehensive application of japonica layered starch. Methods: Japonica starch was extracted by alkaline and enzymatic methods, and the physicochemical indexes such as basic composition, solubility, swelling power and pasting characteristics of the 3 layers of starch after centrifugation were analyzed, and the structural characteristics were studied by scanning electron microscopy and infrared spectroscopy. Results: The contents of the three starch layers extracted by alkali and enzymatic methods ranged from 91% to 99%, with the highest relative proportion of the middle layer starch. The amylose content of the middle layer starch extracted by alkali and enzymatic methods was higher than that of the upper and lower layers, while the protein content and straight chain amylose content of the upper and lower layers starch were higher than that of the middle layer. The solubility and bulking power of all layers of starch extracted by alkali and enzymatic methods increased with the increase of temperature, and the thermal stability of the upper and lower layers of starch extracted by alkali and enzymatic methods was better than that of the middle layer of starch. The results of scanning electron microscopy showed that the starch granules of all layers extracted by alkaline and enzymatic methods were more complete, and the distribution of starch granules of all layers extracted by the enzymatic method was relatively sparse. In the infrared spectra, the main characteristic absorption peaks of all layers extracted by alkaline and enzymatic methods were similar, and the short-range orderliness of the middle layer was higher than that of the upper and lower layers of starch. Conclusion: The upper and lower starch layers of japonica rice can be further exploited to improve the comprehensive utilization of japonica rice resources.