Preparation technology optimization and characteristic analysis of rice resistance starch

Abstract: Yitang is a new type rice with high amylose content, which was bred by spaceflight mutation and physical mutation. It has great potential for developing high resistant starch (RS) products. Until recently, most of the studies on the RS preparation have focused on high-amylose corn starch or root vegetables starch. In addition, there is a greater difference between rice starch and other kinds of starch in particle characteristics, composition, etc. The production processes of RS cannot simply be deduced from previous reports. In order to make use of Yitang rice rationally, this article focuses on the production processes of RS as a functional food ingredient. The production processes of Yitang Rice RS were optimized through a Box-Benhnken center-united experiment design and Response Surface Methodology (RSM), based on single-factor experiments of moisture content (starch concentration), pH value, autoclaving treatment temperature, cooling method, cold storage time, drying temperature, and the number of autoclaving treatments. RS characteristics analysis was discussed by assistant analyses of absorption curves of starch and I2-KI compound, infrared spectroscopy, average polymerization degree, scanning electron microscopy, solubility, and water-holding capacity. The results showed that the most influential process factors were moisture content (starch concentration), pH, autoclaving treatment time, and cold storage time. The optimum conditions were a starch concentration of 31%, pH value 5.8, heating time 50 min (under 0.1 MPa, 120℃), natural cooling and cold storage time 15 h, drying temperature 80℃, three autoclaving treatment times, together yielding an RS fraction of 20.1%. The characteristics analysis showed that the "Yitang Rice" RS has ordered crystalline structure which was formed by recrystallizing during starch retrogradation, and the major component of it is short amylose (polymerization degree is 21.43). The characteristics of RS crystal structure which has a narrow molecular-weight distribution and more hydro-keys than native starch are compact and solid. Therefore, its solubility decreased 85.9% as compared to native Yitang rice. However, the RS surface exhibits a multi-pore structure that makes its water-holding capacity higher than other common RS and dietary fiber products such as potatoes RS and corn RS. This research can provide a method for improving the yield of RS from "Yitang Rice" and an explanation of the mechanisms of RS formation, which can promote the wide development and utilization of "Yitang Rice" resources.