Effects of Superfine Grinding on Physicochemical Properties and In Vitro Starch Digestibility of Red Rice Powder

Abstract

Pigmented red rice is a promising functional whole grain, but conventional milling cannot fully release its intracellular bioactives due to dense bran cell walls. Superfine grinding can effectively destroy compact tissue structures and improve the processing characteristics of cereal powders. In this study, red rice powders (RRPs) with different particle sizes were prepared by superfine grinding, and their physicochemical properties, micromorphology, crystalline structure, total phenolic content (TPC), pasting behaviors, and in vitro starch digestibility were tested by particle size analysis, colorimetric measurement, SEM, XRD, FT-IR, the Folin–Ciocalteu method, RVA, and an in vitro simulated digestion model. The results show that superfine grinding caused severe matrix destruction, reducing the particle size (D90) by 83.5%, and remarkably increasing the specific surface area. Furthermore, superfine grinding improved color brightness, decreased powder flowability, and reduced starch crystallinity, while no new functional groups were generated. Additionally, the TPC and water/oil-holding capacity were effectively enhanced. The pasting properties and in vitro starch digestibility of RRP were modified by superfine grinding. This study provides basic data on RRP properties and recommends the selection of proper grinding intensity in order to obtain powder for diverse food applications, such as functional beverages and bakery products.