Differential Effects of Roasting and Steaming of Resistant Starch-Rich WE Rice on Murine Intestinal Immune and Barrier Functions.

WE rice, a non-genetically modified double mutant of the waxy and amylose-extender genes, is rich in resistant starch (RS) and has potential as a functional staple food. This study investigated how thermal processing (roasting vs. steaming) of WE brown rice affects its physicochemical properties and intestinal immune- and barrier-related functions in mice. Thermal processing altered RS content, X-ray diffraction intensity, and the degree of gelatinization of WE rice. Male BALB/cA mice were fed diets containing steamed waxy-type rice (0% RS), roasted WE rice (2% RS), or steamed WE rice (2% RS) for 8 weeks. Both processed and WE rice diets significantly increased intestinal IgA levels and fecal mucin concentrations compared with the control diet. However, distinct physiological responses were observed depending on the processing method. IgA production was greater in the roasted group, whereas mucin production was higher in the steamed group. The total amount of cecal short-chain fatty acids increased in both WE rice groups, which may have contributed to the basal enhancement of IgA and mucin production. Fecal bacterial counts, a potential inducer of intestinal IgA production, were significantly higher in the roasted group, whereas the relative abundance of Rikenellaceae, a mucin-associated bacterial family, increased in the steamed group. These findings indicate that not only RS content but also processing-dependent physicochemical properties of RS-rich rice influence intestinal functionality. Thermal processing of WE rice differentially modulates intestinal barrier-related responses, supporting its potential as a functional staple food for maintaining intestinal health.