A comparative study of submicron‐ and micron‐sized rice particles: enzymatic hydrolysis in vitro and food efficiency ratio in vivo

Hydrolysis and absorption properties of submicron‐ (below 1 μm) and micron‐sized (over 100 μm) powders of raw rice, heat‐gelatinized rice, fermented rice and wheat were investigated in vitro and in vivo. Nutrient content such as protein, carbohydrate or vitamin C in the samples was not different significantly between submicron‐ and micron‐sized powders, but it showed difference according to processed type of the powders. Submicron‐sized powders were hydrolyzed more easily than micron‐sized powders by α‐amylases such as industrial, human salivary and porcine pancreatic α‐amylase but not by α‐glucosidase in all the tested samples. Patterns of blood glucose change were investigated in rats. The highest glucose levels were obtained at 30 min after oral administration in both submicron‐and micron‐sized powders, but the levels were decreased drastically in groups administered submicron‐sized powders, while they were slow and gradual in groups administered micron‐sized powders. On the contrary, the body weight gained and food efficiency ratios showed a tendency to be decreased slightly in mice fed with submicron‐sized rice powders compared to those with micron‐sized rice powder.