Particle size and concentration of ground rice on tribological properties and in vitro starch digestibility of rice porridge

Abstract

ABSTRACT Rice porridge is a food for general consumption; however, it may vary in food texture and starch digestibility depending on particle sizes and concentrations. This study investigated the tribological properties, steady shear flow, and in vitro starch digestibility of rice porridge with different particle sizes of ground rice (small size, <0.2 mm; large size, 0.2–0.45 mm; based on sieving) and concentrations (5, 7.5, or 10% w/v). The results showed that a high concentration of large-sized ground rice promoted lubrication properties, with the maximum friction coefficient reducing from ~ 0.7 in the 5% w/v concentration to ~ 0.4 in the 10% w/v concentration. In addition, the reduction in the friction started at a sliding speed of ~ 2 mm/s for the high concentration ground rice compared to ~ 20 mm/s for the low concentration rice. The results of high viscosity, small hysteresis loops, and swollen rice particles under morphological observation showed greater porridge stability for the high concentration, thus promoting its lubrication properties. These physical characteristics of the porridge could also play a role in starch digestibility during in vitro gastric digestion. Therefore, the management of ground rice to obtain a large size and a high concentration in rice porridge could benefit food preparation for the elderly and people having difficulty swallowing.