Storage condition effects on stress relaxation and fissuring behavior in rough rice

Abstract

Post drying fissures are directly associated with the head (whole grain) yield of rough rice in milling. Factors which affect the post drying fissures are drying temperature (drying rate) and storage condition (temperature and relative humidity). Effects of the above factors on (1) the percentage of fissured grains, (2) the breaking strength and (3) the stress relaxation behavior of rough rice in storage were investigated. Rough rice samples of Labelle, long-grain and Brazos, medium-grain were dried from 22 percent to 12 percent moisture content (w.b.) at three levels of temperature 60, 40 and 25(DEGREES)C. The rice was then stored at two levels of temperature: 10 and 45(DEGREES)C and four storage conditions (11, 43 and 75% RH and in sealed vials). Vials with saturated salt solutions were used to produce the relative humidity environments in which to store the test grains. Sample grains were removed after each period of storage time (9, 24, 48 and 72 h.) and inspected for fissures before being subjected to bending and stress relaxation tests. Effect of drying temperature (drying rate) was significant on the fissures which developed in the grains during storage. A high drying temperature produced a high moisture gradient inside the rice kernel. The fissures developed in the grains as the moisture gradient reclined.