D. A. Suter

Viscoelastic Behavior of Parboiled Rice

Two varieties of rice were parboiled and their stress relaxation properties were investigated. A four-element Maxwell model best described the viscoelastic behavior of parboiled rice at a storage moisture of 10.5% and above. Bold type medium grains (Rico-1) had greater relaxation time constant than slender long grain (Lemont) signifying more gelatinization in the latter. Relaxation time and decay stress values increased during the first two to three hours of storage compared to sealed storage (control) which decreased over the following 24 h period. Exposure of the dried samples to a 65% relative humidity storage environment increased the relaxation time constant compared to control. A relative humidity of above 75% gradually decreased the relaxation time constant. Prediction models for the stress relaxation parameters have been proposed with respect to relative humidity and storage time for given types of grains.