Quality characteristics of wash-free rice and evaluation of its storage characteristics

Abstract

Wash-free rice (WF rice) had the following characteristics; high moisture content, high degree of brightness (high L-value) and also, low contents of protein, crude lipid and total free fatty acid. However, there were slight differences in the total free fatty acid contents among WF rice samples. For the residues of processed WF rice, the contents of protein and crude lipid were high. These characteristics suggest that the removal of the aleurone layer was more efficiently conducted by the treatment for wash-freeing than by the ordinary polishing treatment. WF rice packed in air underwent the following changes in a storage test. The high degree of brightness initially observed for WF rice were apt to be kept during the storage. The beginning temperature of gelatinization was lower in WF rice compared to the ordinary milled rice for the same raw material. Further, the time-course increases in the maximum viscosity and the final viscosity tended to be low. The increase in the total free fatty acid content in WF rice compared to the ordinary milled rice tended to be small. These tendency was marked for the stored rice under ambient temperature package in polyethylene film and slight for PVDC coated-nylon film package. Storage at a low temperature (at 15°C) resulted in small changes in rice qualities and so, the differences between WF rice and the ordinary milled rice were also small. Determined values by using ADAM and fat acidity determined by the conventional method were in close correlations. The relation between these two values could be expressed in the following equation : y=2.4x-0.15. The correlation coefficient was O.995 and thus, a significant correlation was found between the two (P<0.01). An eating taste test was carried out after storage for 1 year, and significant differences between WF rice and the ordinary milled one were found in respect of flavour (P<0.05) and of stickiness (P<0.01). These significances were assumed to be mostly due to the low content of free fatty acid content.