Effects of storage temperature on viscosity among different rice varieties

Abstract

Rice grain qualities can change during storage depending on variety and storage conditions. This study set out to evaluate the effects of storage temperature on viscosity in five rice varieties with different levels of amylose content: three non-glutinous rice varieties (CNT1—high amylose, and KDML105 and PTT1—low amylose) and two glutinous rice varieties (SPT1 and RD10). Samples of unhusked rice grain were stored at 4°C and 60°C for 6 months. The viscosity value of cooked rice was measured every 2 months during the storage period. Storage temperature affected the viscosity of cooked rice differently among the rice varieties. For example, the peak viscosity of KDML105 decreased throughout the storage duration, while it decreased in the second month and remained unchanged until the end for PTT1 and CNT1. The breakdown of most rice varieties stored at both temperatures decreased throughout the storage. However, this increased in the second month before beginning to decrease for PTT1 stored at 60^oC. The storage of rice grain at 60°C decreased peak viscosity and viscosity breakdown much more than that at 4°C in all rice varieties. The viscosity setback for SPT1 and RD10 were found to have increased at both storage temperatures while for PTT1 it was found to have decreased. The setback of KDML105 and CNT1 stored at 4°C was found to have increased compared with that at 60°C. This study indicated that the quality of rice grain was differently affected by storage temperature depending on rice variety. The selection of appropriate storage conditions for each rice variety can help to maintain grain quality for rice consumers. Further study is required to investigate some other factors that caused rice grain deterioration during storage.