Efficiencies of Chemical Techniques for Rice Grain Freshness Analysis

Two chemical methods which are commonly used for rice grain freshness determination were investigated for their efficiencies. Method 1 is made of bromothymol blue indicator, and the principle is based on indicator's color which is changed in according to pH of the stored rice grains. Method 2 is based on peroxidase activity which deteriorates during storage of rice grains. Both methods were used for determination of fresh-aged rice index of six Thai-rice cultivars, four from non-waxy rice cultivars (KDML 105, Chai Nat 1, Chai Nat 2 and Phitsanulok 2) and two from waxy rice cultivars (San-pah-tawng and RD6). Rice samples were kept in the forms of paddy and polished rice. Fresh-aged rice indices were determined using both methods every two weeks over the storage period of 24 weeks (six months). It was found that both methods were capable of detecting fresh-aged rice indices. The color of chemical solutions changed with regards to the age of rice grains and it could be detected spectrophotometrically. Rice grains which have been kept as paddy provided more consistent results. Method 1 is recommended for industrial application as it is simple, efficient and inexpensive.