Abstract: 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.