Investigation the Effect of Milling Process and Storage Duration on the Aroma Components of Indica Rice Variety (Tarom) by SPME Method

Rice is the predominant staple food for the people in the tropical and semitropical area. Carbohydrate is the main component of rice which accumulate in endosperm cell. Postharvest treatment and storing duration as an aging is a complicated process, which involves changes in physical and chemical properties of the rice grain especially aromatic rice variety. Rice aroma resulted in volatile components from the food which was sensed by the smell under different conditions. In this study, the effect of milling process and storage duration on the stability of aroma indices of Tarom variety was investigated.

Tarom variety was dried and then dehusked by hand. The weight of brown rice was measured manually and polished in multistage polisher. The brown rice and white rice samples were divided in two parts as namely; new and stored brown rice (BSN , BSO) also new and stored white rice (WSN, WSO). The volatile components of BSN, WSN, BSO & WSO samples were absorbed by solid phase micro extraction method. The absorbed volatiles component was measured by gas chromatography (GC). Analysis of variance as a two-factor experiment in completely randomized design was performed. The two factors are expressed as milling type and storage, with two levels and three replicate. The amount of aromatic components of samples were analyzed by using SPSS software and also compared.

The results have shown that the percentage of recognized components of all stored rice samples were significant (p < 0.01) increased but the aromatic components percentage of new white rice samples (WSN) were increased in compare of stored white rice samples (WSO). The results of the present study on the effect of storage duration on the aromatic components exhibited that by removing of bran layer in whitening process result in reduction of aromatic components. The recognized components in samples are as follows; 24 component for BSO (about 92.3% of total), 26 component for WSN (about 65.3% of total), and 24 component for WSO (about 98.4% of total). Storing and whitening could increase the amount of Alkenes in rice volatile component. The higher rate of 2-Methyl-octadecadienol as an alcohol might be due to using of insecticide in paddy fields which was reduced after whitening process. The percentage of Aldehyds & Ketons has no meaningful difference in brown rice stored samples but it was decreased about 30% in white stored rice samples.

From the results of this work, aging the aromatic variety not only increases the cost of keeping but also could reduce the aromatic component as a rice quality index.