Physicochemical Properties of Brown Rice as Influenced by Gamma-Irradiation, Variety and Storage.

Effects of gamma-irradiation, variety and storage on physicochemical properties of brown rice from three Louisiana rice varieties: Mars, a medium grain variety, Lemont and Tebonnet, long grain varieties, were determined. Cooking time was significantly reduced in Mars and Lemont at doses of 200 and 300 Krads. Irradiation increased cooking rate, water uptake at 80$\sp\circ$C, water uptake ratios, total solids content in residual cooking liquid and starch damage from 100 to 300 Krad samples. Water uptake at 96$\sp\circ$C generally decreased with increasing dose levels. Evidence indicated alterations in the rice grain structure and composition. The component drastically affected by gamma-irradiation was starch as shown by reduced cooking time, increased water uptake, increased amounts of starch and protein in residual cooking liquid, reduced volume expansion, increased damaged starch and changes in amylographic pasting characteristics. Scanning electron microscopy showed more simple starch granules in irradiated samples than in nonirradiated samples. Structural changes in the bran layer due to gamma-irradiation were not evident from electron micrographs. Amylose, moisture, fat and protein content were not significantly affected by gamma-irradiation. Total color difference values indicated that brown rice darkened on irradiation and, became lighter on storage. Some changes in irradiated samples on storage were similar to those in nonirradiated samples but the degree of these changes was dependent upon dose. Fat acidity values for irradiated Mars and Lemont samples were generally lower than nonirradiated samples. 100 Krad samples of Tebonnet were higher than that of 0 and 200 Krad samples. Fat acidity values of nonirradiated and irradiated samples of Mars, and nonirradiated samples of Lemont increased on storage while irradiated samples were not significantly affected. Values for Tebonnet were not significantly affected by storage. TBA values for Lemont decreased from that at 0 to 100 Krads and then increased at 200 Krads. There was no definite trend in TBA values for Mars. Dose effects on TBA values were insignificant for Tebonnet. On storage, irradiated samples of Lemont and Tebonnet had lower values than nonirradiated samples. Stored irradiated samples of Mars tended to have higher values than nonirradiated samples