Effects of Storage Temperature on Physical and Chemical Properties of Brown Rice, Parboiled Brown Rice and Parboiled Paddy

Abstract

Thai brown rice (BR), parboiled brown rice (PB) and parboiled paddy (PP) with Chainatl variety were stored in polyethylene bag at different temperatures of 40 degree Celsius, 25 degree Celsius and 37 degree Celsius for six months. The effects on the alteration of chemical and physical properties, namely, moisture content, b-value, hardness value, water absorption and morphological properties of starch were investigated every month. The changes at low temperature (4 degree Celsius) storage were retarded. The moisture content and the water absorption became slightly declining, while the b-value and the hardness were lightly rising. Temperature and duration of storage provided significant affects on those properties. For stored rice samples at high temperatures (25 degree Celsius and 37 degree Celsius), the rate of quality change in BR, PB and PP samples were higher. The changes were much more observed in the samples with longer aging. After 6 months, starch granular structure changed when storage PB and PP grains at the high storage temperature whereas the structure unaltered under 4 degree Celsius storage. These moisture and starch granule structure changes affected the texture of cooked rice. Short storage at below room temperature is suggested to maintain physical and chemical parboiled rice qualities whenever those parboiled rice is produced from brown rice or rough rice.