Effect Of Degree Of Milling On The Physiochemical And Quality Properties Changes During Rice Aging

Rice is one of the world-wide staple food, thus excessive processing of rice not only brought great waste of cereal grains, but also caused serious losses of nutrients in rice. Rice with a low milling degree which is below 10% DOM is in a compromise between the white and brown rice. Low the milling degree can meet the purpose to increase rice yield, reduce waste in production, and guarantee the nutrition retention. In this paper, I treated low milling degree rice (8%-2%DOM),10% DOM white rice and brown rice samples with three different storage temperatures for a period of 90 days. During storage, Physiological and Biochemical Indexes, cooking qualities, pasting properties and thermal properties had been examed and observation of the rice flour microstructure had been record. The conclusions are as following:(A) During aging, "bran flour"and free fatty acid of rice samples with low milling degrees had a bigger increase than brown and white rice, Ea of low DOM rice samples were much lower than white rice and brown rice, meaning that the oil in low DOM rice samples were much more unstable than white rice and brown rice. This is the disadvantage of low DOM rice. Other Physiological and Biochemical indexes Changes were between brown rice and white rice.(B) The cooking qualities of low DOM rice during aging change between white and brown rice, and reduce gradually with the decrease of DOM. Cooking qualities of white rice changed most during storage.(C) Studied aging qualities of different DOM rice samples with DSC and SEM:(1)The gelatinized transition temperatures and ΔH were increased after storage, indicated that the phase transition from an ordered to a disordered state became more difficult and requires much higher temperature and more energy; the increase in R showed that aged rice samples required a longer period of time during cooking.(2) After the storage, the microstructure of rice has also changed. Observation on aged rice sample after aging showed that the surface of starch granules covered by a paste-like covering which diminished with the decreasing of DOM. When the DOM was around 10% to 8%, paste-like coverd on starch granules and wrapped tight; the picture of 6%DOM aged rice sample showed a small amount of uncovered starch granules; when the DOM reached to 2%, starch granules can be seen everywhere; Aged brown rice microstructure picture changed tiny compared with its before aging, almost can be ignored. This observation implies that the DOM of rice samples will influence the microstructure of rice during aging. And the change in microstructure of low DOM rice will be retard as compared with 10%DOM samples’.(3)The paste-like covering were gradually removed and starch particles were exposed again by the treatment of low, high concentrations of Cellulase and protease on Aged 10%DOM, noted that the paste-like coverings may be a cellulase and protease substrates.