The effect of protein on viscosity properties of Iranian rice varieties

In order to understand rice quality well، there is requirement for knowing all components of its seed and investigating their interaction. In this research، to investigate the effect of proteins on the viscosity properties، some of Iranian rice varieties including Hasan Sarai، Khazar، Dorfak، Binam، Hashemi were selected. Using extraction by dilute alkali، protein content deleted and then viscosity of extracted starch was compared with its properties before extraction. The result showed viscosity properties that changes in cooking temperature including Peak (maximum viscosity during heating the sample)، Trough، Final viscosity، Breakdown، Setback، Pasting temperature and pasting time. With rising the temperature due to absorption of water by the starch granules and protein، viscosity properties will increase. The effect of protein on all characteristics was significant at the 1% level except the maximum viscosity however the combined effects of protein and genotype was significant for all traits. The greatest impact of protein on the minimum viscosity was observed in Binam (+119. 16) and the lowest was observed in Khazar (+14. 64). When the sample is cooled during a period time، final viscosity again increases and at the end of test، final viscosity is recorded. Protein Removal from sample decreased the amount of final viscosity and the most influence was observed in Hashemi (+ 99. 25). The rate of setback is changes which occur upon cooling or of gelatinized starch. Effect of protein on setback of obtained gel was significant in all varieties and the most and the lowest effect recorded respectively in Khazar (+ 95. 15) and Hasan Sarai (+23. 87). Also، the effect of protein on the trough was negative in all varieties. With protein removal، viscosity curve will rise in less time. Actually، protein in rice grain، postpones emergence of gelatinization properties and subsequently increases required time for cooking. Different pasting rates for every variety with the same amylose content، implies involvement of proteins in this case. So، although starch has been known as the most important factor in rice quality، protein can also be considered as a measure of influence.