Effect of freezing and hot water soaking on the functional properties of rice flour derived from four Sri Lankan traditional rice varieties

Abstract

Rice cultivation nowadays has become as major concern to Sri Lanka due to high dependency of chemical fertilizers. There is an interest to promote utilization of rice obtained from traditional rice varieties which are well adopted to Sri Lankan environmental conditions, such varieties are highly nutritious and less dependent on agrochemicals. Thus they are ideal candidates in promoting organic food products without chemical inputs. Rice flour is a good substitute for imported wheat flour in bakery industry. However due to lack of gluten protein, rice flour cannot be used directly in bakery products without any modifications. In this study rice grains derived from four traditional rice varieties namely Madathuwalu, Kaluhenati, Pachaperumal and Ratdal were subjected to freezing at -20oC (24 hours and 48 hours), hot water soaking at 80oC (5 minutes and 10 minutes) individually and in dual combinations. Untreated rice flour served as the control and experiments were conducted in triplicates. Water Absorption Index (WAI), Water Solubility (WS), Swelling Power (SP) and pH values were measured in both treated and untreated rice flour. Results showed that these physical treatments to the rice grains brings about a significant difference (p< 0.05) on the functional properties of rice flour both individual and in dual combinations. Strong correlation (p=0.000) was obtained between WAI and SP. Dual modification treatments were found to be highly effective in improving functional properties of all selected traditional rice varieties compared to the single modification. Freezing at -20oC for 48 hours was more effective than the 24 hours freezing to improve the functional properties. Therefore, this study proves that simple physical treatment methods such as freezing and hot water soaking could bring about a significant effect on the functional properties of traditional rice flour.