Quantification of rice and black gram dal proportions in idli batters by estimation of starch, daidzein and trypsin inhibitor activity

The traditionally used proportion of 3:1 (rice: black gram dal, g/g) of ready-made wet idli batters available in the Indian market, might be altered due to a large price difference between rice and dal. In this work, differences between starch, daidzein and trypsin inhibitor activity (TIA) of rice and dal have been utilized to quantify their proportions in idli batters. Starch (R2 = 0.980) and daidzein (R2 = 0.999) served as reliable indicators for quantification of rice and dal ratio in unfermented batters while TIA could be used for both unfermented (R2 = 0.996) and fermented batters (R2 = 0.995). Different varieties of rice and dal were used for making batters, to study varietal influence on these constituents. For unfermented batter, starch content increased from 62 to 89 g/100 g batter as rice proportion increased. Daidzein content reduced from 2.6 to 2.0 mg/100 g batter in unfermented batter while TIA of batter decreased from ∼3.0 to ∼1.4 U/g sample with decreased dal proportion. Robustness of the methods was successfully validated on coded samples and analysis of locally sold idli batters using these parameters indicated the proportion of rice and dal to be in the range of 2:1 to 5:1.