Dhokla, a popular indigenous savoury dish of India, is prepared by soaking bengalgram dal and rice, grinding separately, mixing the batters, and spontaneously fermenting and steaming of mixed batter. Central composite rotatable response surface designs for soaking, fermentation and steaming at five-level combinations were used for optimising preparation of dhokla to achieve reduced contents of antinutrients. Optimum soaking of bengalgram dal (dal-water ratio of 1:5 w/w, pH 7.0, 23 °C, 20 h) and rice (rice-water ratio of 1:5 w/w, pH 5.6, 16 °C, 18 h) resulted in reduced levels of all the antinutrients, except total biogenic amines in rice. Fermentation of dal-rice (3:1 v/v) mixed batter under optimum condition (added NaCl of 8 g/kg, 32 °C, 18 h) further reduced their levels, but total biogenic amines content was enhanced. However, optimum steaming of dal-rice mixed fermented batter for 20 min was effective in reducing all the tested antinutrients. In dhokla, the content of tannins, phytic acid and total biogenic amines reduced by 100, 94 and 20%, respectively; trypsin inhibitor and haemagglutinating activities reduced by 92 and 100%, respectively, over raw ingredients. The optimally prepared product (dhokla) ranked "excellent" in terms of overall sensory quality.
Keywords: Antinutrient; Bengalgram; Dhokla; Process optimisation; Response surface methodology; Rice.