Optimization of soaking condition of blackgram to minimize flatogenic sugar content in blackgram-based products

Raffinose family oligosaccharides (RFOs), comprising 41.7 g/kg blackgram dal (dry wt basis), are important antinutritional factors. In this study, response surface methodology was used to optimize the soaking conditions of blackgram dal in order to reduce these flatogenic sugars. A central composite rotatable design was used to study the effect of four separate soaking parameters. The optimum soaking condition obtained was: bean-water ratio of 1:10, and soaking temperature, time and pH being 16 °C, 21 h and 6.0, respectively, in which the total RFO content predicted in soaked dal was 1.97 g/kg (dry wt basis). The experimentally obtained value was 2.02 g/kg (95.16% reduction over raw dal). Lack of significant difference between the experimental and predicted values validates accuracy of the model. While fermentation of mixed batter prepared by using traditionally soaked dal led to 57.35% decrease in the total RFO content, that prepared by using optimally soaked dal reduced the contents of each of the RFOs below their respective limits of detection (decrease of total RFOs by >93.85%). Steaming of the fermented batter for 15 min had no significant effect on the RFO content.