Steeping-induced physicochemical changes of milled waxy rice and their relation to the quality of yukwa (an oil-puffed waxy rice snack)

The influence of water-steeping periods (0 to 15 days, 25 °C) on the physicochemical properties of raw waxy rice in relation to the yukwa quality was investigated. The moisture contents in waxy rice and reducing sugar in its steeping medium were increased, while contents of protein and minerals of raw waxy rice were decreased in proportion to the water-steeping duration. With longer steeping periods, swelling power, solubility and peak viscosity were increased, while grain hardness was decreased with apparent kernel structural change. Depending on the water-steeping duration of raw waxy rice, the hardness decreased from 26.0 to 1.8 g, and the expansion ratio of yukwa increased from 762 to 1539%. Correlations between the physicochemical properties and yukwa quality indicated that variables having the most positive influential on expansion ratio were reducing sugar ((gamma) = 0.961, P < 0.01) and peak viscosity ((gamma)= 0.897, P < 0.01), and those for hardness of yukwa were crude protein ((gamma) = 0.875, P < 0.01) and hardness ((gamma)= 0.887, P < 0.01) of the steeped waxy rice. It is suggested that steeping-induced physicochemical changes of raw waxy rice had a significant influence on the final quality of yukwa in terms of hardness and expansion ratio.