This study determined the optimal the mixing ratio of rice flour and natto powder by using response surface methodology (RSM). The physicochemical, mechanical, and sensory properties of the resulting sulgidduk models were measured. Significant differences were found in these models for the moisture before steaming, sugar content, color L, color a, color b, chewiness and cohesiveness as calculated by Design Expert 8. Sensory evaluation also showed significant differences in the models for the color, taste, moistness, texture and overall quality rating. The optimum formulation calculated by numerical, graphical and point prediction methods was 209.93 g of non-glutinous rice flour, 90.07 g of glutinous rice flour, and 5.18 g of natto powder.
The optimized sulgidduk with added natto powder was compared with the control sulgidduk sample. Measurement of the antioxidative characteristics showed significant differences in the total phenol content and DPPH free radical scavenging activity.
