Effect of processing and soybean cultivar on natto quality using response surface methodology

In an attempt to commercialize the traditional technology of fermenting soybean into natto on laboratory scale using three locally available soybean varieties, that is, white, black, and brown, response surface methodology (RSM) was used to determine the optimum combination of two factors, that is, the effect of steaming time (20–50 min) and fermentation time (12–48 hr). Thirteen samples from each variety were formulated which were packed in low‐density polyethylene for LDPE using the isolated culture from the natto sample and incubated at 37°C, and the sensory data were analyzed by using Design Expert (RSM). All the responses (taste, hardness, thread/stickiness, and overall acceptance) were significantly (p < 0.05) affected by the two variables except appearance for all three varieties of natto prepared. The optimum combinations of steaming time (min) and fermentation time (hr) were found for white soybean natto (33.4 min and 34.5 hr), for black soybean natto (34.7 min and 30.9 hr), and for brown soybean natto (33.2 min and 34.9 hr), respectively. The proximate composition of soybean and best three formulated natto obtained after sensory evaluation from 13 samples of each variety were studied, that is, moisture, crude protein, pH, calcium, and iron on dry basis found to have increased, whereas carbohydrate and crude fiber found to have slightly decreased, but crude fat and ash found to be almost equal on three varieties than the raw soybean used. Microbiologically, the product was hygienic and safe as coliform and salmonella were not detected.