Utilization of rice bran as nutrient source for fermentative lactic acid production.

To reduce nutrient cost for lactic acid production, rice bran, one of agricultural wastes, was chosen as a nutrient source in this study. Although rice bran is rich in protein and vitamins, the use of rice bran without any treatment was inefficient in lactic acid production. Rice bran was treated by acid-hydrolysis before it was put in experiment, when it was hydrolyzed at initial pH 1, 30 g/L rice bran could provide a productivity to that degree of about 8 g/L YE, showing such a desirable result that the use of rice bran as nutrient source would be a solution for reducing nutrient cost. However, the addition of hydrolyzed rice bran prolonged lag phase of fermentation, especially, in the fermentation with rice bran hydrolyzed at initial pH 0.5, a prolonged lag phase of about 40 h was observed. According to the quantitative determination of thiamine, pyridoxine, organic nitrogen and carbon, the prolongation of lag phase might be the result from the destruction of B vitamins and excessive hydrolysis of protein. To shorten the lag phase, combining hydrolyzed rice bran with yeast extract (YE) of small amount was considered to be a solution. When 3g/L YE was combined with 30 g/L rice bran hydrolyzed at initial pH 1, obtained was a productivity 1.6 times higher than that of the control fermentation with 15 g/L YE.