A low-cost process for efficient hydrolysis of deoiled rice bran and ethanol production using an inhouse produced multi-enzyme preparation from Aspergillus niger P-19

The study deals with the management of deoiled rice bran by converting it into ethanol using a multi-enzyme preparation produced in-house on the same substrate. The thermo-acidic treatment with 1% H₂SO₄ released the highest reducing sugars amounting to 368 mg/g dry substrate (gds) upon enzymatic hydrolysis of pretreated mash, with 25% substrate loading, using multi-enzyme preparation from Aspergillus niger P-19. Steam pretreatment at 15 psi (pound-force per square inch) for 15 min yielding 356 mg/gds of reducing sugars was the best in terms of alcohol productivity (23 g/l) from the released sugars. The sugar yields were further improved to 468 mg/gds (117 g/l) of reducing sugars revealing 95.41% carbohydrate conversion efficiency and 370 mg/gds (92 g/l) of glucose using the statistical tool of response surface methodology for optimization of thermal pretreatment and enzymatic hydrolysis of deoiled rice bran. Upon fermentation with Saccharomyces cerevisiae, the sugars produced 37.63 g/l of ethanol with a yield of 0.41 g/g of sugars utilized. Thus, deoiled rice bran, a rich source of different carbohydrates, was effectively pretreated and enzymatically hydrolyzed to extract maximum sugars for conversion into bioethanol and the study thus holds the potential for validation at a pilot scale.