Bioconversion of De-Oiled Rice Bran (DORB) Hemicellulosic Hydrolysate into Ethanol by Pichia stipitis NCM3499 under Optimized Conditions

Abstract

In the present paper, parametric optimization studies were performed to determine the most influential range of process parameters for maximum ethanol production from Pichia stipitis NCIM3499 by one-at-a-time method under submerged fermentation conditions. Various parameters, such as agitation, pH of medium, temperature and different carbon sources, etc., were taken into consideration. The optimum values of these process parameters were as follows: agitation (200 rpm), pH (5.5), temperature (30°C), and semi-aerobic conditions (150 ml fermentation media in 250 ml Erlenmeyer flask). Among the different carbon substrates tested, glucose and xylose (20±0.21 g/l) showed same ethanol production (8.8±0.35 g/l) with a yield of 0.44±0.11g/g sugar utilized. These process parameters were applied for the ethanol production from de-oiled rice bran (DORB), the left over residue after extraction of oil. It was thermochemically saccharified using sulfuric acid (0.5-5.5% v/v) at 120°C for a fixed residence time of 1h. A maximum of 38.50±0.45 g/l total reducing sugars was obtained at 3.5% v/v H2SO4. This sugar syrup was detoxified by overliming with calcium hydroxide and subsequently fermented with P. stipitis NCIM3499 under the optimized conditions. After 72 h of incubation, DORB hydrolysate (33.50±0.44g/l total reducing sugars) showed maximum ethanol production (12.47±0.26g/l) with the yield 0.42±0.021g/g and fermentation efficiency of 81.74±0.55%. To the best of our knowledge, this is the first report on ethanol production from de-oiled rice bran using P. stipitis NCIM3499.