Release of sugar by acid hydrolysis from rice bran for single cell oil production and subsequent in-situ transesterification for biodiesel preparation

Abstract

Biodiesel is one of the promising alternative biofuel to petro-diesel. Efficient and effective utilization of low value feedstock is required to meet the current demand on biodiesel. Rice bran is a byproduct of rice milling that contains significant amounts of sugar (~ 48%) and lipids (~ 14%). Immediate recovery of the lipids is uneconomical owing to its moderate lipid content. In this work, hydrolysis of raw rice bran was firstly carried out to concentrate lipids in the hydrolyzed bran to ~ 42%. Hydrolysis of rice bran using 2% sulfuric acid at 90 °C for 3.5 h with stirring at 300 rpm resulted in hydrolysates containing ~ 41 g/L sugars and 3.75 g/L proteins. Rice bran hydrolysate (RBH) obtained was further utilized as growth media for Lipomyces starkeyi, an oleaginous yeast. Lipid content of 40 to 65% can be achieved, suggesting the potential of using RBH in single cell oil production. Composition of microbial oils obtained was similar to that of vegetable oils, which may potentially be adopted as a feedstock for biodiesel production. Furthermore, dried hydrolyzed rice bran was subjected to in-situ (trans)esterification with methanol under subcritical condition which resulted in high FAME yield (87.81%) and conversion (94.82%). This work demonstrated the maximized utilization of rice bran in the production of hydrolysate for fermentation and as biodiesel feedstock. This is to further support the use of direct acid hydrolysis of biomass in the recovery and use of its content of sugars and lipids.