Abstract
The aim of this study was to optimize the enzymatic hydrolysis of defatted rice bran (DRB) for release fermentable sugars with subsequent bioethanol production. Optimization of enzymatic hydrolysis was achieved using a sequential experimental design, performing a fractional factorial design (FFD) followed by two Central Composite Rotatable Designs (CCRDs). The optimization was achieved under the conditions of 200 g L -1 of DRB concentration, 30 μL of α-amylase g -1 of DRB and 40 μL g -1 of amyloglucosidase (AMG), at action times of two and three hours, respectively. In bioethanol production, it was evaluated the effect of adding of 15 μL g -1 of protease prior to the action of amylases. Fermentation was conducted at 29°C, with 4.0% Saccharomyces cerevisiae and initial pH of 5.0. The hydrolysis with protease yielded 3.55% ethanol, an increase of 115.15% in relation to the medium without protease addition, and the conversion had a yield of 101.5% in 24h of alcoholic fermentation. This study demonstrates the possibility to obtain bioethanol from DRB.
Highlights
Defatted rice bran (DRB) is an important byproduct obtained by processing of polished rice
The starch hydrolysis is initiated by the starch liquefaction in the water and subsequent action of the α-amylase enzyme which randomly cleaves the α1,4 bonds of polysaccharides dispersed in aqueous medium
In the responses of fractional factorial design (FFD), the lowest value observed of reducing sugars (RS) was 13.95% (g 100 g-1) in run 9, where only the action time of α-amylase was at a higher level within the range studied
Summary
Defatted rice bran (DRB) is an important byproduct obtained by processing of polished rice. The processing of white rice results in several by-products such as bran, that is high in protein, fat, carbohydrate, and a number of micronutrients such as vitamins, minerals, antioxidants, and phytosterols (Schramm, Abadie, Hua, Xu, & Lima, 2007; Shirakawa, Koseki, Ohinata, Hazhizume, & Komai, 2006; Loypimai, Moonggarm, & Chottanom, 2009; Bhatnagar, Prabhakar, Prasanth, Rajan, & Gopala Krishna, 2014; Wang et al, 2015). The chemical composition and nutritional quality of rice grains vary considerably because of genetic factors, environmental influences, fertilizer treatment, grinding and storage conditions (Amissah, Ellis, Oduro, & Manful, 2003). Amissah et al (2003) observed that the concentration of carbohydrate in 16 varieties of rice bran ranged from 26 to 46%, which was confirmed in a study by Moongngarm, Daomukdaa and.
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