Valorization of damaged rice grains: Optimization of bioethanol production by waste brewer’s yeast using an amylolytic potential from the Paenibacillus chitinolyticus CKS1

Abstract

Damaged grains that are not useful for food or feed are abundant and cheap. The main objective of this paper was to valorize damaged rice grains for bioethanol production using presacchararification step followed by simultaneous saccharification and fermentation (SSF) by using waste brewer’s yeast. Presacchararification step was carried out using crude amylases that produce naturale isolate Paenibacillus chitinolyticus CKS1. Maltose, a fermentable sugar, was the main product during presaccharification. Statistical design, central composite design (CCD), was used for optimization of process parameters for ethanol production, yeast cell yield and utilized sugars. Under optimal conditions 0.5% malt extract, 3.84% inoculum and 2.76 days of fermentation maximum ethanol production of 4.69% was achieved. The obtained ethanol concentration was in a good correlation with yeast cell yield and utilized reducing sugars. The results obtained in this study indicate that the economical production of ethanol could be achieved using cheap waste materials also using low cost enzymes derivated from natural bacterial isolates.