Processing wheat bran into ethanol using mild treatments and highly fermentative yeasts

Wheat bran, low-cost residue of the milling industry, is an interesting substrate for ethanol production. This study reports on the pre-treatment of wheat bran for high hexose and pentose recovery in the following enzymatic hydrolysis step using optimised dosages of commercial enzymes. Acid addition, milling and heat treatment were compared in terms of total sugar yield and inhibitory by-product release. The maximum total sugar amount was obtained when limited concentrations of acid were added to milled bran at the pre-treatment step. The whole unfiltered hydrolysates were fermented by highly fermentative wild type yeasts. A glucose-to-ethanol conversion of 95% was attained by Saccharomyces cerevisiae s1, while Saccharomyces diastaticus ATCC 13007 proved effective for the secretion of extracellular glucoamylase resulting in additional ethanol production.