A combination of chemical and physical pretreatments in the saccharification of malt bagasse: the effects of ultrasonication in diluted acid medium

Abstract

Malt bagasse is a lignocellulosic byproduct of the brewery industry and is rich in fibers and proteins. It is produced in abundance and can be reused as a substrate to obtain fermentable sugars. However, to obtain an efficient enzymatic saccharification, pretreatments must be used. The objective of this study was to evaluate the combination of ultrasonication in diluted acid medium as a pretreatment of lignocellulosic biomass to obtain fermentable sugars and residual solid fractions with increased susceptibility to enzymatic hydrolysis. The residual solid fractions were characterized according to their composition, morphology, crystallinity, and thermal stability. Malt bagasse was submitted to different pH values (3–5), ultrasonication times (10–60 min), and biomass contents (6–10%, w/v). The effect of the time was the most important variable; more time resulted in higher sugar release and greater changes in the residual solid fraction recovered after pretreatment. In general, the residual solid fractions of pretreated samples demonstrated a higher crystallinity index and thermal stability than raw malt bagasse. The sample processed at pH 5 for 60 min with a biomass concentration of 8% resulted in the highest cellulose content and lowest lignin content. In this study, the use of acid hydrolysis combined with ultrasonication decreased the time required for the maximum hydrolysis efficiency when compared with literature data, and it was which is an interesting result considering an economical point of view; however, future studies should be conducted with the aim of reducing the process times and energy costs.