Soybean hull valorization for sugar production through the optimization of citric acid pretreatment and enzymatic hydrolysis

Abstract

Soybean hull is a worldwide produced lignocellulosic waste from the soybean industrial sector. Its exploration through biotechnological approaches could increment considerably the value and economic return of soybean production-chain. The present study evaluated a citric acid pretreatment, an organic acid with eco-friendly characteristics and low inhibitors generation, in the valorization of soybean hull for fermentable sugars recovery. The optimized condition through response surface methodology was 4.2 % (w:w) citric acid, LSR of 5, 105 min, and 120 ºC, with 80.42 % of mass yield and a very high recovery of cellulose fraction. Subsequent enzymatic hydrolysis was evaluated varying solid contents (10–20 %) and enzyme loading (10–20 FPU/g), reaching 72.28–97.10 % enzymatic conversions and 36.52–72.03 g/L glucose final titers. Final proposed process resulted in high enzymatic conversion of 82.86 %, with glucose and xylose final titers of 72.03 and 31.13 g/L, respectively. Citric acid pretreatment has shown to be effective to improve soybean hull conversion into sugars, resulting in a process that can be potential applied in further fermentation processes for the production of biomolecules in a biorefinery context.