Enzymatic hydrolysis and fermentation of soy flour to produce ethanol and soy protein concentrate with increased polyphenols

Abstract

AbstractThere is a need to effectively concentrate soy protein from defatted soy flour (DSF) while simultaneously valorizing the carbohydrate‐rich byproduct, which would otherwise be a waste. This study aims to evaluate a process developed to produce soy protein concentrates (SPC) by substantially hydrolyzing carbohydrates from DSF with the help of enzymes into water‐soluble saccharides and monomeric sugars, which were simultaneously utilized by Saccharomyces cerevisiae for fermentation into ethanol. The enzyme mixture consisted of cellulase, pectinase, and ‐galactosidase blend. The effect of process time on SPC, overall protein recovery, carbohydrate hydrolysis, yeast growth, ethanol concentration, and total polyphenol concentration (TPC) of SPC and hydrolysate was evaluated. Control and enzymes‐only (EO) systems were maintained in conjunction with the enzymes + yeast (EY) system to individually assess the impact of isoelectric precipitation of soy proteins and enzymatic hydrolysis of carbohydrates without yeasts. After 12.25 h of EY process, 100 g of dry DSF produced 68.45 g dry SPC containing % protein and 384 ml hydrolysate containing mg/ml ethanol. Flatulence‐causing raffinose‐series‐oligosaccharides (RSOs) were completely hydrolyzed. Soluble carbohydrates in the EY treatment were consistently lower than in the control and EO treatment. TPC of SPC prepared by EY treatment increased by 2.5 times compared to the control. Thus, this novel process successfully produced a high‐protein SPC with hydrolyzed RSOs, lower insoluble carbohydrates, high TPC, and a coproduct ethanol.