Co-Production of Protein Hydrolysates and 2,3-Butanediol from Brewer’s Spent Grain

Abstract

Brewer’s spent grain (BSG) is the major byproduct of the brewing industry. Although BSG contains 20–30% protein, the high fiber content (50–70%) makes it difficult to be used as a food ingredient. Therefore, BSG is used as a low-value ruminant feed or buried in landfills, causing substantial resource losses. In this study, an integrated process was developed to produce protein hydrolysates and 2,3-butanediol (2,3-BDO) from BSG, aiming to holistically utilize BSG with minimal secondary waste generation. BSG was first subjected to enzyme-assisted fractionation to separate protein from fiber residues. The fiber residue was then pretreated and hydrolyzed to obtain sugars. Finally, sugars were fermented to 2,3-BDO by the newly isolated thermophilic and alkaliphilic Bacillus licheniformis YNP5-TSU. The integrated process could be used to recover over 80% of protein from BSG to produce protein hydrolysates with a high protein concentration of 41.4%. Released sugars from the pretreatment and hydrolysis of fiber residues can be fermented to 2,3-BDO with a high yield (0.39–0.49 g/g sugar) under both sterile and non-sterile conditions. Based on the mass balance, the optimized process can valorize 1 kg of dry BSG by converting it into 437.6 g of protein hydrolysates and 126.3 g of 2,3-BDO.

Highly efficient production of 2,3-butanediol from xylose and glucose by newly isolated thermotolerant Cronobacter sakazakii

“…Moreover, this strain was able to produce the compound from both sugars at high temperatures. Fermentation experiments with other microbes were carried out at temperatures of 30 ˚C to 37 ˚C, except for Bacillus licheniformis YNP5-TSU [25]. Recently, the production of 2,3-BD by P. polymyxa DSM 742 has been reported, and the titer of 2,3-BD was 10.57 g/l (0.26 g/g) at 30 ˚C for 40 h in a medium containing 30 g/l glucose [26].…”