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Impact of Oxalic Acid Pretreatment on the Solubility and Fermentability of Hemicelluloses in Brewer’s Spent Grain

Aline R. Schmidt,A. Dresch,Julia Marth,Anderson Giehl,Odinei Fogolari,R. Dallago,Helen Treichel,G. M. Mibielli,S. L. Alves Jr.,J. P. Bender

Published 2025 in Industrial Biotechnology

ABSTRACT

Strong mineral acids such as sulfuric acid are still mainly used to break down carbohydrates in processes that prepare plant-based waste for further use. However, researchers are increasingly studying the use of organic acids as alternatives. This study aimed to obtain organic compounds by fermenting a hemicellulosic extract rich in simple sugars from the organic acid pretreatment of brewer’ spent grain. Hydrolysis tests using 4.5% oxalic acid for 24 minutes at 125.6°C dissolved over 99% of the hemicellulose, producing 14.9 g/L of xylose and 4.9 g/L of glucose. The production of inhibitory compounds was relatively low (0.05 g/L and 0.12 g/L of 5-hydroxymethylfurfural and furfural, respectively), which is beneficial for the yeast’s performance during the next step. The extract was then fermented by three strains of Saccharomyces cerevisiae: one industrial strain (PE-2) and two genetically modified strains (MP-P5 and JDY-01). Despite the hydrolysate containing around 45 g/L of oxalic acid, which significantly inhibited yeast activity in producing ethanol, for example, the three strains still produced several important volatile organic compounds, including 2-phenylethanol, known for its antimicrobial properties, and 4-hydroxy-2-methylacetophenone, a phenolic compound with antioxidant and antiseptic properties.

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