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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