Impact of pre-treatments and bioprocessing on the carbohydrate and polyphenol profile of brewers' spent grain

Brewers' spent grain (BSG), the solid waste of the brewing industry, is high in fibres, proteins and health- beneficial compounds such as polyphenols. This research investigated bioprocessing with enzymes and microbes to modify the properties of BSG for its utilisation as a food ingredient. Pre-treatment studies showed that wet milling performed better than dry milling, and heat and homogenisation either before or after the enzyme hydrolysis did not significantly influence the release of reducing sugars and free amino nitrogen (FAN). Four treatments were applied to wet-milled BSG: fermentation with Lactiplantibacillus plantarum POM1 with or without the enzyme Ondea pro and enzymatic bioprocessing without any fermentation. Control was the condition without enzyme and starter. Without the enzyme, there was negligible free sugar and FAN, and the starter had limited growth and organic acid production. Only the combination of enzymatic hydrolysis and fermentation reached a pH of 4 and 10 mg/g DW lactic acid. The microbial preference for monosaccharides was evident, and the enzyme influenced the release of oligosaccharides that can have a prebiotic effect. Bioprocessing impacted the phenolic acid composition and microbial consumption, with a significant release of ferulic acid during enzyme hydrolysis.