Enzymatic Mechanism of a β-Glucosidase from <i>Lactiplantibacillus plantarum</i> Dy-1 with Potential Applications in the Release of Bound Phenolics in Fermentation Barley

In whole grains, phenolics are covalently bound to cell-wall dietary fibers, forming nonextractable bound phenolics. Enhancing the release of bound phenolics has garnered significant attention to improve the nutritional value of whole grains. Our findings revealed that fermentation of raw barley dietary fiber with <i>Lactiplantibacillus plantarum</i> dy-1 led to a decrease of 2408.69 μg/g in bound phenolics. We identified a 6-phospho-β-glucosidase responsible for this process through proteomic analysis, which was increased more than 4 times during fermentation with <i>Lactiplantibacillus plantarum</i> dy-1 and conducted a heterologous expression of this 6-phospho-β-glucosidase gene (LPBG). Enzymatic hydrolysis with LPBG led to a decrease of 1707.35 μg/g of bound phenolics. LPBG-mediated enzymatic hydrolysis altered the surface microstructure, monosaccharide composition, functional groups, and chemical bonds in the dietary fiber. This study demonstrates that the 6-phospho-β-glucosidase LPBG from <i>Lactiplantibacillus plantarum</i> dy-1 plays a pivotal role in the release of bound phenolic acids during barley fermentation.