Accumulation of Water-Soluble Polysaccharides during Lychee Pulp Fermentation with <i>Lactiplantibacillus plantarum</i> Involves Endoglucanase Expression

In the current work, lychee pulp was subjected to <i>Lactiplantibacillus plantarum</i> ATCC 14917 fermentation, leading to a substantial increase (2.32-2.67-fold) in water-soluble polysaccharides (WSP). Concurrently, a significant degradation occurred in water-insoluble polysaccharides (WISP) composed of glucose (28.73%), arabinose (28.25%), galacturonic acid (25.07%), and galactose (11.00%). To clarify polysaccharide conversion and its relevant mechanism, carbohydrate-active enzyme encoding sequences in the <i>L. plantarum</i> ATCC 14917 genome and structural alterations of two polysaccharide fractions were dissected. By integrating the transcriptional assay, prokaryotic expression, and enzymic hydrolysis, three endoglucanases were demonstrated to catalyze WISP degradation, leading to WSP accumulation during lychee pulp fermentation with <i>L. plantarum</i> ATCC 14917. Reductions in proportions of galactose and galacturonic acid in WSPs were partly attributed to the actions of multiple galactosidases. These findings provide an enzyme-based explanation for WSP accumulation during <i>Lactobacillus</i> fermentation and serve as a practical foundation for directional polysaccharide conversion.