Screening of <i>Lentinula edodes</i> Strains for High Polysaccharide Production and In Vitro Antioxidant Activities

Lentinan is one of the main metabolites of <i>Lentinula edodes</i> and exhibits numerous biological properties, such as antitumor and antioxidant activity. Despite recent advancements, its commercialization remains constrained by a lengthy cultivation cycle, low yield, and high cost. Therefore, screening strains with high polysaccharide production or enhanced bioactivity at the mycelial fermentation stage is of significant importance. In this study, the mycelial polysaccharide content and in vitro antioxidant activity of 18 <i>L. edodes</i> strains were evaluated under shaking and static culture conditions. The total polysaccharide content and IC₅₀ values under both culture conditions served as indicators for screening high-yielding and high in vitro antioxidant activity strains. Strain XG21 demonstrated superior polysaccharide production, with a total polysaccharide content of 78.80 mg in 50 mL of culture medium, which was 1.82 times higher than that of the main cultivated strain Xin808 (43.30 mg). Additionally, strain XG19 was identified for its high in vitro antioxidant activity, with total IC₅₀ values of 3.11 and 3.38 mg mL⁻¹ under shaking and static culture conditions, respectively. Further analyses on polysaccharide components, molecular weight, and enzyme activities were conducted on strains XG19, XG21, and Xin808. The results reveal that the polysaccharide from strain XG19 exhibited high uronic acid content and a significant weight-average molecular weight. Specifically, the intracellular polysaccharide uronic acid content (2.96%) was 2.22 and 1.14 times higher than that of Xin808 and XG21, respectively, while its weight-average molecular weight (Mw, 702.924 kDa) was 2.60 and 1.28 times greater than that of Xin808 and XG21. While the uronic acid content in its extracellular polysaccharides (EPSs) (8.26%) was similar to Xin808 and XG21, the Mw (83.894 kDa) was 1.56 times greater than that of XG21. Correlation analysis revealed that the content of extracellular polysaccharides and total polysaccharides was positively correlated with phosphoglucose isomerase (PGI) activity but negatively correlated with phosphoglucomutase (PGM) activity. These findings provide valuable strain information for the screening of mycelial polysaccharides with high yields and bioactivities.