Screening of Lentinula edodes Strains for High Polysaccharide Productions and In Vitro Antioxidant Activities

Lentinan is one of the main metabolites of Lentinula edodes, and exhibits numerous biological activities such as anti-tumor and antioxidant. 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 19 L. edodes 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, which was 1.82 times higher than that of the main cultivated strain Xin808 (43.3 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 were, respectively. Further analyses on polysaccharide components, molecular weight, and enzyme activities were conducted on strains XG19, XG21 and Xin808. The results revealed that the polysaccharide from strain XG19 exhibited a 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. Similarly, the extracellular uronic acid content (8.26%) was 1.02 and 1.04 times higher than that of Xin808 and XG21, and its Mw (83.894 kDa) was 1.05 and 1.56 times greater than that of Xin808 and 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 materials for the screening of mycelial polysaccharides with high yields and bioactivities.