Variation of Bioactive lentinan-containing preparations in Lentinula edodes strains and stored products

Lentinan, a s-(1→3)-D-glucan isolated from the common edible mushroom, Lentinula edodes (Shiitake), is a biologically active macromolecule with a potential medical application towards immune functions. The immunomodulatory activities of s-glucans depends on their degree of branching, conformation and the inter- and intra-molecular association of the polysaccharide. Up to now, there is a lack of understanding the relationship between the structure and function of lentinan and no quality controlling methods are available to analyse bioactivity of lentinan containing supplements or for the Shiitake mushrooms. Therefore, we attempted to clarify the relation between structural details and biological responses of lentinan extracts isolated from fresh and stored mushrooms. From freshly harvested fruiting bodies, the yield of crude lentinan extract varied from 260 to 825 mg/100g fresh weight. After 4 days of cold storage, the variation in crude lentinan extract content was more pronounced among the six strains analysed. As a general tendency, the yield decreased during storage with the exception of one strain for which lentinan content appeared to increase during storage. The bioactivity of the crude lentinan extracts was studied using the RAW264.7 macrophage cell line and the ability to modulate the NO production of LPS challenged. Results indicated that the crude lentinan extracts could inhibition of LPS-induced NO production but again some strains showed higher immune modulatory effects than others. Size exclusion chromatography (SEC) was applied to examine molecular weight distribution of the crude lentinan extracts. It appeared that in crude lentinan extracts of some of the strains, the polysaccharide consisted of a different conformation or modification of lentinan or contained other polysaccharides. In general, the presence and ratio of some of the different polysaccharide forms that could be distinguished by SEC analysis are correlated to in vitro bioactivity. In conclusion, our study resulted in a broader insight into structure-function relationship and the possible influences of strain, growth and storage condition on bioactivity of Shiitake lentinan. The SEC and bioactivity analyses together presented a possible direction of quality control for lentinan-containing products. The standardisation of lentinan-containing bioactive products should include the background knowledge of strain, and of growth and storage conditions of the mushroom.