Combining UV Irradiation and Alkaline Deacetylation to Obtain Vitamin D- and Chitosan-Enriched Fractions from Shiitake Mushrooms (Lentinula edodes)

Abstract

Shiitake mushrooms (Lentinula edodes) contain compounds with hypocholesterolemic and immune-modulatory activities such as ergosterol and chitin that can be partially transformed into vitamin D and chitosan to yield extracts with enhanced bioactivities. A method was optimized to increase vitamin D2 levels by irradiating a non-soluble fraction obtained from shiitake mushrooms during 1 h with UV-light (254 nm) at 50 °C in methanol. After 1 h, almost all of the ergosterol was transformed into vitamin D2. The conversion ratio can be simply adjusted by reducing the irradiation time. A deacetylation treatment with 50% NaOH for 24 h at 95 °C was needed to generate chitosan and other water-soluble lower molecular weight derivatives from chitin. To obtain an extract enriched in both compounds, the defined methods can be combined, but the extracts should be firstly deacetylated and later irradiated. In this order, an extract is obtained containing vitamin D2 (4.65 mg/g) and chitosan (2.83%).