Subcritical water extraction of shiitake (Lentinula edodes) and characterization of its components

In this study, polysaccharides in Shiitake (Lentinula edodes) mushroom were extracted by hot water under atmospheric pressure and by subcritical water at a constant pressure of 280 bar (4060 psi) in CO2 atmosphere. Subcritical water extractions were carried out at three different temperatures (50ºC, 100ºC and 150ºC) at 280 bar constant pressure. Molecular weight characterization of the polysaccharides were measured using high performance size-exclusion chromatography-multi angle light scattering system (HPSEC-MALLS). Two main peaks called, Fraction I and II were determined. Weight average molecular weight (Mw) of Fraction I obtained in hot water extraction was found to be 1.333x107 Da. Mw value of Fraction I was sharply decreased in all subcritical water extracts. These values were 1.644x106, 1.114x106, and 8.37x105 Da for 50ºC, 100ºC and 150ºC, respectively. On the other hand, Fraction II from hot water extraction had 1.282x106 Da molecular weight and Fraction II of subcritical water extracts had 4.118x104, 5.682x104, and 3.374x104 Da for 50ºC, 100ºC and 150ºC, respectively. Solubility tests showed that all subcritical water extracts were completely soluble in both neutral and alkali medium while hot water extracts left 26.60% and 8.46% insoluble residues in neutral and alkali, respectively. HPSEC analysis at 280 nm UV dedector and Lowry protein assay results showed that hot water extract of Shiitake contained 6.49% of protein. The polysaccharide-protein complex was treated with protease enzyme for 24 and 48 h to identify the actual molecular weights of polysaccharide. The results of monosaccharide analysis in HPLC showed that polysaccharides of Shiitake composed of mainly glucose and and some of amount of mannose. Keywords: Lentinula edodes (Shiitake), subcritical water extraction, polysaccharide, molecular weight distrubition