Optimization of Microwave-assisted Extraction of Polysaccharides from the Fruiting Body of Mushrooms

Abstract

From ancient times, mushrooms have been said to have a variety of pharmacological actions and therefore to be good for our health. Since it was suggested that mushrooms had a hostmediated anticancer effect, 1) mushrooms have attracted much attention as an elixir of life. One of the active compounds was identified as a kind of polysac-charide called βglucan, 2) and many researchers have been discussing the relationships between the biological activity and the structure of βglucan. 3) Recently, roles for β glucan receptors in immunity were reported in a review. 4) The general way to extract polysaccharides from the fruiting body of mushrooms is to stir the pulverized fruit-ing bodies in hot water (about 100 C) for several hours. This procedure is very timeconsuming. We, therefore, examined the applicability of a heattreatment by microwave irradiation instead of a conventional heattreatment using a hot water bath to carry out this extraction procedure more speedily. Microwaves have direct internal heating effects on molecules by dipole rotation. 5) Therefore, by using microwaves we can heat the materials speedily and uniformly. Higher yields and cleaner reaction profiles can be realized. Furthermore, the existence of nonthermal effects (also called specific microwave effects) has been discussed. 6) Based on the merits mentioned above, microwave irradiation methods are drawing much attention in various fields as a tool of "green technology," for example , analytical and environmental chemistry, 5) organic synthesis , 7) processing of biomass resources 810) and inorganic chemistry. 11,12) Especially in the field of organic synthesis, microwave irradiation methods are making remarkable progress because of spectacular accelerations, higher yields and higher reaction selectivity. 6,13) In inorganic chemistry, synthesis of smaller nano metal particles was achieved only by using microwave irradiation. 14) In these circumstances, in recent years a heattreatment by microwave irradiation has been applied to extract a variety of materials such as bioactive saponins from chickpeas, 15) alizarin and purpurin from Rubiaceae plants, 16) ergosterol from various fungi 17) and carrageenans from seaweed. 18) All the extractions were more efficient than an extraction using ordinary external heating. But, no report that poly-saccharides from the cell wall of fungi were extracted by using microwave irradiation has been seen. The fruiting body of Hericium erinaceum is a well known edible and medicinal mushroom in oriental countries. This mushroom is called Yamabushitake in Japan, and has βglucan and other polysaccharides as components of the cell wall like many other basidiomycetes. 19,20) Recently, Yamabushitake became commercially available in Nagano Prefecture, Japan. However, the chemical properties of this mushroom have not been fully investigated. In this study, to examine an applicability of microwave irradiation for extraction of polysaccharides from the fruit-ing body of mushrooms, we investigated the effects of microwave irradiation temperature and time on solubiliza-tion of polymers including βglucan in the fruiting body of H. erinaceum. MATERIALS AND METHODS Materials. A column of YMCPack Diol120 (8 × 500 mm) was supplied by YMC Co., Ltd. Pullulans (Shodex Standard P82) used for estimation of molecular weight as the standard were obtained from Showa Denko, Co., Ltd. Abstract: Microwave irradiation in the presence of water was applied for extraction of polysaccharides from the fruiting body of Hericium erinaceum, a mushroom called Yamabushitake. In this study, the effects of microwave irradiation temperature and time on solubilization of polymers in H. erinaceum were investigated. The results indicated that the degree of solubilization of polymers proceeded with an increase in heating temperature up to 200 C, although the polymers solubilized gradually depolymerized with the increase in heating temperature. The results also suggested that lengthening irradiation time had effects on solubilization of polymers similar to the increase in heating temperature. Comparison of the results obtained by microwave-assisted extraction with those obtained by extraction using conventional external heating indicated that extrac-tability of the former extraction for 5 min at 140 C was almost equivalent to that of the latter extraction for 6 h at 100 C. This result suggests that microwave irradiation has an advantage for extraction of polysaccharides from the fruiting body of mushrooms in terms of extraction time.