Effects of Microwave Irradiation on Water-soluble Polysaccharides of the Fruiting Body of Hericium erinaceum

Abstract

Several polysaccharides have been isolated from the fruiting body of Hericium erinaceum (Yamabushitake) by hot water extraction and their structures have been investigated: fucogalactan containing 3Omethyl rhamnose (Zhang et al. 1)), rhamnoglucogalactan (Jia et al. 2)), and ga-lactan and (16)βDglucan (Wang et al. 3)). Previously we extracted polysaccharides from the fruiting body of H. erinaceum by microwave irradiation in water. 4) The duration of time necessary to obtain water extractable polysac-charides from the fruiting body of H. erinaceum could be reduced to about 170 by applying microwave irradiation. The amounts of materials including carbohydrates extracted by microwave irradiation in water (140 C, 5 min) and their molecular weight distributions were similar to those of the extracted materials obtained by conventional extraction using a hot water bath (100 C, 6 h). Thorough chemical analysis, however, indicated presence of a slight difference in monosaccharide compositions of the polysac-charides extracted by the two different methods. Since βglucan included in mushrooms has been reported to have a variety of physiologically important bio-activities such as antitumor activity and immunomodulat-ing activity, much attention has been focused on this type polysaccharide. 5) This study was intended to further investigate the structure of polysaccharides extracted by microwave irradiation in water in comparison with polysaccharides extracted by conventional external heating used as reference materials, in an effort to improve extractability of βglucan from H. erinaceum. MATERIALS AND METHODS Materials. Columns of YMCPack Diol120 and Diol 300 (8 × 500 mm) were supplied by YMC Co., Ltd. Standard pullulans (Shodex Standard P82) used for estimation of molecular weight were obtained from Showa Denko, K.K. Pustulan and curdlan were obtained from CALBIO-CHEM, Merck Ltd. and Wako Pure Chemical Ind., Ltd., respectively. All reagents used were analytical reagent grade. Pulverized fruiting bodies of Hericium erinaceum (Yamabushitake) were supplied by Saishin, Co., Ltd. in Nagano Prefecture, Japan, and used as the original dried fruiting body for calculation of the yields of the separated materials. Before use, the raw materials were ovendried for more than 48 h at 40 C, delipidated by extraction with acetone for 31 h at room temperature and extracted with 80% aqueous ethanol for 31 h at room temperature to remove lowmolecularweight constituents such as oligosac-charides and peptides, as described previously. 4) The residue (R1), obtained in a yield of 58.8% on the basis of original dried fruiting body, was used for this study. Extraction of polysaccharides by using microwave irradiation in water. The equipment for microwave irradiation was the same that used in the previous paper. 4) Two grams of the residue R1 were soaked in 30 mL of distilled water placed in a closed high pressure TFM TM vessel. Then the vessel containing the sample and a magnetic stirrer was settled inside the microwave oven, and subjected to microwave irradiation under stirring. Duration of time before attaining 140 C was set for 2 min and this temperature was maintained for 5 min. After irradiation , the vessel was cooled to room temperature in an ice bath before opening. The solubilized materials were recovered by filtration, and the filtrates were evaporated to Abstract: To examine the applicability of microwave irradiation for the extraction of polysaccharides in the fruiting body of Hericium erinaceum, structures of polysaccharides obtained by microwave irradiation in water were compared to those obtained by hot water extraction using conventional external heating. A major polysaccharide obtained by microwave irradiation in water (140 C, 5 min) was (13;16)-β-Dglucan rich in (13) linkages, whereas polysaccharides obtained by hot water extraction using conventional external heating (100 C, 6 h) were fucogalactan and (13;16)-β-Dglucan rich in (16) linkages. In the case of microwave irradiation in water, fucogalactan was suggested to be depolymerized during heating. Microwave heating in water has an advantage over the conventional external heating for extraction of β-glucan rich in (13) linkages from the fruiting body of H. erinaceum.