.BETA.-Glucans in the Water-insoluble Residue of Hericium erinaceum

Abstract

Fruiting bodies of Basidiomycetes mushrooms have been attracted increasing attention of pharmaceutical and functional food industry because of their health promotion and disease alleviation effects on human health. 1) On account of bioactive and medicinal activities, immune stimulation, antiinflammatory antimicrobial, antitumoral, hepatoprotective, cholesterollowering properties are representative as well as antifibrotic, antidiabetic and hypogly-cemic activities. 26) The origin of these effects are best known to be derived from polysaccharides belonging to βglucans. Recently, the importance of βglucans contained in the mushrooms was reviewed by several authors. 1,7) The fruiting body of Hericium erinaceum called Yamabushitake in Japan is growing much attention as a source of βglucans based on recent success of commercial availability. Mizuno et al. reported that βglucan from H. erinaceum had antitumor activity. 8) We are, therefore , interested about βglucans in H. erinaceum and previously reported about extractability of βglucans from its pulverized fruiting body by using microwave heating in water. 9) The results showed that only 22.0% of βglucans were extracted by this treatment. The reason of this low extractability of βglucans may be due to their complex distribution in cell wall. In the case of Schizophyllum commune, three types of glucan were present in the multilayered cell walls; (1 3)βDglucan with branches of single glucose units attached by (16) linkages in the outer layer, (13)αD glucan in the middle layer and covalently linked chitin (13;16)βDglucan complex in the inner layer. 10) In the case of Hericium erinaceum, so far Wang et al. extracted (16)βDglucan having (13) branch points with hot water. 11) Dong et al. extracted (13)βDglucan with single glucosyl branch substituted at O6 for every third backbone residue with alkaline solution. 12) Our previous results further showed the presence of watersoluble (13;16)βDglucan extractable by microwave irradiation in water 9) and alkalisoluble (13;16)βDglucan having (16) linked branch points at every five (13) linked glucose residues. 13) Use of alkali was shown to be effective for extraction of glucans amounting to 42.3% of the total quantity in H. erinaceum. However, since substantial amount (35.7%) of glucan is still remained in the alkaliextracted residue, development of method for extraction of whole βglucans and characterization of their chemical structures are necessary for utilization of H. eri-naceum as an origin of βglucans in future. In this study, an effective procedure to extract βglucan from the residue given after microwave irradiation in water was developed by stepwise treatments with alkali, enzymemicrowave irradiation followed by reextraction with alkali, taking the multilayered cellwall structure into consideration. In addition, since alkali split hydrogen bonds connecting mainly hydroxyl groups in the cell wall of H. eri-naceum to solubilize βglucans, urea which was known as a strong hydrogen bond disrupting reagent 14) could be used as an extraction reagent alternative to alkali. Therefore we tried to use 8 M urea as an extraction solvent for βglucan and structure of the extracted material was compared to that of alkaliextracted materia1, in order to get information of the state of alkalisoluble βglucan in the cell wall of H. erinaceum. MATERIALS AND METHODS Materials. Pulverized fruiting bodies of Hericium eri-naceum (FERMP19600) were supplied from Saishin, Co., Ltd. in Nagano Prefecture, Japan. 13) Fruiting bodies developed by cultivation of mycelia on sawdustbased medium at 1820 C for 2030 days followed by incubation at 1012 C with 90% humidity. Before use, the raw mate-Abstract: Totally 92.7% of glucan present in the fruiting body of H. erinaceum could be solubilized. Of this value, 42.3, 17.7 and 10.7% were extractable by alkali, enzyme, second alkali treatments, respectively, from the residue given after microwave irradiation in water. The remained 22.0% were water-soluble (13; 16)-β-D-glucan extractable by microwave irradiation in water (Ookushi et al.: J. Appl. Glycosci., 53, 267 272 (2006)). Sugar linkage analysis of the glucan extracted from the water-insoluble residue indicated the presence of three distribution profiles of (13;16)-β-D-glucan in the water-insoluble residue; (13;16)-β-D-glucan rich in (13) linkages forming heavily hydrogen bonded networks, (13;16)-β-D-glucan rich in (16) linkages forming complex networks with protein and chitin, and (13;16)-β-D-glucan rich in (13) linkages forming complex networks with protein and chitin.