In recent years, demand for gelling agents has expanded due to diversifying food preferences and growing health consciousness. However, the supply of these gelling agents has become unstable due to factors such as climate change and exchange rate fluctuations. Therefore, the development of new gelling agents derived from novel food ingredients is required. The polysaccharide β-1,3-1,6-glucan found in mushrooms has potential as a new gelling agent, and its rheological properties have been studied for various mushroom species. However, previous studies have only suggested gel-forming ability without confirming “true gel” formation. In this study, gelling components were extracted from five major Japanese mushroom species and from Sparassis crispa, one of the mushrooms with the highest β-1,3-1,6-glucan content. Their gelling ability was evaluated, and their characteristics were compared.

The extraction as described previously [1] was applied to dried powders of various mushrooms. Briefly, they were defatted with ethanol (80 v/v%) and the resulting residue was dissolved in 0.15 M NaCl to remove salt-soluble substances. The residue from this process was then treated with hot compressed water at 128 °C for 1 h, the resulting suspension was centrifuged and the residue was removed. The supernatant was concentrated using a vacuum rotary evaporator. The concentrate was precipitated with ethanol (40 v/v%). The resulting precipitate was dissolved in distilled water, and α-glucanase treatment was performed only for the sample of Lentinula edodes. Trypsin treatment was performed to all samples to degrade the proteins. The treated material was dialyzed against distilled water and then precipitated with ethanol (40 v/v%). The resulting precipitate was dissolved in distilled water again and freeze-dried. The samples were dispersed in distilled water at 1.5 wt% and stirred overnight. The dispersion was heated at 80 °C for 10 min and cooled at 4 °C for 24 h, then gel formation was examined.

The main component of extracts was identified as β-1,3-1,6-glucan from NMR analysis. Gel permeation chromatography indicated that molar mass of all samples except for Grifola frondosawas within the range of 107,000 to 365,000. When samples were dispersed in water and cooled after heating, gel formation was visually confirmed for all species of extracts at 4 °C. The G. frondosa sample formed a brown gel, while the others formed colorless gels. The G. frondosa sample could not be decolorized and was therefore not used in subsequent experiments. Dynamic viscoelasticity and large-deformation measurements showed that extracts from L. edodes , S. crispa, Flammulina velutipes and Pleurotus eryngii formed true gels. The temperature dependence of the storage shear modulus G' suggested that conformational transition and gelation occurred below 6–10°C. On the other hand, the Hypsizygus marmoreus sample did not form a true gel, probably due to its low molar mass (< 110,000). Among the true gels, L. edodes β-glucan gels showed the most fracture-resistant and highest flexiblity. Differences in gel properties were examined not only in terms of molar mass but also based on the degree of side group branching. Furthermore, the binding ability of these gelling components, β-glucans, to a receptor called dectin-1 was also investigated.

Reference

[1] I Yamashita, T Yaguchi, Y Kobayashi, H Ito, H Komori, K Noda, Y Sato, K Nishinari, Y Nitta

Rheology and NMR studies of true gel formation and gelation mechanism for lentinan

Food Hydrocoll., 167, 111415 (2025)