Evaluation of Antifreeze Activity of Enzyme-Treated Extract from Mushroom Cell Wall

Ice formation and growth during freezing in processed foods containing water can deteriorate food quality. Naturally derived antifreeze proteins and antifreeze polysaccharides are an attractive solution to this problem. Alkaline extracts from the basidiomycete <i>Flammulina velutipes</i> (enokitake) are known to inhibit ice crystal growth and are expected to maintain frozen food quality. In this study, polysaccharides/oligosaccharides (POS) were obtained from the readily available edible mushrooms <i>F. velutipes</i>, <i>Hypsizygus marmoreus</i>, <i>Pleurotus eryngii</i>, and <i>Grifola frondosa</i>. POS extracts were isolated by treatment of the fruiting mushroom body with the cell wall-lytic enzyme Uskizyme, then precipitated by ethanol addition. All POS showed antifreeze activity by suppressing ice crystal growth. The benefit of the POS isolated from enzyme-treated edible mushrooms towards frozen processed products quality and shelf-life for foods containing egg protein, fish protein, and rice starch was evaluated. POS derived from <i>F. velutipes</i> was effective in maintaining egg protein (chawanmushi) quality. For fish protein (surimi), the POS derived from <i>F. velutipes</i> and <i>G. frondosa</i> mushrooms suppressed freezing-induced increases in hardness and elasticity. However, for rice starch (shiratama), none of the POS had any effect in preventing retrogradation. This study is the first report to show that components obtained from mushroom cell walls by enzymatic treatment can be effectively used to improve the physical properties of foods. These results suggest the possibility of new applications for mushrooms as potential cryoprotectants in the frozen food industry.