Effect of vacuum and oven drying on the radical scavenging activity and nutritional contents of submerged fermented Maitake (Grifola frondosa) mycelia

Abstract Maitake (Grifola frondosa) mycelia contain high dietary and medicinal values that have gained great attentions from consumers. Proper drying can preserve their bio-availabilities prior to subsequent processing or consumption. Pure Maitake (Grifola frondosa) strain was cultivated in Mushroom Complete Medium (MCM) using submerged fermentation for 14 days. Maitake mycelia were harvested and treated respectively by vacuum, oven drying treatments while the fresh mycelia were assigned as control. All the samples were tested for Total Phenolic Content, DPPH radical scavenging assays and nutritional contents. Submerged fermentation produced mycelia biomass (1.3 ± 0.1 g/L) within 14 days of fermentation. Both the pH and reduced sugar content had decreased (P < 0.05) throughout fermentation. Vacuum dried mycelia had shown higher (P < 0.05) total phenolic (20.0 ± 0.4 mg GAE/g), DPPH radical scavenging activity (84.7 ± 0.1%), and soluble protein content (283.6 ± 7.1 µg/mL) as compared to other treated samples. The crude protein (39.1 ± 0.2), fat (5.7 ± 0.7), ash (11.1 ± 0.3%) of mycelia were well preserved using vacuum drying as compared to oven dried samples. The study has suggested that vacuum drying at 70 °C, 1000mBar has the advantage to preserve the nutritional and radical scavenging activity of high value maitake mycelia effectively at lower cost.