Antibacterial and antioxidant activities of aqueous extracts of eight edible mushrooms

Polysaccharides extracts of eight edible mushroom species, including five species collected from New Zealand forests and parks, were tested for their ability to inhibit the growth of five common bacterial strains. Antibacterial activity was assayed using the disc diffusion and microdilution methods. An aqueous extract from Cordyceps sinensis inhibited the growth of Bacillus subtilis and Streptococcus epidermidis with minimum inhibitory concentration (MIC) values of 938 and 469 μg/mL, respectively. A Pleurotus australis extract had the same MIC of 469 μg/mL against S. epidermidis. Comparatively, the microdilution method was more efficient and accurate than the disk diffusion method at measuring the antimicrobial activity of high molecular weight polysaccharides. All polysaccharides exhibited DPPH (1,1-diphenyl-2-picrylhydrazyl) radical scavenging activities, with P. australis having the highest antioxidant activity (EC50 of 4.03 mg/mL). Fourier transform infrared (FT-IR) analyses indicated that some extracts contained α or β-conformations. Their relative quantities of OH, evaluated by the ratios of OH group/CH group, did not correlate with their scavenging activity based on EC50 values. Several of the mushroom polysaccharide extracts investigated in this study have antibacterial and antioxidant activities that warrant further study as potential dietary supplements to improve health and well-being.