Harvest-wise Comparison of Nutrient Content, Antioxidant and Antimicrobial Properties of Pleurotus ostreatus Cultivated on Rubber Sawdust Media

Abstract

Mushrooms are recognized for their health benefits, rich protein content and other nutritional compounds. Various edible mushrooms are cultivated globally and Pleurotus can be considered as one of the most widely cultivated species. Rubber sawdust is commonly used as a substrate to cultivate Pleurotus species in Sri Lanka. However, research is limited on how nutritional and biochemical parameters change with different harvests. Hence, this study was designed to investigate the harvest-wise differences in nutrient content, antioxidant, and antimicrobial properties of Pleurotus ostreatus (American Oyster) cultivated on rubber sawdust. Mushrooms were grown on substrate bags containing rubber sawdust and the fruiting bodies of three consecutive harvest cycles were dried and aqueous extracts were prepared. Qualitative tests were done to identify the presence of bioactive compounds. Total carbohydrates, proteins, flavonoids, and phenols were measured using spectrophotometric assays such as phenol-sulphuric, Lowry, aluminum chloride, and Folin Ciocalteu respectively. Antioxidant capacity was evaluated using phosphomolybdenum and DPPH assays. Antibacterial properties were tested with disc diffusion method against Escherichia coli and Staphylococcus aureus. In comparison with the second and third harvests, the first harvest had significantly high antioxidant capacity (12.5 mg of AAE/g) and flavonoid content (2.6 mg QE/g). Furthermore, total carbohydrates (50.1 g/100g) and total phenolic content (1.2 mg GAE/g) of the first harvest was significantly high compared to the third harvest. However, none of the harvests showed antibacterial activity against E. coli and S. aureus. In conclusion, our findings highlight the harvest-wise effectiveness of Pleurotus ostreatus grown on rubber sawdust media and the first harvest cycle can be considered as the best harvest with respect to nutritional and antioxidant properties compared to its subsequent harvests. Further research on investigating methods to supplement the nutrient content in the substrates could be done to enhance the nutritional and bioactive compound content in these mushrooms.