Impacts of paper waste and paddy straw on the growth, nutritional profile, and antioxidant activity of Pleurotus ostreatus (American oyster mushroom) and Pleurotus eous (Bhutan oyster mushroom)

Abstract

Pleurotus species are an extensively cultivated type of mushroom and are consumed as a nutritious, healthy source of food all over the world. Numerous agricultural wastes can be used to grow these mushrooms, such as sawdust, paddy straw, coconut coir, etc., which further contributes to the prevention of environmental pollution. In this study, two commonly cultivated oyster mushroom species; Pleurotus ostreatus (American oyster) and Pleurotus eous (Bhutan oyster) were grown separately on paper waste and paddy straw and the yield, nutritional composition, levels of bioactive compounds, and antioxidant activity were evaluated. The main objectives of this study were to determine the most nutritious oyster mushroom variety with health benefits and to investigate the best substrate to cultivate it. Various tests including the protein analysis using the Lowry assay, phenol sulfuric assay to determine total carbohydrates, qualitative tests for bioactive compounds, antioxidant capacity using DPPH assay, and total phenolic content assay were performed. Bhutan oyster cultivated on paddy straw showed significant results in the number of fruiting bodies (7.3±2.3) and fastest growth (9.7±6.7 days) compared to other groups. However, American oyster cultivated on paddy straw and paper waste had the highest protein (5.5±1.5g/100g) and carbohydrate contents (8.2±0.9g/100g) respectively. The bioactive compounds, terpenoids and polyphenols were present in all the samples. Furthermore, there was no significant difference in the total phenolic values although all the study groups exhibited substantial phenolic levels. Bhutan oyster cultivated on paper waste displayed a significantly low IC50 or half-maximal inhibitory concentration (23.4±26.2μg/mL) compared to Bhutan oyster cultivated on paddy straw (93.9±26.2μg/mL), showing higher antioxidant properties. When considering the substrates, although paper waste took less number of days for the mycelium growth to complete, both substrates did not have any significant difference with respect to the water holding capacity. In conclusion, the outcomes for nutritional properties and antioxidant activity of both species grown on the two substrates were remarkably similar and showed promising results. Therefore, both Bhutan and American oyster mushrooms grown on the substrates of paper waste and paddy straw can be consumed as an affordable and good food source with many nutrients, antioxidants, and bioactive compounds.