The effect of pineapple waste and sawdust substrates on the bioactivities of different parts of Pleurotus mushroom

Mushroom cultivation is a promising industry worldwide due to its nutritional, medicinal, and pharmaceutical value. In Malaysia, sawdust is the primary substrate for cultivating mushrooms. However, with increasing price of rubber trees, alternative substrates need to be explored to sustain the mushroom farming industry in the country. Pineapple leaf waste, which contains phenolic acids and bromelain enzyme, could be a great alternative substrate for mushroom cultivation in Malaysia. Different substrates influence the bioactivities of cultivated mushrooms, which also impact the biological activities of various mushroom parts (cap, stem, and stem waste). Therefore, this study focuses on the different parts (cap, stem and stem waste) of the mushrooms cultivated with both sawdust (Ss) and pineapple waste (Ps) substrates to determine the actual capabilities of each part of the mushroom, especially the stem waste part, in terms of nutritional and potential bioactivities. The objectives of this study were to investigate the nutritional values, bioactivities, and compounds present in the oyster (Pleurotus) mushroom. Proximate analysis was employed to assess nutrient composition, while bioactivities studies were conducted using calorimetric assays, microdilution methods, and specific enzyme inhibition reactions (tyrosinase, elastase and collagenase). Quantification of α- and β- glucan content and phenolic acids was performed using a glucan assay kit and high- performance liquid chromatography with a photo-diode array detector (HPLC-DAD). The results showed significant mean differences in all nutrient compositions of the different mushroom parts. The mushroom’s stem waste cultivated in both substrates (Ps- SW and Ss-SW) exhibited higher levels of ash, fiber, and carbohydrate, with values ranging from 1.64% to 1.84%, 3.43% to 3.67%, and 13.36% to 13.66%, respectively. Meanwhile, the antioxidant assays showed that the cap parts of mushrooms from both substrates (Ps-C and Ss-C) demonstrated higher antioxidant activity compared to the stem and stem waste, with the lowest IC50 value recorded at 231.99 μg/ml (Ps-C). In terms of antimicrobial activity, the cap (Ps-C) and stem waste (Ps-SW) parts from pineapple waste displayed the lowest minimum inhibitory concentration (MIC) against Staphylococcus aureus (125 μg/ml) and the highest MIC against Candida albicans (7000 μg/ml). For anti-aging activities, the cap part in both substrates has a significantly higher IC50 value in most tests, ranging from 20 to 40 mg/ml. The glucan composition in the stem and stem waste samples cultivated in both substrates had significantly higher β-glucan (31.45 to 49.94 w/w %) compared to α-glucan. Additionally, the SW in both substrates contained a significant amount of p-coumaric acid (5.99-7.37 mg/g) compared to other parts. In summary, various parts of mushrooms exhibit distinct potencies in terms of nutritional composition, bioactivities, and phenolic profiles. The cap of the mushroom in both substrates (Ps-C and Ss-C) demonstrates significant potential in antioxidant and anti- aging activities. Conversely, the stem and stem waste of the mushroom in both substrates exhibit higher levels of beta-glucan. Consequently, this research emphasizes the potential novel application of Pleurotus mushroom stem waste in nutraceuticals and pharmaceuticals due to its rich fiber and carbohydrate content.