A multifaceted analysis of spent mushroom substrate of selected oyster mushrooms for enzymatic activity, proximate composition, and antimicrobial activity

Abstract

The global market for mushrooms is growing due to its nutritional enrichment, potential usage as a bioremediation, enzyme production, and functional food development. However, the leftover post-harvest mushroom substrate (SMS) generates certain environmental concerns. This study aimed to investigate the potential of SMS obtained from two oyster mushroom species—Pleurotus ostreatus and Pleurotus djamor. These were examined regarding sustainability by analyzing their lignocellulosic enzyme production, cellulose yield, antimicrobial properties, and proximate composition. The findings for both P. ostreatus and P. djamor showed higher activity of amylase, that is, 0.3 U (μmol/min) and 0.7 U (μmol/min), respectively, compared to activity of cellulase, which showed 0.3 U (μmol/min) and 0.5 U (μmol/min), respectively. SMS showed the highest activity of lignocellulosic enzymes, compared to non-SMCs and controls at p ≤ 0.00 and ≤0.01), proving fungual mycelia as the precursor of enzymes activity, as no mushroom is cultivated due to least enzymatic activity. The results for proximate analysis of SMCs showed a significant difference from non-SMCs. The findings for P. djmor revealed protein (1.23%), fats (1.3%), and ash (8.11), which were significantly higher than in P. ostreatus. A positive co-relation of 52% was established between SMCs with amylase, while a correlation of 20% was observed with cellulase, depicting an impact of mycelia in the breakdown of protein for amylase production. The SMC samples were also subjected to antibacterial analysis against Staphylococcus aureus, E. coli, and Xanthomonas. A higher minimum inhibition concentration (MIC) was recorded for P. djamor, that is, 8.80 mm, 11.66 mm, and 9.04 mm, compared to P. ostreatus, which showed its highest MIC as 9.18 mm, 9.30 mm, and 9.28 mm for S. aureus, E. coli, and Xanthomonas, respectively. It was evident from the study that SMC has a potential of being utilized for bioremediation, as it is therapeutically active against pathogens. Additionally, Pleurotus spp. is of great interest because of its ability to produce high nutritive value, cellulose yield, and a vast amount of lignocellulosic enzymes. The current experiment recommends the use of distilled water for mushroom farming, as enzymatic activities can significantly be affected by pH and buffers. Furthermore, the spent compost, being rich nutritionally, can be used for soil enrichment or as a biofertilizer.