Antioxidant activity and nutritional composition of different mushroom extracts grown on different bush encroachers as substrates in Namibia

Abstract

Mushrooms are a good source of antioxidants with a range of health benefits owing to their bioactive compounds, such as polyphenols, vitamins, and minerals. The objective of this study was to evaluate the antioxidant activity and nutritional composition of mushrooms cultivated on four different encroaching bushes as substrates. Antioxidant activity was measured using reducing power and DPPH scavenging assays. The IC50 values ranged from 0.380±0.098 mg/ml to 0.7780±0.007 mg/ml. The inhibition of the DPPH radical by PS extracts cultivated on Terminalia sericea (0.380±0.098 mg/ml) showed the highest activity compared to other mushroom extracts. All the mushroom species grown on different bushes showed an appreciable ability to reduce ferricyanide complex to ferrous form at different levels of concentration (0.063–1.00 mg/ml). TPC varied from 3.93 mg GAE/g to 8.016 mg GAE/g. TFC ranged from 0.515 mg QE/g to 12.1 mg QE/g, which showed a significant difference in the bush species at a p-value of less than 0.01. There was a significant difference in the interaction of bush substrates and mushroom species on crude protein and ash content at p-values of 0.01 and 0.015, respectively. In the current study, crude protein content ranged from 28.0% to 39.0%, with PF grown on Terminalia sericea having a high protein content. A significant difference in % NDF on mushroom species was found, where a variation was detected in HK35, while PF, PO, and PS showed a similar performance in % NDF. The study showed that ash content ranged from 5.77% to 17.9%. Percentage moisture ranged from 86.0% to 87.5%. A significant difference in mineral composition, with PO showing a high content of potassium (2.292%), PF showing a high content of sodium (0.059%), and PS showing a high content of phosphorus (0.746%) as compared to other mushroom species. Among the four different bushes, Combretum collinum (potassium 2.256%, sodium 0.05%, and phosphorus 0.74%) had the greatest effect on the mineral composition of the different mushrooms cultivated. In conclusion, mushrooms are accessible natural food rich in antioxidants, which may boost the immune system against oxidative damage and can be used as potential sources of therapeutic agents.