Comparative study on the quality of Namibian commercial oyster mushrooms cultivated on encroacher bushes as substrates

A thesis submitted in fulfilment of the requirements for the degree of master of science in biochemistry

Humans need a wide range of nutrients to have a well-balanced diet, nutritious edible mushrooms can be part of a healthy lifestyle. The objectives of the study were to evaluate the yield and yield components, to determine antioxidant activity, total phenolic content (TPC), total flavonoid content (TFC) and nutrient composition of different mushroom species cultivated on four different bush encroacher substrates. To provide mushroom cultivation training to farmers in Okondjatu district. Mushrooms were cultivated in 2kg bags of dry substrate, harvested, dried and powdered. Mushrooms powder was extracted in 99.9% methanol. Antioxidant activity of the mushroom extracts were analysed by reducing power and 2, 2 Diphenylpicrylhydrazyl (DPPH) assay. The TPC and TFC were quantified. Crude protein was calculated (N x 6.25) from determining the amount of nitrogen (N) in mushroom powder using the Dumas combustion method. Potassium and Phosphorus were determined by using the flame emission spectroscopy, while Phosphorus was determined by colorimetry. Neutral detergent fibre (NDF) and Acid detergent fibre (ADF) were analyzed using the Ankom 220 fibre analyzer unit. Mushroom cultivation training was conducted at three randomly selected villages. There was a significance difference in weight of fresh mushrooms, days to first harvest and number of fruiting bodies which was due to mushroom species used at p=0.002, p<0.001 and p=0.019 respectively. Pleurotus florida (PF) yielded more mushrooms with 350 g, followed by PS with 322 g, followed by Pleurotus ostreatus (PO) with 314 g, and the least was on HK 35 with 243 g. The inhibitory concentration at 50% (IC50) values ranged from 0.380±0.098 mg/ml to 0.780±0.007 mg/ml on different mushroom species grown. The inhibition of the DPPH radical by PO extracts cultivated on Terminelia sericea ii (0.380±0.007 mg/ml) showed the highest activity. All Mushroom species grown on different bushes showed an appreciable ability to reduce ferricyanide complex to ferrous form at different concentrations (0.063–1.00 mg/mL). The 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 on the bush species (p-value < 0.01). Crude protein content ranged from 28.0% to 39.0%. 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. A total of 45 community members participated in the training. In conclusion, all four encroaching bushes can be used as the substrate for mushroom cultivation. All mushroom species showed antioxidant activity and appreciable nutrient and mineral composition, thus can be used as a remedy to illnesses and a supplement to human diets. Therefore, it is essential to promote awareness and train farmers on mushroom cultivation