Effect of Processing Methods on the Proximate Composition, Total Phenols and Antioxidant Properties of Two Mushroom Varieties

Abstract

Mushrooms are traditionally consumed as food and are known to possess nutritional and medicinal properties. However, the choice of processing methods for mushrooms are often based on preference rather than the impact on nutritional or health benefits. The effect of solar drying, steaming and roasting on the proximate, phytochemicals and antioxidant activity of two mushroom varieties (Termitomyces schimperi and Volvariella volvacea) were investigated. Proximate analysis and phytochemical screening were carried out using standard protocols. The total phenols content and antioxidant activity were determined by means of Folin-Ciocalteu method and 1, 1-Diphenyl-2-picryl-hydrazyl (DPPH) assay, respectively. Results indicate that both processing methods and varietal differences had effects on nutrient composition of mushrooms. Solar drying retained most nutrients in both varieties. Dried T. schimperi had the highest protein content of 29.09 % whereas dried V. volvacea had the highest carbohydrate and ash contents of 60.71% and 5.56 %, respectively. Steamed mushrooms retained moisture and had the lowest carbohydrate content with steamed V. volvacea having the highest moisture and lowest carbohydrate values of 91.15% and 54.71%, respectively. Roasting also showed a high protein content of 28.65% in T. schimperi and a high carbohydrate of 58.65% in V. volvacea. None of the processing methods however had a significant effect on fat and fibre contents of both varieties used. The phytochemicals tested were present in both varieties in the processed and unprocessed forms. The steamed extract was the strongest scavenger of DPPH with 50 % inhibitory concentration (IC50) value of 3.03 ± 0.40 mg/mL whereas the unprocessed extract had the least effect with IC50 value of 9.35 ± 0.42 mg/ml. Similarly, the steamed extract recorded the highest total phenol content with value of 1644 ± 39 mg GAE/100 g whereas the unprocessed extract was the lowest with value of 1336 ± 93 mg GAE/100 g respectively. The present findings suggest that steamed mushrooms possess the highest antioxidant activity.