Evaluation of drying method and pretreatment effects on the nutritional and antioxidant properties of oyster mushroom ( Pleurotus ostreatus )

Abstract

Effect of drying (solar and oven), blanching (steam and water), and chemical pretreatments (lemon juice, vinegar, and potassium bisulfite) on oyster mushroom (Pleurotus ostreatus) quality was studied. Total phenolic content, total flavonoid content, ergothioneine, oxygen radical absorbance capacity, moisture, mineral content, protein, and mold infestation were evaluated. Ergothioneine and total phenolics were lower in blanched mushrooms compared to un-blanched ones. Total flavonoids were highest in water blanched (2.87 ± 0.32–5.98 ± 0.41 mg/g, dry wt.) and least in un-blanched mushrooms (1.16 ± 0.16–0.3.46 ± 0.3 mg/g, dry wt.). Among the chemical pretreatments, higher total phenolics were observed with vinegar and potassium bisulfite treatments. Blanching resulted in lower K, Mg, Na, S, and P content. Mineral nutrients varied with chemical pretreatments. Blanching followed by either lemon juice or no chemical treatment resulted in high mold infestation. Among the un-blanched samples, those treated with vinegar had the least mold. Drying method, blanching, and chemical pretreatments affect oyster mushroom quality as demonstrated in this study. Practical applications This study focuses on drying and pretreatment methods that can be adopted in resource limited environments. The study shows no difference in the observed nutritional attributes of solar and oven dried mushroom, hence where solar energy is the only option for drying, there is no consequence incurred. While commercial processors have access to several preservation treatments, this may not be so for the subsistence producer. The use of lemon juice, vinegar, or blanching would be inexpensive thus practical even where resources are limited. Since mushroom consumers place much value nutritional and antioxidant properties, knowledge of how these simple inexpensive preservation methods may affect these quality characteristics may help inform preservation decisions.