Effect of Sunlight-assisted Drying on Vitamin D2 Enhancement in Oyster Mushroom

Abstract

Background: Vitamin D deficiency, often described as a form of hidden micronutrient hunger, remains relevant among populations with limited effective sunlight exposure and low intakes of vitamin-D-rich foods. Because most natural dietary sources of vitamin D are animal-derived, plant-forward and vegetarian diets require practical, acceptable and scalable alternatives. Rationale: Oyster mushroom (Pleurotus ostreatus) contains ergosterol, a fungal sterol that can undergo photochemical conversion to previtamin D₂ and subsequent thermal isomerisation to ergocalciferol (vitamin D₂). Sunlight-assisted drying may therefore combine moisture reduction, shelf-life extension and nutrient bio-enhancement in a single post-harvest step. Objective: This study evaluated solar drying as a low-input strategy for enhancing vitamin D₂ in oyster mushroom powder and compared it with conventional hot-air tray drying. Methods: Fresh oyster mushrooms were cleaned, cut into pieces measuring approximately 0.5 × 4 cm, dried either in a solar dryer at 45–55 °C for 3 h or in a hot-air tray dryer at 60 °C for 2 h, powdered and analysed for vitamin D₂ by HPLC using a C18 column, an acetonitrile:methanol (85:15, v/v) mobile phase and UV detection at 264 nm. Results: Solar-dried mushroom powder contained 45.21 µg/g vitamin D₂, compared with 7.73 µg/g in hot-air-tray-dried powder. Under the tested conditions, the solar process therefore produced an absolute increase of 37.48 µg/g and an approximately 5.85-fold enhancement relative to hot-air drying. Conclusion: Sunlight-assisted drying increased the vitamin D₂ content while maintaining favourable dehydration-quality attributes. The findings indicate that solar-dried oyster mushroom powder may be a promising natural ingredient for the vitamin D fortification of food products.