UV induced conversion during drying of ergosterol to vitamin D in various mushrooms: Effect of different drying conditions

BACKGROUND: Mushrooms are increasingly popular around the world as a nutritional food which is an excellent source of vitamin D(2). Although natural mushrooms often contain very little vitamin D(2) as many are grown in the dark, they are rich in ergosterol, a precursor to vitamin D(2). Ergosterol can be converted to vitamin D(2) under ultraviolet radiation. Due to the high water content of fresh mushroom, its quality deteriorates rapidly after harvest, and drying is the most commonly used technology to extend the shelf life. The vitamin D(2) content of dried mushrooms depends on the drying conditions used. SCOPE AND APPROACH: In this review, the chemistry of the photo-conversion process of ergosterol to vitamin D(2) under ultraviolet radiation is introduced. The ergosterol and vitamin D contents in different mushroom varieties are discussed. The effects of several drying methods and the influence of different drying conditions are reviewed. Key findings and conclusions: Thermal drying in the presence of UV has been proven to convert ergosterol into vitamin D and enhance the nutritional content of all types of edible mushrooms. Solar drying, hot air drying, freeze drying, microwave drying and infrared drying can be used for mushrooms drying under selected operating conditions. A critical evaluation of published literature demonstrates the importance of applying appropriate drying methodology to maximize the nutritional value of various types of edible mushrooms.