Volume 19 Part 1 Article 11
Title: Drying as a method of adding value and reducing losses in the mushroom industry
Author: Dimitrios Argyropoulos and Joachim Müller
Although cultivated mushrooms are mainly consumed in their fresh state, drying is a standard postharvest technology to extend the shelf life of several wild mushroom species for off-season use by reducing water activity to a microbial safe level for storage. In particular, convective air drying of one of the most commercially important wild mushrooms (Boletus spp.) is performed in cabinet-, tunnel- and conveyor dryers at a temperature range between 50 and 70 °C. Correctly dried mushrooms with a maximum moisture content of 12% intensify their distinctive flavor without significant loss of their color and pleasant texture. Optimal final moisture content is also required to avoid spoilage of mushrooms due to insect infestation during storage. Experiments with a range of air conditions (temperature, humidity, velocity) were carried out using a high precision laboratory dryer in order to study the drying behavior and relevant quality aspects of some cultivated (Agaricus bisporus, Pleurotus ostreatus, Lentinula edodes) and wild (Boletus edulis, Morchella vulgaris, Cantharellus cibarius, Craterellus cornucopioides) mushrooms via mathematical modeling. Drying kinetics was described by a first-order reaction kinetics model, in which the drying constant was function of the air conditions and particle size. The dried samples were compared with those obtained by alternative drying methods such freeze drying in terms of color, texture and rehydration ratio. Air temperature and slice thickness were the most influential parameters on drying acceleration, whereas the effects of humidity and velocity of drying air on drying time were considered as lower than that of temperature. Different drying behaviors were also observed among the mushrooms due to differences in species geometry. Specifically, black trumpet was dried faster, followed by morel, whereas chanterelle indicated significantly longer drying periods. High drying temperatures (70 °C) in the beginning of the process caused dried mushrooms of hard texture with visible effects of browning. However, a stepwise increase of air temperature during the final stage of drying is recommended to ensure long-term stability of dried mushrooms. Freeze drying resulted in dried mushrooms of superior quality, preserving surface color, pleasant texture as well as greater rehydration ratio. Therefore, drying represents a fundamental processing step for the development of novel value-added products, which could also reduce the losses caused by surplus production enhancing the income of the mushroom growers.