Volume 19 Part 1 Article 47
Title: Increasing vitamin D2 content of cultivated mushrooms by processing and drying
Author: Nils Nölle, Dimitrios Argyropoulos, Stefan Ambacher, Joachim Müller, Hans Konrad Biesalski
Cultivated mushrooms contain little (0.005-0.080 μg vitamin D2 per g dry matter) to no vitamin D2 due to the absence of sunlight in growing rooms. However, vitamin D2 in mushrooms can be significantly increased by irradiation with natural or artificial UV-light. Drying is a standard method for the postharvest preservation of mushrooms on industrial scale. Therefore, experiments using different drying methods namely conventional hot-air drying in a high precision laboratory dryer (T=60 °C, x=10 g/kg, v=0.6 m/s), sun drying, solar drying and freeze drying (T=20 °C, p=0.28 mbar) were carried out and their effects on drying behavior and vitamin D2 content of cremini (brown) Agaricus bisporus mushrooms were investigated. Prior to drying, samples were divided into three batches: The first batch of samples was sliced to approx. 30 mm thickness and then dried under the sun or in a forced convection-type solar drying system. The second batch of mushroom slices was irradiated with an UVB dose of 1.5 J/cm2 at 25 °C for 20 min before hot-air drying and freeze drying, while a batch of uncut UVB-treated fruiting bodies was used for control. For the determination of vitamin D2, all dried samples were subjected to saponification, the analytes were extracted with n-Hexane and injected into the HPLC. Mushroom slices subjected to 60 °C were dried significantly faster than those dehydrated by other methods. Also, solar drying enhanced the drying rate of samples considerably resulting in a shorter total drying time in comparison with sun drying. Freeze drying took about 22 h to reach optimum final moisture content for safe storage. Slicing of mushrooms prior to UVB exposure induced a ten-fold increase in vitamin D2 content. In particular, UVB irradiation of whole mushrooms resulted in 44.50 μg/g dry matter, while sliced mushrooms produced 406.26 μg/g. Vitamin D2 content of sun- and solar dried mushroom slices was about 36.40 and 38.86 μg/g dry matter, respectively. Apart from the irradiation dose or the exposure time, slicing of samples before UVB treatment is an essential processing step to maximize vitamin D2 in mushrooms. Furthermore, drying in natural or forced convection type solar dryers can be an effective approach for increasing vitamin D2 content in mushrooms.
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