Black truffle (Tuber melanosporum) is considered a gourmet product due to its sensory properties, particularly because of its flavour. However, they also showed an interesting nutritional composition i.e. they are low fat, high dietary fibre food and contain many biological compounds such as antioxidants, hypocholesterolemic sterols, etc. Ergosterol (ergosta-5,7,22-trienol) and brassicasterol (ergosta-5,22-dienol) are the two major fungal sterols of T. melanosporum hyphae representing respectively almost 60 and 40% of total sterols. Ergosterol is a vitamin D2 precursor since it is transformed into previtamin D2 which turns into ergocelciferol (vitamin D2) by ultraviolet light (UV) exposure. Vitamin D-enriched mushroom can also be achieved by fruiting bodies irradiation however, to our knowledge no report has been published studying the irradiation of truffles carpophores to increase their vitamin D2 levels. Therefore, in this work, the effect of UV irradiation at two wavelengths on black truffles was studied to investigate whether they were able to transform ergosterol into ergocalciferol. Thus, fresh T. melanosporum ascocarps were irradiated with UV-light (254 or 312 nm) for 30, 60 and 90 min. Ergosterol levels were determined by GC–MS-FID2 and vitamin D2 quantification was carried out using an HPLC method. T. melanosporum ascocarps contained no ergocalciferol since they are usually buried in the woods but showed 0.8-1.8 mg/g ergosterol and 0.5-0.7 mg/g brasicasterol. They also contained other sterols such as ergosta7,22-dienol and 9,19ciclolanost-7-en-3-ol. Truffle UV-irradiation resulted in a remarkable and constant increase in vitamin D2 content up to 60 minutes of exposure. Conversion at 254 nm was higher than at 312 nm reaching levels of 0.03 and 0.02 mg/g of vitamin D2, respectively, after 30 min of irradiation. Afterwards, longer irradiation times at 254 nm induced a slight decrease in vitamin D2 levels whereas at 312 nm did not further enhanced its biosynthesis, indicating that perhaps an excess of exposure induced vitamin degradation.

Trabajo presentado a las III Jornadas Científicas CIAL Fórum, celebradas del 22 al 23 de noviembre de 2018 en el Instituto de Investigación en Ciencias de la Alimentación (CIAL).

Peer reviewed