Gamma irradiation protects oleic acid from oxidation: an experiment in Lactarius deliciosus wild mushroom

The short shelf-life of mushrooms is an obstacle to the distribution and marketing of the fresh product. Thus, prolonging postharvest storage, while preserving their quality, would benefit the mushroom industry as well as consumers [1]. There has been extensive research on finding the most appropriate technology for mushrooms preservation and a particular interest arises for wild species. Treatment by irradiation emerges as a possible conservation technique that has been tested successfully in several food products and is regulated in the European Union by the Directive 1999/2/EC. In the present work, the influence of gamma irradiation dose (0.5 and 1 kGy) over the fatty acids profile of Lactarius deliciosus L. wild mushroom, collected in the Northeast of Portugal (November 2011), was evaluated by gas-chromatography coupled to flame ionization detection (GC-FID). The analyses were performed after 0, 4 and 8 days of storage at 4 ºC in irradiated and non-irradiated samples (control). The control and the irradiated samples revealed an identical profile, with C18:0 (stearic acid), C18:2n6c (linoleic acid), C18:1n9c (oleic acid) and C16:0 (palmitic acid) as main fatty acids. These results are in agreement to the reported by our research group in a previous study with nutritional characterization of this species [1]. Nevertheless, some differences were found in the percentage of some fatty acids in the different samples, mainly in oleic acid. Control sample (non-irradiated) after 8 days of storage, showed a lower C18:1n9c percentage (decreased from 8 to 4.4%) contributing to a decrease in monounsaturated fatty acids (MUFA) levels. Otherwise, in the sample irradiated with 0.5 kGy the percentage of the mentioned fatty acid did not changed until day 8. Overall, irradiation could be an alternative to ensure the quality and extend the life of mushrooms, protecting their fatty acids from oxidation, as is was demonstrated herein for oleic acid. In fact, food irradiation is now being commonly used in many countries, as people are becoming more aware of the role of food irradiation in regards to food safety and product shelf-life extension.