Evaluation of gamma-irradiated aromatic herbs: Chemometric study of samples submitted to extended storage periods

The preserving capacity of gamma radiation (10 kGy) on the chemical, nutritional and antioxidant components of Aloysia citrodora Paláu, Melissa officinalis L., Melittis melissophyllum L. and Mentha piperita L., stored for 12 and 18 months, was evaluated. Despite the maintenance of the main characteristics during the first 12 months of storage, the additional 6 months induced several significant changes in individual compounds. In general, the analyzed species reacted dissimilarly throughout time, but it was possible to verify that the fatty acids, tocopherols and antioxidant capacity presented the most significant changes after 18 months of storage, inclusively in samples submitted to gamma radiation. In fact, the applied treatment (10 kGy) did not seem to be effective to prevent the decrease of free sugars, organic acids and tocopherols, especially considering the 18 months period. On the other hand, the evolution in color parameters indicated a greener color (yet slightly more yellow) among irradiated samples. Likewise, gamma radiation had a positive effect on oleic acid, β-carotene bleaching inhibition (in infusions), DPPH scavenging activity and reducing power (in methanolic extracts). Nevertheless, it might be generally concluded that gamma radiation is less suitable than electron-beam to maintain the characteristics of dried herbs during extended storage periods.