Variation in organic acids content in Tuberaria lignosa extracts induced by ionizing radiation and extraction procedures

Abstract

Organic acids are important nutritional phytochemicals and some of them have biological activity, and thus a significant impact on human health. Additionally, they also act as precursors of phenolics and flavour compounds [1]. Tuberaria lignosa (Sweet) Samp. is one of the most quoted medicinal plants in several regions of the Iberian Peninsula, used to treat various diseases and ailments [2]. It was previously highlighted by our research group as a source of bioactive compounds [3], but its content in organic acids was still unknown. As biomolecules can be degraded by improper processing treatments or even extraction methods [3], this work aims to find variations in organic acids content in T. lignosa extracts induced by both ionizing radiation and extraction procedures. Dried T. lignosa samples, obtained in a Northeastern Portuguese region, were exposed to 0 (control), 1, 5 and 10 kGy of γ-rays in a 60Co experimental chamber, and then extracted by water infusion and decoction. The organic acids were analysed by ultrafast liquid chromatography coupled to a photodiode array detector (UFLC-PDA). Oxalic, quinic, malic, shikimic and succinic acids were quantified in all the extracts, being shikimic acid the most abundant. In infusion preparations, irradiated samples exhibited lower contents than the non-irradiated control (except for oxalic acid in the sample irradiated with 10 kGy). On the other hand, in decoctions, only oxalic acid was negatively affected by the irradiation treatment; while the other organic acids values remained unchanged or were improved. But, despite the negative effect of irradiation on samples extracted by infusion, the total organic acids content remained higher in these samples than in those extracted by decoction. Thus, infusion is preferable over decoction to extract organic acids from irradiated T. lignosa.