Development of analytical strategies for phytochemical investigation of «superfoods», with particular attention to Botanicals.

Abstract

There is a great attention to functional foods exerting health benefits. In this frame the claim ‘superfood’ to characterize products with high nutritional value and bioactive phytochemicals is more and more used. In the course of current PhD project, the chemical and biological profile of food plants, selected on the basis of their growing interest, has been investigated. During the first year, the chemical fingerprint of Portuaca oleracea L. (Portulacaceae), a widespread herbaceous plant typically appreciated in the Mediterranean and Asiatic diet, showed the presence of complex polar lipids and polyphenolic alkaloids, known as oleraceins. A deep investigation of both classes was carried out with articulate extraction procedures and chromatographic steps. The methanol extract was fractionated by SPE chromatography to obtain 2 lipid enriched fractions from leaves and stems. LC-HRMS analysis of the obtained fractions highlighted the occurrence of phospholipids, glycerolipids, oxylipins and sphingolipids, described in detail by accurate mass, molecular formulae and fragmentation pattern compared with literature data. The polyphenolic alkaloids were studied by choosing the extract with high yield of oleraceins, through HRMS flow injection analysis of several “green” extracts. The structures of oleraceins isolated by HPLC-UV were elucidated by 1D and 2D NMR experiments. During the second year, the chemical profiles of the sprouts of Raphanus sativus L., better known as daikon and okra fruit (Abelmoschus esculentus L.), were studied. The methanol and “green” extracts of daikon showed the occurrence of polyphenolics and glucosinolates reported for anticancer and antioxidant activity. Preliminary studies about the radical scavenging activity of selected extracts were performed by Total Phenolic content, DPPH and TEAC assays, providing high activity of green extracts. Okra fruit is used in oriental traditional medicin for the treatment of diabetes. The inhibition of α-glucosidase in the intestinal tract could be a target for reducing the assorbtion of glucose. In this view, the ability to inhibit α-glucosidase along with antioxidant activity were evaluated. Moreover, the chemical profile of the species was investigated highlighting the occurrence of polar lipids and phenolic acid derivatives. During the third year, a quali-quantitative analysis of mangosteen fruit (Garcinia mangostana L.), reported as source of bioactive xanthones, has been provided. In a first step, the isolation and the NMR characterization of the main xanthones was performed to select the specific NMR signals of each isolated compound for further quantitative approach. In the second step, several extracts, and commercially available supplements as capsules, tablets and juices, were submitted to 1H and 2D NMR experiments and each compound was accurately quantified. The EtOH extracts and hydroalcoholic mixtures showed the highest amount of alpha and gamma mangostin, reported as bioactive xanthones. Regarding commercial food supplements, a certain variability in the amount of biologically active xanthones (i.e. α-mangostin and -mangostin) could be observed. Moreover, in collaboration with the Division of Pharmacognosy of the University of Vienna, bioactivity assays on portulaca and daikon extracts were carried out. The “green” extracts of daikon, in agreement with the observed radical scavenging activity, showed a high capacity to activate Nrf2, involved in the trascription of detoxyfying enzymes. The ability of portulaca extracts to interfere with Nrf2, NF-kB and PPAR-ɣ targets was evaluated. The lipid enriched fractions resulted the most active in eliciting a concentration-dependent induction of Nrf2 and in promoting PPAR- activation. [edited by Author]