LC–MS–MS and GC–MS analyses of biologically active extracts of Tunisian Fenugreek (Trigonella foenum-graecum L.) Seeds

Abstract

The objective of this study is to investigate the chemical composition of biologically active extracts from Fenugreek (Trigonella foenum-graecum L.) Seeds. A variety of in vitro models such as β-carotene-linoleic acid and 1,1-diphenyl-2-picryl hydrazyl (DPPH) were used to measure the antioxidant activity. Alpha-amylase inhibitory activity was evaluated by enzyme inhibition using in vitro assay. The hexane extract with a potent inhibition ability against linoleic acid (95.4%) as well as a powerful α-amylase inhibitory activity (IC50 = 26.9 µg/mL) was analyzed by gas chromatography coupled with mass spectrometry (GC–MS). A total of 20 compounds were identified, some of them being reported for the first time in fenugreek seeds [e.g. β-thujone (10.8%), (2E, 4E)-decadienal (7.8%), heptanal (6.7%), and (2E, 4E)-heptadienal (5.3%)]. On the other hand, methanol extract exhibited a strong DPPH radical-scavenging activity (IC50 = 19.0 µg/mL) compared to that of BHT as well as the highest alpha-amylase inhibitory activity (IC50 = 52.1 μg/mL). HPLC technique coupled with negative ion electrospray ionization mass spectrometry and diode array detection (HPLC-DAD–ESI/MS) was employed to identify polyphenols in the methanol extract. The obtained results allowed the detection of 3 flavonoids glycosides and one amino acid identified on the basis of their UV and MS spectra, and comparisons with standards when available, as well as with literature data. A systematic study of the obtained MS spectra and the observed fragmentation allowed identifying for known compounds: vicenin-2, 4-hydroxyisoleucine, isoschaftoside and isoorientin. These two last compounds were identified for the first time in Fenugreek Seeds.