Edible seaweed as future functional food: Identification of α-glucosidase inhibitors by combined use of high-resolution α-glucosidase inhibition profiling and HPLC-HRMS-SPE-NMR

Crude chloroform, ethanol and acetone extracts of nineteen seaweed species were screened for their antioxidant and alpha-glucosidase inhibitory activity. Samples showing more than 60% alpha-glucosidase inhibitory activity, at a concentration of 1 mg/ml, were furthermore investigated using high-resolution alpha-glucosidase inhibition profiling combined with high-performance liquid chromatography-high-resolu tion mass spectrometry-solid-phase extraction-nuclear magnetic resonance spectroscopy (HR-bioas say/HPLC-HRMS-SPE-NMR). The results showed Ascophyllum nodosum and Fucus vesicolosus to be rich in antioxidants, equaling a Trolox equivalent antioxidant capacity of 135 and 108 mM Trolox mg(-1) extract, respectively. HR-bioassay/HPLC-HRMS-SPE-NMR showed the alpha-glucosidase inhibitory activity of A. nodosum, F. vesoculosus, Laminaria digitata, Laminaria japonica and Undaria pinnatifida to be caused by phlorotannins as well as fatty acids - with oleic acid, linoleic acid and eicosapentaenoic acid being the most potent with IC50 values of 0.069, 0.075 and 0.10 mM, respectively, and showing a mixed-type inhibition mode. (c) 2016 Elsevier Ltd. All rights reserved.