Potential health enhancing properties of edible flowers from Thailand

Tagetes erecta, Cosmos sulphureus, Antigonon leptopus and Bougainvillea glabra are edible flowers frequently used by the ethnic population of northern Thailand for preparation of salads and flower teas. The main constituents of ethanolic extracts of these flowers, identified with the help of a high-performance liquid chromatography (HPLC) method, were phenolic acids and flavonoids. T. erecta flowers contained the highest level of phenolic compounds, 1107.5 mg/100 g dry weight (DW), which was 3- to 4-fold the level of phenolic compounds in three other flowers evaluated in this study. Lyophilised aqueous extract of T. erecta had the highest Folin–Ciocalteu value (212 ± 9.0 mgGAE/g DW) and exhibited the highest total reducing capacity (Ferric Reducing Antioxidant Power, FRAP assay; 329.4 ± 21.8 μmol Fe2+/g DW) and cellular antioxidant activity (CAA assay; EC50 = 413 μg/ml). However A. leptopus extract exhibited a superior oxygen free radical scavenging ability (oxygen radical absorbance capacity, ORAC-H assay). The extracts were evaluated for their abilities to suppress the proliferation of human cancer cells associated with the digestion system and to inhibit the activity of two enzymes, α-glucosidase and pancreatic lipase. A pronounced anti-proliferative activity against the colorectal adenocarcinoma (HT-29) cells exhibited T. erecta extract (IC50 = 1.5 mg/ml), while A. leptopus was most active against the gastric adenocarcinoma (AGS) (IC50 = 0.2 mg/ml) and bladder cancer cells (BL-13) (IC50 = 0.9 mg/ml). T. erecta extract was identified as an efficient inhibitor of α-glucosidase enzyme (IC50 = 0.06 mg/ml). T. erecta, C. sulphureus and B. glabra extracts equally inhibited the activity of pancreatic lipase (IC50: 4.82 and 4.60 mg/ml, respectively). The results obtained in this study for the first time identified a number of potential health-enhancing properties of aqueous extracts obtained from edible flowers consumed by the indigenous people of Thailand.

Research highlights
► Tagetes erecta contained the highest of phenolic compounds and antioxidant capacity.
► Tagetes erecta actively inhibited proliferation of HT-29 cell.
► Antigonon leptopus actively inhibited proliferation of ASG and BL-13 cells.
► Tagetes erecta extract efficiently inhibited the activity of α-glucosidase.
► Flowers extracts moderately inhibited the activity of pancreatic lipase.