Edible Flowers as Bioactive Food Ingredients with Antidiabetic Potential: A Study on Paeonia officinalis L., Forsythia × intermedia, Gomphrena globosa L., and Clitoria ternatea L.

Type 2 diabetes is a serious public health problem in the 21st century. To find new substances supporting diabetes therapy, researchers are increasingly paying attention to the biological potential of edible flowers. This study assessed the antidiabetic potential of ethanol, 50% ethanol, and water extracts from <i>Paeonia officinalis</i> L., <i>Forsythia</i> × <i>intermedia</i>, <i>Gomphrena globosa</i> L., and <i>Clitoria ternatea</i> L. flowers. Extracts were tested for antioxidant activity (DPPH, ABTS, FRAP, CUPRAC, and Fe²⁺ chelation), enzyme inhibition (α-glucosidase, α-amylase, hyaluronidase, and cholinesterases), and anti-inflammatory effects (NO inhibition in LPS-stimulated RAW264.7 macrophages). Phytochemical composition was also analysed. Extracts of <i>P. officinalis</i> stood out with the highest total phenolic content (50% ethanol extract of <i>P. officinalis</i> 178.49 mg GAE/g) and total flavonoid content (aqueous extracts of <i>P. officinalis</i> 4.27 mg QE/g), high gallic acid level, and the effective inhibition of α-glucosidase and α-amylase (α-glucosidase inhibition 98-99% for all <i>P. officinalis</i> extracts, and α-amylase inhibition ~ 100% for ethanolic extract). Strong hyaluronidase (76.9-95.5%) and cholinesterase inhibition was also observed. <i>F.</i> × <i>intermedia</i> extracts were rich in rutin and chlorogenic acid and showed potent inhibitory effects on α-glucosidase (50% ethanol extract 91.59%), α-amylase (aqueous extract 89.35%), and hyaluronidase (aqueous extract 73.8%). Ethanol extracts of <i>G. globosa</i> exhibited a high α-amylase inhibition (93-95%). Although <i>C. ternatea</i> showed moderate antioxidant activity, it showed an apparent anti-inflammatory effect, effectively reducing NO production in activated macrophages for 50% ethanol extract. In summary, <i>P. officinalis</i> and <i>F.</i> × <i>intermedia</i> flowers are promising sources of extracts with antioxidant, antidiabetic, and anti-inflammatory effects supporting their use in further research on type 2 diabetes therapy.