<i>In vitro</i> comparative study of enzyme inhibitory properties of herbal plants and their phenolic, tannin, and flavonoid content as natural inhibitors in public health

Medicinal herbs are used to treat numerous diseases all over the world. This study investigates the enzyme inhibitory potential, antioxidant properties, and phytochemical composition of methanolic extracts from Cinnamomum verum, Nerium oleander, Laurus nobilis, and Eucalyptus camaldulensis leaves. These plants, known for their healing properties, were tested to determine how effectively they inhibit α-amylase and α-glucosidase. These essential enzymes help break down carbohydrates, and their antioxidant capacities were evaluated using DPPH and ABTS assays. Phytochemical profiling revealed significant levels of phenolics (26.44–63.56 mg GAE/g), flavonoids (6.09–37.56 mg QE/g), and tannins (12.98–34.80 mg TAE/g), with E. camaldulensis and L. nobilis exhibiting the highest phenolic content. Methanolic extracts of L. nobilis and N. oleander demonstrated the strongest inhibition of α-amylase (0.586 ± 0.015 and 0.564 ± 0.0001 mmol acarbose/g) and α-glucosidase (7.570 ± 0.107 and 8.242 ± 0.113 mmol acarbose/g), outperforming synthetic controls. Antioxidant activity correlated with phenolic content, with E. camaldulensis showing the lowest IC50 in DPPH (8.83 µg/mL) and L. nobilis in ABTS (30.32 µg/mL). These findings highlight the therapeutic promise of these plants as natural sources of enzyme inhibitors and antioxidants, supporting their use in oxidative stress-related disorders. The study underscores the significance of plant-derived bioactive compounds in developing safer, cost-effective pharmaceuticals and functional foods.