Investigation of the inhibitory effect of the fennel (Foeniculum vulgare) on some metabolic enzymes

Fennel (Foeniculum vulgare) is a strongly aromatic plant belonging to the Apiaceae family. It is known as "arapsaçı" (wild fennel) in our country, especially in the Aegean Region, and is frequently consumed in Aegean cuisine. In the presented study, it was aimed to investigate in vitro the possible inhibitory effect of fennel leaves on three enzymes selected as a model, which are found in the body. Fennel leaves were extracted with 80% ethanol in a shaking water bath for six hours. The effect of the obtained crude extract on the catalytic activity of α-amylase, which plays a role in carbohydrate metabolism; lipase, which is effective in lipid metabolism; and tyrosinase, which plays a role in melanin biosynthesis, was investigated. The total phenolic content of the extract was determined by the Folin-Ciocalteu method, and the free radical scavenging activity was determined by the DPPH method. Essential oil was obtained from fennel leaves by hydrodistillation using Clevenger apparatus, and the volatile components of the oil were analyzed by the GC-MS method. Also, the phenolic compounds of the extract and essential oil were determined by the LC-MS/MS method. As a result of the study, it was seen that fennel crude extract inhibited α-amylase and lipase enzymes at high concentration but did not significantly inhibit the tyrosinase enzyme. The total phenolic substance amount and DPPH radical scavenging power were determined as 52.79±0.84 µg GAE/g and EC50=500 µg/mL, respectively. In the phenolic compound analysis performed by the LC-MS/MS method, sixteen compounds were detected in the extract, the highest levels of which were abscisic acid, indole-3 acetic acid, trans-ferulic acid, rutin, protocatechuic acid, p-coumaric acid, and jasmonic acid, while ten compounds were detected in the essential oil, the highest level of which was rosmarinic acid. In the volatile compound analysis performed by the GC-MS method, trans-anethole, thymol, DL-fenchone, and alpha-phellandrene compounds were determined. The fennel plant, like other plant sources, is rich in functional secondary metabolites. It can be said that it has potential for future antidiabetic activity studies due to the anti-amylase activity shown by the crude extract of the plant.