*3.7. In Vitro Enzyme Inhibitory Properties of Beech Bark Extracts—*α*-Glucosidase (Antidiabetic) and Tyrosinase Inhibitory Activity*

Diabetes mellitus is a chronic, life-long disorder and is characterized by high blood glucose levels. One of the ways of treating diabetes mellitus is based on glucose absorption delay by inhibiting enzymes such as α-glucosidase in digestive organs [35]. By inhibiting α-glucosidase in the intestine, the rate of oligosaccharides hydrolysis is low, and the carbohydrate digestion process extends into the lower part of the small intestine [36]. Many studies have demonstrated the α-glucosidase inhibitory activity of some bark herbal extracts, proving their strong biochemical potential [37,38]. For example, different extracts of *Canarium tramdenum* bark were evaluated in terms of α-glucosydase inhibition showing a strong inhibitory activity. The different enriched extracts in terpenoids and phenolics appeared as a promising source of natural α-glucosidase inhibitors [38].

As shown in Table 9, the α-glucosidase inhibitory activity was determined for all BBEs and was higher in comparison with the standard acarbose (Table 9). The order of α-glucosidase inhibition is BBE3 > BBE1 > BBE2 > acarbose corresponding to IC50 values 38, 92, 168, and 838 μg/mL, respectively.


**Table 9.** Enzyme inhibitory effects of beech bark extracts.

Notes: BBE1—extracts obtained with water 100%, BBE2—extracts obtained with ethanol–water 50:50, BBE3—extracts obtained with ethanol–water 80:20, PI—procent of inhibition, NF—not found.

Tyrosinase inhibitors are compounds capable of reducing enzymatic reactions, especially from the skin, which makes them commercially relevant for cosmetic industry [39]. At a concentration of 4.025 mg/mL, inhibitory effects have been shown only for BBE2 sample. However, kojic acid (a standard inhibitor) showed an excellent tyrosinase inhibitory activity of 97.61 ± 0.24%.
