Polyphenol Content, Antiradical Properties, and α-Amylase Inhibition Activity of Vaccinium myrtillus L. (Bilberry) and Vaccinium vitis-idaea L. (Lingonberry) Leaf and Aerial Parts Extracts

The utilisation of medicinal plants has gained importance due to emerging drug resistance in diseases, including type 2 diabetes mellitus (T2DM). Vaccinium myrtillus (VM) and Vaccinium vitis-idaea (VV) are particularly noteworthy as their leaves and aerial parts (no flowering leaves with stems) are rich in polyphenols and antioxidants with potential positive impacts on blood sugar levels. The aim of this study was to compare the chemical composition, antiradical, and alpha-amylase inhibitory activities of the leaves and aerial parts of the Latvian VM and VV. Two samples of VM and two samples of VV were collected from two different locations. Dried plants were used to prepare 70% ethanol extracts and freeze-dried samples. The total tannin and phenolic contents were determined, and the phytochemical compounds were characterised by LC-MS. The alpha-amylase inhibition activity and the antiradical activity in the extracts were measured. The VV ethanol extracts had the highest polyphenol content at 632.80 mg/100 g, followed by the freeze-dried extracts at 968.52 mg/100 g. The highest polyphenol content in the VV ethanol extracts was 632.80 mg/100 g and 968.52 mg/100 g in the freeze-dried extracts. The ethanol extracts of VM (1.34%) and VV (2.85%) had the highest content of tannin, whereas the freeze-dried extracts showed significantly lower tannin content in VM (0.21%) and VV (0.18%). A high correlation was observed between DPPH (2,2-diphenyl-1-picrylhydrazyl) and alpha-amylase inhibition activity (R = 0.86, p = 0.015). This information can be used for additional control of sugar levels in T2DM patients. Comparing both plants with each other and different types of samples (ethanol extracts, freeze-dried samples), it was concluded that the difference exists in both variants. The VM samples showed higher results (alpha-amylase inhibition activity, DPPH radical scavenging activity) than the VV samples, and the freeze-dried samples had higher results than the ethanol extracts.