Natural α-Amylase Inhibitors from Medicinal Herbs: In Vitro Evaluation of Extracts Prepared with Food-Compatible Solvents

Medicinal plants represent a promising source of bioactive compounds with potential antidiabetic activity, while the efficacy of plant extracts depends on both plant matrix and extraction conditions. This study aimed to systematically compare selected medicinal plants and extraction solvents to evaluate their impact on extracts’ in vitro α-amylase inhibitory activity, total polyphenol content (TPC), antioxidant capacity, and antimicrobial properties. Extracts of sage (Salvia officinalis), blueberry leaf (Vaccinium myrtillus), nettle (Urtica dioica), wormwood (Artemisia absinthium), and green and roasted coffee (Coffea arabica) were prepared using different solvent systems (50% (v/v) ethanol, propylene glycol, glycerol, and water), as well as a traditional aqueous infusion protocol. Extraction solvent strongly affected bioactivity: ethanol extracts showed the highest α-amylase inhibition, particularly in sage extract (79.60%) and blueberry leaf (57.71%). No significant correlation with TPC was observed (r = 0.229, p = 0.108), but aqueous ethanol yielded the highest TPC, with blueberry leaf being richest (64.16 ± 0.82 mg GAE/g), followed by roasted coffee (49.36 ± 0.83 mg GAE/g). Ethanol extracts demonstrated antibacterial activity against Staphylococcus aureus. Overall, sage and blueberry leaves showed the most promising multifunctional activity, highlighting their potential for further investigation as functional food ingredients.