Targeted Phenolic Profiles, Antioxidant Capacity, and Digestive Enzyme Inhibition of Six Conifer Needle Extracts: Ultrasound-Assisted Recovery and Mechanistic Insights

Conifer needles are a renewable forestry biomass and a potential source of bioactive phenolic compounds. In this study, ultrasound-assisted extraction of polyphenols from Pinus banksiana needles was optimized, and the validated conditions were subsequently applied to six conifer species for comparative evaluation of phenolic composition, antioxidant capacity, and digestive enzyme inhibitory activity. Under the optimal conditions of 53% (v/v) ethanol, a liquid-to-solid ratio of 29 mL/g, 21 min, and 45 °C, the total phenolic content of P. banksiana reached 36.13 ± 0.89 mg GAE/g DW. Significant interspecific differences were observed in phenolic composition and bioactivity. Nine phenolic compounds were quantified by targeted HPLC-DAD analysis, with (+)-catechin being the most abundant among these analytes in all six extracts (1.523–9.974 mg/g DW). P. banksiana exhibited the strongest ABTS+ radical-scavenging activity (IC50 = 0.306 ± 0.010 mg/mL) and the strongest inhibition of both α-glucosidase (IC50 = 5.352 ± 0.113 μg/mL) and α-amylase (IC50 = 0.374 ± 0.003 mg/mL). Kinetic analysis suggested an apparent mixed-type inhibition pattern of α-glucosidase by P. banksiana extract, although a pure noncompetitive inhibition model could not be conclusively excluded. Mantel analysis revealed that (+)-catechin showed the strongest association with α-glucosidase inhibition, while molecular docking predicted favorable interactions of (+)-catechin with both human digestive enzyme models. These findings identify (+)-catechin as a potential contributor to α-glucosidase inhibition and highlight P. banksiana as a promising source of antioxidant phenolics with carbohydrate digestion-modulating potential.