Unlocking the Functional Potential of Lonicera caerulea: Chemical Profile, Antioxidant, and α-Amylase and α-Glucosidase Inhibitory Activities of Extracts from Ripe, Unripe, and Lactofermented Fruits

Honeysuckle berries (Lonicera caerulea) represent a valuable source of bioactive compounds, primarily flavonoids, and iridoids. This study compared the chemical composition and in vitro antioxidant and antidiabetic properties of resin-purified extracts from ripe, unripe, and unripe lactofermented honeysuckle berries. Polyphenols and iridoids were identified using UPLC-ESI-qTOF-MS/MS and quantified using HPLC-PDA. A total of 6 anthocyanins, 7 phenolic acids, 9 flavan-3-ols, 8 iridoids, 8 flavonols, 3 flavones, and 1 flavanonol were identified in the extracts. The extract from ripe fruits was characterized by a high cyanidin glycoside content (273.59 mg/g) and high iridoid content (138.30 mg/g). The amount of individual iridoids varied among the extracts, with the highest level of loganic acid detected in the unripe fruit extract (39.42 mg/g) and the highest level of sweroside in the ripe fruit extract (55.59 mg/g). Phenolic acid content was approximately twofold higher in extracts from unripe and fermented fruits compared with ripe fruit extracts, suggesting a decrease during ripening, while fermentation did not significantly affect phenolic acid content. Among flavonols, quercetin and isorhamnetin derivatives were identified, with quercetin 3-O-rutinoside being the predominant compound in all extracts. The ripe fruit extract exhibited the strongest radical scavenging activity (in ABTS and DPPH assays), ferric ion-reducing power (FRAP), and α-amylase inhibition, while all extracts exhibited comparable α-glucosidase inhibition. These findings indicate that L. caerulea extracts, especially from ripe fruits, are a rich source of biologically active compounds with potential relevance for managing oxidative stress and hyperglycemia.