Abstract: Phenolics were extracted from the by-products (leaves, green leafy covers, shells, branches and seed coats) of the hybrid hazelnut Corylus heterophylla Fisch. × Corylus avellana L. using four different polar solvents (water, methanol, 80% ethanol and ethyl acetate) and their antioxidant, hypoglycemic and anti-inflammatory activities were evaluated in vitro. The phenolics were identified by ultra-high performance liquid chromatography-mass spectrometry (UPLC-MS). The leaf and branch extracts showed stronger antioxidant, hypoglycemic and anti-inflammatory activities in vitro than the extracts from green leafy covers, shells and seed coats. The biological activities were largely correlated with total phenols and proanthocyanidins in the by-products of hazelnut. The methanol extract of hazelnut branches had the highest content of total phenols (calculated as gallic acid equivalent per dry mass) and procyanidins (calculated as proanthocyanidin equivalent per dry mass), which were (37.13 ± 0.22) and (2.27 ± 0.04) mg/g, respectively. The content of total flavonoids (calculated as rutin equivalent per dry mass) in the 80% ethanol extract of hazelnut leaves was the highest, which was (18.21 ± 1.37) mg/g. For each plant part, the contents of total phenols, total flavonoids and proanthocyanidins in the ethyl acetate extract were lower than those in the other solvent extract, but the ethyl acetate extract inhibited the activities of α-amylase and lipoxygenase significantly (P < 0.05). The ethyl acetate extract of green leafy covers had the best inhibitory effect on α-amylase, while the ethyl acetate extract of leaves showed the strongest inhibitory activity on lipoxygenase. According to UPLC-MS analysis, the majority of phenolic compounds in hybrid hazelnut by-products were flavonoids along with many bioactive compounds such as terpenes, alkaloids, lignans and organic acids. Bioactive ingredients in hybrid hazelnut by-products have the potential to be used in functional foods or pharmaceuticals.

Key words: hybrid hazelnut by-products; phenolic compounds; biological activity; principal component analysis; correlation analysis