Phenolic acid profile and antioxidant capacity of hazelnut (Corylus avellana L.) kernels in different solvent systems

Summary Limited information is available relating to the qualitative and quantitative composition of phenolic acids in hazelnut kernels. Many authors have proposed different techniques to extract phenolic compounds from nuts, therefore, the objective of this study was to investigate how the experimental conditions commonly used to detect soluble phenolics affected the yield of phenolic acids and the antioxidant capacity of hazelnut kernel extracts. Phenolic compounds were extracted using three different solvent mixtures (80% v/v ethanol, methanol and acetone), at different temperatures. The extracts were examined for their total phenolic contents (TPC) and phenolic acid profiles. In addition, antioxidant capacities were tested using four different spectrophotometric assays. The results showed that acetone/water mixture applied at 50 °C exhibited the best extracting capacity, and 80% acetone extracts had the highest TPC and antioxidant capacity. HPLC analysis of the extracts highlighted the presence of eight phenolic acids (gallic acid, protocatechuic acid, 4-hydroxybenzoic acid, vanillic acid, syringic acid, p-coumaric acid, o-coumaric acid and sinapic acid). In all extracts, benzoic acid derivatives were the most abundant. The acetone solution (80% v/v) at 50 °C was the most effective solvent for the quantitative extraction of both benzoic and cinnamic acid derivatives.