Abstract: The ultrasonic-microwave assisted extraction of free phenolic acids from Chinese bayberries was optimized and compared with the individual use of either extraction treatment. The distribution and contents of eight major phenolic acids from Chinese bayberries of different maturities were determined by the optimized extraction process combined with high-performance liquid chromatography. Thereafter a comparative study of the antioxidant activity of phenolic acid extracts was carried out. According to the results of the single-factor experiments, ethanol concentration, solid-to-solvent ratio and ultrasonic-microwave treatment time were selected as independent variables for Box-Behnken design. The optimal extraction conditions were determined as follows: ethanol concentration 60%, solid-to-solvent ratio 1:23 (m/V), and 30 s microwave and then 15 min ultrasonic treatment. The yield of phenolic acids was determined to be 36.21 μg/g under the optimized conditions. The main phenolic acids in Chinese bayberries were gallic acid, protocatechuic acid and p-hydroxybenzoic acid, and the distribution and content of phenolic acids varied with the maturity of the fruit. The content of phenolic acids was the highest (45.50 μg/g) at 50% maturity. Phenolic acid extract from 50% mature bayberries exhibited strong antioxidant activities as determined by 1,1-diphenyl-2-picrylhydrazyl (DPPH), hydroxyl radical scavenging and ferric reducing antioxidant power assays. The total phenolic acid content was significantly positively correlated with the DPPH radical scavenging capacity and reducing power (P < 0.01). In summary, this study can provide a scientific basis for the comprehensive utilization and development of Chinese bayberry fruit.

Key words: Chinese bayberry; phenolic acids; ultrasonic-microwave assisted extraction; response surface methodology; antioxidant activity; high-performance liquid chromatography