Optimizing polyphenol extraction techniques of walnut male flowers by surface response methodology and its composition and antioxidant activity

【Objective】 The surface response method was used to optimize the polyphenol extraction process of walnut male flowers, the composition and antioxidant activity were analyzed to provide technical support for the comprehensive utilization of walnut male flowers.【Method】 Dry walnut male flowers was used as the material. On the basis of single factor experiment, the solid to liquid ratio, extraction time, ethanol volume fraction, extraction temperature were selected to optimize the polyphenol extraction process of walnut male flowers, and the optimal extraction process conditions for polyphenol of walnut male flowers was determined under ultrasound effect, and the scavenging rate of superoxide anion and hydroxyl radicals were as indicators to study the antioxidant activities of walnut male flowers polyphenol. The types of polyphenol of walnut male flowers were identified and analyzed by high performance liquid chromatography. Finally, the microstructure of walnut male flowers powders before and after the extraction was characterized by scanning electron microscope.【Result】 The results showed that the ultrasound power was 300 W, and the optimization process parameters of polyphenol of walnut male flowers were obtained by multivariable quadratic regression equation model:solid to liquid ratio was 1:41, extraction time 30 min, ethanol volume fraction 50% and extraction temperature 52℃, the polyphenol yield of walnut male flowers under this condition was 21.32 mg/g, the solid to liquid ratio, extraction temperature and the interaction between solid to liquid ratio and ethanol volume fraction had extremely significant impact on the extraction rate of polyphenols(P<0.01), and the interaction between solid to liquid ratio and extraction time had a significant effect (P<0.05). Through the test of clearing the free radicals in vitro, it was found that vitamin C had the best antioxidant effect, walnut male flowers polyphenol were better, and the 2, 6-di-tert-butyl-4-methylphenol(BHT) was the weakest. Four kinds of monophenol were identified from walnut male flowers by high performance liquid chromatography, the rutinum content was the highest(804 μg/g), followed by chlorogenic acid content(181 μg/g), quercetin content was low(41 μg/g), and gallic acid content was the lowest(18 μg/g). The results of scanning electron microscope(SEM) showed that ultrasound treatment destroyed the tissue structure of walnut male flowers and facilitated the infiltration of polyphenols.【Conclusion】 The multiple quadratic regression equation model can simulate and predict the polyphenols extraction rate of walnut male flower, the polyphenols extraction rate of male flowers is a complex result of the interaction of many influencing factors. Walnut male flowers are rich in polyphenols, and has strong antioxidant activity, which can be developed and utilized as a source of natural antioxidant materials.