Separation and purification of rosehip polyphenols by macroporous resin and its antioxidant activity

Abstract: Rosehip contains many kinds of beneficial active substances that human body needs, for example, polyphenols. The present study focuses on the separation and purification technology of crude polyphenol extracted from rosehip by using a macroporous adsorption resin method. Four different types of macroporous resins (ADS-17, AB-8, NKA-9 and D101) were adopted. Through the comparison of the separation effect, AB-8 was selected as the experimental adsorbent due to the strong adsorption ability and high desorption rate. Based on the adsorption isotherm, the adsorptive amount of AB-8 increased gradually with the increasing of polyphenols equilibrium concentration at first and then tended to change gently. The nonlinear curve fitting was conducted with the Langmuir and Freundlich models. Both of the models performed effectively with the R2 of over 0.99, and the Langmuir (R2=0.9999) was more suitable than the Freundlich (R2=0.9948). Static and dynamic adsorption, and desorption experiment results indicated that sample concentration, temperature, pH value, flow velocity of sample, ethanol concentration, and flow velocity of desorption were the major parameters in the process of separating and purifying the rosehip polyphenols by macroporous adsorption resin technology. The optimum conditions were as follows: at room temperature, using AB-8 macroporous resin, the concentration of crude polyphenol extract was 0.80 mg/mL at pH=6.5, with the 1 mL/min flow and the adsorption injection of 200 mL, and the eluting solvent was 70% ethanol with the flow rate of 1.5 mL/min and the volume of 70 mL. Then the effect of purification was determined by total phenol content and total antioxidant capacity. Total phenol content was measured by the Folin-phenol reagent method. The result showed that purified polyphenol solution gained a concentration of 399.42 mg/g, which was 3.25 times higher than the crude polyphenol extract that was 122.90 mg/g. Also the total antioxidant capacity was evaluated by total antioxidant capacity (T-AOC) kit. The T-AOC was significantly increased from 289.70 to 918.34 U/mL after purification. These indicated that AB-8 could be well applied in enrichment of polyphenols from rosehip. In addition, the antioxidant activity of crude polyphenol extract and purified extract were investigated in vitro. The scavenging capacity of DPPH·, O2-· and ·OH known as the common free radicals was evaluated. Vitamin C and butylated hydroxytoluene (BHT) were treated as the positive control. In this work, the sample concentration values needed for purifying 50% of DPPH· were obtained from the linear curve fitting based on the scavenging capacity for the samples with different concentrations and used to assess the antioxidant activity. The results were reported as follows: the effect of purifying DPPH· was vitamin C > purified polyphenol extract > BHT > crude polyphenol extract; the effect of purifying O2-·was vitamin C > BHT > purified polyphenol extract > crude polyphenol extract; the effect of purifying·OH was vitamin C > purified polyphenol extract >BHT > crude polyphenol extract. Obviously, purified polyphenol performed better than crude polyphenol on these methods. Even purified extract had higher antioxidant activity than BHT in DPPH· and ·OH scavenging tests. The present study provides a theoretical reference for the industrial production and further application of rosehip polyphenols.