Study On Extraction, Purification, Identification And Antioxidant Activity Of Polyphenols From Lotus Seed Epicarp

Lotus seed epicarp is one of the inedible parts of lotus (Nelumbo Nucifera Gaertn), which grows from green into brown and become more and more hard during maturation. Some literatures have reported that lotus seed epicarp at green mature stage contained polyphenols and other active ingredients. Therefore, the by-product of Lianzi (lotus seed epicarp at full mature stage) has not been fully utilized. So, to know of the values of full mature lotus seed epicarp has very important practical significance.In this paper, lotus seed epicarp in different mature stages were used as the materials, the conditions of ultrasonic extraction and purification on resins were optimized. Through HPLC-MS analysis, the structures of lotus seed epicarp polyphenols in different mature periods were identified. The antioxidant activities and stabilities of lotus seed epicarp polyphenols were also studied. The main results of this research were as follows:1. The ultrasonic extraction conditions of lotus seed epicarp polyphenols in different mature periods were optimized by four-factor and three-level orthogonal experiment. To lotus seed epicarp polyphenols at green mature stage, the best extraction conditions were ethanol concentration 50%, extraction temperature 40℃, extraction time 60 min, solid-liquid rato 1:50; To lotus seed epicarp polyphenols at half mature stage, the best extraction conditions were ethanol concentration 60%, extraction temperature 60℃, extraction time 30 min, solid-liquid rato 1:50; To lotus seed epicarp polyphenols at full mature stage, the best extraction conditions were ethanol concentration 60%, extraction temperature 50℃, extraction time 45 min, solid-liquid rato 1:30. Under the optimal conditions, yields of lotus seed epicarp polyphenols at three stages of green mature stage, half mature stage and full mature stage were 16.02%,12.98, and 8.59%, respectively. We also confirmed that polyphenols was not damaged by ultrasonic extraction.2. The polyphenol extracts of lotus seed epicarp at full mature stage was used as the material to purify by macroporous resin. According to static adsorption and desorption properties of six macroporous resins, the best one was choosed to optimize the purification technology of lotus seed epicarp polyphenols. The results indicated that AB-8 resin had the optimal static adsorption and desorption performance. The optimal dynamic adsorption and desorption conditions of purification onto AB-8 were determined as follows:solution concentration 4.5 mg/mL, feeding rate 0.5 mL/min, ethanol concentration 50%, elution rate 2 mL/min, elution volume 4 BV. Under these conditions, the purity of preliminary purification polyphenols at three stages of green mature stage, half mature stage and full mature stage were 71.2%,66.5%,69.3%.3. The lotus seed epicarp polyphenols in different mature periods were separated by Sephadex LH-20, nine fractions were obtained from all samples. Fraction 5 was identified by HPLC-MS2 at negative mode. Catechin, epicatechin, hyperoside, isoquercitrin were all existed in different mature lotus seed epicarp, but the contents of these 4 compounds were distinct. The percentages of catechin and epicatechin were decreased and the percentages of hyperoside and isoquercitrin were increased with prolonging of lotus seed epicarp maturity date.4. Lotus seed epicarp polyphenols in different mature periods all had antioxidant abilities. The scavenging abilities on DPPH and ABTS+ radical were better than Vc and the scavenging ability was negatively correlated with maturity.5. The stabilities of lotus seed epicarp polyphenols could be improved by low temperature, light-avoiding and midly acidic conditions. Lotus seed epicarp polyphenols could protected by glucose and saccharose, sodium chloride, sodium benzoate has no effect on it. Fe3+, Fe2+, Al3+, Sn2+, Cu2+ and Pb2+ had destructive effect on it. Lotus seed epicarp polyphenols was influenced by pasteurization, microwave sterilization, boiling sterilization, autoclaving and the degree of damage was increased in turn.