Antioxidant Activity Of Pomegranate Peel Polyphenols In Different Ways And Quality Of Pomegranate Peel

Pomegranate is very abundant and relatively concentrated in China, which was mainly cultivated in Lintong Shaanxi, Huaiyuan Anhui, Zaozhuang Shandong, Huili Sichuan, Yecheng Xinjiang, Mengzi Yunnan, and other places. Polyphenol is one of the most important active substances in pomegranate, especially, abundant in the pomegranate peel. It has many functions such as antioxidant, antiatherosclerosis, antitumor, antibacterial, prevention and cure of cardiovascular diseases. However, some pomegranate processing enterprises dispose most of the pomegranate peel as garbage, which resulting in serious resources waste. So, it is necessary to use the pomegranate peel, in order to improve the added value of pomegranate by-products.As the fresh pomegranate peel is difficult to preserve, it is impractical to produce polyphenols. But after drying, the pomegranate peel can be preserved for a long time, which can solve the problem of raw materials supplying in extracting polyphenols from the pomegranate peel. Moreover, choosing different drying methods is to find a suitable preservation method for pomegranate peel, which does neither decompose nor affect the quality and antioxidant activity. Therefore, the effects of different drying process on the quality of pomegranate peel and antioxidant activity were carried out in this thesis, which will provide new ideas and theoretical basis for the comprehensive utilization of the pomegranate peel.The main research contents and results of this paper are as follows:1. This paper used ultrasonic assisted aqueous two-phase system to extract polyphenols from pomegranate peel. On the basis of single-factor experiment, Box-Behnken design and response surface analysis method were applied to evaluate the effects of each single-factor and its interaction on the polyphenols yield, and the best extraction technology was optimized by selecting ultrasonic time, ultrasonic temperature, ammonium sulfate dosage and liquid/material ratio as independent variables, and the yield of pomegranate peel polyphenols as the response value. The results showed that:the best extraction conditions were ultrasonic time,32min, ultrasonic temperature,40?, the dosage of ammonium sulfate,0.36g/mL (ammonium sulfate dosage 0.36g per milliliters of water), liquid/material ratio,37(mL/g), under these conditions, the polyphenol yield was (10.63±0.28)%(n=3), which was better fitting to the predicted value of 10.7086%. So the technology of ultrasonic assisted aqueous two-phase extract polyphenols from pomegranate peel was feasible.2. Different drying methods [natural drying(dried in the sun, dried in the shade), microwave drying, hot air drying(40?,60?,80? and 100?), vacuum freeze drying, vacuum drying] were used to dry the pomegranate peel of Huili and Lintong. The influence of different drying methods on antioxidant activity of pomegranate peel polyphenols was compared by analyzing the following antioxidative indexes:total reducing power, scavenging rate of DPPH free radical, scavenging ABTS+ free radical capacity, superoxide anion free radical scavenging rate. The results showed that:the antioxidant activity of pomegranate peel polyphenols produced in Huili was stronger than that in Lintong. The pomegranate peel polyphenols derived in Huili and Lintong showed the highest antioxidant activity by hot air drying at 40? and 60? while the weakest at 100?. The total reducing power and scavenging superoxide free radical ability were strong by vacuum drying, while scavenging DPPH and ABTS+ free radical ability were the strongest by vacuum freeze drying. The antioxidant activity was weak by microwave and natural drying, but it was close to Vc in certain concentration.3. The quality of the pomegranate peel products produced in Huili and Lintong was investigated after being treated by different drying methods from the following indexes: the yield of pomegranate peel polyphenols, the content of total reducing sugar, pectin and Vc. The results showed that:the content of polyphenol and pectin of pomegranate peel produced in Huili was higher than that in Lintong, but the content of reducing sugar and Vc of pomegranate peel produced in Huili was less than that in Lintong.Comprehensive consideration, hot air drying at 60? for pomegranate peel was the best drying method, which can protect the antioxidant activity of polyphenols and slightly affect the quality of pomegranate peel.