What Is the Benefit of Pomegranate Peel Extract Powder?

Pomegranate (pomegranate) is a deciduous shrub or small tree in the genus Punica, native to Central Asia. It was introduced to China during the Western Han Dynasty by Zhang Qian during his diplomatic mission to the Western Regions. It is cultivated in Lintong, Shaanxi Province; Zaozhuang, Shandong Province; Huaiyuan, Anhui Province; Huili, Sichuan Province; and Mengzi, Yunnan Province [1].

Pomegranate peel is the dried rind of the pomegranate. It is sour and astringent in nature, and has the effects of astringing the intestines, stopping bleeding and killing insects [2]. Pomegranate peel polyphenols are the general name for the hydroxylated compounds in pomegranate peel, including ellagitannins, gallotannins, ellagic acid, gallic acid, catechins, anthocyanins, chlorogenic acid, ferulic acid, and quercetin, among other compounds, accounting for 10% to 20% of the dry weight. Research has shown that it has antioxidant, anti-aging, antibacterial, anti-mutagenic, blood pressure lowering, and skin moisturizing and beautifying effects, and has enormous application value in fields such as food, medicine, and daily chemicals.

1 Extraction method of pomegranate peel polyphenols

The extraction methods for polyphenols generally include hot water extraction, solvent extraction, alkaline dilute alcohol or alkaline water extraction, ultrasonic-assisted extraction, microwave extraction and supercritical CO2 extraction. Choosing the appropriate extraction method during the extraction of polyphenols will help to improve the extraction efficiency and enhance the extraction effect, thereby obtaining the desired experimental results and creating favorable conditions for subsequent experiments.

1. 1 Solvent extraction method

The solvent extraction method is based on the solubility of various components in plants in solvents. A solvent with high solubility for active ingredients and low solubility for components that do not need to be dissolved is selected to dissolve the active ingredients from plant tissues [3]. At present, the main method for extracting polyphenols is the organic solvent extraction method, and the commonly used organic solvents include methanol, ethanol, acetone, and ethyl acetate [4-6]. These organic solvents have good solubility for polyphenols, do not chemically react with polyphenol substances, and have the advantages of less impurities and being easy to separate. Jia Dongying et al. [7] used 20% ethanol by volume as the solvent, a liquid-to-material ratio of 1:20, and extracted at 50 °C for 1 h, achieving a polyphenol yield of 22.86% and very good results. Sun Lanping et al. [8] also used 50% ethanol as the extraction solvent at a liquid-to-material ratio of 25:1 and 70 °C for 1.5 h, the polyphenol yield from pomegranate peel was 16.28%.

Wang Xiaoyu et al. [9] used methanol, ethanol, ethyl acetate and water to extract the total polyphenols from Xinjiang pomegranate peel in a pre-experiment. The results showed that the polyphenol yield was methanol > ethanol > water > ethyl acetate. Since the yield of polyphenols from methanol and ethanol as solvents is not significantly different, and ethanol is the safest of the three solvents, it is the least expensive, widely available, and has a high recovery rate. Therefore, ethanol was selected as the extraction solvent. It can be seen that ethanol is the preferred extraction solvent for the extraction of polyphenols from pomegranate peel.

1. 2 Microwave-assisted extraction method

The material is heated by microwaves, causing an increase in internal temperature and pressure. When the pressure reaches a certain level, the cells of the raw material rupture, and the substances to be extracted from the cells dissolve in the extraction solvent. In addition, the electromagnetic field generated by microwaves accelerates the diffusion rate of the extracted components from the inside of the material to the interface with the extraction solvent, thereby shortening the extraction time [10-11]. Song Weiwei et al. [12] found that under optimal experimental conditions: 40% ethanol, extraction power of 242 W, extraction time of 60 s, and a material-to-liquid ratio of 1:35, the polyphenol content of the crude extract after three extractions was 19.548 g/100 g.

 Liu Hong et al. [13] used microwave extraction to extract polyphenols from pomegranate peel in Huili, Sichuan. The optimal extraction process was determined by orthogonal experiments: 30% ethanol solution, material-to-liquid ratio 1:20, extraction power 300 W, extraction temperature 60 °C, extraction time 100 s, The polyphenol yield was 26.91% after three extractions. The order of influence of each factor on the polyphenol yield from pomegranate peel was as follows: extraction power > extraction temperature > extraction time > number of extractions. Microwave-assisted extraction of pomegranate peel polyphenols is a new way of comprehensively studying the extraction process, as it is faster and the polyphenol yield is higher.

1. 3 Ultrasonic-assisted extraction

Ultrasonic-assisted extraction uses ultrasonic waves to create cavitation in plant tissues in a solvent, rupturing the cells and allowing the solvent to penetrate into the interior of the plant cells and dissolve their active ingredients. Ultrasonic-assisted extraction has the characteristics of high extraction efficiency, does not damage the active ingredients, and can prevent degradation or discoloration of the extract during prolonged exposure to high temperatures or air. It is currently widely used to extract bioactive ingredients such as alkaloids [14-15].

Zhao Yanhong et al. [16] optimized the ultrasonic extraction of pomegranate peel polyphenols by response surface methodology, and explored the relationship between the yield of pomegranate peel polyphenols and the secondary extraction time under the optimal extraction conditions. They also compared shaking extraction with ultrasonic-assisted extraction. Ultrasonic extraction does not require heating, and the total extraction time is only 35 min, which is 1/7 of the shaking extraction time. The optimal extraction conditions for industrial production were obtained: an ethanol volume fraction of 59%, an ultrasonic time (26 min for the first time and 10 min for the second time), an ultrasonic power of 90 W (an ultrasonic intensity of 0. 2 W / cm), and an extraction yield of 321. 26 mg / g. Cao et al. [17] used orthogonal experiments to extracted three times under the optimal process conditions of a solvent of 40% ethanol, a liquid-to-liquid ratio of 1:30, an extraction time of 30 min, and an extraction temperature of 60°C. According to these optimal conditions, the extraction rate of pomegranate peel polyphenols was 25.45%. Therefore, ultrasonic-assisted extraction can effectively increase the extraction rate of total polyphenols, with the advantages of short time and high extraction yield.

1. 4 Supercritical fluid extraction

Supercritical fluid extraction and separation is carried out using the effects of pressure and temperature on the solubility of supercritical fluids. When supercritical fluids are brought into contact with substances to be separated under supercritical conditions, they selectively extract components in order of polarity, boiling point and molecular weight. Supercritical CO2 extraction technology is safe, hygienic, high-quality, efficient, and can operate at room temperature. It is especially suitable for the extraction of volatile and heat-sensitive substances and can ensure the “naturalness” of the extract.

Yu Jicheng et al. [18] used single-factor condition selection and orthogonal test optimization to extract the optimal conditions for the extraction of tea polyphenols from green tea using supercritical CO2 extraction technology: temperature 60 °C, pressure 25 MPa, extraction time 1 h, and an extraction rate of 43.68% for tea polyphenols. From the experimental data, we can see that the polyphenol extraction rate is quite high. Feng Wq et al. [19] used supercritical CO2 extraction, ultrasonic extraction, microwave extraction and maceration extraction to extract gallic acid from pomegranate peel and determined its content by HPLC. The results showed that the contents of gallic acid extracted by the four methods were 0.396%, 0.311%, 0.271% and 0.498%, respectively. It can be seen that supercritical CO2 extraction is a highly efficient method for extracting gallic acid from pomegranate peel.

2  Research results on the activity of pomegranate peel extract

2. 1   Antioxidant effect

Free radicals are intermediate metabolites in many biochemical reactions in the human body. Under normal circumstances, the body is in a dynamic balance between the continuous production and removal of free radicals. Excessive production or insufficient removal of free radicals can cause damage to tissues [20]. Harman [21] improved the free radical theory based on previous research: he believed that free radicals attack macromolecules of life, thereby causing damage to tissue cells, and are the root cause of aging, tumors, and some other diseases. Modern medicine and free radical science are increasingly proving that free radicals are closely related to many life phenomena and diseases, such as atherosclerosis, hypertension, cataracts, cancer, myocardial ischemia reperfusion injury, arthritis and rheumatoid arthritis. Pomegranate peel polyphenol extract can effectively remove free radicals, thereby playing an antioxidant role.

Zhang Qian et al. [22] showed that the four extracts of pomegranate peel, namely, water, methanol, acetone and ethyl acetate, all have the ability to resist lipid peroxidation and scavenge DPPH free radicals, and their antioxidant activity increases with the increase of the amount added. Among them, the acetone extract has the strongest anti-lipid peroxidation effect. When the addition amount is 0.1% of the lard mass, the anti-lipid peroxidation activity is close to that of 0.02% of the added amount of tea polyphenols or BHT. The water extract with a mass concentration of 0.0175 mg/mL has a high scavenging rate of 85.2% for DPPH free radicals, which is higher than that of BHT, but slightly lower than that of tea polyphenols. Tian et al. [23] used a bath of pomegranate peel extract and mouse liver homogenate, and induced lipid peroxidation either spontaneously or with free radical inducers CCL4, H2O2 and iron ion-ascorbic acid (Fe2+–VitC), using the amount of MDA produced as an indicator of the degree of lipid peroxidation. The results showed that pomegranate peel extract can significantly reduce the spontaneous generation of MDA in mouse liver tissue and reduce the lipid peroxidation reaction in the liver caused by CCL4, H2 O2 and (Fe2 + -VitC). Pomegranate peel extract has a good anti-lipid peroxidation effect.

Zhou Benhong et al. [24] studied the protective effect of pomegranate peel on lipid peroxidation damage to cell membranes caused by free radicals. A model control group, a normal control group, and three pomegranate peel extract administration groups were set up using a lipid peroxidation induced by three reactive oxygen species production systems as the experimental model. The MDA content in each group was observed and compared. The results showed that compared with the control group, the three groups of pomegranate peel extracts had an inhibitory effect on the increase in malondialdehyde, a product of lipid peroxidation in cell membranes, caused by the xanthine-xanthine oxidase system, H2 O2 and UV irradiation. Negi et al. [25] used ethyl acetate, acetone, methanol and water extracts of pomegranate peel to form phosphomolybdenum compounds to evaluate their antioxidant capacity. The experimental results showed that they all had strong antioxidant capacity, with the water extract being relatively low.

The mutagenic effect of the extracts on the sodium azide mutagen was examined by the Ames experiment. The results showed that the four extracts exhibited strong ability to reduce the sodium azide-induced mutations in Salmonella typhimurium when the content of each plate was 2500 μg.   Shahid et al. [26] found that pomegranate peel methanol extract can effectively stabilize sunflower oil due to its strong antioxidant properties.

Li Yunfeng et al. [27] compared the antioxidant capacity of pomegranate peel extract and pomegranate pulp extract. As pomegranate peel extract is rich in total polyphenols, flavonoids and vitamin C, it is superior to pomegranate pulp extract in scavenging superoxide anion radicals, hydroxyl radicals, peroxyl radical, and its ability to inhibit CuSO4-induced oxidation of low-density lipoprotein, is stronger than pomegranate pulp extract, exhibiting strong antioxidant properties. As a natural antioxidant, pomegranate peel has the advantages of being widely available, having a high extraction rate, strong antioxidant activity, strong affinity with the body, and high safety, which are unmatched by synthetic antioxidants. Pomegranate peel is a research focus in the future.

2. 2 Antibacterial effect

With the widespread clinical use of antibiotics, the problem of bacterial drug resistance is becoming increasingly serious and has become a hotspot of global concern. Chinese herbal medicine has incomparable advantages over Western medicine due to its characteristics such as low toxicity and side effects, low residues, low susceptibility to drug resistance, and antibacterial and antiviral effects [28]. A large number of synthetic chemical pesticides are used to prevent crop pests and diseases. Due to the problem of pesticide residues, they pose a great hazard to human health.

Bacteriostatic plants are the best alternative to chemical fungicides. Polyphenols can inhibit the growth of microorganisms by disrupting the integrity of cell walls and cell membranes, causing microbial cells to release intracellular components, which in turn causes functional disorders such as membrane electron transport, nutrient absorption, nucleotide synthesis, and ATP activity. Xiong Yingying [29] studied the inhibitory effects of pomegranate peel water and ethanol extracts from Pishan County, Hotan, Xinjiang, on bacteria, yeast, and molds. The results showed that the antibacterial activity of the ethanol extract was stronger than that of the water extract. The inhibition effect on Staphylococcus aureus and Bacillus subtilis was most significant, with a diameter of 32 mm. The minimum inhibitory concentration for Staphylococcus aureus was 3.125%, and the minimum inhibitory concentrations for brewer's yeast and baker's yeast were 50%.

Hu Wei et al. [30] used the agar dilution method to detect the minimum inhibitory concentration (MIC) of pomegranate peel water extract on Helicobacter pylori metronidazole-resistant and sensitive strains. The results showed that the MIC50 of pomegranate peel for H. pylori metronidazole-resistant and sensitive strains was 29.9 and 28.0 mg/mL, MIC75 were 65. 1 and 59. 1 mg / mL, respectively, and MIC90 were 131. 1 and 115. 9 mg / mL, respectively. Pomegranate peel has a good bacteriostatic effect, and both H. pylori metronidazole-resistant strains and sensitive strains are sensitive to it. Zoreky [31] studied the inhibitory effect of 80% pomegranate peel methanol extract on Listeria monocytogenes, Staphylococcus aureus, Escherichia coli, Yersinia enterocolitica, and Salmonella enterica. Since the methanol extract contains a total polyphenol content of 262.5 mg/g, its MIC against Salmonella enterica is only 4 mg/mL.

Qiao Shuhua et al. [32] studied the in vitro biological activity of methanol, chloroform and n-hexane extracts of pomegranate peel against the cucumber wilt fungus. The results showed that the methanol extract had the most significant antibacterial activity. The biological activity of the solvent extracts of pomegranate peel against four pathogens, including cucumber wilt fungus, gray mold fungus, corn smut fungus and cotton root rot fungus, was then determined using the growth rate method and spore germination method. Among the petroleum ether, chloroform, ethyl acetate and n-butanol extracts of the methanol extract, the n-butanol extract had the strongest antibacterial activity. When the mass concentration was 200 g/L, the inhibition rate of the four test fungi was greater than 70%, and the inhibition of the corn small spot fungus was 90.67%.

In terms of preventing the deterioration of soy sauce, Shao Wei et al. [33] used pomegranate peel extract to replace chemical preservatives with toxic side effects on the human body in the storage of soy sauce, and achieved a good antibacterial effect. When the concentration in soy sauce reaches 1.2%, it can effectively inhibit microorganisms, and its bacteriostatic effect is better than 0.1% sodium benzoate and potassium sorbate. The powerful inhibitory effect of pomegranate peel on various bacteria has laid the foundation for the development, research and application of anti-infective traditional Chinese medicine, and has also opened up new fields of traditional Chinese medicine research.

2.3 Pharmacological effects

As a traditional Chinese medicine, pomegranate peel can treat various infectious diseases such as bacterial dysentery and amoebic dysentery [34]. With the deepening of research, the application of pomegranate peel extract is becoming more and more extensive. Cheng Huichang et al. [35] used an isolated rabbit intestinal tube test to observe the response of isolated intestinal tube movement by injecting different doses of chebulic acid and pomegranate peel extract into the duodenum, jejunum and ileum of rabbits. The results showed that both extracts could inhibit intestinal tube movement, reduce its tension and contractile frequency, thereby exploring their effects on the smooth muscle movement of the small intestine and providing a reliable physiological basis for clinical application.

Lv Qin et al. [36] investigated the effect of pomegranate peel extract on the humoral immune function of mice. By measuring the antibody-secreting cell function (antibody OD value) and the level of serum hemolysin (HC50) in the blank control group, immunocompromised model group, and pomegranate peel extract low-, medium-, and high dose group and the positive control spirulina group, the levels of antibody secreting cell function (antibody OD value) and serum hemolytic factor (HC50) were measured, and it was concluded that pomegranate peel extract has a certain effect on improving the humoral immune function of mice.

Ross [37] gavaged experimental rabbits with pomegranate peel extract, and the results showed that pomegranate peel extract can enhance leukocyte migration inhibition and cause a significant increase in antibody titer. Chen Lei et al. [38] injected different concentrations of pomegranate peel polyphenol compound solution into the abdomen of toads, recorded the changes in heart rate and myocardial contractility before and after administration in anesthetized toads to observe its effect on the heart rate and myocardial contractility of in vivo toads. The results showed that pomegranate peel polyphenol compounds can inhibit the heart rate and myocardial contractility of in vivo toads. Cheng et al. [39] used ethyl acetate to extract and enrich pomegranate peel polyphenols, and established a hyperlipidemia model in rats with a high-fat diet to observe the effect of feeding the high-fat diet extract for 28 days on the blood lipid and liver lipid levels of rats.

The results showed that after the high-fat group rats were fed with the polyphenol extract, their serum TC, TG, LDL-C, FFA and liver TC, TG, FFA were 42.4%, 58.5%, 48.9%, 20.6% lower than those in the high-fat control group, and 32.6%, 11.9%, 25.5% lower than those in the high-fat group, respectively. It also had the effect of increasing the level of high-density lipoprotein cholesterol (HDL-C) in the blood. Pomegranate peel polyphenol extract has the effect of lowering blood lipids and liver lipids, but its active ingredients need to be further analyzed. Yang Lin et al. [40] used pomegranate peel tannins to gavage Wistar rats that had been gavaged with 5.2 g/kg adenine solution for a period of time to produce a chronic kidney failure-like condition. The rats were killed, blood was taken, and kidney tissue was retained. and measured blood creatinine (Scr), blood urea nitrogen (BUN), methylguanidine (MG), guanidinosuccinic acid (GSA), calcium ions (Ca2+) and phosphorus ions (P3+). The results showed that pomegranate tannins can reduce the blood Scr, BUN, MG, GSA and P3+ levels in rats with chronic kidney failure, and elevated Ca2 + levels. The efficacy was significantly better than that of the model group. Pomegranate tannins can basically restore the normal structure of the kidneys in rats with chronic renal failure, and have a certain effect in reducing uremic toxins.

Lian Jun et al. [41] experimentally observed the therapeutic effect of pomegranate peel water extract on rats with a chronic ulcerative colitis model. Pomegranate peel water extract can significantly relieve the symptoms of chronic ulcerative colitis caused by the DNCB compound acetic acid method, and the therapeutic effect is obvious. Pomegranate peel extract can astringent the intestines, stop bleeding, and expel worms. It can treat chronic diarrhea, chronic dysentery, bloody stools, prolapse, spermatorrhea, uterine bleeding, vaginal discharge, abdominal pain due to worm infestation, scabies, etc., and shows great development prospects in medicine!

2. 4 Other effects

Pomegranate peel has strong antioxidant capacity, antibacterial capacity, and pharmacological properties, it can also be used as a new adsorbent to adsorb heavy metals or dyes in wastewater. Ashtoukhy et al. [42] used pomegranate peel as a new adsorbent to successfully remove heavy metals lead and copper from wastewater. Bhat-nagar et al. [43] also found that pomegranate peel can effectively adsorb 2,4-dichlorophenol in wastewater, with an adsorption capacity of 65.7 mg/g. Nevine et al. [44] used pomegranate peel as activated carbon to adsorb the blue-106 dye in wastewater, and investigated the effects of initial pH, temperature, initial dye concentration, adsorbent dosage and reaction contact time on adsorption capacity.

The results showed that the adsorption capacity of pomegranate peel adsorbent was the strongest at pH 2, and the adsorption capacity was proportional to the amount of adsorbent and inversely proportional to the initial concentration of dye and temperature. The thermodynamic parameters of the adsorption process were also investigated, and it was concluded that the adsorption of dye by pomegranate peel was an exothermic process. Pomegranate peel, as a new and inexpensive adsorbent, has great development and application value, but it has not been reported in China. Pomegranate peel extract also has a very good enzyme inhibitory effect.

Xie Zhenjian et al. [45] studied the inhibitory effect of pomegranate peel extract on α-amylase and α-glucosidase. The inhibitory effect of pomegranate peel extract on the two enzymes increased with increasing concentration. When the mass concentration is 60 mg/mL, the inhibition of α-amylase is 39.55%; when the concentration is 1-10 μg/mL, the inhibition of α-glucosidase is linearly related to the concentration; when the mass concentration is ≥10 μg/mL, the increasing trend tends to be flat. The inhibition rate of the extract at a mass concentration of 10 μg/mL is 90%. Pomegranate peel extract is a potential hypoglycemic factor.

Sun Hui et al. [46] studied the inhibitory effect of pomegranate peel extract on aldose reductase (AR), and the effect size also increased with increasing concentration. Among the acetone, methanol and water extracts, the acetone extract had the strongest inhibitory effect on the enzyme, with a half-inhibitory concentration IC50 of 34.77 μg/mL, the IC50 of the methanol extract was 44.18 μg/mL, and the IC50 of the water extract was 62.07 μg/mL. The acetone and methanol extracts both exhibit competitive inhibition of AR; the Ki values for inhibition of AR at a mass concentration of 0.033 mg/mL are 49 μg/mL and 71 μg/mL, respectively. Pomegranate peel extract can effectively inhibit enzymes related to glucose metabolism in diabetic complications, and can prevent and delay the occurrence and development of diabetic complications.

3 Conclusion

Pomegranate peel extract contains a variety of physiologically active ingredients such as polyphenols, flavonoids, alkaloids, etc., which have the functions of anti-oxidation, anti-aging, anti-mutation, anti-bacterial, anti-viral and protecting the reproductive and digestive systems. In the future, further research on the pharmacological active ingredients and other activities of pomegranate peel is needed to provide a new effective natural medicine for clinical use and lay a good foundation for new drug development. With the deepening of research, pomegranate peel will better benefit mankind!

References

[1] Wu Yunliang. Development and utilization of pomegranate resources and industrialization [J]. Resource Development and Market. 1999, 15(4): 208-209.

[2] National Pharmacopoeia Commission. Pharmacopoeia of the People's Republic of China: Part I [S]. Beijing: Chemical Industry Press, 2005: 63.

[3] Zhou Liguo. Natural food colors and their extraction and application [M]. Beijing: Science and Technology Publishing House, 1993.

［4］Kanda T，Akiyama  H，Yanagida  A，et  al. Inhibitory  Efects  of  Apple Polyphenol  on  Induced  Histamine  Release  from  RBL-2H3  Cells  and Rat  Mast  Cells［J］． Bioscience，Biotechnology  and  Biochemistry， 1998，62( 7) :  1284-1289 .

［5］Matej Stopar，Uros Bolcina，Andreha，et al．Lower Crop Load for  CV．Jonagold Apples( Malusdomestica Bo-rkh) Increases Polyphenol Content and Fruit  Quahty［J］．Agricultural  and  Food  Chemistry，2002，50  ( 6) :  1643-1646 .

［6］Alonso-Salces R M，Korta E，Barranco A，et al．Pressurized Liquid Extraction for the Determination of Polyphenols in Apple［J］．Chromatography A，2001，933( 1) :  37-43 .

［7] Jia Dongying, Yao Kai, Tan Wei, et al. Optimization of polyphenol extraction conditions from pomegranate peel [J]. Forest Chemical Industry, 2006, 26(3): 123-126.

[8] Sun Lanping, Zhang Bin, Zhao Daqing, et al. Optimization of alcohol extraction process of polyphenols from pomegranate peel [J]. Packaging and Food Machinery, 2007, 25(4): 20-23.

[9] Wang Xiaoyu, Gao Xiaoli, Mahemuti Maerdan. Experimental study on the extraction of polyphenolic substances from pomegranate peel in Xinjiang [J]. Chinese Ethnic and Folk Medicine, 2008(1): 8-10.

[10] Fan Xingjun, You Jinmao, Tan Ganzu, et al. Research progress on microwave-promoted organic chemical reactions [J]. Chemical Progress, 1998(3): 285-295.

[11] Li He, Li Ganke, Zhang Zhanxia. Discussion on the mechanism of microwave-assisted extraction in an airtight system [J]. Journal of Analytical Testing, 2004, 23(5): 12-16.

[12] Song Weiwei, Jiao Shirong, Zhou Jia, et al. Microwave-assisted extraction of polyphenols from pomegranate peel and study of the antioxidant and antibacterial effects of the extract [J]. Modern Food Science and Technology, 2008, 24(1): 23-27.

[13] Liu Hong, Ao Bo, Fan Shuhui, et al. Experimental study on microwave extraction of polyphenols from pomegranate peel in Huili, Sichuan [J]. Food and Fermentation Industry, 2008, 36(26): 11172-11173.

[14] Cai Jinxing, Liu Xiufeng, Li Zhaomeng, et al. Extraction of strawberry pigments by microwave-ultrasonic method and study of their physicochemical properties [J]. Food and Fermentation Industry, 2003, 29 (5): 69-73.

[15] Li Yunyuan, Song Guangsen. Study on the extraction of chestnut shell pigments assisted by ultrasound [J]. Food Science and Technology, 2003 (8): 57-59.

[16] Zhao Yanhong, Li Jianke. Response surface method to establish a mathematical model for the extraction of pomegranate peel polyphenols assisted by ultrasound [J]. Agro-Products Processing, 2009 (3): 126-131.

[17] Jiao Shirong, Wang Ling, Chen Mingxia, et al. Study on the ultrasonic-assisted extraction of total polyphenols from pomegranate peel and its antioxidant activity [J]. Journal of Xihua University: Natural Science Edition, 2009, 28 (1): 60-62.

[18] Yu Jicheng, Jin Li, Bo Erlin, et al. Application of supercritical CO2 extraction technology in the extraction of tea polyphenols [J]. Food Science and Technology, 2007, 3(1): 85-87.

[19] Feng Wuqun, Li Hui. Comparison of four methods for extracting gallic acid from pomegranate peel [J]. Chinese Medicine Herald, 2008, 14(8): 16-17.

[20] Ling Guanting. Antioxidant Foods and Health [M]. Beijing: Chemical Industry Press, 2004.

[21] Harman D A. Theory Based on Free Radical and Radiation Chemistry [J]. J Gerontol, 1956(11): 298-300.

[22] Zhang Qian, Jia Dongying, Yao Kai, et al. Study on the antioxidant effect of pomegranate peel extract [J]. China Oil and Fat, 2006, 31(8): 51-54.

[23] Tian H, Liu Y. In vitro lipid peroxidation inhibitory effect of pomegranate peel extract [J]. Journal of Shihezi University: Natural Science Edition, 2007, 25(4): 475-477.

[24] Zhou Benhong, Wang Huiyuan, Wu Yue, et al. Protective effect of pomegranate peel on lipid peroxidation of red blood cell membranes [J]. Journal of Guangdong Pharmaceutical College, 2007, 23(5): 547-549.

［25］Negi P S，Jayaprakasha G K，Jena B S．Antioxida-nt and An- timutagenic Activities of Pomegranate Peel Extracts［J］．Food Chemistry， 2003，80 ( 3) :  393-397 .

［26］Shahid Iqbal，Saba Haleem，Mubeena Akhtar，et al．Efficiency  of Pomegranate Peel Extracts in Stabilization of Sunflower Oil under Ac- celerated Conditions［J］．Food  Research  International，2008，41 (  2 ) :  194-200 .

［27］Li Yunfeng，Guo Changjiang，Yang Jijun，et al．Evaluation of Antioxidant  Properties  of  Pomegranate  Peel  Extract  in  Comparison  with Pomegranate Pulp Extract［J］．Food Chemistry，2006，96( 2) :  254-260 .

[28] Wu Guotao, Yao Jingming, Zhang Lijun, et al. Study on the antibacterial effect and toxicity of pomegranate peel tannin [J]. Chinese Journal of Veterinary Medicine, 2006, 25(6): 32-33.

[29] Xiong Suying. Preparation and antibacterial properties of pomegranate peel bacteriostatic solution [D]. Xi'an: College of Biological Engineering, Northwest A&F University, 2007.

[30] Hu Wei, Dai Wei, Yang Yumei, et al. In vitro antibacterial experiment of pomegranate peel on Helicobacter pylori [J]. Journal of Kunming Medical College, 2006 (4): 25-27.

[31] Al-Zoreky N S. Antimicrobial Activity of Pomegranate (Punica granatum L.) Fruit Peels [J]. International Journal of Food Microbiology, 2009, 134(15): 244-248.

[32] Qiao Shuhua, Jiang Hongyun, Zhang Yanning, et al. A preliminary study of antibacterial substances in pomegranate peel [J]. Pesticides, 2009, 48(4): 299-300.

[33] Shao Wei, Xiong Ze, Le Chaoyin, et al. Application of pomegranate peel extract in soy sauce storage [J]. China Brewing, 2006(2): 21-23.

[34] Yang Liping, Yang Yonghong. Research progress on pomegranate peel [J]. Yunnan Traditional Chinese Medicine Journal, 2004, 25(3): 45-46.

[35] Cheng Huichang, Huo Jun, Song Yuzhen. Comparative experimental study on the effect of Hovenia dulcis and Punica granatum peel extracts on the motility of isolated rabbit intestinal tubes [J]. Anhui Agricultural Science, 2008, 36 (21): 9067-9068.

[36] Lu Qin, Liu Jinbao. Effect of punicalagin extract on the humoral immune function of mice [J]. Journal of Xinjiang Medical University, 2007, 30(5): 484-486.

[37] Gracilus Ross R. Immunomodulatory Activity of Punica Granatum in Rabbits-a Preliminary Study [J]. Journal of Ethnopharmacology, 2001 (78): 85-87.

[38] Chen Lei, Ren Qiang, Xu Fei. Effect of pomegranate peel polyphenols on the cardiac activity of the common toad [J]. Food and Drugs, 2007, 9(12): 24-26.

[39] Cheng Shuang, Guo Changjiang, Yang Jijun, et al. Experimental study on the hypolipidemic effect of pomegranate peel polyphenol extract [J]. Journal of Preventive Medicine of the Chinese People's Liberation Army, 2005, 23(3): 160-163.

[40] Yang Lin, Zhou Benhong, Feng Qi, et al. Study on the effect of pomegranate peel tannins in reducing urinary toxins [J]. Chinese Pharmacy, 2007, 18(30): 2345-2347.

[41] Lian Jun, Ding Wei, Sun Jianxin, et al. Experimental study on the treatment of pomegranate peel extract in rats with ulcerative colitis model [J]. Pharmaceutical Services and Research, 2009, 9(2): 107-110.

［42］El-Ashtoukhy E S Z，Amin N K，Abdelwa-hab O．Removal of Lead  ( II)   and  Copper  (  II)    from  AqueousSolution  Using  Pomegranate Peel as a New Adsorbent［J］．Desalination，2008，223( 1 /3) :  162-173 .

［43］Bhatnagar Amit，Minocha A K．Adsorptive Removal of 2，4- dichlorophenol from Water Utilizing Punica Granatum Peel Waste and Stabilization with  Cement［J］．Journal  of  Hazardous  Materials，2009，168  ( 15) :  1111-1117 .

［44］ Nevine Kamal Amin．Removal of Direct Blue-106  Dye from  Aqueous Solution Using New Activated  Carb-ons  Developed from Pome- granate Peel:  Adsorption Eq-uilibrium and Kinetics［J］．Journal of Hazardous Materials，2009，165( 15) :  52-62 .

[45] Xie Zhenjian, Fan Jue, Tang Pengcheng, et al. Study on the enzyme inhibitory effect of pomegranate peel extract [J]. Anhui Agricultural Science, 2009, 37(7): 2829-2831.

[46] Sun Hui, Jia Dongying, Yao Kai. Inhibitory effect of polyphenol extract from pomegranate peel on aldose reductase [J]. Natural Product Research and Development, 2008(20): 508-510.