Study Of Tannins In Pomegranate Extracts

Tannins are a large class of polyphenol compounds which are a strong naturalantioxidants and widely exist in nature plant and food. Much emphasis has been put onstudies of tannin in recent years, and a great amount of work has made clear that tanninhas many outstanding characteristics such as the ability of antioxidation, the ability ofscavenging·OH and excellent biological and pharmacologic activities. Today tannin hasbeen widely used in healthy food, medicine, cosmetics. Because of the complex structureof tannin, it is difficult to artificially synthesize. Tannin is mostly extracted from naturalplants such as gallnut, but natural resources are limited, and resulted in rising in price.Therefore, it will make sense to extract tannin from other new plants which is rich intannins.Pomegranate is very nutritious. It is rich in protein, amino acid, mineral, organic acid,and has a spot of procyanidins, anthocyanins and flavones. These compounds arebeneficial to our health. At present, there have been few reports for pomegranate tannin.According to the analysis of pomegranate, all parts (peel, juice, seed) of the fruitcontained abundant tannins (10%～21%), so pomegranate can be exploited as a goodnatural sourse of tannin. This paper has studied the extraction, purification, andidentification of pomegranate tannin from different varieties and parts. Their biologicalactivities were also studied and analyzed.The results of this research are as follows:1. Total phenols, tannins, procyanidins, anthocyanidins and flavones in the 3 parts(peel, juice and seed) of 3 pomegranate varieties were respectively analyzed. Theresults showed that sour pomegranate, red pomegranate, and white pomegranate,which grow in Lin Tong of Shan xi province in our country all have a high rate oftannins. Therefore they were chosen as material of this study.2. Water extraction technique of pomegranate peel was studied. According to theorthogonality experiments, we determined the optimal condition of extraction fortannin in pomegranate peel: 100℃, 1h, the ratio of solution/material was 20:1,pH=7, 0.5% NaHSO₃ addition, extract 3 times. In this conditions, the extractionyield was more than 90%. For pomegranate seeds, degreased with petroleumether, then dried seeds were extracted with 70% aqueous acetone. For juice, thefiltrate was centrifuged at 4000rpm for 20 min to yield tannins.. 3. Following the optimal extraction, the aqueous extracts were purified byAmberlite ADS-17 resin. Freeze-dried them to yield 9 pomegranate tannins(PTEs).4. Extract of sour pomegranate peel tannin (SPTE) was studied by such means asHPLC and LC/MS. The structures of punicalagin, punicalin, ellagic acid andother 5 compounds from SPTE were identified. Also, their possible pathwaysbreaking were speculated.5. Antioxidant activities of 3 parts (peel, juice, and seed) and extracts of 3pomegranate varieties in China were investigated by using a chemiluminescence(CL) method in vitro. The scavenging ability of pomegranate extracts (PTEs) onsuperoxide anion, hydroxide radical, and hydrogen peroxide was determined bythe pyrogallol-luminol system, the CuSO₄-Phen-Vc-H₂O₂ system, and theluminol-H₂O₂ system, respectively. Protection effect of PTEs on DNA damagewas determined by the CuSO₄-Phen-Vc-H₂O₂-DNA CL system. The resultsshowed that the peel extract of red pomegranate had the best effect on thescavenging ability of superoxide anion because its IC₅₀ value (4.01±0.09μg/mL)was the lowest in all PTEs. The seed extract of white pomegranate couldscavenge hydroxide radical most effectively of the nine extracts (the IC₅₀ valuewas 1.69±0.03μg/mL). The peel extract of white pomegranate had the bestscavenging ability on hydrogen peroxide, which had the lowest IC₅₀ value(0.032±0.003μg/mL) in the nine extracts. The seed extract of white pomegranate(the IC₅₀ value was 3.67±0.03μg/mL) was the most powerful on the DNAdamage preventing effect in all of the PTEs. Also, the statistical analysisindicated that there were significant differences (at P＜0.05) among the extractsof the different varieties and parts in each system.6. The antibacterial ability of 9 PTEs was studied. All the 9 PTEs have markedlyrestraining and germicidal effect for Staphylococcus aureus and Escherichia coli.However, at the concentration of 0.2 mg/mL, 9 PTEs have a little restraining butno germicidal effect for Aspergillus niger and Saccharomycet.