Free And Bound Polyphenol Contents Detemination And Bioactivities Assay Of Pomegranate Peel Of Different Regions

As a traditional medicine, pomegranate peel contains abundant polyphenols, which havemany chronic disease-preventing properties revealed in the recent scientific researches such ascancer, cardiovascular diseases, arthritis and diabetes diet. To provide theoretical basis onutilizion, peels of10pomegranate cultivars grown in4main production regions of Chinawere investigated to ascertain and compare their free and bound polyphenols contents,compositions, antioxidant activities, and anticancer activities in this study. The results are asfollowings.（1） The total free polyphenols, flavonoids and tannins contents of the10peelsranged in104.17~200.91mgGAE/gDW,23.12~54.5mgQUE/gDW and155.02~299.95mgTAE/gDW respectively; the total bound polyphenols, flavonoids and tannins contentsranged in10.34~15.94mgGAE/gDW,2.89~5.17mgQUE/gDW and11.79~16.37mgTAE/gDW. The contents among different cultivars were significantly different to eachother(p<0.05). The total free polyphenols content was significantly consistent with the localtotal precipitation, average temperature, and total sunlight time during the fruit mature period,while no significant correlation was found between the total bound polyphenols content andclimate conditions.（2） The total free polyphenols, flavonoids, and tannins contents of the peels were inthe ranges of107.55~157.60mgGAE/gDW,24.24~44.53mgQUE/gDW and143.03~224.65mgTAE/gDW respectively. The total bound polyphenols, flavonoids, and tannins contents ofthem were in the ranges of7.35~30.89mgGAE/gDW、2.24~11.80mgQUE/gDW and9.01~18.86mgTAE/gDW respectively. The phenolic compositions of whole peel’s, outerpeel’s, inner peel’s, and whole peel juicing marc’s dry powers were significantly differentwith each other (p<0.05), and the powers of the juicing marc had the lowest free polyphenolscontent and the highest bound polyphenols content among them. Cultivars and peel parts havesome different impact on these polyphenol contents’ difference.（3） The antioxidant activities of the peels were assayed by4methods. The resultsshowed that the peel of all cultivars and all parts had effective antioxidant capacities.The DPPH scavenging, ABTS+scavenging, total reducing and total antioxidant capacities of thefree polyphenols of peels from the4regions ranged in55.13~109.89,77.72~118.91,87.91~177.60, and136.85~275.44mgGAE/gDW respectively. And that of the boundpolyphenols ranged in4.71~6.37,3.96~7.50,4.68~12.20and14.31~22.55mgGAE/gDWrespectively. Moreover the antioxidant activities of the samples were highly correlated withtheir phenolics contents（4） The results of HPLC analysis showed that punicalagins B was the maincompound in both the purified free and bound polyphenol extracts. Free polyphenol extractshad higher punicalagins B and ferulic acid contents and less catechine and ellagic acidcontents than bound polyphenol extracts. There were a few differences in the peelpolyphenols constitutes among the different regional cultivars, while the main phenolics ofthem were same (including punicalagins A&B, catechine, and elligic acid（5） The polyphenols extracted from peels of10pomegranate cultivars all hadcytotoxicity in human colon cancer cell line, Caco-2cells. The extracts decreased cellviability in a dose-dependent manner for24h treatment, with a39.3%decrease in cellviability at100μg/mL. AO/EB and DAPI assay showed that the pomegranate peelpolyphenols induced toxicity could cause Caco-2cells apoptosis in different degree.Apoptotic cell signaling pathway proteins expressions showed that polyphenols could induceCaco-2cells apoptosis at concentration of100μg/mL effectively. And pomegranate peelpolyphenols could induce Caco-2cells apoptosis through multiple cell signaling pathways.