Study On Antimicrobial Activity Of Pomegranate Peel Extract

The pomegranate (P.granatum L.), a species belonging to the family Punicaceae, originated from Central Aia Area such as Iran's, Afghanistan, etc. It has been 2000 years since pomegranate was cultured in China during the Western Han Dynasty. Pomegranate has high nutritional and pharmaceutical value. The researches showed pomegranate has several physiological functions such as antioxidation, anticancer, antivirus and reducing blood lipid. At present, the researches about biological activity of pomegranate peel focus on antioxidation. The studies about antimicrobial activity are relatively scarce (limited). Moreover, the reports about antimicrobial activity are rare in the terms of food safety and preserving. Pomegranate peel is byproduct in pomegranate juice process. In order to investigate antimicrobial activity of pomegranate peel, common food contaminating microorganisms were used as tested microorganisms and the diameter of inhibition zone was used as the activity monitoring parameter. This paper studied the technology for extracting antibacterial substances from pomegranate peel, antagonistic property and mechanism, the antiseptic effect of pomegranate peel extract in chilled pork. These researches would give reference for exploitation and to other researches of pomegranate peel. The results were described as follows:(1) Preliminary results revealed that the antimicrobial activity of methanol extract was the most potent. The antibacterial activity of pomegranate peel extract was better than the yeast-anti activity. It could hardly inhibit the growth of mildew. The antimicrobial activity was in sequence of S.aureas > L.momocytogenes > B.megaterium, B.subtilis > S.typhimurium> E.coil > Candida lipolytica.(2) The methanol extract of ' Yichengruanzi' had the highest antibacterial activity in 10 tested varieties. The antibacterial activity of pomegranate external tissue was higher than velamen and calyx.(3) The optimum extraction conditions were obtained by quadric regression orthogonal rotary experiments. The result showed that the main factors influencing the extracting effect from more important to less were as follows: ethanol concentration, extracted temperature, ratio of liquid to solid and extracted time; the optimum extraction conditions were that the concentration of ethanol was 60%, the ratio of liquid to solid was 10:1, the temperature of extraction was 60℃and the time of extraction was 4h. By the above conditions, the inhibition zone diameter was 16.30 mm.(4) The results showed that the antimicrobial spectrum of pomegranate peel extract in optimum conditions was similar to that of methanol extract, but the antimicrobial activity of the pomegranate peel extract was better than methanol extract. The MIC and MBC of pomegranate peel extract to S.aurea were 1.562 mg/mL and 3.125mg/mL respectively. The antibacterial activity of the pomegranate peel extract was similar to that of Nisin and higher than that of Sorbic acid potassium and Sodium benzoate.(5) The antibacterial activity of the pomegranate peel extract was stable to temperature, light and ultraviolet radiation. The pomegranate peel extract had the most powerful antibacterial activity under the medium pH 6. Salt, sugar, Na⁺, Ca²⁺, K⁺, Fe²⁺, and Fe³⁺, could increase the antibacterial activity and Fe²⁺ exhibited best effect in these metal ions.(6) The pomegranate peel extract was successively partitioned with petroleum ether, chloroform, EtOAc, butanol. Butanol extract showed the highest antibacterial activity among these extracts. Chemical composition analysis result showed that the antibacterial substances in pomegranate peel were pomegranate polyphenols. 25 fractions were obtained by separating the butanol extract with silica gel column chromatography. Almost all fractions had inhibition activity against S.aureas. But the inhibition activities of all these fractions were slightly lower than that of butanol extract. The antibacterial activities of most of fractions were similar to the pomegranate peel extract.(7) Respiratory inhibition experiment showed that the respiration of thallus was inhibited mainly through the hexose monophosphate pathway, which leaded to be short of NADPH, and induced metabolic function dysfunction. Growth curve assay showed that the pomegranate peel extract inhibited cytodieresis in logarithmic growth phase. After exposure to the pomegranate peel extract, bacterial protein was analyzed by SDS-PAGE. The results showed that protein synthesis was inhibited, especially for large molecular weight protein. After treated by the pomegranate peel extract, it was observed by electron microscopy that the surface and inner structure of bacterial cells were destroyed and induced cells plasmolysis. This study suggested that the antibacterial mechanism of the pomegranate peel extract was that it inhibited HMP and leaded to metabolic function dysfunction and inhibited the synthesis of proteins associated with growth and cleavage of bacteria, then blocked their division and development, leaded to cell pyknosis. Eventually growth and reproduction of cells were inhibited and death.(8) Inhibition of S.aureas by pomegranate peel extract was evaluated in chilled pork. The results showed that all treatment groups had good inhibition activity against S.aureas, 1 % pomegranate peel extract and Fe²⁺+0.5 % pomegranate peel extract both were better than Nisin in the aspect of inhibition activity. Preservation effect of pomegranate peel extract on chilled pork was evaluated by investigating pH value, TVB-N value, total bacterial count, sensory evaluation during storage period. The preservation effect of 1 % pomegranate peel extract was best in all treatment groups.The innovation points were as follows:(1) Biological activity was used as the monitoring parameter and the antimicrobial activity was studied systematically in the terms of food safety and preserving. The results showed that the antimicrobial substances of pomegranate peel mainly were pomegranate polyphenolic compounds.(2) The antimicrobial mechanism of pomegranate peel extract was studied systematically for the first time.(3) Pomegranate peel extract was applied to chilled pork preservation, and it achieved a good effect.