Mphahlele Rebogile R, Fawole Olaniyi A, Makunga Nokwanda P, Opara Umezuruike L
Postharvest Technology Research Laboratory, South African Research Chair in Postharvest Technology, Department of Horticultural Sciences, Faculty of AgriSciences, Stellenbosch University, Private Bag X1, Stellenbosch, 7602, South Africa.
Postharvest Technology Research Laboratory, South African Research Chair in Postharvest Technology, Department of Food Science, Faculty of AgriSciences, Stellenbosch University, Private Bag X1, Stellenbosch, 7602, South Africa.
BMC Complement Altern Med. 2016 May 26;16:143. doi: 10.1186/s12906-016-1132-y.
The use of pomegranate peel is highly associated with its rich phenolic concentration. Series of drying methods are recommended since bioactive compounds are highly sensitive to thermal degradation. The study was conducted to evaluate the effects of drying on the bioactive compounds, antioxidant as well as antibacterial and antityrosinase activities of pomegranate peel.
Dried pomegranate peels with the initial moisture content of 70.30 % wet basis were prepared by freeze and oven drying at 40, 50 and 60 °C. Difference in CIE-LAB, chroma (C*) and hue angle (h°) were determined using colorimeter. Individual polyphenol retention was determined using LC-MS and LC-MS(E) while total phenolics concentration (TPC), total flavonoid concentration (TFC), total tannins concentration (TTC) and vitamin C concentration were measured using colorimetric methods. The antioxidant activity was measured by radical scavenging activity (RSA) and ferric reducing antioxidant power (FRAP). Furthermore, the antibacterial activity of methanolic peel extracts were tested on Gram negative (Escherichia coli and Klebsiella pneumonia) and Gram positive bacteria (Staphylococcus aureus and Bacillus subtilis) using the in vitro microdilution assays. Tyrosinase enzyme inhibition was investigated against monophenolase (tyrosine) and diphenolase (DOPA), with arbutin as positive controls.
Oven drying at 60 °C resulted in high punicalin concentration (888.04 ± 141.03 mg CE/kg dried matter) along with poor red coloration (high hue angle). Freeze dried peel contained higher catechin concentration (674.51 mg/kg drying matter) + catechin and -epicatechin (70.56 mg/kg drying matter) compared to oven dried peel. Furthermore, freeze dried peel had the highest total phenolic, tannin and flavonoid concentrations compared to oven dried peel over the temperature range studied. High concentration of vitamin C (31.19 μg AAE/g dried matter) was observed in the oven dried (40 °C) pomegranate peel. Drying at 50 °C showed the highest inhibitory activity with the MIC values of 0.10 mg/ml against Gram positive (Staphylococcus aureus and Bacillus subtili. Likewise, the extracts dried at 50 °C showed potent inhibitory activity concentration (22.95 mg/ml) against monophenolase. Principal component analysis showed that the peel colour characteristics and bioactive compounds isolated the investigated drying method.
The freeze and oven dried peel extracts exhibited a significant antibacterial and antioxidant activities. The freeze drying method had higher total phenolic, tannin and flavonoid concentration therefore can be explored as a feasible method for processing pomegranate peel to ensure retention of the maximum amount of their naturally occurring bioactive compounds.
Not relevant for this study.
石榴皮的使用与其丰富的酚类物质含量密切相关。由于生物活性化合物对热降解高度敏感，因此推荐采用一系列干燥方法。本研究旨在评估干燥对石榴皮生物活性化合物、抗氧化以及抗菌和抗酪氨酸酶活性的影响。
将初始湿基含水量为70.30%的石榴皮通过冷冻干燥以及在40、50和60℃下烘箱干燥制备而成。使用色度计测定CIE-LAB、色度（C*）和色相角（h°）的差异。采用液相色谱-质谱联用（LC-MS）和液相色谱-质谱/质谱联用（LC-MS(E)）测定单个多酚的保留量，同时采用比色法测定总酚浓度（TPC）、总黄酮浓度（TFC）、总单宁浓度（TTC）和维生素C浓度。通过自由基清除活性（RSA）和铁还原抗氧化能力（FRAP）测定抗氧化活性。此外，采用体外微量稀释法，对甲醇提取的石榴皮提取物针对革兰氏阴性菌（大肠杆菌和肺炎克雷伯菌）和革兰氏阳性菌（金黄色葡萄球菌和枯草芽孢杆菌）的抗菌活性进行测试。以熊果苷作为阳性对照，研究对单酚酶（酪氨酸）和二酚酶（多巴）的酪氨酸酶抑制作用。
60℃烘箱干燥导致石榴皮苷浓度较高（888.04±141.03 mg CE/kg干物质），同时红色较差（色相角较高）。与烘箱干燥的石榴皮相比，冷冻干燥的石榴皮含有更高浓度的儿茶素（674.51 mg/kg干物质）以及儿茶素和表儿茶素（70.56 mg/kg干物质）。此外，在所研究的温度范围内，与烘箱干燥的石榴皮相比，冷冻干燥的石榴皮总酚、单宁和黄酮浓度最高。在烘箱干燥（在40℃）的石榴皮中观察到高浓度的维生素C（31.19 μg AAE/g干物质）。50℃干燥显示出最高的抑制活性，对革兰氏阳性菌（金黄色葡萄球菌和枯草芽孢杆菌）的最低抑菌浓度（MIC）值为0.10 mg/ml。同样，在50℃干燥的提取物对单酚酶显示出有效的抑制活性浓度（22.95 mg/ml）。主成分分析表明，果皮颜色特征和生物活性化合物区分了所研究的干燥方法。
冷冻干燥和烘箱干燥的石榴皮提取物均表现出显著的抗菌和抗氧化活性。冷冻干燥法具有更高的总酚、单宁和黄酮浓度，因此可作为一种可行的方法用于加工石榴皮，以确保保留其最大量的天然生物活性化合物。
本研究不涉及。
