The use of natural preservatives became of great interest; good examples of these natural preservation agents are plant peels. The use of plant peels has dual benefits; first is their antimicrobial activity against food-borne pathogens, while the second is minimizing agro-industrial wastes. The evaluation of the antimicrobial potential of both methanolic and ethanolic extracts of three fruit peels (orange, pomegranate, and banana), against 4 Gram-positive (G+), 3 Gram-negative bacteria (G−), and 2 fungal strains revealed that both pomegranate peel extracts exhibited significantly higher inhibitory effect on all tested G+ bacteria. Methanolic extract of pomegranate peel gave higher activity than the ethanolic one against G+ and G− bacteria except for S. typhimurium. Against A. flavus and A. niger, both pomegranate and orange extracts showed activity ranging between 65 and 100% more than the positive control. The ethanolic extracts of all tested peels showed a considerable capacity of antioxidant compounds compared to the methanolic extracts. The highest antioxidant capacity was found for ethanolic and methanolic extracts of pomegranate, 66.870 and 56.262 mg/ml, respectively. Generally, the concentration of total phenolic compounds was higher than that of total flavonoids followed by tannins. The highest readings of all tested constituents were reported for pomegranate extracts followed by orange and then banana. The total phenolic content, total flavonoids, and tannins were proportional to antioxidant values. GC-MS of pomegranate peel extracts identified 23 compounds in the methanolic extract versus 31 compounds in the ethanolic one. These components were identified based on their retention times and mass spectral fragmentation pattern. 5-hydroxymethylfufural (HMF) represented the major component in both methanolic and ethanolic extracts with peak area percentage of 65.78% and 48.43%, respectively. The results showed negative effect of methanolic and ethanolic extracts of pomegranate on G+ and G− bacteria and two fungal pathogenic strains. The phytochemical analysis regarded these results to the high content of phenols, flavonoids, and tannins. GC-MS chromatogram identified many compounds known to be effective as antioxidants and antibacterial and antifungal agents. These indications show that pomegranate peel may be a superior natural food-preserver, but further studies about the suitable formulation, dosage, and possible side-effects are still needed.

中文翻译：

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石榴、橙子和香蕉皮提取物对病原微生物的化学分析、体外抗菌和抗氧化活性

天然防腐剂的使用引起了人们的极大兴趣。这些天然防腐剂的很好例子是植物皮。使用植物皮有双重好处；首先是它们对食源性病原体的抗微生物活性，而第二个是尽量减少农工业废物。对三种果皮（橙子、石榴和香蕉）的甲醇和乙醇提取物对 4 种革兰氏阳性菌 (G+)、3 种革兰氏阴性菌 (G-) 和 2 种真菌菌株的抗菌潜力的评估表明，两种石榴皮提取物对所有测试的 G+ 细菌均表现出显着更高的抑制作用。除鼠伤寒沙门氏菌外，石榴皮的甲醇提取物对 G+ 和 G- 细菌的活性高于乙醇提取物。针对 A. flavus 和 A. niger，石榴和橙子提取物的活性均比阳性对照高 65% 至 100%。与甲醇提取物相比，所有测试果皮的乙醇提取物都显示出相当大的抗氧化化合物能力。石榴的乙醇和甲醇提取物的抗氧化能力最高，分别为 66.870 和 56.262 毫克/毫升。通常，总酚类化合物的浓度高于总黄酮类化合物，其次是丹宁酸。石榴提取物报告了所有测试成分的最高读数，其次是橙子，然后是香蕉。总酚含量、总黄酮和单宁与抗氧化值成正比。石榴皮提取物的 GC-MS 鉴定出甲醇提取物中的 23 种化合物与乙醇提取物中的 31 种化合物。这些组分是根据它们的保留时间和质谱碎片模式进行鉴定的。5-羟甲基糠醛 (HMF) 是甲醇和乙醇提取物中的主要成分，峰面积百分比分别为 65.78% 和 48.43%。结果显示石榴的甲醇和乙醇提取物对 G+ 和 G- 细菌以及两种真菌致病菌株有负面影响。植物化学分析将这些结果视为苯酚、类黄酮和单宁的高含量。GC-MS 色谱图鉴定了许多已知可有效用作抗氧化剂、抗菌剂和抗真菌剂的化合物。这些迹象表明，石榴皮可能是一种优良的天然食品防腐剂，但仍需要进一步研究合适的配方、剂量和可能的副作用。