Background and Objectives: Orange peel extract has been used in Iranian traditional medicine since the long past. The aim of this study was to investigate the antimicrobial activity of methanol extract of orange peel, Sangynla species, on the microorganisms of Staphylococcus aureus, Escherichia coli and Candida albicans as an alternative for conventional chemical preservatives.

Materials and Methods: In this study, the effect of 31 mg/ml orange peel extracts was investigated by using disk diffusion method and minimum inhibitory concentration (MIC) on Staphylococcus aureus, Escherichia coli and Candida albicans. Also the effect of orange peel extract on the biochemical, microbiological and sensory characteristics of milk was studied during 7 days in 4, 25 & 37°C. The controls were milk samples without extract.

Results: The research showed that orange peel extract has an antimicrobial effect on Staphylococcus aureus, Escherichia coli and Candida albicans. In MIC method, the growth inhibitory activity of the extract on Staphylococcus aureus and Escherichia coli was more than on Candida albicans. At 0/15 g/ml concentration of orange peel extract, the growth of all microorganisms in the milk was reduced at 6, 12, 24, 48 and 72 hours. There was a significant correlation between temperature and growth of Candida albicans. In comparison, the orange peel extract is more effective on the growth of Staphylococcus aureus than on Escherichia coli.

Results and Conclusion: In this research, the inhibitory effect of orange peel extract on Staphylococcus aureus, Escherichia coli and Candida albicans has been proven; therefore, it can be used as a herbal combination to inhibit the growth of pathogens in milk. According to the research results, in addition to the orange peel extract, pH and temperature have more bacterial inhibitory activity simultaneously.

Keywords: Orange peel, Extract, Antimicrobial activity, Milk