Abstract
Leptospermum petersonii (family Myrtaceae) is often cultivated for ornamental purposes but also serves as a rich source of bioactive essential oils. While several studies focused on the activities of the essential oils, this study analysed the potential of spent L. petersonii leaves as a natural food preservative. Method: We investigated the in vitro antioxidant and antimicrobial activities of crude L. petersonii extracts against activities of the purified isolated flavonoid, 6-methyltectochrysin, which was characterized using spectroscopic methods. The antioxidant assays followed ORAC, FRAP and TEAC tests. The antimicrobial activities of the extract and purified flavonoid were analysed against six multi-drug resistant microbial strains in broth dilution assays. Result: The results revealed that both the crude extracts and isolated 6-methyltectochrysin exhibited positive radical ion scavenging antioxidant potential, however the crude extract was about 6-fold more potent antioxidant than the purified 6-methyltectochrysin. The crude extract also showed strong antimicrobial activities against Bacillus cereus, and even more potent antimicrobial agent than the reference ampicillin antibiotic against Klebsiella pneumoniae subsp. pneumoniae. A higher resistance was observed for the tested Gram-negative strains than for the Gram-positive ones. 6-methyltectochrysin was generally inactive in the antimicrobial assays. Conclusion: The crude methanolic extract showed significant bioactivity which validates the medicinal relevance of the plant. The observed biological activities, especially against a notorious strain of B. cereus, suggest that L. petersonii could be a promising natural source of food preservatives.
Highlights
Natural products have been used in folk medicine since ancient times
It was initially suggested that the flavonoid constituent of Leptospermum species might be responsible for its medicinal properties given its wide application in folk medicines as a sedative, and in the treatment of respiratory infections and diarrhea [25], this study has shown that, the flavonoid exhibited levels of antioxidant activities, there may be other constituents of the crude extract which may influence the overall biological activities
Gram-negative bacteria, including B. cereus; the methanolic extract from this study showed high inhibition strength against B. cereus, it was inactive against S. aureus
Summary
Natural products have been used in folk medicine since ancient times. These naturally occurring compounds are often considered priori harmless [1] and may be sourced from plants or microbes. Leptospermum plant species have reportedly provided significant benefits in folk medicine. Ethnobotanical survey revealed that Leptospermum flavescens is used in Malaysian folk medicine to improve appetite, treat stomach disorders and relieve menstrual pain [2], while the essential oils from. L. scoparium are widely used in New Zealand as an antibacterial agent [2,3]. The use of Leptospermum in the treatment of wounds/skin diseases was highlighted by Robson and Cooper [4].
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