Essential Oil Applications, Leptospermum|

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

Afolabi, W. O., et al. (2020). “Leptospermum petersonii as a Potential Natural Food Preservative.” Molecules 25(23): 5487.

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