Antioxidant activity of Australian tea tree (Melaleuca alternifolia) oil (TTO) was determined using two different assays. In the 2,2-diphenyl-1-picrylhydrazyl assay, 10 microL/mL crude TTO in methanol had approximately 80% free radical scavenging activity, and in the hexanal/hexanoic acid assay, 200 microL/mL crude TTO exhibited 60% inhibitory activity against the oxidation of hexanal to hexanoic acid over 30 days. These results were equivalent to the antioxidant activities of 30 mM butylated hydroxytoluene in both tests at the same experimental conditions. This indicated that the TTO could be a good alternative antioxidant. Inherent antioxidants, i.e., alpha-terpinene, alpha-terpinolene, and gamma-terpinene, in the crude TTO were separated and identified chromatographically using silica gel open chromatography, C(18)-high-pressure liquid chromatography, and gas chromatography-mass spectrometry. Their antioxidant activities decreased in the following order in both assays: alpha-terpinene > alpha-terpinolene > gamma-terpinene.
Green tea catechins (GTCs) as a mixture of (−)-epicatechin (EC), (−)-epicatechin gallate (ECG),
(−)-epigallocatechin (EGC), and (−)-epigallocatechin gallate (EGCG) possess a variety of biological
activities. We have previously studied the stability of GTCs either as a mixture or as individual
epicatechin derivatives in various pH, demonstrating that GTCs as a mixture in alkaline solutions
were extremely unstable and degraded almost completely in a few minutes, whereas in acidic
solutions (pH < 4) they were very stable. For the pH ranging from 4 to 7, the stability of GTCs was
inversely associated with the pH value of the incubation solutions. The present study examined
the effect of ascorbic acid and citric acid on the stability of GTCs incubated in sodium phosphate
buffer (pH = 7.42). Ascorbic acid added to the incubation mixture significantly increased the stability
of GTCs whereas citric acid exhibited no effect. Four epicatechin derivatives examined demonstrated
varying stability, with EGCG and EGC being equally instable and EC and ECG being relatively
stable. The addition of ascorbic acid significantly increased the stability of all four derivatives,
particularly EGC and EGCG. The present results, although not directly transferable to in vivo
conditions, may suggest that the presence of ascorbic acid may stabilize the GTCs in the intestine
where the pH is neutral or alkaline before absorption.
Keywords: Catechin; epicatechin, epicatechin gallate; epigallocatechin gallate; epigallocatechin;
longjing tea
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.