The plant is already used commonly in Asia as a flavour additive for tea and other beverages, and shows potential for inhibiting the action of the enzyme tyrosinase in foods, according to findings published in the journal LWT - Food Science and Technology.
Tyrosine is a non-essential amino acid obtained in the diet from various sources, including many high protein products such as soy, poultry, fish, almonds, avocados, bananas, and dairy. The amino acid is also the precursor to melanin, a class of pigmented compounds that contribute to the browning of foods, such a fruit and vegetables.
By inhibiting the action of the enzyme tyrosinase, food processors and manufacturers may slow or prevent the formation of dark colours, off-flavours and a loss of nutritional content, explained the researchers, led by Li-chen Wu from National Chi Nan University.
The Taiwanese researchers used acetone to obtain a phenolic rich extract. According to their findings, the extract contained 264.7 milligrams of gallic acid equivalents per gram of extract of phenolics, and 190.7 mg of catechin equivalents per gram of extract of flavonoids.
The extract also displayed good antioxidant activity when tested in the DPPH and ABTS radical-scavenging assays, they noted.
Experiments to study how the extract may affect the oxidation of tyrosine revealed that the presence of luteolin in the extract was behind the “uncompetitive inhibitory effect upon the oxidation of tyrosine”.
“We have confirmed in current study that the OFE contained substantial amounts of total phenolic compounds and flavonoids, which not only acted as tyrosinase inhibitors but also provided antioxidant activity, as revealed by the scavenging activity toward ABTS and DPPH radicals,” said the researchers.
In terms of melanin formation, in vitro studies with B16F10 cells showed a reduction in tyrosinase activity and melanin formation in a dose-dependent manner. Being able to reduce the formation of melanin also suggests potential for the extract in cosmetics, as a skin-lightening ingredient.
“Our findings support that O. fragrans is a potential natural, functional antioxidant food flavour additive. Additionally, because OFE inhibits melanin formation, it appears to have potential use as an anti-browning food additive, in skin-whitening cosmetics, or as a new drug for treating melanoma,” they concluded.
The chemistry of browning
The Maillard reaction is also known as non-enzymatic browning. The carbonyl group of the sugar reacts with the amino group of the amino acid to form N-glycosylamine, which is unstable and, via the ‘Amadori rearrangement’, produces ketosamines.
These so-called Amadori compounds are involved in a cascade of further reactions that can eventually result in the formation of dark colours, off-flavours and a loss of nutritional content.
Source: LWT - Food Science and Technology
Volume 42, Issue 9, Pages 1513-1519
“Antioxidant activity and melanogenesis inhibitory effect of the acetonic extract of Osmanthus fragrans: A potential natural and functional food flavor additive”
Authors: L. Wu, L.-H. Chang, S.-H. Chen, N. Fan, J.A. Ho