Kinetics and yields for the formation of coloured and aromatic thermal degradation products of annatto in foods
2001
Scotter, M.J. | Castle, L. | Appleton, G.P.
The thermal stability of annatto food colouring has been studied in model systems and foods. High-performance liquid chromatography with photodiode-array detection has been used to monitor the isomerization products of 9'-cis-bixin, the principal colouring component of annatto, and its major coloured C17 degradation product. Headspace gas chromatography-mass spectrometry has been used to determine the degradation products toluene and m-xylene in the head space of model systems and foods containing annatto heated in situ. Fish and cheese spiked with 9'-cis-norbixin produced m-xylene whereas control samples did not. Low levels (ca. 10-50 microgram/kg) of m-xylene were detected in the headspace of annatto-coloured retail samples of custard powder, extruded snacks, margarine and bread crumbs. Higher levels of m-xylene were detected in the headspace of kippers (ca. 150-200 microgram/kg) and observed in the headspace of Red Leicester type cheese (not quantified). The findings indicated that annatto is readily degraded to form both coloured degradation products and the aromatics m-xylene and, to a lesser extent, toluene. In practice however, degradation is slow under heating conditions normal for foods. Neither aromatic species was detected in the headspace of any food studied above 200 microgram/kg.
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