Anthocyanins of red cabbage (Brassica oleracea L.) display colour over a la
rger range of pH-values than the majority of anthocyanins from other natura
l sources, being pink at pH 3, violet at pH 5 and blue at pH 7. Using rever
sed phase high-performance liquid chromatography with diode array detection
, cyanidin was found to be the only anthocyanidin of red cabbage extract an
d, tentatively, identified as cyanidin-3,5-diglucoside and cyanidin-3-sopho
roside-5-glucoside, the latter found in various acylated forms. The apparen
t quantum yield for photobleaching has been determined for red cabbage extr
act at 25 degreesC in air-saturated McIlvaine buffer, using monochromatic l
ight at each of the irradiation wavelengths, 313, 366, and 436 nm, in conti
nuous photolysis experiments, in order to provide an objective measure for
the sensitivity of this food colorant to ultraviolet and visible light. The
quantum yield was found to depend on both pH and irradiation wavelength, r
anging from 0.2x10(-4) mol einstein(-1) for 436 nm light at pH 7.0 to 3.7x1
0(-4) mol einstein(-1) for 366 nm light at pH 5.0. The thermal stability at
pH 3.0 in McIlvaine buffer of four different anthocyanin extracts was comp
ared and, for the temperature range investigated (25-80 degreesC) the degre
e of stability was red cabbage > blackcurrant > grape skin > elderberry. Th
e thermal stability of the same anthocyanin extracts was also compared for
a non-carbonated soft drink medium of pH 3.0 yielding the same order of sta
bility but with rates of degradation approximately twice as high as in buff
er,, which may indicate a detrimental effect of sugar and ascorbic acid. Du
e to the high thermal stability of red cabbage extract in solution, photobl
eaching will be the primary destabilising factor for red cabbage anthocyani
n-coloured products in display. (C) 2001 Elsevier science Ltd. All rights r
eserved.