Light sensitivity of elderberry extract. quantum yields for photodegradation in aqueous solution

The quantum yield for photobleaching of a commercial elderberry (Sambucus nigra L.) extract, mainly composed of anthocyanins, has been determined at 25°C for air-saturated 10 mM citrate buffer solutions, using monochromatic light at each of the wavelengths 313 nm, 366 nm, and 436 nm, respectively, in continuous photolysis experiments, in order to provide an objective measure for the sensitivity of this food colorant to ultraviolet and visible light. In the pH region investigated, pH 3.0-3.8, typical of fruit-based products, the quantum yield for photodegradation was found to depend only on the wavelength of irradiation, being 2.1 ±0.2.10-4 mol·einstein-1 at 313nm, 1.6±0.2.10-4mol.einstein-1 at 366 nm, and 2.8±0.6.10-5mol.einstein-1 at 436 nm, whereas solution pH only affects the colour intensity. Results show that light bleaching will be the major destabilising factor for anthocyanin-coloured products in display and that exclusion of uv-light will greatly improve their colour stabilty. © 1997 Elsevier Science Ltd