l of 1 mM XTT, and 190 l phosphate buffer pH 7.0 were added. The mixtures were illuminated within a custom-made reactor equipped with four ventilators to exclude heating of the samples and an LED-stick (Nichia Corporation; NSPB500AS) (λ = 470  10 nm, 15.7 mW measured with a Hioki 3664 optical power meter set to 470 nm). The samples were monitored via UV-vis spectroscopy after 0, 1, 5, 10, 30, 60, 90, and 120 minutes.