The procedure for determining total vitamin C was the same as that used to deter- mine ascorbic acid, with the difference that dithiothreitol was added to the milk before the addition of metaphosphoric acid and the mixture was left to react for 15 min in order to reduce dehydroascorbic acid to ascorbic acid. All the analyses were done in a dimly lit room. Ascorbic acid was resolved by reversed-phase HPLC, using a mobile phase of Milli-Q water with acetic acid (0.1% v/v) and methanol (in a relative proportion of 95:5, v/v). It was de- tected at 254 nm.