Effect of ascorbic acid on deterioration of carotenoids and colour in ultrafrozen orange juice

The influence of externally added ascorbic acid (AA) on the deterioration of carotenoid pattern and colour of orange juices has been assessed. Regardless of the enrichment of the samples with ascorbic acid, the changes in their carotenoid profile were analogous and involved mainly the epoxycarotenoids. The decreases in the levels of the two major carotenoids, namely (9Z)-violaxanthin and (9Z)- or (9′Z)-antheraxanthin, due to acid-elicited 5,6-epoxide to 5,8-furanoxide isomerizations, were markedly distinct, with the levels of the former dropping more markedly. It was observed, in any event, that the decreases were higher in the sample spiked with the higher amount of ascorbic. In view of these results it has been hypothesized that the location of (9Z)-violaxanthin in orange cloud particles could be more accessible to the juice acids to that of (9Z)- or (9′Z)-antheraxanthin. In addition, the enrichment of the juices seems to promote the contact of the carotenoids and the acids during their deterioration. In terms of colour, it has been concluded that these changes in the carotenoids led to colour differences that can be discerned visually and that the use of a black background for the measurements yielded a better differentiation among the samples.