Carotenoids and colour diversity of traditional and emerging Tunisian orange cultivars (Citrus sinensis (L.) Osbeck)

- Tunisian sweet orange juices studied show a large diversity in color and carotenoid composition.
- The juice of Maltaise demi-sanguine showed the highest carotenoid content.
- An unusual lycopene accumulation was identified in the juice of Meski Ahmer cultivar.
- (all-E)-violaxanthin and ζ-carotene were correlated to yellow color intensity index (b*).
- Zeaxanthin and lutein were positively related to Chroma (C*) and (b*) indices.

Citrus are among the most cultivated fruit crops worldwide and occupy a paramount importance in the Tunisian agricultural sector being one of the strategic products. Despite of that, little is known about the quality parameters of Tunisian sweet oranges and some cultivars have not been characterized yet. This work aims to study the coloration diversity of twenty-five Tunisian grown oranges by analyzing their total and individual carotenoids content and the relationship with CIELab color coordinates. Experimental results proved large diversity in the carotenoid composition of the studied juices. Maltaise demi-sanguine cultivar was distinguished from the rest due to its high content of ζ-carotene, lutein and total carotenoids. An unusual lycopene accumulation was detected in the juice of Meski Ahmer. The Tunisian grown Washington Navel cultivar ranked within the rich-carotenoids juices. In addition, significant negative correlations were found between lightness parameters (L*) and Hue angle (H) while they were positively related with redness attributes (a*). Furthermore, (all-E)-violaxanthin and ζ-carotene were both significantly correlated to yellow color intensity index (b*) while zeaxanthin and lutein were positively related to Chroma (C*) and (b*) indices. These findings are of interest since the carotenoids content and composition are directly related to color and citrus juice quality. The results obtained could be part in a selection program-guide of Tunisian cultivars and help to understand the physiological and biochemical bases of sweet orange coloration.

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