Monitoring the changes in phenolic compounds and carotenoids occurring during fruit development in the tissues of four citrus fruits.

Citrus are fruit crops that are widely cultivated in Southern Italy. The phytochemical profile of citrus depends on the species, the tissue and the ripening stage. This study aimed to perform a comprehensive analysis of the phenolic compounds and carotenoids from four citrus species cultivated in the region of Sicily, Southern Italy, between and within the different tissues and the ripening stages. The selected species were pummelo [C. maxima (Burm. ex Rumph.) Merr.] cv. 'Chandler', lemon [C. limon (L.) Burm. f] cv. 'Akragas', and sweet orange [C. sinensis (L.) Osbeck] cvs 'Tarocco' and 'Washington navel'. Fruits were harvested four times every five weeks from Sep 2018 to Jan 2019. At any stage, flavedo and albedo showed the highest contents of phytochemicals. Elevated levels of phenolic compounds, e.g., narirutin, were found in the flavedo of unripe lemon and 'Tarocco' orange (54.8 ± 8.15 and 248 ± 30.3 mg kg-1 dw, respectively). Narirutin decreased significantly (p < 0.05) during maturity. An analogous trend (p < 0.05) was observed in the albedos of unripe pummelo and 'Washington navel' orange for vanillic acid (47.7 ± 8.31 and 54.7 ± 9.06 mg kg-1 dw, respectively). Phenolics decreased during maturity in the juice sacs as well, apart from lemon, e.g., hesperidin peaked at the last developmental stage (2213 ± 173 mg kg-1 dw; p < 0.0001). With regard to carotenoids, flavedos were the richest tissues. In general, flavedos increased the levels of carotenoids during ripening, apart from pummelo in which cumulative carotenoids were the highest in September (135 ± 16.5 mg kg-1 dw). Violaxanthin was the main carotenoid of the juice sacs, and was abundant in ripe 'Washington navel' orange (9.09 ± 1.73 mg kg-1 dw in Jan). The present investigation delivers valuable information for the comprehensive utilization of citrus fruits from Southern Italy by the local food industry.