Characterization of maturity stages in blood oranges: external and internal parameters

Citrus fruit development can be divided into cell division, the expansion phase, and their ripening stage. In oranges, the ripening stages are characterized by total soluble solids (TSS) accumulation and by a simultaneous decrease in total acidity (TA); the ratio of TSS/TA or ripening index (RI) is one of the most used parameters for measuring the maturation process of the fruit. Blood orange (Citrus sinensis L. Osbeck) is characterized by a red-pigmented skin and flesh that makes it more attractive to the consumer and is due to the presence of anthocyanins (flavonoids). Currently, there are no research works focused on characterizing maturity stages in blood oranges, this being the main objective of the present study. Thus, five maturity stages (S1-S5) of the ‘Sanguinelli’ cultivar have been characterized. Average fruit weight, fruit diameter, firmness, external and internal colour, TSS and TA content, and RI were evaluated. In addition, total anthocyanins and phenolics, carotenoids, total antioxidant activity of hydrophilic (H-TAA) and lipophilic (L-TAA) phases, as well as protein and individual sugars and organic acids were quantified in the juice. Blood oranges showed a significant decline in hue, which leads to a higher red colouration of the rind, and a content of TSS and total anthocyanins significantly higher in the last maturity stages. However, the internal colouration did not correlate with the externally observed reddish colour. The total phenolics content, H-TAA and L-TAA significantly increased from the evaluated S3. On the other hand, the content of some individual organic acids, such as oxalic acid significantly decreased in the last maturity stages evaluated. In conclusion, results show that external and internal parameters related to fruit ripening evolve in a different pace on blood oranges.