Pigment variations in peel and pulp during fruit ripening of Opuntia megacantha from Argentina

Abstract

Cactus fruits are good sources of nutrients, vitamins and pigments such as betalains. Peel colour is the simplest parameter to evaluate fruit ripeness status, together with total soluble solids value (TSS). In consequence, they are related to the decision for the most convenient time for harvesting. However, colour has another important role due to its strong influence in the consumer acceptance of the fruits. The external signs of ripening are colour changes; however, little research has been done concerning pigment content variations during Opuntia fruit development. The main aims of this study were to determine the evolution of pigments and other bioactive substance contents in fruit at several stages in the ripening process. Changes in the pigment compositions (betalains and chlorophylls) in fruit pulp and peel were determined in yellow and orange Opuntia megacantha fruits cultivated in Santiago del Estero, Argentina. Besides, variations of the antioxidant activity, vitamin C and phenolic compound contents were also monitored in the studied period. Size and TSS evolution and other physicochemical parameters were measured during fruit development in the plant. O. megacantha (yellow and orange) fruits were collected at random at five different development stages every two weeks since four weeks before physiological maturity until four weeks after that moment. Chlorophylls, responsible for the green colour of immature fruit, were degraded while betalains were biosynthesized during the eight-week period studied. Betalain concentrations were higher in pulp than in peel, for mature as well for immature fruits. Betaxanthin concentration was significantly higher than that of betacyanins in all cases as expected for orange and yellow fruits. Total chlorophyll contents decreased in fruit peel 46 and 38% during ripening process, in respect to the initial values of 86.8 and 104.5 μg/g, in yellow and orange fruits, respectively.