Betacyanin and other antioxidants production during growth of Opuntia stricta (Haw.) fruits.

Mature cactus pears from Opuntia stricta have a dark purple color due to high betacyanin concentration, whose biosynthesis is initiated with the amino acid L-tyrosine as a primary precursor. This study followed the maturation and ripening processes of Opuntia stricta fruits to harvest them at high betacyanin and other antioxidant concentrations. Fruits lasted 9 months for final ripening. Physical and compositional changes at different maturation and ripening stages have been determined. Thus, ripe fruits were around 4.72 ± 0.10 cm length, 2.94 ± 0.05 cm diameter and 22.71 ± 0.20 g weight; moisture and pH were maintained at 87.05 ± 0.19 % and 3.37 ± 0.12, respectively. Purple pigment production started in the ovary of immature fruits four months after anthesis (MAA). Concentration of all analyzed metabolites increased from immature (4 MAA) until ripe (9 MAA) stage. In ripe fruits, reducing sugars were 4.72 ± 0.54 g/100 g ff and total phenols 135.17 ± 0.68 mg gallic acid/100 g ff. Metabolites identified by HPLC were the betacyanins: betanin (60.17 ± 1.08 mg/100 g ff), isobetanin (7.58 ± 0.94 mg/100 g ff) and betanidin (13.48 ± 0.87 mg/100 g ff). Also, L-ascorbic acid (35.03 ± 1.06 mg/100 g ff) and L-tyrosine (4.43 ± 0.73 mg/100 g ff) were determined. Furthermore, the addition of L-tyrosine or L-dopa to fruit pulp of moderately ripe fruits, increased betacyanin concentrations 17 (103.3 ± 3.8 mg/100 g) and 32 % (114.3 ± 4.1 mg/100 g), respectively.