The isolation and properties of a concentrated red-purple betacyanin food colourant from Opuntia stricta fruits

A red-purple food colourant from Opuntia stricta fruits was obtained and studied. Four steps were involved in its isolation: washing, extraction, centrifugation and concentration. Ethanol:water 60:40 (v/v) was selected as the optimum extraction solvent to reduce the viscosity caused by the presence of mucilage and pectins. The resulting 40-fold concentrated extract had a high colour strength (3.9, OD 535nm, 1% v/v sol), a high betanin concentration (4.7gL(-1)) and low viscosity (59.0 cP). It also showed high stability (t(1/2) = 236.6 d, 4 degrees C) mainly due to its low pH (3.4) and low water content (571 g kg(-1)). These characteristics were in the same range as shown by three commercially available liquid concentrated colourants studied (red beet, red carrot and red grape skin). The colour parameters of this concentrated extract of Opuntia stricta were compared with those of commercial red colourants (red beet, red carrot, red grape skin, cochineal, elderberry, hibiscus and red cabbage). CIELAB values of Opuntia stricta (1.5 mL L-1) were L* = 69.8, a* = 59.7 and b* = -23.5. Opuntia stricta presented a vivid red-purple colour which was distinguishable from the colours shown by the other natural red food colourants. (c) 2005 Society of Chemical Industry.