STABILITY OF BETACYANIN PIGMENTS FROM RED PURPLE PITAYA FRUIT (Hylocereus polyrhizus) : INFLUENCE OF PH, TEMPERATURE, METAL IONS AND ASCORBIC ACID

Betacyanin pigments from red-purple pitaya fruit (Hylocereus polyrhizus) could be an attractive source of red colourant for food application. This paper presents results on the extraction of betacyanin pigments from pitaya fruits grown locally in Malaysia. Both the flesh of the fruit and its mesocarp were investigated and it was found that the flesh had higher pigment contents compared to its peel component. The concentration of betacyanins expressed as betanin equivalents per 100 g of flesh and peel were 10.1 ± 0.6 mg and 6.7 ± 0.2 mg, respectively when 80% methanol was used.  The stability of betacyanin pigments were investigated at different pH, temperature and in presence of different concentrations of metal ions (Cu2+ and Fe2+) and ascorbic acid. The results showed that the pigment was most stable at pH range between 5 and 6. However, it forfeited its stability to the heat induced at elevated temperatures. Metal ions (Cu2+ and Fe2+) proved to be capable of accelerating betacyanin degradation, with Cu2+ exhibiting the greatest effect. By contrast, supplementation with ascorbic acid could enhance the pigment stability against the detrimental effects caused by pH, temperature and metal ions. Nevertheless, if the concentration of ascorbic acid exceeds 0.7 %, it may change its role from pigment stabilizer to become a pro-oxidant.    Keywords: Betacyanin, pigments, pitaya fruit, Hylocereus polyrhizus, ascorbic aci

Pectins from dragon fruit (Hylocereus polyrhizus) peel

The extraction of pectin from a by-product of dragon fruit processing, was identified as an alternative source for commercial pectin. In this work, dried alcohol-insoluble residues (AIR) of dragon fruit peels were treated separately with ammonium oxalate/oxalic acid 0.25 %, pH 4.6, 85oC; HCl 0.03 M, pH 1.5, 85oC; and deionised water, 75oC. The pectin obtained from these methods were compared in term of yield, color, gelling characteristic and chemical structure. The highest yield for the extracted pectin from dragon fruit peels was 20.1 % (dry weight basis) by ammonium oxalate/oxalic acid extraction, contained 11.2 % moisture and 6.9 % ash. Extraction by deionised water yielded 15.4 % pectin, 11.3 % moisture and 11.6 % ash. Whereas, the acid extraction gave the lowest yield 15 %), 11.1 % moisture and 12 % ash. The amount of pectin from all extraction conditions were comparable to pectin obtained from commercial apple (12 %) or citrus (25 %). Gel hardness test was performed for gelling properties measurement. The Fourier Transform Infrared Spectroscopy (FTIR) was useful in the identifying dragon fruit pectins. Different conditions used in the extraction do not show a difference in the pectin structure. With a good recovery yield and gelling properties, ammonium oxalate-extracted dragon fruit pectin present good characteristics to be exploited industrially as food additive

STABILITY OF BETACYANIN PIGMENTS FROM RED PURPLE PITAYA FRUIT (Hylocereus polyrhizus) : INFLUENCE OF PH, TEMPERATURE, METAL IONS AND ASCORBIC ACID

Betacyanin pigments from red-purple pitaya fruit (Hylocereus polyrhizus) could be an attractive source of red colourant for food application. This paper presents results on the extraction of betacyanin pigments from pitaya fruits grown locally in Malaysia. Both the flesh of the fruit and its mesocarp were investigated and it was found that the flesh had higher pigment contents compared to its peel component. The concentration of betacyanins expressed as betanin equivalents per 100 g of flesh and peel were 10.1 &plusm