Influence of enzyme treatment on bioactive compounds and colour stability of betacyanin in flesh and peel of red dragon fruit Hylocereus polyrhizus (Weber) Britton and Rose

The role of commercial pectinase enzyme, Pectinex^® Ultra SP-L (10,292 PGU/ml) was studied with respect to the degradation of polysaccharide structure in middle lamella releasing bioactive compounds such as antioxidant, phenolic, total flanovoid and betacyanin in structural cell of flesh and peel of red dragon fruit. The effects of acid, salt, sugar and hydrocolloids on colour stability of betacyanins was also studied. The results showed that samples with enzymatic hydrolysis of the highest reducing sugar content was 70.56 in flesh and 44.54 mg glucose/g FM in peel containing higher bioactive compounds than other stages significantly (p 0.05). Their antioxidant activities measured by DPPH method were 3 and 8 times higher than undegraded samples (control) (1.05, 2.71 μg FM/μg DPPH), and those determined by ABTS method were 4 and 7 times higher than control (1,029.60, 815.03 μg Trolox equivalents/g fresh mass (FM)). Their total phenolic contents were 2 and 3 times higher than control (1,049.18, 561.76 mg gallic acid equivalents/100 g FM), and total flavonoid contents were 5 and 7 times higher than control (1,310.10, 220.28 mg catechin equivalents/100 g FM). Moreover, their betacyanin contents have increased from 15.53 to 45.66 (flesh) and 14.27 to 61.65 mg/100 g FM (peel). The soluble dietary fiber has increased from 0.90 to 1.63(flesh) and 1.93 to 3.53(peel) g/100 g FM. The prebiotic activity scores from using L. acidophilus La5 were 0.15 and 0.12 for flesh and peel, respectively, and those from B. lactis Bb12 were 0.34 and 0.29. Furthermore, it was found that all samples of flesh and peel of red dragon fruit composed of the same type of betacyanin which was betanin. Colour stability of betacyanin from the enzyme degrading samples was compared with those from non-enzymatic treatment. The results showed that food-grade acids with high pKa brought about the highest stability of a* color in flesh and peel (76.02, 78.46). While, the higher salt concentration decreased color stability (28.05, 27.09), and the addition of sugar affected to higher color stability (61.46, 60.13). The outcome from hydrocolloid adding showed that carageenan could increase the stability of betacyanin color (60.76, 60.03). The optimum condition to result the strongest red color was the temperature which is not higher than 25°C, pH range of 4-6, and the light exposure of not more than 2 d. Moreover, the samples degraded by enzyme had more betacyanin content which leaded to get redder color stability with every studied factor than ones without enzymatic degradation. Therefore, red dragon fruit’s flesh and peel extracted by enzyme can be a good material to be developed as food colorant with bioactive compound and to be used instead of synthetic agent in the future.