Abstract:
The research aimed to study the effect of enzymatic treatment on bioactive compounds from peel and flesh of red dragon fruit. It was found that red dragon fruit harvested 45-50 d after bloom restored higher bioactive compounds and betacyanin than other levels significantly (p<0.05). The pretreatment condition of heating at 85◦C for 3 min together with adding ascorbic acid concentration of 0.2 and 0.1 % (w/w) was suitable to inhibit the browning reaction in flesh and peel, respectively. After enzymatic treatment by pectinase, the flesh sample (F3) and peel sample (P3) degraded until highest reducing sugar of 70.56 (flesh) and 44.54 µg glucose/g FM (peel) showed higher bioactive compounds than other levels significantly (p<0.05). Their antioxidant activities measured by DPPH method were 8 and 2 times higher than control (F0, P0) (2.71,1.05 µg FM/µg DPPH), and those determined by ABTS method were 4 and 7 times more than control (1,029.60, 815.03 µg Trolox equivalents/g FM). Their total phenolic contents were 3 and 4 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 more than control (1,310.10, 220.28 mg catechin equivalents /100gFM). Moreover, their betacyanin contents increased from 15.53 to 45.66 (flesh) and 14.27 to 61.65 mg/100gFM (peel). The dietary fiber was improved from 0.65 to 0.76 and 0.32 to 0.52 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 red dragon fruits flesh and peel composed of the same type of betacyanin which was betanin. The betacyanin stabilities of samples degraded by enzyme were 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). 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 can increase the stability of batacyanin color (60.76, 60.03). The optimum condition to result in the highest red color was the temperature not higher than 25 ˚C, pH range of 4-6, and the time period of lightening not later than 2 d.