Abstract:
The objective of this research was to study the production of bael fruit (Aegle marmelos (L.) Correa) syrup using enzyme processing and the characterization of this syrup. From the selection of the ripeness level, results showed that ripened fruit at 30±2ºC for 10 days had yellowish-orange pulp, fragrant and pleasant flavor and sweet taste significantly higher than other levels (p<0.05). Therefore, the bael fruit at this ripeness level was used as raw material in bael fruit syrup production. This pulp had total, soluble, and insoluble dietary fiber contents of 19.84, 11.22 and 8.62 g/ 100 g dry weight (dw), respectively. It was also found that the antioxidant activities, phenolic, flavonoid, carotenoid, and ascorbic acid contents were 6.21 µg dw/ µg DPPH or 102.74 µM trolox equivalent/ g dw, 87.34 mg gallic acid equivalent/ g dw, 15.20 mg catechin equivalent/ g dw, 32.98 µg/ g dw, and 26.17 mg/ 100 g dw, respectively. Prebiotic activity scores for B. lactis Bb12 and L. acidophilus La5 were 0.20 and 0.01, respectively. A total of 28 volatile compounds were identified by SPME/GC/MS method, and the dominant component of bael fruit flavor was terpenes. The optimum condition to control browning reaction in bael fruit pulps was evaluated by varying the acid content and blanching time during pretreatment (0-0.5% w/w ascorbic acid or citric acid and 0-5 min for blanching at 85ºC). The result showed that browning reaction was controlled when treated with 0.3% ascorbic acid and blanching at 85ºC for 3 min. The process conditions (1.0-3.0% v/w enzyme concentration, 0-6 h hydrolysis time and controlled temperature at 32±2ºC) of bael fruit syrup treated with Pectinex® Ultra SP-L were studied. The results showed that bael fruit pulp treated with enzyme concentration of 2.5% and hydrolyzed for 0, 1, 2, 4, and 6 h can be hydrolyzed in five levels different in the amount of reducing sugars (39, 55, 68, 77 and 85 mg glucose/ g fresh weight) released during the treatment. The effect of these treatment conditions on bael fruit syrup properties showed that syrup at hydrolysis time higher than 2 and 4 h had significantly greater total carotenoid content and antioxidant activities, respectively than other hydrolysis times (p<0.05). The bael fruit syrup at a hydrolysis time of 6 h had the smallest particle size of 79.92 µm. The rheological behavior of bael fruit syrup from all treatments fitted the Herschel-Bulkley model exhibited pseudoplastic with yield stress and thixotropic behavior. An increase in hydrolysis time is associated with an increase in yield stress (o) and flow behavior index (n) while the consistency coefficient (K), apparent viscosity (Ƞ) at shear rate 100 s-1, and hysteresis loop area decreased. In addition, bael fruit syrup at hydrolysis time higher than 4 h also had significantly higher yellowish-orange color, pleasant flavor and smoothness, but lower thickness than other hydrolysis times (p<0.05). When compare with the homogenized and antibrowning controlled bael fruit pulp, bael fruit syrup at 6 h hydrolysis time gave higher in soluble dietary fiber and volatile compounds, but constant in prebiotic activity score. Sensory evaluation on assorted éclair stuffed with bael fruit syrup at hydrolysis time higher than 4 h showed significantly greater scoring in color, bael fruit flavor, texture, and overall acceptability than other hydrolysis times (p<0.05).