EFFECT OF DISSOLVED OXYGEN ON THE STABILITY OF ASCORBIC ACID AND THE BROWNING OF SONICATED CASHEW APPLE JUICE DURING REFRIGERATED STORAGE

The effect of different initial dissolved oxygen concentrations on the stability of ascorbic acid in sonicated cashew apple juice stored at 4°C was investigated. Sonication process was carried out at 100% of total input power (500 W) at 20 kHz for 5 or 10 min. The juice was placed in a glass reactor with temperature control, and the ultrasound probe was submerged to a depth of 25 mm in the juice. Ascorbic acid was measured using the liquid chromatograph method and browning degree was measured by colorimetric method. The initial content of ascorbic acid in fresh juice was 2790 mg/L. The effects of ultrasound processing on ascorbic acid of cashew apple juice, showed that the ascorbic acid retention ranged from 98% to 110% in all ultrasound-treated juice as compared with control juice, indicating that ultrasound is a suitable technology for ascorbic acid retention in cashew apple juice. With extending treatment time, ascorbic acid gradually increased, and the dissolved oxygen decreased with the highest concentration achieved at 373 W/cm2 for 10 min. The results show that ultrasonic processing decreases the concentration of oxygen dissolved in the juice and a significant effect on rate of ascorbic acid degradation could be attributed to the different oxygen levels. During refrigerated storage, some degradation of ascorbic acid occurred and could be related to oxidation reactions promoted by the interaction with free radicals formed during ultrasound. The preservation of ascorbic acid during refrigerated storage could be directly attributed to the removal of entrapped oxygen because of cavitation. Lag period before browning also increased depending on oxygen level.