Effect of Thermal Treatment on Physicochemical Stability and Antioxidant Properties of Locally Available Underutilized Star Fruit Juice

Industrial processing of the fruit juice is responsible for the changes in some quality attributes. Thermal treatment is a most applicable operation for any processing and it affects the physicochemical and antioxidant properties of the juice. This study was conducted to observe the changes in some physical properties and the bioactive compounds of star fruit (Averrhoa carambola L.) juice during thermal treatment at 70°C, 80°C and 90°C for 10, 20, 30 and 40 min by a temperature-controlled water bath. During thermal treatment of the juice pH and browning index increased significantly (P≤ 0.05) with time and increasing temperature whereas the Cloud index of the juice decreased. No significant variation (P≥ 0.05) noticed in the case of total soluble solids. Color differences gradually increased in case of color parameter (0 to 7.83 ± 0.20) and negatively increased in case of (0 to -7.33± 1.00). Irregular results observed for and maximum difference (3.01±0.08) noticed at 90°C for 40 min. The highest overall color change (∆E= 11.04±0.76) observed when the juice treated at 90°C for 40 min. In consideration of the bioactive compounds, maximum ascorbic acid estimated (24.17±0.70mg/100ml) in fresh juice and with rising temperature and time it decreased. β-carotene also decreased significantly during heat treatment. The Total Polyphenol Content (TPC) found in fresh juice as (540.08±16.64 mg GAE/100 ml) and it was not changed in a regular manner with temperature change. Flavonoid content increased significantly (P≤0.05) when the juice was heat-treated at 70°C and 80°C while no significant change observed at 90°C. Maximum DPPH scavenging activity found in fresh juice (60.19±1.39%) and decreased to (53.83±1.43%) when 90°C temperature was applied for 40 min. This study may help to find out the nutritional value of locally available star fruit and physicochemical changes of this fruit juice during thermal processing.