The color of the juice showed a critical change as per the data reported in Table 1 for different processing approaches. Unpasteurized juices showed considerable decrease in the L⁄, a⁄ and b⁄ values which are indicator of deterioration in the juice quality. Ultrasound processed orange juice possessed higher freshness and quality attributes in terms of color than the thermally processed orange juice. The ultrasound irradiated samples maintained its original color over a significant shelf life (of 4 weeks as per the represented data) whereas the color of the control samples or the thermally processed juice became darker. This result can be explained on the basis of a decrease in the polyphenol oxidase activity due to the cavitational effects induced by ultrasonic irradiations [30]. It is important to note here that polyphenol oxidase is generally responsible for the browning of fruit and vegetables. The positive effect of ultrasound in the preservation of processed products compared to raw products can be attributed to the removal of oxygen. During cavitation, degassing of fluid takes place, and thus
oxygen is removed from the media preventing oxidation. Thermal processing strongly changes the sensory property of orange juice, however ultrasound processing gives orange juice with more retention of the flavor compounds, less non-enzymatic browning, and brighter color indicating that ultrasound and ultrasound combined with UV treatments presented more acceptable quality, and no statistically significant differences with respect to untreated samples could be observed. Fresh juice is a natural antioxidant as confirmed by the fact that the measurement of ORP of fresh juice yields a negative value. Most raw organic green vegetable juices show an initial ORP over the range of 100 to +160, indicating a fairly good content of primitive (reducing) antioxidants in the juice. As a juice ages and gradually oxidizes due to any of the factors viz. heat, exposure to air and light as well as storage time, ORP can increase steadily to about
+350 to +450. The juice steadily loses the nutrient value due to oxidation indicated by an increase in ORP. In general, raw organic green juices with ORP in the range of +180 to +210 can be said to have acceptable content of the oxidants [31]. Considering this
importance in terms of the content of oxidants, ORP was quantified during the storage of orange juice. It was observed that the ORP increased during the storage (Fig. 1) and the extent of increase was dependent on the processing method. The increase in the ORP over the entire storage duration investigated in the work was the maximum for the case of untreated juice whereas minimum change was observed for the treatment using ultrasound.
The changes in the ORP in the case of thermal treatment and