Effect of Continuous Flow Microwave Processing System on Quality Attributes of Orange Juice

Technological advances in the food industry have led to development of various processing methods to increase the shelf life of fruit and products divided from fruit to ensure access to them during the year, even for seasonal fruits. The conventional heating method causes undesirable changes in the final product such as color changes, unpleasant taste and degradation of Ascorbic acid. The Aim of this study was to investigate the effect of microwave processing as an alternative the conventional method on the physicochemical properties of orange juice.

All chemicals used in this study were purchased with High-Purity from reputable companies. Jaffa orange was purchased from the local market in Gorgan (a city in north of Iran). Effect of continuous flow microwave treatment (MW) on physicochemical and qualitative properties of orange juice including vitamin C, browning index (BI), turbidity, cloud value, soluble solids (Brix), acidity, viscosity and pH of orange juice (com up time “CUT” phase) was evaluated. All indices were monitored until the end of the Holding phase (inactivation of PME to 90%).

Results of the experiments showed that various temperature treatments at full power microwave (900 W) caused a slight decrease in pH and a slight increase in acidity and Brix during the CUT phase (p <0.05). But no significant change was observed in these parameters at Holding phase (p> 0.05). All spectrophotometric parameters of juice including browning index, turbidity and cloud value was raised after exiting from microwave (CUT phase) with increasing in temperature (p <0.05). These parameters increased slowly until the end of the Holding phase. Increasing in temperature to the CUT phase; the viscosity was decreased significantly at high temperatures (70 and 80 ° C) and no significant change was observed after the CUT phase. Vitamin C raised with increasing in temperature in all thermal treatments. The degradation rate was high (at 80 ° C) at the Holding phase. Different thermal treatments caused 70 to 80% decline in PME activity during CUT phase.

Continuous flow microwave heating is an emerging technology that can potentially be used to heating of liquid foods. Microwave aid processing of orange juice is an effective method to inactivating of PME enzyme, through significant increasing in degradation rate. The results showed that increasing in temperature, enhanced the browning index, turbidity and cloud value. Different treatments had no significant effect on the Brix, acidity and pH in the holding phase. On the other hand, increasing in temperature, enhanced the rate of vitamin C and PME degradation.