Electrical processing could boost yields for juice makers

11 May 2011

Electroplasmolysis and microwave heating beat conventional thermal processing methods hands down in terms of yields and quality in juice production, claims new research from Turkey. Yield increase is one of the main objectives of fruit and vegetable juice processors.

Writing in this month’s edition of the Journal of Food Science, the authors said their study’s findings showed electroplasmolysis induced hike in carrot juice yield of nearly 10 per cent, while a microwave heating alternative to traditional pasteurization resulted in 100 per cent pectin methylesterase (PME) inactivation.

PME inactivation is responsible for phase separation and cloud loss in fruit juice manufacturing.

“The results showed that the highest values for quality characteristics, such as antioxidant capacity and total pectin, total phenolic and total carotenoid contents, were obtained with the combined applications of the electrical methods,” note the authors.

They claim the technology can be adapted to existing juice production lines.

Novel technologies

To protect nutritional and sensory quality characteristics of foods during processing, new techniques, such as electrical methods, are being explored as alternatives to conventional heat processes.

The researchers, based at the University of Engineering in Izmir, argue that electrical methods provide rapid inactivation of enzymes and killing of microorganisms in comparison to thermal processes while minimizing quality loss.

Electroplasmolysis (EP), a new electrical processing method, destroys cellular membranes by electric field application. It has previously been found effective, said the authors, on improving yield and quality of citrus fruits, tomato pulp and in wine making.

Microwave (MW) heating, they note, can be used in the food industry for blanching, cooking, pasteurization, preheating, and drying.

The study

The authors said that the effects of electrical methods on natural carrot juice during storage have not yet been investigated in detail: “For this reason in our study, EP was applied as a pre-treatment in carrot juice production in order to juice yield and also MW heating was used as an alternative to traditional pasteurization.”

Furthermore, said the researchers, during 4 months of storage at +4 ?C, the change in quality characteristics was compared with EP, MW, and conventionally processed lots.

The team explained that production of carrot juice was carried out by using optimum conditions including a voltage gradient of 22.2 V/cm and treatment time of 60 seconds for EP.

The flow rate of 90 mL/min with power of 900 W was used for the microwave heat treatment of the juice, with a heating period of 4 minutes. The exit temperature of carrot juice was 99?C after MW heating.

As a control, carrot juices were pasteurized in glass (200 mL) at 100 ?C for 10 minutes, added the engineers.

Findings

EP was shown to provide a significant increase in yield (9.49 per cent) compared to the control group, said the authors.

They report that MW provided complete inactivation of PME in carrot juice and it did so faster than the thermal treatment.

Meanwhile, the researchers also found that EP application increased the pectin and the β-carotene contents due to degradation of cell membranes.

The highest carotenoid content was obtained in the combined electrical (EP + MW) group, continued the team.

“Phenolic content also increased by EP effect, and after the electrical treatments, the losses in phenolic contents were low compared to traditional pasteurization.

Due to these increases, there was an important improvement in antioxidant capacity of carrot juice,” added the researchers.

Furthermore, they noted that Brix and acidity values increased after the EP application.

“As a result, electrical methods can be used for the improvement of quality characteristics and yield of carrot juice when using the drum-type electroplasmolyzator that can be easily adapted to industrial production lines,” claim the team.

They added that the quality characteristics of juices can be preserved better and for longer those processed using electrical rather than conventional methods.

Source: Journal of Food Science