Consider manothermosonication an alternative to thermal processing for treating juice.

The thermal treatments commercially used to inactivate pectic enzymes and secure microbially safe orange juice often cause off-flavor and a loss of nutrients from the product. The loss of ascorbic acid during thermal processing is the most important issue related to orange juice processing. New processing methods, including a combination of mild heat, low pressures and sonication in a technique called manothermosonication (MTS), have gained interest in recent years for producing a better quality orange juice.

Researchers at the University of Illinois undertook a study to examine changes in the quality of orange juice treated with MTS and a thermal pasteurization technique during storage at 4 C. Their results indicate that MTS may be a promising alternative to traditional thermal juice processing methods.

In experiments, the scientists heated unpasteurized orange juice samples at 91 C for 12 seconds to get thermal pasteurized juice. Or they heated the juice at 70 C using a pressure of 400 kPa for 30 seconds to obtain MTS-treated juice. The investigators selected the MTS treatment conditions based on results from a preliminary experiment.

The soluble solids content, pH, acidity, pulp content and browning index of unpasteurized, pasteurized and MTS-treated orange juice were evaluated immediately after treatment. A validation test was conducted with E. coli K12 to ascertain if a 5-log reduction could be achieved by using the MTS treatment.

The investigators measured the concentration of ascorbic acid, cloud stability and the pectinmethylesterase activity of the juice samples during storage for 77 days at 4 C. No significant changes in the amount of soluble solids, pH, acidity, pulp content and browning index were observed for juice treated with the MTS technique with the thermal treatment.

Both treatments effectively reduced pectinmethylesterase activity, resulting in juice samples with stable cloudiness and no pulp separation during storage. The MTS-treated juice showed a slower degradation of ascorbic acid compared to the thermal pasteurized product. The MTS approach also achieved a 5-log reduction in the population of E. coli K12.

Further information. Mosbah Kushad, Extension Specialist, Food Crops, Department of Natural Resources and Environmental Sciences, University of Illinois, 279 ERML, 1201 W. Gregory MC-051, Urbana, IL 61801; phone: [phone]; email: [e-mail].