Orange Juice

DOWEX™ ion exchange resins are used to process orange juice in two different ways, for the reduction of acid content and to remove bitter components.

Reduction of Acid

Some orange juice consumers prefer a reduced acid version of the juice. Figure 1 outlines the basic flow schematic for treating orange juice to reduce acidity.

Fresh juice, stabilized concentrate or concentrates reconstituted back to 15 Brix can be treated using the process in Figure 1. First, the pulp is removed from the juice via centrifugation and the pulp free juice can then be passed through a weak base anion column, which reduces the citric acid content of the juice. The resin will also retain the ascorbic acid (Vitamin C) and folic acid portions of the juice. Note that the resin is more selective for the citric acid so if enough juice is passed, the citric acid portion of the feed juice will displace the ascorbic acid and folic acid held by the resin. This can be monitored by following the pH of the juice effluent coming off the column. Below a pH of 4.6, the ascorbic and folic acid portions are washed through the resin. The processed deacidfied juice effluent can then be blended back to unprocessed juice to achieve the right balance of reduced acid and fresh juice tastes. The pulp can also be added back, or the juice can be sold as a reduced pulp juice.

Removal of Bitter Components

Roughly 15-20% of navel oranges harvested in a given season are not used directly and are processed into a juice that is bitter and requires processing or back-blending with other sweeter juice. The bitter fraction of the orange juice arises from a tetracyclic triterpenoid called limonin. The limonin is produced over time from limonic acid, which is a species found in the seeds and membranes of most citrus fruits. Figure 2 shows how limonoic acid estrifies to limonin.

Figure 2. Limonic Acid to Limonin

Suggested Reading:

S.I. Norman, Chapter 9 "Juice Enhancement by Ion Exchange and Adsorbent Technologies." Published in Production and Packaging of Non-Carbonated Fruit Juices and Fruit Beverages, Edited by D.Hicks. Van Nostrand Reinhold, New York, NY 1990.