NATURE OF THE PROTEIN CONSTITUENT OF COMMERCIAL ORANGE JUICE CLOUD

The cloud of five commercial orange juice concentrates contained an average of 52.4% protein. Most of the cloud protein was soluble in the chaotropic reagent 10 M urea-6% citric acid, pH 2.5. The cloud of two ready-to-serve pasteurized orange juices showed much the same behavior as the concentrates, although the total cloud weights and cloud protein contents were less. Some of the cloud appears to be formed during juice processing. The primary causes of the protein insolubility in the juice are due to inherently insoluble protein, complex formation with low molecular weight organic cloud constituents, and covalent bonding to other cloud constituents. Protein-pectin complex formation is believed to play only a minor role.