Optimizing stability of orange juice fortified with whey protein at low pH values

The influence of temperature, heating time and pH on the stability of whey protein-fortified Valencia orange juice was determined by uronic acid content, degree of esterification (DE), % transmission measurements (%T) and capillary electrophoretic analysis of the juice-protein supernatants. Uronic acid content and charge of pectins showed no significant change in heat-treated samples with added proteins. The %T decreased with decreasing pH and increasing temperature and heating time for alpha-lactalbumin (alpha-lac), beta-lactoglobulin (beta-lg) and whey protein isolate (WPI). The lowest transmission values were shown at pH 3.0 and 85C. Capillary electropherograms confirmed more extensive juice-protein interactions in WPI and beta-lg added juices than in those containing a-lac, especially at low pH, resulting in more stable juice-protein mixtures.