30C-11 |
Effect of differences in whey protein composition on the stability of fortified valencia orange juice |
M. KAZMIERSKI1, S. Agboola2, and M. Corredig1. (1) Food Science and Technology, University of Georgia, Food Science Bldg., Athens, GA 30602, (2) Wine and Food Sciences, Charles Sturt University, Wagga Wagga, NSW 2650, Australia Whey protein addition to juice induces aggregation and interactions with polysaccharides and other constituents, resulting in loss of turbidity, cloud destabilization and protein flocculation. This effect is attributed to extensive protein-protein and protein-polysaccharide interactions and changes induced during heating at the pH environment of the juice. The focus of this work was to investigate temperature, heating time and pH influence on the stability of Valencia orange juice after addition of 2% a-lactalbumin (a-lac), b-lactoglobulin (b-lg) and whey protein isolate (WPI) solutions. Juice was filtered, centrifuged to remove sedimenting pulp, and heat-treated to inactivate the pectin methylesterase enzyme. The protein-juice mixtures were adjusted to pH 3.0, 4.0 or 5.0. Aliquots (50 ml) of samples were heated at 65, 75 and 85°C for 10, 20 and 30 minutes, cooled, and recentrifuged. Uronic acid content, degree of esterification (DE), percent transmission and capillary electrophoresis determinations were carried out on the soluble phase. All data were analyzed statistically by the general linear model procedure. Neither the pectin content nor its DE changed significantly in the soluble phase upon addition of protein or at various heating times/temperatures (p-value < 0.05). Percent transmission increased with increasing pH and decreased with temperature for a-lac, b-lg and WPI showing significant stabilization at pH 3.0 and 85°C. Capillary electrophoretograms of the supernatant confirmed more extensive juice-protein interactions for WPI and b-lg mixtures than the a-lac mixtures, especially at low pH, as indicated by increased peak size and number. These results indicated that presence of WPI and b-lg influenced the formation of more charged soluble aggregates at low pH and high temperature of heating. Decreasing % T at low pH and high temperature also gave indication of higher cloud of the protein added juice. These data indicated the significance of these parameters in estimating stability of whey-juice beverages.
Session 30C, Food Chemistry: Proteins
|