109-3 |
|
Q. ZHONG, Dept. of Chemical Engineering, Iowa State Univ., 2157 Sweeney Hall, Ames, IA 50011-2230 and C. R. Daubert, Dept. of Food Science, North Carolina State Univ., 129-H Schaub Hall, Box 7624, Raleigh, NC 27695-7624. During process cheese production, the emulsifying salts disintegrate casein micelles into smaller units, and a cheese network is formed upon cooling. A slower cooling rate yields a firmer cheese, and the mechanisms dictating network formation during cooling are unclear. To study structure formation and cooling rate effects on processed cheese, a rennet casein model system was identified to simulate processed cheese conditions, including fixed emulsifying salt types and concentrations and a pH range from 5.8 to 12. Rheological properties of rennet casein gels were studied during cooling from 80 to 5 °C at different schedules, and the final structures were analyzed using a confocal laser scanning microscope. Storage modulus of rennet casein gels increased with pH monotonically, consistent with the pH effects on the net charge of casein mixture. At a pH of 5.8 and 6.5, there was no continuous network observed from both rheology and microscopy. Continuous networks were formed at pH 7.2 and above. Furthermore, cooling effects did not show trends for gels at pH 5.8 and 6.5, while a stronger gel was created when cooled at a slower rate at pH 7.2 and 12. A stronger gel at a higher pH resulted from a smaller floc fractal dimension, and the cooling effects were caused by smaller flocs of similar fractal dimensions during a slower cooling schedule. Both scenarios created more flocs, cross-links, and subsequently a stronger gel. On the other hand, the manipulation of casein network structure through cooling schedules was possible by the existence of sufficient repulsive colloidal interactions between protein particles (at higher pHs). This study illustrated that floc number and thus cross-links are important for the texture of dairy products, and floc numbers can be manipulated by either physical or chemical approaches.
Session 109, The rheology of dairy foods
|