30E-6 |
A fractal analysis of casein model gels subjected to different cooling rates |
Q. ZHONG, Department of Food Science, North Carolina State University, Raleigh, NC 27695-7624 and C. R. Daubert. The texture and functional properties of process cheese are affected by the type and age of natural cheeses, the type and amount of emulsifying salts, and processing conditions. Cooling is a critical operation and is believed to impact the casein network structure. Therefore, understanding the mechanisms and kinetics of network formation at different cooling rates may improve the efficiency of process cheese manufacturing. The objective of this study was to evaluate the effects of cooling rates on casein gelation using small amplitude oscillatory shear rheology and fractal analysis. To study casein network formation in cheese, a model system was prepared to simplify preparation and analysis. Casein was isolated from skim milk by ultra-filtration, then redispersed at 50 °C and pH 4.6. Next, the dispersions were analyzed by a Bohlin VOR rheometer while at 80 °C for 30 minutes and during cooling to 5 °C at three different cooling rates (1.0, 0.5, and 0.1°C/min). Dynamic shear tests were used at a strain of 0.1% while cooling. Frequency and strain sweeps were performed at 5 °C for each concentration. Fractal dimensions were derived from the linear viscoelasticity region strain limit and storage moduli (G') at different concentrations. Storage moduli and the fractal dimensions showed higher values at slower cooling rates. A higher fractal dimension at slower cooling rates indicates a more compact structure in the gel network. Cooling conditions impact process cheese quality, yet cooling rate effects are poorly understood. This investigation begins to divulge the effects of cooling rates on network development and may impact the manner in which process cheese is cooled.
Session 30E, Food Engineering: Rheology and texture
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