Cooling Effects on the Funcitonality and Microstructure of Processed Cheese

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Title: Cooling Effects on the Funcitonality and Microstructure of Processed Cheese
Author: Zhong, Qixin
Advisors: Saad A. Khan, Committee Member
Christopher R. Daubert, Committee Chair
Orlin D. Velev, Committee Co-Chair
Brian E. Farkas, Committee Member
Abstract: Cooling is the final stage of process cheese manufacturing, and a slower cooling process generates a stronger structure requiring a larger force to shear cheese loaves while yielding a poor melt quality. To interpret cooling mechanisms, a model rennet casein system was formulated to include emulsifying salts and rennet casein powder, as used in processed cheese analogs. At pH 5.8 and 6.5, protein networks were discontinuous, and no cooling trends on rheological data were observed when cooled from 80 to 5 °C at 0.025, 0.05, 0.1, and 0.5 °C/min. At pH 7.2 and 12, networks were formed, and slower cooling delivered a firmer gel. The rennet casein network was described as cross-linked flocs, and the aggregation of two particles into a doublet was the first stage of floc formation. At lower pHs, the overall force between protein particles was more attractive, the doublet formation time was short, and therefore the number of doublets formed was not affected by cooling rates. Accordingly, floc numbers and rheology did not show a trend with cooling effects at the lower pHs. At pH 7.2 and above, the doublet formation time was comparable to the time for temperature changes during cooling because of stronger repulsive forces. As a result, doublet formation was influenced by cooling rate, generating more doublets and more sites for floc growth at slower rates. A larger number of smaller flocs were created, delivering a stronger gel at slower cooling rates. More flocs at higher protein concentrations and slower cooling rates simplified the network formation. Finally, cooling effects on processed cheese resulted from more uniform structures at slower cooling rates. A more uniform protein network formed prior to fat crystallization and confined the volume for fat crystallization, creating a more uniform cheese matrix and a firmer product. Cheese manufacturers can benefit from this research by adopting an appropriate cooling schedule to deliver specific functional properties.
Date: 2003-09-25
Degree: PhD
Discipline: Food Science
Chemical Engineering
URI: http://www.lib.ncsu.edu/resolver/1840.16/5148


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