Microstructure and Functionality of Processed Cheese: The Role of Milk Fat

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Title: Microstructure and Functionality of Processed Cheese: The Role of Milk Fat
Author: Price, Kristin Michelle
Advisors: Dr. Orlin Velev, Committee Member
Dr. Brian Farkas, Committee Member
Dr. Christopher Daubert, Committee Chair
Abstract: Cooling, the final stage in processed cheese manufacturing, plays a significant role in determining the texture and firmness of the final product. To interpret cooling mechanisms of processed cheese, model processed cheese analogues were formulated including rennet casein powder, anhydrous milk fat, and emulsifying salts. Small amplitude oscillatory shear (SAOS) and large deformation compression tests analyzed rheological properties and trends exhibited in processed cheese analogues when cooled with different cooling schedules. Two cooling rates, 0.5 oC⁄min and 0.05 oC⁄min, were selected, and based on protein network formation and fat crystallization, two significant cooling phases were identified: 80-40oC and 40-5oC. In all, four cooling schedules were developed from a two-by-two matrix of cooling rates and cooling phases. After the cheese analogues were cooled with the desired cooling schedules, SAOS rheology measured the complex shear modulus (G*) of cheese analogues through a frequency sweep range of 0.01-10 Hz. Utilizing the same cooling schedules, the normal, compressive strength of cheese analogue cylinders was measured and converted into shear modulus (G) values. Rheological analysis revealed that a slower cooling rate through the first phase of coolig (80-40oC) created a firmer cheese product (larger G* and G values) when compared with a faster rate of cooling through the same temperature range. The cooling rate through the second phase of cooling, during fat crystallization, did not impact final cheese storage modulus. Small and large deformation rheological analyses found that the final cheese texture was governed by the cooling rate through the first phase of cooling (80o-40oC), formation of the protein network. Confocal laser scanning microscopy (CLSM) was used to investigate the effects of cooling rate on the microstructure of processed cheese analogues. Micrographs of cheese analogues stained with Rhodamine B and Nile Red fluorescent probes revealed a protein ring surrounding fat droplets that formed during cooling from 80-5oC. The protein ring thickness was not influenced by cooling cheese analogues at two different rates, 1 oC⁄min and 10 oC⁄min. However, the presence of the protein ring surrounding fat droplets in processed cheese analogues lays the framework for future study on the effects of very slow cooling rates on the thickness of the protein ring. With a better understanding of cheese rheology and cheese microstructure during cooling, cheese manufacturers can control cooling schedules to help optimize quality attributes in processed cheese.
Date: 2007-12-20
Degree: MS
Discipline: Food Science
URI: http://www.lib.ncsu.edu/resolver/1840.16/260


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