A Rheological Analysis of Shear on a Model Emulsion System.

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Title: A Rheological Analysis of Shear on a Model Emulsion System.
Author: Yurgec, Matthew Joseph
Advisors: Mitzi Montoya, Committee Member
Christopher Daubert, Committee Chair
Allen Foegeding, Committee Co-Chair
Abstract: Shear work and shear power intensity are two rheological terms developed to quantify the amount of shear energy that a fluid is exposed to during processing. In this study, the effect of shear work and shear power intensity on a model corn oil-in-water emulsion was evaluated. Results revealed that when the model emulsion was homogenized at a constant shear work, the median particle size was statistically identical even though the homogenization pressures or shear power intensities required to achieve that shear work level were different. Median particle size was considered a function of the shear work input and the surfactant concentration, and a simple mathematical model using a power function was formulated. Median particle size decreased initially as shear work was applied, but at some critical value, the median particle no longer reduced, maintaining a constant level. Using a statistical piece-wise linear or “hockey-stick†model, an isolated critical value for shear work and the corroborating median particle size was found with a fit accounting for greater than 90% of the variability. The effect of shear magnitude and position was also studied by evaluating the median particle size and viscosities of the same model emulsion cycled through the homogenizer twice at two different pressures. Results showed that when both passes were complete (at constant shear work), the final median particle size was statistically similar between the samples. However, there was evidence that accumulated shear following the most intense shear treatment did not have any further effects on the emulsions particle size. Viscosity results from this study showed that Newtonian viscosities were not significantly different when shear work or shear power intensity were different. There was some evidence that increasing the shear power intensity increased the viscosity slightly, but not significantly. In this study, surfactant concentration was critical to median particle size. The calculation of shear work and shear power intensity by a food technologist could be a means of identifying the shear limits on a food product and designing a processing line around those limits, allowing the process to reach a target window for shear input. Conducting this analysis could lead to less product loss caused by excessive shear, improved consumer acceptance caused by improved product quality, and reduced maintenance and utility costs caused be less equipment breakdown and less energy use. Understanding and adapting a process to the shear limits of a product could lead to the improved financial bottom line of a food manufacturer.
Date: 2009-07-29
Degree: MS
Discipline: Food Science
URI: http://www.lib.ncsu.edu/resolver/1840.16/2966

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