Expanding the Utility of a Modified Whey Protein Ingredient via Carbohydrate Conjugation.

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Title: Expanding the Utility of a Modified Whey Protein Ingredient via Carbohydrate Conjugation.
Author: Lillard, Stephen Jonathan
Advisors: E. Allen Foegeding Ph.D., Committee Member
George L. Catignani Ph.D., Committee Member
Christopher R. Daubert, Ph.D., Committee Chair
Abstract: Whey proteins are commonly used in foods for their thickening and emulsifying properties. As a one time by-product of the cheese making process, roughly 30% of whey protein still remains unused. Therefore, the need for ingredients with novel functionality provides the impetus to modify whey proteins for desired performance. Previously, an acidified, thermally treated whey protein concentrate (MWPC) was developed to produce a cold-set, thickening ingredient. For these studies, a MWPC was obtained from a whey manufacturer which contained around 7% lactose post processing. In an attempt to optimize the functionality, the Maillard reaction was employed to covalently couple, or conjugate, the MWPC with two separate dextrans (35kDa and 200kDa) under varying thermal conditions at pH 3.5. A commercially available whey protein concentrate (CWPC) was studied along with the modified ingredient for comparison purposes. Maillard reactivity was confirmed through several biochemical analyses including colorimetry, o-Phthaldialdehyde assays (OPA), sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), and ionization mass spectrometry. Colorimetry showed that the MWPC containing only lactose exhibited the greatest degree of color formation as a result of Maillard end products generated during heat treatment. These results were complemented by o-Phthaldialdehyde assay data that showed a decrease in the level of free amino groups in all samples after thermal treatment, an indicator that covalent attachment of the sugars had occurred. The SDS-PAGE banding profiles also displayed new and diffuse higher molecular weight bands formed after coupling as detected by protein (Coomassie) and glycoprotein staining methodologies. Ionization Mass Spectrometry results revealed the lysine content in the MWPC to be 8.5% lactosylated as a result of the manufacturing process, itself. Review of the dextran added samples showed them to have a high molar concentration which may have lead to reduced diffusivity due to an increased viscosity, thereby diminishing reaction conditions suitable for the Maillard reaction to occur. Once verification of glyco-conjugation was established, rheological analyses, interfacial analyses including emulsion stability and emulsifying capacity, image analyses, and water holding capacity measurements were completed to assess structural changes and possible functional benefits. Improvements in both steady shear and small amplitude oscillatory rheology were dependant on the reducing sugar present. The MWPC samples containing dextran prior to heat treatment exhibited a 3.4 times greater apparent viscosity over the MWPC alone. After heat treatment, however, the apparent viscosity of the MWPC-dextran samples showed no improvement over non-heated samples while the viscosity of the MWPC alone increased 3-fold measured at 50 s-1. The increased solubility of the MWPC-dextran samples, along with excluded volume interactions, may have played a role in the rheological impact. Interfacial analysis was conducted through emulsion stability and emulsifying capacity testing. The emulsion stability of MWPC-dextran fractions were 2 to 3 times greater than either MWPC alone or CWPC, based on the creaming index. The higher solids content and increased molecular size of the MWPC-dextran conjugate may have increased the steric stabilization of the system, and enhanced the stability of the emulsion. Emulsifying capacity measurements showed minimal differences between the samples with a slight improvement noted in MWPC-dextran (100 kDa to 200 kDa) samples. Image analysis accomplished with scanning electron microscopy uncovered porous network formation upon the addition of dextran which differed from the dense network of MWPC, alone. Although the water holding capacity of all samples decreased upon additional heat, the MWPC-dextran samples still held nearly six times their weight of water. The porous nature of the new network could have affected both rheological properties and the ability of MWPC-dextran samples to bind water. It was concluded that modified whey ingredients can be further enhanced by conjugation with carbohydrates through non-toxic means such as the Maillard reaction. The specific application into which the ingredient will be introduced will dictate which carbohydrate is most appropriate to obtain the desired functionality.
Date: 2007-07-26
Degree: MS
Discipline: Food Science
URI: http://www.lib.ncsu.edu/resolver/1840.16/154


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