Item – Theses Canada

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OCLC number
1019481318
Author
Gomaa, Ahmed I.
Title
An Investigation of Effects of Microwave Treatment on the Structure, Enzymatic Hydrolysis, and Nutraceutical Properties of beta-Lactoglobulin.
Degree
Ph. D. -- McGill University, 2011
Publisher
Ottawa : Library and Archives Canada = Bibliothèque et Archives Canada, 2012.
Description
microfiches
Notes
Includes bibliographical references.
Abstract
<?Pub Inc> Whey proteins are used extensively by the food industry in such products as infant formulas and dietetic and health foods owing to the high nutritional value and useful functional properties of these milk-derived proteins. In addition, in recent years, the nutraceutical properties of native or predigested whey proteins have become the focus of much research. Both the functional and nutraceutical properties of whey proteins can be enhanced by exposing them to various non-denaturing physicochemical conditions that modify their native structure. It is within this context that the present investigation of the effects of microwave treatments (MW) on the structure, degree of enzymatic hydrolysis, and nutraceutical properties of [beta]-lactoglobulin ([beta]-Lg), the predominant whey protein in cow's milk, was undertaken. Microwave treatment of [beta]-Lg in D2O solution under various conditions was monitored by Fourier transform mid infrared (mid-FTIR) spectroscopy. At sub-ambient and ambient temperatures, no microwave-induced changes in the conformation of the protein were detected. Microwave heating of the [beta]-Lg solutions to temperatures in the range of 40-60 C resulted in a marked increase in the rate of hydrogen-deuterium (H-D) exchange by comparison with conventional heating (CH) at the same temperature. At heating temperatures in the range of 70-90 C, the microwave-heated solutions exhibited more extensive protein aggregation than conventionally heated solutions. Application of two-dimensional (2D) correlation analysis to the Fourier self-deconvolved FTIR spectra recorded as a function of number of cycles of microwave or conventional heating revealed that the unfolding pathway of [beta]-Lg was different in these two temperature ranges but was not altered by microwave heating as compared to conventional heating. Kinetic analysis of the FTIR data revealed that the accelerated rate of protein unfolding observed in microwave-heated samples is attributable to a lower energy of activation and supported the existence of non-thermal effects of microwaves. Circular dichroism (CD), fluorescence spectroscopy, and 2D 1H NMR spectroscopy were used to confirm and complement the results obtained by FTIR spectroscopy. The effects of microwave and conventional heat treatments at three temperatures (40, 60, and 90 °C) on the enzymatic hydrolysis of [beta]-Lg and on the peptide profiles of the hydrolysates were also investigated. The degree of hydrolysis of [beta]-Lg by pepsin, trypsin and chymotrypsin as well as in a two-stage hydrolysis with pepsin followed by trypsin and chymotrypsin, simulating gastrointestinal conditions, was determined. Microwave-treated samples exhibited more extensive enzymatic hydrolysis than conventionally heated samples under all hydrolysis conditions, with the greatest degree of hydrolysis being found following microwave treatment at 60 °C, and hydrolysates of microwave-treated [beta]-Lg exhibited both enhanced angiotensin-converting enzyme (ACE) inhibition and enhanced antioxidant activity. LC-ESI-MS and MS/MS in conjunction with the use of advanced bioinformatics software were employed in the identification of the peptide profiles of the hydrolysates and revealed the presence of unique peptides in hydrolysates of microwave-treated samples, suggesting that the microwave treatment may have exposed new cleavage sites within the interior of the protein. Overall, the findings of these studies indicate that microwave heat treatments may be an attractive approach to enhance the nutraceutical properties of whey and other proteins.
ISBN
9780494745199
0494745193