ABSTRACT
Soluble wheat protein (SWP), a product of the deamidation (20%) of gluten aggregated at room temperature when hydrated through hydrophobic interactions. The aggregates were broken on heating to 60°C although for concentrations greater than 16% (w/v) dispersions, higher temperatures of 90°C resulted in an increase in viscosity and an increase in network formation.

The addition of 2% NaCl to SWP at room temperature caused a decrease in viscosity which was proposed to be due to the formation of a diffuse double layer and also to an increase in the dielectric constant of the medium.

Although SWP does not gel below 100°C, reduction of the disulphide bonds with beta-mercaptoethanol gelled SWP at room temperature.

Gelation of SWP was also induced with basic proteins such as lysozyme and clupeine at temperatures lower than required to gel it on its own which was proposed to be electrostatic between the positively charged lysozyme and clupeine residues and the negatively charged residues in SWP.

SWP interacted with whey protein isolate (WPI) through both an indirect and a direct mechanism. In the indirect mechanism, WPI scavenged sodium salts associated with SWP to induce its own gelation. In the direct mechanism, disulphide bonds are thought to form between WPI and SWP. The SWP/WPI gels formed were most likely to be phase separated gels made up of viscous SWP sol trapped in WPI gel network.

The mechanism of SWP - BSA interaction was considered to be electrostatic, between SWP carboxyl groups and basic groups on BSA and hydrophobic interaction between exposed hydrophobic residues. Although SWP does not form a gel at 90°C, it enhanced the gelation of BSA when added in small quantities.

SWP was found to bind metals (iron, copper, zinc and cadmium) with a very high affinity for cadmium, therefore, has a potential as a detoxifying agent.


OBJECTIVES

The aim of this project was to elucidate the mechanism of interaction of deamidated soluble wheat protein (SWP) with whey protein isolate (WPI), bovine serum albumin (BSA) and lysozyme.

The objectives for the study were:


DEDICATION

This thesis is dedicated with affection to my daughter Iris and my wife Shelia, whose courage, good humour, and patience have been an inspiration to me.


ACKNOWLEDGEMENT

I am taking this opportunity to thank individually, all those who have assisted me in one way or the other with my Ph.D Project.

Dr. Stefan Kasapis of Cranfield University had a great influence on my work. He introduced me to rheology, differential scanning calorimetry, phase separation and the application of phase contrast microscopy in food science, and supervised the work I have reported in this report on phase separation, differential scanning calorimetry and some of the rheological studies. I thank Professor E. R. Morris for giving me the opportunity to work in his laboratory in Cranfield University during which period I was fortunate enough to meet one of the purists in science, Dr. R. K Richardson. The rheometer I used (Bobometer) was designed and built by Dr. Richarson. The Ph.D students I met in Professor Morris’s Laboratory were very friendly and helpful and I would like to thank in particular Miss P. Manoj and Mr. I. Chronakis.

The circular dichroism (CD) studies were carried out at Birkbeck College, University of London under the supervision of Dr. Drake and Mrs. Beaulah Banford. I thank Mrs. Banford for showing me how to use the CD equipment and discussion of the results.

I thank Dr. Andrew Taylor at the Robens Institute, University of Surrey for helping me with atomic absorption spectrometry, and Dr. M. Dobrota at the School of Biological Sciences, University of Surrey for discussions on metal binding studies. Dr. Dobrota had been very helpful to me through out my Ph.D. studies. He has always been the first person I usually run into when I am faced with complicated assays, and at the blink of an eye, he always left whatever he was doing to listen to me.

The small angle neutron scattering studies were carried out at the Rutherford Appleton Laboratory, under the supervision of Dr. Steve King. The study was done with a grant provided by the Science and Engineering Research Council. I thank Dr. S. King and Dr. Richard Heenan of the Rutherford Appleton Laboratory for checking my calculations and results.

I thank Dr. Nana Yeboah, formerly of the School of Biological Sciences, University of Surrey, who is presently at the National Food Research Institute in Japan for introducing me to protein chemistry and showing me how to run SDS-PAGE and Acid-PAGE.

I also thank Dr. Abraham Iyambo, who is presently the Deputy Minister of Fisheries in the Namibian Goverment for his frienship and collaboration on a number of experiments. We worked together on the Kjeldahl protein determination method, isoelectric focusing, hydrophobicity studies and the phase contrast microscope. Peter Somers filled the vacuum when Dr. Iyambo left. I thank Peter and Dr. Tony Avades for scientific discussions and their friendship.

I thank the staff at Daresbury Laboratory and Brookhaven National Laboratory for giving me access to their databases.

Thanks are also due to Professor P. Zhadan, Material Science department, University of Surrey for introducing me to the Atomic Force technique.

I am totally responsible for any mistakes in experimental design, discussion of results and the conclusions.

This studentship was funded by the MAFF Industry Food processing LINK Scheme as part of the LINK project on “Protein-Protein and Protein-Polysaccharide Interactions in Food Gels”. Funding from MAFF, Nestle, St. Ivel, Four Square, Pedigree Petfoods and Amylum is gratefully acknowledged and the members of the LINK project consortium are thanked for their valuable input.