David S. Reid
B.S. in Chemistry (1st Class Honors) University of Glasgow, Scotland, 1963
Ph.D. in Physical Chemistry, University of Glasgow, Scotland, 1966
RESEARCH OBJECTIVES - LAY TERMS
Control of the status of water is a key part of many strategies for food preservation. My research objective is to improve our understanding of the roles played by water in the properties of foods. In my lab we study the freezing process, and the concentration process in order to identify similarities and differences, and help find better means of preserving the national food resource through improved water management procedures. Similar methods to those we employ to study the freezing process are now being applied to studying the crystallization of fats. This should result in a better control of the properties of fats, for example more spreadable fats.
RESEARCH OBJECTIVES - FOR PEERS
Water is a key component of most foods. In chemical terms it may be the solvent, or it may be a contributory reactant, in processes of change. It is my objective to better understand the role of water in mediating the interactions in foods. In frozen systems we study mechanisms of ice nucleation and growth, employing seeded emulsion methodology. We also study the effect of the phase relationships on stability and reaction rates. The role of ice, and the role of the unfrozen phase, are studied. We are characterizing the glass dynamics in frozen systems. In food concentration processes, we are studying the aggregation which occurs on the removal of water. On redilution, this aggregation results in irreversible loss in functionality. The study of fat crystallization compares the crystallization of bulk and emulsion samples. From the comparison, we should be able to derive information about the nucleation process, and the growth process.
RECENT SIGNIFICANT FINDINGS/ACCOMPLISHMENTS
Heterogeneous nucleation of ice follows a temperature dependence similar to that of homogeneous nucleation. Solute lowers the nucleation temperature more rapidly than the melting point. Nucleation control might therefore be able to influence the structure of frozen products, and could lead to new ways of manufacturing ice cream. The temperature of the maximally freeze concentrated glass, Tg', is key to the stability of frozen foods. It can be seen as a "mobility temperature" at which significant molecular motions commence. We have demonstrated that the rate of change is controlled by the difference between the storage temperature, Ts, and Tg'. Methods of measuring Tg' have been developed for use in QA/QC. Magnetic resonance imaging and calorimetry can be combined to yield a detailed timeline and picture of the progress of freezing. Engineering models can be tested. Images show that the nucleation process plays a very important role in determining the structure of the surface layer of the frozen product. This will influence moisture migration, and affect storage life. The results suggest a novel freezing process. Stepwise DSC is proving to be a useful technique in characterizing polymorphic transitions in fats.