Effect of high pressure at low temperature on the molecular structure and functionality of dairy proteins

High hydrostatic pressure processing (HPP) is a nonthermal process in which foods are subjected to pressures in the range of 100--700 MPa at room temperatures or higher. HPP is effective in reducing microbial counts and enzyme activity. The ability of HPP to modify the functional properties of proteins has become the focus of research only recently. Covalent bonds within proteins are unaffected during HPP however; hydrogen bonds, covalent bonds and hydrophobic bonds are modified resulting in changes to protein structure and function.; The ability to control the protein denaturation process by applying HPP and low temperature has only recently been investigated as a method that minimizes the loss of native protein structure and reduces subsequent aggregation reactions. The objective of this thesis was to demonstrate that low temperature HPP treatment could be useful in controlled protein structural changes and thereby improving product functionality and quality.; The first part of this thesis investigated targeted denaturation of beta-lactoglobulin through low temperature HPP treatment that optimizes the protein's ability to lower surface tension at air-water interfaces, while minimizing protein aggregation. In addition, structure/function relationships of denatured beta-lactoglobulin are investigated.; Samples treated at 510 MPa, for 10 minutes at 0.5 mg/ml, pH 7.5 at 8°C resulted in decreased aggregation as monitored by native PAGE and significantly higher surface pressure values at the air-water interface. Circular dichroism (CD) data indicated that secondary structural changes occurred. Intrinsic and extrinsic fluorescence and free thiol reactivity were also used to understand the degree of denaturation induced by HPP treatment.; The second part of the study was to apply the cold HPP treatment to yogurt to evaluate the quality benefits of this process in a dairy food system. The present study was conducted to investigate the effects of cold HPP treatment on the color, texture and microbiology of blackberry yogurt formulated with fruit and the shelf-stability of this product over time at refrigerated and room temperature storage conditions.; Low temperature HPP is an effective tool for targeted protein denaturation, which opens the potential for novel food products.