During storage of long shelf life dairy products undesired changes can appear in the products. One major change in liquid UHT products and re-dissolved dairy product powders is an increase in viscosity, creation of “fluffy” material or “clouds” caused by aggregation of material including proteins. Both floating and pelleted solids can be observed. This change is irreversible and renders the product deteriorated in regard to functionality, flavor, and nutritional value. This deterioration appears only in some batches and seemingly randomly. A determining step in the gelation can be aggregation of proteins and/or proteolysis from heat stable proteases – either native bovine proteases or from psychrotropic bacteria in the raw milk, or in combination. The project therefore aims at analyzing and outlining the formation of aggregates by proteomic characterizations combined with peptidomic profiles of different dried and liquid products that qualitatively, and hopefully also quantitatively, characterize the proteolysis and its relation to deterioration in dairy products. Research strategy The strategy chosen for studying proteolytic activity is to monitor changes in the product of the proteolysis that happen during storage instead of characterization of enzyme activties. A matrix of storage conditions such as time, temperature, pH etc should be constructed, and proteolysis is investigated e.g. by detection of increase in free amino acid terminals or by creating peptide profiles by means of LC-MS. The physical properties of the products will be analyzed by means of rheological methods and texture analysis, and the aggregates characterized by proteomic methods. The results obtained should be compared and combined by applying univariate and multivariate statistical analysis as well as pattern recognition. Ultimately a peptidomic profile should be made out which can be used to predict and explain proteolytically related quality problems in dairy products.
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International Symposium on Spray Dried Dairy Products, 2012