Effects of Protein Quality on the Functional and Rheological Properties of Skimmed Milk Powders

Louise Elizabeth Bennett, Sunanda Sudharmarajan, Katherine Robinson, Geoffrey Smithers

Research output: Contribution to conferenceAbstract


Proteins represent the major functional components of dairy products when used as food ingredients. Functional performance of these products as ingredients can be highly variable and this inconsistency generates an adverse perception of product quality. As dairy processors endeavour to add value by tailoring the functional properties of their products to the intended end-use, it is necessary to understand the role of composition on functionality and moreover, to adopt testing methodologies which are sensitive to protein quality. Ultimately, there is a need for convenient and sensitive methods for testing the functional properties of protein-based food ingredients so as to provide a means for differentiation of products in the marketplace. Dairy proteins are well known for their thermal instability and undergo structural and chemical modifications as a result of thermal processing treatments. Consequent structural and chemical deviations from the native state are here collectively referred to as ‘protein quality’. However, relationships between protein quality and functionality are not well understood and in particular, which functional properties are sensitive to protein quality. 30 SMPs were prepared using pilot scale facilities at Food Science Australia in which the control of pre-heat temperature (72°Cto 112°C) and holding times (30 s to 270 s) yielded a set of SMPs differing over a broad range of protein quality. Protein quality was characterised in terms of loss of whey protein solubility and increases in disulfide cross-linking-mediated aggregation.
These powders were further characterised with respect to selected functional properties including: protein solubility at pH 4.6, protein solubility at pH 7.0, hydrophobicity, emulsification activity, foaming capacity and rheological properties by ‘Rapid Visco Analysis’. The Rapid Visco Analyser monitors the viscosity changes accompanying a programmed heating and cooling cycle under constant shear. Microscopic characteristics of the pastes produced during Rapid Visco Analysis were also recorded. Correlations between protein quality and selected functional properties revealed the relative sensitivity and limitations of these methods in discriminating between the SMPs on the basis of protein quality.
Original languageEnglish
Number of pages2
Publication statusPublished - 1999
Externally publishedYes

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