Rehydration and Solubility Characteristics of High Protein Dairy Powders
Dairy powders derived from membrane filtration processes, such as milk protein concentrate (MPC) and phosphocaseinate (PC) powders, have considerable potential as functional ingredients due to their high protein content and quality. However, the use of these powders is sometimes limited or impaired by their poor rehydration characteristics in aqueous media, which has been linked with the formation of an inter linked network of casein micelles at particle surfaces during processing and storage. Analytical tools are now available which can monitor the rehydration of dairy powders dynamically. This is a considerable development, as the rate limiting stages of rehydration for individual powders (e.g. wetting, dispersion) can now be identified, quantified and targeted in attempts to improve rehydration properties. In addition, these technologies allow the negative effects of sub optimal processing or storage conditions on powder rehydration and solubility characteristics to be measured, which allows preventative strategies against loss of solubility to be developed. Moreover, it is foreseeable that some of these technologies could be useful for in line analysis and process control at an industrial scale. This review provides a detailed description of the underlying principles, data outputs and industrial relevance of current methods to monitor dairy powder rehydration. The technologies discussed in this review include viscometry and rheometry, turbidimetry, static light scattering, focused beam reflectance measurement (FBRM) image analysis, nuclear magnetic resonance (NMR) relaxometry, thermochemistry, conductimetry and sound based technologies. The contribution that these technologies have made to the current understanding of rehydration phenomena, with a particular emphasis on high protein dairy powders =80 protein) is discussed throughout. In addition, a comprehensive overview of rehydration and solubility characteristics, and the effects of process storage and additive induced changes thereon, is given for high protein dairy powders.