Shane V. Crowley

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.

Drying: Effect on Nutrients, Composition and Health

Drying is an effective method of extending the shelf life of nutrient-dense foods and facilitating their transport around the world. To ensure that the nutritional quality of foods is retained, appropriate drying technologies (e.g., air-, spray-, and freeze-drying) and drying conditions (e.g., heating intensity and feed composition) must be selected based on the properties of the product to be dried. The macronutrients and micronutrients that are present and the interactions that may occur between them during drying largely determine the sensitivity of the system to degradative dehydration-induced changes. Factors influencing the nutritional quality of dehydrated foods are discussed in this article, with a particular focus on process- and storage-induced degradation of micronutrients and advances in encapsulation technologies.

Short communication: Multi-component interactions causing solidification during industrial-scale manufacture of pre-crystallized acid whey powders

Acid whey (AW) is the liquid co-product arising from acid-induced precipitation of casein from skim milk. Further processing of AW is often challenging due to its high mineral content, which can promote aggregation of whey proteins, which contributes to high viscosity of the liquid concentrate during subsequent lactose crystallization and drying steps. This study focuses on mineral precipitation, protein aggregation, and lactose crystallization in liquid AW concentrates (∼55% total solids), and on the microstructure of the final powders from 2 independent industrial-scale trials. These AW concentrates were observed to solidify either during processing or during storage (24 h) of pre-crystallized concentrate. The more rapid solidification in the former was associated with a greater extent of lactose crystallization and a higher ash-to-protein ratio in that concentrate. Confocal laser scanning microscopy analysis indicated the presence of a loose network of protein aggregates (≤10 µm) and lactose crystals (100-300 µm) distributed throughout the solidified AW concentrate. Mineral-based precipitate was also evident, using scanning electron microscopy, at the surface of AW powder particles, indicating the formation of insoluble calcium phosphate during processing. These results provide new information on the composition- and process-dependent physicochemical changes that are useful in designing and optimizing processes for AW.

Colloidal properties of protein complexes formed in β-casein concentrate solutions as influenced by heating and cooling in the presence of different solutes

Monomeric bovine β-casein self-associates into micelles under appropriate conditions of protein concentration, serum composition and temperature. The present study investigated self-association characteristics of a β-casein concentrate (BCC) prepared from milk at pilot-scale using membrane filtration. The BCC had a casein:whey protein ratio of 77:23, with ∼95% of casein consisting of β-casein, and the remainder being mostly κ-CN. BCC was reconstituted to 1.2% protein (a typical level in infant formula) in various liquid media at pH 6.8 and incubated at different temperatures from 4 to 63 °C for 30 min. Self-association of β-casein on heating was thermo-reversible in deionised water, lactose (4, 6 or 8%) or calcium (9 mM) solutions. In most serum phases, BCC became highly opaque after incubation at 63 °C, but clarified rapidly during cooling to 25 °C. However, in simulated milk ultrafiltrate (SMUF), which has a high ionic strength and is supersaturated in calcium phosphate (CaP), BCC remained opaque during cooling to 25 °C, and retained residual turbidity after 15 h of holding at 4 °C; if SMUF was prepared without phosphate then turbidity development in BCC solutions was markedly reduced. The complexes responsible for this turbidity development were successfully dissociated with 50 mM trisodium citrate. Analysis of pH during heating and holding at 60 °C indicated that SMUF acidified continuously under the period of study, while acidification in BCC/SMUF mixtures terminated after a short period, indicating that the type of CaP formed on heating is altered in the presence of BCC. This study demonstrates that BCC ingredients exhibit pronounced temperature-dependant changes in colloidal properties that are strongly affected by the presence of minerals commonly found in nutritional product formulations.