Physicochemical properties of micellar casein retentates generated at different microfiltration temperatures.

Processing temperature has a significant influence on the composition and functionality of the resulting streams following microfiltration (MF) of skim milk. In this study, MF and diafiltration (DF) were performed at 4 or 50°C to produce ß-casein (ß-CN)-depleted and nondepleted (i.e., native casein profile) micellar casein isolate retentates, respectively. Microfiltration combined with extensive DF resulted in a 40% depletion of ß-CN at 4°C, whereas no ß-CN depletion occurred at 50°C. Microfiltration at 4°C led to higher transmission of calcium into permeates, with retentate generated at 4°C containing less total calcium compared with retentate generated at 50°C, based on the volume of retentate remaining. Higher heat stability at 120°C was measured for retentates generated at 4°C compared with those at 50°C, across all pH values measured. Retentates generated at 4°C also had significantly lower ionic calcium values at each pH compared with those generated at 50°C. Higher apparent viscosities at 4°C were measured for retentates generated at 4°C compared with retentates generated at 50°C, likely due to increased voluminosity of ß-CN-depleted casein micelles. The results of this study provide new information on how changing the composition of MF retentate, by appropriate control of processing temperature and DF, can alter physicochemical properties of casein micelles, with potential implications for ingredient functionality.

Cold Microfiltration as an Enabler of Sustainable Dairy Protein Ingredient Innovation.

Classically, microfiltration (0.1-0.5 µm) of bovine skim milk is performed at warm temperatures (45-55 °C), to produce micellar casein and milk-derived whey protein ingredients. Microfiltration at these temperatures is associated with high initial permeate flux and allows for the retention of the casein fraction, resulting in a whey protein fraction of high purity. Increasingly, however, the microfiltration of skim milk and other dairy streams at low temperatures (≤20 °C) is being used in the dairy industry. The trend towards cold filtration has arisen due to associated benefits of improved microbial quality and reduced fouling, allowing for extended processing times, improved product quality and opportunities for more sustainable processing. Performing microfiltration of skim milk at low temperatures also alters the protein profile and mineral composition of the resulting processing streams, allowing for the generation of new ingredients. However, the use of low processing temperatures is associated with high mechanical energy consumption to compensate for the increased viscosity, and thermal energy consumption for inline cooling, impacting the sustainability of the process. This review will examine the differences between warm and cold microfiltration in terms of membrane performance, partitioning of bovine milk constituents, microbial growth, ingredient innovation and process sustainability.

Physical and colloidal stability of conventional and micronised calcium citrate ingredient powders in the formulation of infant nutritional products.

The fortification of food systems with calcium remains difficult; one challenge is to maintain the colloidal stability of insoluble calcium salts during processing and shelf life. Particle size reduction of insoluble salts may result in improved product stability. In this study, insoluble calcium citrate in two different particle sizes, conventional calcium citrate and micronised calcium citrate, were first evaluated in terms of physical and bulk handling properties, followed by protein adsorption and colloidal stability when dispersed in two dairy-based nutritional beverages differing in composition, i.e. infant milk formula stage 1 and 3. Particle size distribution analysis showed micronised calcium citrate (volume-weighted diameter = 5.10 µm) to have significantly smaller (p < 0.05) particle size than conventional calcium citrate (volume-weighted diameter = 88.2 µm). The adsorption of dairy proteins onto particles of calcium citrate resulted in caseins having greater affinity for both salts, followed by ß-lactoglobulin. The smaller particle size of the micronised citrate resulted in higher affinity for casein and greater colloidal stability when dispersed in both infant milk formula solutions compared to conventional calcium salts. The results of this study provide knowledge on the application of micronised insoluble calcium salts in the fortification of nutritional dairy-based products.