Challenges are commonly encountered in the bulk handling and application of high-protein dairy powders, and are strongly influenced by their poor flowability. Powder flowability can be defined as the ability of a powder to flow under set environmental or processing conditions and it is ultimately determined by the type and extent of interparticle interactions occurring in the bulk powder (e.g., van der Waals and electrostatic interactions). High-protein powders are particularly susceptible to the occurrence of interparticle interactions, resulting in increased cohesive forces being experienced in the bulk powder, thereby reducing powder flowability. This review summarises the major factors responsible for poor flowability in high-protein dairy powders and critiques traditional (e.g., agglomeration) and some of the more relevant novel approaches (e.g., dry- and wet-coating and roller compaction) available for improving the flowability of powders post-spray drying. This review material will be of considerable interest to dairy scientists, technologists and engineers challenged with understanding, predicting and controlling the bulk handling and flowability of high-value dairy protein powders.

Agglomerated powders are susceptible to breakdown on handling, most notably, during powder conveying. In this study, three agglomerated dairy powders (whey protein concentrate powder, WPC; fat-filled milk powder, FFMP and infant formula powder, IF) were conveyed through a custom-fabricated dispersion rig to understand the effects of agglomerate breakdown on dairy powder handling and application. All samples displayed significant breakdown on dispersion, evidenced by reducing particle size and increasing bulk density. The resulting flowability of these powders was impaired (flow index: WPC: 9.3 to 5.1, FFMP: 5.7 to 4.9 and IF: 16 to 10) via increased particle-particle interactions. The initial stages of rehydration were impeded by agglomerate breakage (42.9–47.0% wettability reduction and 7.22–16.4% dispersibility reduction), while powder solubility remained relatively unchanged. This study provides insights into the alterations of agglomerated dairy powder properties on agglomerate breakdown, while identifying the effects these alterations have on the functional properties of these powders.

Fat filled milk powders (FFMP) are formulated by blending skim milk and vegetable oil, to which lactose, permeate, sugar, maltodextrin, vitamins and minerals may also be added. The liquid mix is usually homogenised and spray dried, with agglomeration and lecithination, to produce powders for a range of end-user applications including drinking milk, yoghurt base and coffee whitening. Thus, it is important to avoid common powder defects such as inconsistent whitening, feathering or white flecking on reconstitution. The phenomenon of white flecking, and in particular, the underlying causes of fleck formation, are poorly understood. To better understand white fleck formation, six size fraction samples from two different FFMPs, a good (low level flecking) and a poor powder (high level flecking), were profiled. Most extensive flecking was observed in the coarse fraction of the poor powder, which also had an 8-fold higher free fat content than all other fractions and displayed poor emulsion stability (D-3,(2) = 15 +/- 3.9 mu m compared to 0.45-0.75 mu m for all other fractions). Treatment of the reconstituted emulsions with an anionic surfactant or a reducing agent suggested that integrity of white flecks was based mainly on electrostatic interactions between proteins, with little contribution from covalent bonds. Although the extent of whey protein denaturation ranged between 22.6-47.5%, whey protein insolubility appeared to play a sub-ordinate role in white fleck formation. These results suggest that presence of flecks in FFMP was mainly associated with poor thermal stability of the emulsions.

In this work, the strength of tablets made from mixtures of whey protein concentrate (WPC) powder and different types of sugar was investigated. The agglomerated WPC powder was pneumatically conveyed (lean phase) at three different air speeds of 10, 20 or 30 m/s to simulate the effects of industrial powder transport, resulting in agglomerates with reduced integrity. Conveyed and control WPC powder, and sugar of three different particle size distributions (i.e., granulated, GS; caster, CS and icing sugar, IS) were analysed for microstructure, particle size, moisture, and flowability. Tensile strength of tablets from WPC powder alone or blended with 0.5-10% sugar was tested. Conveying of WPC powder led to a significant increase in tablet strength, (i.e., from failure strength of 1.67 N/mm(2) for control tablets to 2.33, 2.11 and 2.11 N/mm(2) after conveying at 10, 20 or 30 m/s, respectively), suggesting that the generation of smaller powder particles led to increased mechanical strength of tablets. The addition of sugar also resulted in a significant increase in tablet strength (e.g., failure strength of 2.34, 2.12 and 2.47 N/mm(2) at 1.5% addition level of GS, CS and IS, respectively) and strongest tablets were obtained at 1.5-3% sugar addition and by blending with icing sugar. This study demonstrated, for the first time, that conveying and dry blending of whey protein and sugar powders significantly influenced the rheological properties of resultant tablets.

Title Mechanical integrity and rehydration properties of agglomerated nutritional dairy ingredient powders Author(s) Hazlett, Ryan Publication date 2019-12-22 Original citation Hazlett, R. 2019. Mechanical integrity and rehydration properties of agglomerated nutritional dairy ingredient powders. MRes Thesis, University College Cork. Type of publication Masters thesis (Research) Rights © 2019, Ryan Hazlett. https://creativecommons.org/licenses/by-nc-nd/4.0/ Item downloaded from http://hdl.handle.net/10468/10907