Introduction
Milk powders made by spray drying are utilized all over the food industry for products spanning from confectionery and baked goods to sauces, soups, and beverages. They are also directly supplied to consumers.
The flow properties of these powders characterize their use and value for efficient and effective food processing. Powders that flow easily and reliably throughout the production chain maximize industrial output by reducing unplanned stoppages and inefficiencies, thereby improving profitability.
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Understanding how to produce milk powders with superior flow properties is advantageous. Lipid content is a significant factor, although moisture content and particle size also play roles in determining flow behavior.
In a study conducted by researchers at the Université de Lorraine in Nancy, France, the flowability of spray-dried milk powders was examined in relation to the composition of the feed concentrate and an aeration pre-treatment.1
Spray-dried powders with varying lipid content—1.5 %, 14 %, and 26 %—were produced from skimmed, semi-skimmed, and whole milk concentrates. These three samples were assessed in comparison with aerated analogues, generated by whipping the concentrates prior to spray drying under strictly comparable conditions.
Dynamic and shear flow properties were assessed for all six spray-dried milk powders using the FT4 Powder Rheometer®. The study revealed valuable correlations between the properties of the feed concentrates and the process-relevant flow properties of the resulting powders.
Flowability
Basic Flowability Energy (BFE) values describe a powder’s proclivity to flow in confined or forcing environments when in a low to moderately stressed state. BFE values are strongly linked to performance in processes such as blending and flow through the feedframe of dosing systems or tablet presses, making them particularly relevant in food processing operations. Moreover, they are largely differentiating, frequently able to identify even small variations in samples that other flow properties might classify as identical or very similar.
In the case of these milk powders, BFE was found to increase with higher lipid content (1.5 % for skimmed, 14 % for semi-skimmed, and 26 % for whole milk) in both untreated and treated/aerated samples. These findings indicate that aeration significantly impacts BFE, resulting in increased resistance to flow.
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Shear properties like cohesion measure the behavior of consolidated powders under relatively high stress, which is particularly relevant to hopper discharge performance. The results for these milk powders reveal minimal differences between the semi-skimmed and whole milk samples, but the skimmed milk powder exhibited notably lower cohesion. Aeration had only a slight effect on the behavior of all three samples.
The physicochemical properties of the milk powders offer insight into these trends. For instance, semi-skimmed and whole milk powders were found to have high and disproportionate surface lipid content. This increased surface "stickiness" due to lipid distribution likely explains the higher cohesion and resistance to flow observed in the semi-skimmed and whole milk powders compared to the skimmed variety. The more pronounced effect under high-stress conditions may result from the release of free fat at the powder surface under consolidation pressure.
Aeration leads to more even lipid dispersion, yet simultaneously enables smaller particle size distributions centered on a finer particle size. This latter trend may influence particle packing, which is crucial for understanding BFE values, and could help explain the flow behavior observed under low-stress conditions. Under high consolidation, the differences induced by pretreatment may be less apparent.
Importantly, these trends offer valuable insight into how different milk powders will behave during processing. Low lipid content is clearly associated with low cohesion and good flowability in hoppers, silos, and other contexts. However, processors aiming to aerate dairy concentrates to enhance properties like wettability and solubility should be cautious, as this could inadvertently reduce flowability and, consequently, overall processability.
Conclusion
The findings discussed here demonstrate the value of assessing dynamic and shear powder characteristics to collect process-relevant insight into various milk powders and the effect of concentrate pretreatment.
This type of multivariate analysis offers a level of detail that cannot be achieved through simple, single-parameter powder testing methods and can be highly effective in guiding the development of optimal ingredients for food processing.
References
- T. Fournaise, J. Burgain, C. Perroud, J. Scher, G. Gaiani, J. Petit ‘Impact of formulation on reconstitution and flowability of spray-dried milk powders’ Powder Technology 372 (2020) 107-116.
This information has been sourced, reviewed and adapted from materials provided by Micromeritics Instrument Corporation.
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