Dairy powder breakage: mechanisms, impact factors, and influences on powder properties

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Han, Jie
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University College Cork
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Dairy powders provide a good form for convenient and stable preservation and transportation of milk ingredients, and most commercial dairy powders are agglomerated to improve powder functionalities. However, particle breakage during production and transportation is an important issue for agglomerates and only a few studies on dairy powder breakage have been published. Therefore, there is limited information to understand this phenomenon and find ways to decrease it. The present study investigated the breakage mechanisms of dairy powders, the influence of dairy powder breakage on powder properties, and the impact of powder characteristics on dairy powder breakage. This provides more information to better understand and control dairy powder breakage in an effort to improve the functionalities of dairy powders. The main breakage mechanisms of agglomerated infant milk formula (IMF) during transportation and mixing included dispersion, chipping (surface breakage), and fragmentation (body breakage, which includes both disintegration and splitting), which correspond to an increasing extent of breakage. The breakage mechanism of whole samples was one or a combination of breakage mechanisms because the breakage behaviour of samples with different particle sizes at the same process condition was different. Dairy powder breakage significantly decreased the particle size and porosity of powders and increased the specific surface area, particle density, and bulk density of samples. It also changed the shapes and surface composition of particles as seen with the increase in lactose content and the decrease in protein and fat contents for most samples. These changes in physical properties significantly deteriorated the rehydration properties of dairy powders, including the wettability and dispersibility, while it had only a small influence on powder flowability. In addition, body breakage had greater influences on powder physical properties than surface breakage. Thus, surface breakage had no influence on water sorption and mechanical properties of powders but body breakage significantly deteriorated these properties as seen with the increase in water sorption rates and final water contents, the acceleration in the crystallization, and the decrease in the overall molecular mobility. Dairy powder breakage degree or mechanisms was determined by the process conditions and particle characteristics. Breakage increased with increasing intensity of processing conditions, such as the transportation velocity and air pressures. In addition, fatigue affected the breakage of agglomerates dairy powders. For powder characteristics, the breakage degree of dairy powders increased with increasing particle size and decreasing particle structural strength. Considering particle structure, the strength of crystals and continuum solids were the highest, followed by particles with numerous holes throughout the particle, followed by the hollow sphere particle with a very thin shell. Under the same spray drying conditions, the formulation of dairy powders significantly affects dairy powder breakage by influencing the physical properties of powder particles, especially for particle size and particle structure. For whey protein/lactose model agglomerated powders, the two higher whey-protein powders were smaller in particle size, were less irregular in shape and had higher particle densities, which resulted in less breakage in comparison to the two lower whey-protein powders. For agglomerated model IMF powders that contained different protein and carbohydrates, whey protein powders were bigger in particle size, weaker in structural strength, and more irregular in shape in comparison to pure casein powders. This resulted in the better rehydration properties of whey protein powders but more breakage. Similarly, sucrose IMF samples had better rehydration properties but suffered more breakage than maltodextrin and pure lactose powders because of their bigger particle size. Findings in this study indicate that body breakage significantly deteriorates powder properties, so breakage should be limited to surface breakage. Since powder breakage cannot be avoided, changes to processing conditions (using lower conveying speeds or air pressures) and powder physical properties (mainly particle size and particle structure by changing production conditions or formulations) should be done to reduce breakage intensity.
Dairy powder breakage , Powder breakage mechanisms , Mechanical characteristics , Water sorption behaviour , Rehydration property , Particle structure , Particle size
Han, J. 2022. Dairy powder breakage: mechanisms, impact factors, and influences on powder properties. PhD Thesis, University College Cork.