Abstract
Plant-based milk alternatives (PBMAs) are increasingly used in food applications owing to their nutritional value and lower environmental impact compared with conventional dairy products. However, their successful reconstitution remains challenging because plant proteins and dietary fibers promote lump formation, thereby impairing wetting and dissolution. Although fluidized bed agglomeration is widely applied to improve the instant properties of food powders, the combined influence of formulation composition and process parameters on the reconstitution behavior of PBMAs has not yet been systematically investigated.
In this study, three representative PBMA formulations with different dominant compositional characteristics were agglomerated in a fluidized bed. A statistical Design of Experiments (DoE) approach was applied to investigate the interaction between formulation composition and fluidized bed process parameters on powder structure, wettability and lump formation during reconstitution. The results identified liquid spray rate and spray air pressure as the dominant process parameters governing agglomerate growth, while formulation composition strongly affected powder wettability.
The protein- and fiber-enriched formulations exhibited larger contact angles and reduced wettability than the carbohydrate-rich reference formulation. Furthermore, contact angle correlated with lump diameter, indicating that wetting represents a rate-limiting step during powder reconstitution. The generated DoE models provide a framework for formulation-specific adjustment of fluidized bed process parameters to tailor powder structure and minimize lump formation.
Highlights
- Water activity and glass transition temperature impact the powder wettability.
- Depending on the formulation, different process parameter combinations were found for optimization.
- Correlation between contact angle and lump diameter was established.
- Powder formulations have the main influence on the formed lumps.
Introduction
The demand for plant-based milk alternatives (PBMAs) has increased considerably in recent years, driven by health, environmental, ethical and animal welfare concerns [1], [2], [3]. In addition to providing valuable nutrients, PBMAs are generally associated with a lower environmental impact than conventional cow’s milk, including reduced greenhouse gas emissions and freshwater consumption, although the magnitude of these benefits depends on the raw materials and production systems employed. To improve shelf life, reduce transportation and storage costs, and facilitate their incorporation into a broad range of food applications, PBMAs are increasingly commercialized as powder products. However, despite these practical advantages, the successful reconstitution of plant-based powders remains considerably more challenging than that of conventional dairy powders due to their more complex multi-component composition.
Powder reconstitution is a complex multi-step process comprising wetting, sinking, dispersion and dissolution [4]. Efficient reconstitution requires rapid penetration of water into the porous powder structure, followed by particle disintegration and complete dissolution. Insufficient wetting frequently leads to the formation of persistent lumps, which hinder water transport into the particle interior, delay hydration and negatively affect product quality and consumer acceptance. Consequently, understanding the mechanisms governing lump formation is essential for the rational design of instant plant-based powders.
The reconstitution behavior of food powders is strongly governed by both particle structure and material composition. Besides particle size and porosity, properties such as wettability, surface composition, moisture content and glass transition behavior determine liquid penetration and dispersion kinetics [5], [6]. Compared with dairy powders, PBMAs represent considerably more complex multi-component systems comprising carbohydrates, proteins, lipids and dietary fibers, whose interactions during reconstitution are still poorly understood [3], [7]. In particular, plant proteins and dietary fibers may substantially alter wettability, moisture sorption and structural stability, thereby affecting the formation and persistence of lumps. Furthermore, plant proteins differ fundamentally from dairy proteins in their molecular structure, surface activity and hydration behavior, which may influence particle formation during spray drying and fluidized bed agglomeration as well as the subsequent reconstitution process.
Fluidized bed agglomeration is commonly employed to improve the instant properties of food powders due to its high heat and mass transfer rates, which enable short processing times at comparatively low temperatures [8], [9]. Previous studies have consistently identified liquid spray rate, atomization conditions and drying kinetics as the key process variables governing agglomerate growth and structure [10], [11], [12]. Under the laboratory-scale conditions investigated by Hemati et al. [10], the nozzle position and the associated process parameters were identified as critical factors controlling agglomeration. The atomization process determines droplet size distribution, spray pattern and particle wetting and is therefore essential for the formation of stable liquid bridges between particles [11]. In agreement with these findings, Kramm et al. [13] demonstrated that spray air pressure primarily governs spray angle, radial mass distribution and droplet size distribution of a two-fluid nozzle. In addition to the atomization conditions, increasing liquid spray rates promote particle growth by enhancing particle wetting and adhesion during collisions [14], [15]. Drying kinetics, which are largely controlled by the inlet air temperature, further determine the moisture content and consolidation of the agglomerates [10], [16]. Besides these process parameters, agglomerate formation is strongly affected by the material properties, including particle size distribution, wettability, solubility and formulation composition [15], [16]. Consequently, understanding the interactions between formulation composition and process parameters is essential for the targeted design of powder properties.
Although numerous studies have investigated either formulation composition or fluidized bed operating conditions individually, the combined influence of both aspects on the structure formation and reconstitution behavior of PBMAs has not yet been systematically investigated. This knowledge gap is particularly relevant because the increasing complexity of plant-based formulations limits the direct transferability of findings obtained for conventional dairy powders. Furthermore, quantitative investigations linking formulation composition, agglomeration process parameters and reconstitution behavior using a statistical Design of Experiments (DoE) approach remain scarce.
Therefore, the objective of this study was to systematically investigate the interactions between formulation composition and fluidized bed process parameters using a DoE approach. Accordingly, the objective was establishing the relationships between powder structure, wettability and lump formation during reconstitution. The results provide new insights into the coupled effects of formulation composition and agglomeration process parameters on powder structure and reconstitution behavior and thereby support the targeted design of plant-based powders with improved instant properties.
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Materials
The study was conducted using a plant-based alternative to conventional cow’s milk. A simplified model system was developed to facilitate the transfer of the obtained findings to more complex formulations. The formulation consisted of glucose syrup (dextrose equivalent, DE 21), soy protein isolate, sunflower oil, and oat bran. To date, studies examining the combination of the plant-based ingredients soy protein isolate and oat bran within the complex matrix of carbohydrate and lipid sources.
Source: K. Kramm, S. Pietsch-Braune, V. Meunier, K. Haas, S. Heinrich,
Influence of fluidized bed process parameters and material properties on plant powder characteristics and reconstitution behavior, Powder Technology, 2026, 123065, ISSN 0032-5910, https://doi.org/10.1016/j.powtec.2026.123065.
