Agglomeration during spray drying: Physical and rehydration properties of whole milk/sugar mixture powders
Introduction
The rehydratability of a powder in water is an essential property of food powders for the consumer (King, 1966). Three main stages are usually distinguished in the rehydration process: wetting, dispersion and solubilization (Freudig et al., 1999, Písecký, 1997). These stages are characterized by three indices: the wettability index (WI), the dispersibility index (DI) and the solubility index (SI), respectively. The WI measures the ability of the powder to adsorb water on its surface, to be wetted, and to penetrate the free surface of still water (Sharma, Jana, & Chavan, 2012). The DI represents the ability of a powder to separate into individual particles when dispersed in water with gentle mixing (Sharma et al., 2012), and the SI provides an overall measurement of the ability of a powder to dissolve in water (Schuck, Dolivet, & Jeantet, 2012). In order to realistically consider the rehydratability of a powder, Schuck et al. (2012) proposed considering the ‘instant’ criterion (IC), which applies to powders that are wettable (WI < 20 s), dispersible (DI > 95%) and soluble (SI > 99%) at the same time.
Rehydratability depends on the composition and structure of a powder, especially the affinity between its components and water (Dupas-Langlet et al., 2012, Crowley et al., 2016) and the accessibility of the water to its components, and on the rehydration conditions (Jeantet, Schuck, Six, Andre, & Delaplace, 2010). Whole milk powder cannot be wetted within a reasonable time (Kim, Chen, & Pearce, 2002) and the dispersibility is not satisfactory compared to skim milk powder (Tamime, 2009, Vignolles et al., 2009) due to the hydrophobic nature of the surface of the particle incorporating free fat (Petit et al., 2017). To improve these rehydration properties, manufacturers are required to add natural surfactants such as oil lecithin or a hygroscopic ingredient such as an amorphous carbohydrate.
Apart from this approach based on modifying the composition, powder agglomeration is recognized to be one way to control and improve certain properties of a disperse system, especially with regard to rehydratability (Buffo et al., 2002, Gaiani et al., 2005). Indeed, agglomeration is known to have an impact on certain physical properties of powders such as density, granulometry, stickiness and cakiness, as well as on instant properties. The latter are mainly determined by the agglomeration process and then by the time/temperature to which the product is subjected in the system, including the processing steps prior to spray drying. The agglomeration mechanism consists of joining fines or small primary particles in order to form larger particles. Different agglomeration techniques, either in the dry or the wet state, are currently proposed, but the wet granulation process in a fluid bed is by far the most commonly used in the food industry (Cuq et al., 2013, Gaiani et al., 2007, Turchiuli et al., 2012).
The aim of this study was to determine the impact of six configurations of a semi-industrial drying pilot on the physical and rehydration properties of a given dairy formulation consisting of a sweet whole milk powder whose biochemical composition was kept constant. The efficacy of five different agglomeration processes was compared to a control non-agglomeration process.
Section snippets
Preparation of the concentrate
Concentrates with 40 g.100 g-1 total solids (TS) were recombined at Bionov (Rennes, France) from a non-agglomerated medium-heat Whole Milk Powder (WMP, Lactalis Ingredients, Bourgbarré, France) and a mix of carbohydrates composed of sucrose (Begin-say, Tereos, Lille, France) and lactose (Lactalis Ingredients, Bourgbarré, France) at a 40/60 g/g sucrose/lactose ratio. The final target of the carbohydrate content was 55 g/100 g TS. The carbohydrate solution was dissolved at 70 °C to obtain a
Concentrate
As explained above, the dry matter of the concentrate was good at 40.00 ± 0.01 g/100 g. The D[4.3] of the fat droplet size in the presence of EDTA was 0.76 ± 0.01 μm. The correlation between the free fat content and greater fat droplet diameters has already been established: to achieve low free fat content in powders, the fat droplet size in the concentrate has to be less than 1 μm before spray drying (Vignolles et al., 2009).
Biochemical composition of powders
The average biochemical composition of all the powders was
Conclusion
This study showed that different dryer configurations may have an impact on the physical properties of powders, influencing rehydration properties. In general, powder agglomeration enhanced rehydration properties. For instance, the best technological approach from a rehydratability point of view appeared to be a combination of the reintroduction of fine particles with simultaneous steam injection in the internal fluid bed, but this approach is highly dependent on the specific drying tower
References (34)
- et al.
Evaluation of particle measures relevant for powder bed porosity - a study of spray dried dairy powders
Powder Technology
(2014) - et al.
Food powder agglomeration
- et al.
Dispersion of powders in liquids in a stirred vessel
Chemical Engineering Processing
(1999) - et al.
Use of a turbidity sensor to characterize micellar casein powder rehydration: Influence of some technological effects
Journal of Dairy Science
(2005) - et al.
Dairy powder rehydration: Influence of protein state, incorporation mode, and agglomeration
Journal of Dairy Science
(2007) - et al.
Surface characterization of four industrial spray-dried dairy powders in relation to chemical composition, structure and wetting property
Colloids and Surfaces B: Biointerfaces
(2002) - et al.
Storage-induced caking of cocoa powder
Journal of Food Engineering
(2017) - et al.
Jet agglomeration processes for instant food
Food Science and Technology
(1993) - et al.
Water vapour adsorption properties of agglomerated baby food powders
Journal of Food Engineering
(2012) - et al.
Fat properties during homogenization, spray-drying and storage affect the physical properties of dairy powders
Journal of Dairy Science
(2009)
Size distribution of agglomerates of milk powder in wet granulation process in a vibro-fluidized bed
Brazillian Journal of Chemical Engineering
Milk powder agglomerate growth and properties in fluidized bed agglomeration
Dairy Sciences and Technology
Adsorption of gases in multimolecular layers
Journal of the American Chemical Society
Effects of agglomeration on the properties of spray-dried encapsulated flavours
Flavour and Fragrance Journal
Rehydration and solubility characteristics of high-protein dairy powders
Combined crystallization and drying in a pilot-scale spray dryer
Drying Technology
Deliquescence lowering in mixtures of NaCl and sucrose powders elucidated by modeling the water activity of corresponding solutions
Journal of Food Engineering
Cited by (48)
A comprehensive approach about comparison between drying technologies and powdered dairy products
2023, Food Research InternationalImproving the physical and wettability properties of skim milk powders through agglomeration and lecithination
2023, Journal of Food EngineeringAgglomeration of gum tragacanth as a promising novel approach to structural modification
2023, Powder TechnologyFood powder rehydration
2023, Handbook of Food Powders: Chemistry and Technology, Second EditionDairy powder enriched with a soy extract (Glycine max): Physicochemical and polyphenolic characteristics, physical and rehydration properties and multielement composition
2022, Food Research InternationalCitation Excerpt :The rehydration characteristics of the samples were investigated through the three stages of reconstitution: wetting, dispersion, and solubilization (Table 3). Powders considered wettable must present complete wetting of the surface within 120 s (Chever et al., 2017). The soy extract does not fit into this classification, as the reconstitution of the powder is generally hampered by the physical and chemical changes that occur during the spray dry spray drying process.