The contribution of dehydration to the growing market of food powders from slurry/liquid matrices is inevitable. To overcome the challenges posed by conventional drying technologies, several innovative approaches have emerged. However, industrial implementation is limited due to insufficient information on the best-suited drying technologies for targeted products. Therefore, this review aimed to compare various conventional and emerging dehydration technologies (such as active freeze, supercritical, agitated thin-film, and vortex chamber drying) based on their fundamental principles, potential applications, and limitations. Additionally, this article reviewed the effects of drying technologies on porosity, which greatly influence the solubility, rehydration, and stability of powder. The comparison between different drying technologies enables informed decision-making in selecting the appropriate one. It was found that active freeze drying is effective in producing free-flowing powders, unlike conventional freeze drying. Vortex chamber drying could be considered a viable alternative to spray drying, requiring a compact chamber than the large tower needed for spray drying. Freeze-dried, spray freeze-dried, and foam mat-dried powders exhibit higher porosity than spray-dried ones, whereas supercritical drying produces nano-porous interconnected powders. Notably, several factors like glass transition temperature, drying technologies, particle aggregation, agglomeration, and sintering impact powder porosity. However, some binders, such as maltodextrin, sucrose, and lactose, could be applied in controlled agglomeration to enhance powder porosity. Further investigation on the effect of emerging technologies on powder properties and their commercial feasibility is required to discover their potential in liquid drying. Moreover, utilizing clean-label drying ingredients like dietary fibers, derived from agricultural waste, presents promising opportunities.
Desiccation , Powders , Porosity , Powders/chemistry , Desiccation/methods , Freeze Drying/methods , Food Handling/methods
Shrinkage and collapse phenomena are the two mechanisms involved in the evolution of pores within food products during dehydration. These phenomena can be mathematically represented by shrinkage and collapse functions, which can be derived from theoretical models of porosity, bulk density, or volume reduction coefficient. In this contribution, these two functions were simplified to capture four extreme scenarios of dehydration, which consist in the combination of total or no shrinkage with total or no collapse. The four simplified equations were used to generate theoretical maps characterized by three distinct zones that are associated with pore evolution. Each of these zones represents a key dehydration situation. By superimposing experimental data of porosity, bulk density, or volume reduction coefficient on these theoretical maps, it is possible to assess dehydration processes, i.e., drying technologies and/or dehydration conditions, in terms of pore formation and evolution over time. These theoretical maps can be constructed for each food product before starting the dehydration processes. Therefore, when the experimental data is available, the suggested mapping approach is a simple, fast, and reliable tool to: (i) assess the performance of a given dehydration process versus specific cases of pore formation, and (ii) compare different dehydration processes in terms of their ability to promote pore formation. This practical tool can be used by the industry and academia to quantitatively evaluate how far a drying technology and/or its dehydration conditions are from the ideal scenario in terms of pore formation. This gap quantification will provide a basis for converging towards the ideal scenario by fine-tuning the dehydration conditions or choosing the appropriate drying technology.
Dehydration , Desiccation , Humans , Models, Theoretical , Porosity
