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Díaz-Montes, E. Wall Materials Used in Spray-Drying. Encyclopedia. Available online: (accessed on 29 November 2023).
Díaz-Montes E. Wall Materials Used in Spray-Drying. Encyclopedia. Available at: Accessed November 29, 2023.
Díaz-Montes, Elsa. "Wall Materials Used in Spray-Drying" Encyclopedia, (accessed November 29, 2023).
Díaz-Montes, E.(2023, June 21). Wall Materials Used in Spray-Drying. In Encyclopedia.
Díaz-Montes, Elsa. "Wall Materials Used in Spray-Drying." Encyclopedia. Web. 21 June, 2023.
Wall Materials Used in Spray-Drying
The wall material refers to the protective matrix that safeguards the core material, such as particles, substances, or compounds, throughout the encapsulation process and subsequent handling. It should possess the ability to withstand mechanical stress (e.g., handling) and environmental conditions (e.g., humidity, temperature, and water activity). In spray-drying processes, the chosen wall material must ensure the stability and shelf-life of the encapsulated particle, substance, or compound, while also being cost-effective in terms of encapsulation yield and efficiency. It is essential to understand the characteristics of the materials, regardless of this section aiming to define the primary materials utilized in spray-drying processes.
wall material biopolymers carbohydrates gums proteins lipids

1. Polysaccharides

Polysaccharides are chains of simple sugars linked by glycosidic bonds. They are naturally synthesized by plants (e.g., starch and cellulose), animals (e.g., chitosan and chitin), and microorganisms (e.g., dextran and gellan gum) to produce energy and fulfill physiological and structural functions [1]. Some polysaccharides can also be enzymatically and chemically synthesized (e.g., condensation), such as certain cyclodextrins and chitosan derivates, to create non-natural, well-defined, and pure structures [2]. In commercial applications, polysaccharides are widely used as emulsifiers, gelling agents, flavorings, and encapsulants [3] as a result of their physicochemical properties such as viscosity and solubility [1]. They are commonly employed as ingredients in confectionery, beer, fried foods, ice creams, and sausages [3]. The most frequently used polysaccharides in spray-drying processes due to their low costs are starch, maltodextrin, chitosan, dextran, carrageenan, and gums [4]. The main characteristics of each are as follows:
  • Starch is a complex polysaccharide composed of amylose and amylopectin, primarily derived from tubers (e.g., potatoes, cassava, and sweet potatoes) and cereals (e.g., corn, sorghum, wheat, rice, rye, oats, and barley) [5]. This carbohydrate is made up of glucose monomers with free hydroxyl groups (-OH) at positions C2, C3, and C6, giving it a highly hydrophilic helical structure [6]. Starch finds applications in various industries such as textiles, chemicals, healthcare, and food, due to its physicochemical properties such as solubility, viscosity, texture, and thermal stability [6].
  • Maltodextrin is a polysaccharide derived from the hydrolysis of starch (from corn, rice, wheat, tapioca, sorghum, barley, etc.) with a dextrose equivalent value (DE: the ratio of reducing sugars to total sugars) of less than 20 [7]. Maltodextrin has different characteristics and properties compared to starch, leading to varied applications [8]. It is used as an additive in food products and beverages [9] and as a fat replacer in dairy, meat, and baked goods due to its ability to form gels, its hygroscopicity, solubility, viscosity, and sweetness [10].
  • Chitosan is a structural polysaccharide extracted from microorganisms (such as fungi and algae), marine animals (such as crustaceans and mollusks), and insects (such as scorpions and spiders), or obtained through the chemical deacetylation of chitin [11]. Chitosan is highly regarded for its antibacterial, antifungal, and antiviral activity, attributed to its cationic polyelectrolyte character. It also possesses the ability to form gels due to its viscosity, plasticity, and solubility [12]. In recent years, chitosan has found applications in post-harvest pathogen control [13] and the development of biodegradable packaging [14].
  • Dextran is a polysaccharide synthesized by microorganisms, particularly lactic acid bacteria, and it possesses various thermal, rheological, viscosity, and solubility properties due to its branching structure [15]. The application of dextran has been primarily explored as a food additive in the formulation of emulsions, nanoparticles, and immobilizers [16]. It is also used as an excipient in the formulation of inhaled drugs (such as rifampicin and budesonide) due to its humectant, stabilizing, and preserving action [17][18].
  • Carrageenan is a sulfated polysaccharide extracted from red seaweeds such as Kappaphycus and Eucheuma. It exhibits structural diversity due to the degree of sulfation and can be classified as κ-, ι-, θ-, μ-, ν-, and λ-carrageenan [19]. Carrageenan does not have proven nutritional value, but it finds special application in the food industry due to its gelling, stabilizing, binding, and thickening properties. It is used in products such as jellies, dressings, fat substitutes, and pet food. Additionally, carrageenan has been utilized in experimental medicine, pharmaceuticals, and cosmetics as anti-inflammatory agents, hydrogels, drug carriers, and vehicle for drug delivery [20].
  • Gums are water-soluble polysaccharides that do not have a specific classification but are recognized for producing viscous–sticky dispersions at low concentrations. Gums are extracted from algae (such as agars and alginates), microorganisms (such as gellan and xanthan), or higher plants (such as pectin, Arabic, and arabinogalactans) [21]. The gel-forming properties of gums are due to their affinity for water, allowing for rapid hydration and swelling of the structure. The degree of hydration results in various rheological properties that enable their application in construction materials (such as adhesives), food products (such as texture enhancers, stabilizers, and coatings), medical and pharmaceutical products (such as encapsulants), and textile products (such as additives) [22].

2. Proteins

Proteins are macromolecular structures composed of amino acids and play a vital role in all biological processes of living organisms. They can exist in the form of enzymes, hormones, antibodies, and receptors [23]. Proteins are part of the human diet as they are present in varying proportions in all animal- and plant-based products that are consumed. These macromolecules are valued in the industry for their gel-forming and foaming properties, particularly in the food industry, allowing their application to enrich existing products [24]. The use of proteins in spray-drying processes is feasible due to their ability to form rigid matrices, especially with proteins such as gluten, isolated proteins (e.g., soy and pea proteins), caseins, whey proteins, and gelatin [4]. Below, their main characteristics are described:
  • Gluten is a mixture of insoluble, gummy proteins found in cereals such as wheat, rye, and barley. It is obtained by removing starch and soluble material from a dough made with grains [25]. The rheological properties of gluten facilitate the retention of air in the dough, making it particularly useful in processed food products such as breads, pasta, cookies, cakes, and other fermented goods [26].
  • Casein is a group of proteins found in milk, which can be divided into four phosphoproteins: αS1, αS2, β, and κ-casein. These proteins organize themselves into micellar networks. Casein can be obtained through milk precipitation at pH 4.6, electrophoresis, or membrane processes [27]. The primarily significance of casein lies in the realm of sports, as it contributes to the nutritional composition of dietary supplements. However, it can also be applied in the formulation of nano and micro materials, food additives, and biodegradable films, as it can form gels when interacting with other polymers [28].
  • Gelatin is a water-soluble protein derived from the hydrolysis of collagen, an insoluble product found in animal cartilage, skin, fibers, and tendons. Gelatin is classified as a hydrocolloid due to its high water-holding capacity. Its viscosity is its main property, which allows it to texture, thicken, stabilize emulsions, create foams, and form thermo-reversible gels [29]. Gelatin is free of sugars and fats and is rich in proteins. It is commonly used as an additive in food products such as confectionery, beverages, sweets, and dairy products. It also serves as an excipient in the pharmaceutical industry [30].
  • Whey proteins are by-products obtained during the processing of dairy products such as cheese and casein. They can be classified into protein concentrates and protein isolates [31]. Whey proteins can be further categorized into four main proteins: β-lactoglobulin, α-lactalbumin, serum albumin, and immunoglobulin. Apart from their nutritional value, whey proteins possess binding and gelling properties, and they are capable of stabilizing foams and forming emulsions. As a result, they are used in various food products, including supplements, soups, sausages, desserts, and sweets) [32].

3. Lipids

Lipids are organic molecules that, as polysaccharides and proteins do, also play important biological and structural roles within living organisms. They are characterized by their insolubility in water [4]. Lipids exhibit a high degree of diversity due to their infinite structures; however, they can be generally classified into triacylglycerols, waxes esters, phosphoglycerides, sphingolipids, and sterols [33]. Lipids are used as fuels, plastics, detergents, soaps, paints, lubricants, and cosmetics. In the food industry, they are utilized as edible oils and coatings [34]. Among lipids, waxes are the most commonly employed in spray-drying encapsulation. Below, their main characteristics are described.
  • Waxes are soft or sticky substances that form on the surface of plants (e.g., carnauba and candelilla), as well as on the body of animals (e.g., whales and sheep) and insects (e.g., bees). They are composed of long-chain aliphatic compounds that vary depending on their source of production, Waxes may contain fatty acids, primary and secondary alcohols, aldehydes, sterol esters, ketones, triacylglycerols, and triterpenes [35]. Waxes exhibit high hydrophobicity and resistance to hydrolytic degradation, making them suitable for use as protectants, surface polishes, lubricants, and repellents in the food, cosmetic and automotive industries [36].


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