Spray drying carrier material

Fig. 6.22 Effect of feed emulsion droplet size 1 43 on the retention ofo-limonene during spray drying (Carrier materials blend of CA-MD, blend ofSSPS-MD, V blend of HI-CAP lOO-MD).

Spray Drying. Spray-dry encapsulation processes (Fig. 7) consist of spraying an intimate mixture of core and shell material into a heated chamber where rapid desolvation occurs to thereby produce microcapsules (24,25). The first step in such processes is to form a concentrated solution of the carrier or shell material in the solvent from which spray drying is to be done. Any water- or solvent-soluble film-forming shell material can, in principle, be used. Water-soluble polymers such as gum arable, modified starch, and hydrolyzed gelatin are used most often. Solutions of these shell materials at 50 wt % soHds have sufficiently low viscosities that they stiU can be atomized without difficulty. It is not unusual to blend gum arable and modified starch with maltodextrins, sucrose, or sorbitol. 

The most common method to simultaneously dry and encapsulate flavours is the spray-drying technique (Fig. 21.11). For this technology, carrier materials like maltodextrin, starch and gum arabic are dissolved in water. As a next step, the liquid flavour raw material is emulsified in this slurry. Also non-volatile flavour components can be added. The slurry is atomised and dried in a spraydrying facility. 

The initial step in spray drying of a flavor is the selection of a suitable carrier material. One can divide the major flavor carriers into three classes (and blends thereof) hydrolyzed starches, emulsifying starches, and gums (essentially gum arabic). 

While the infeed solids content of the infeed material has an unquestionably greater influence on the retention of volatile flavors than does the type of carrier used, carrier type does influence flavor retention during spray drying (4, 16, 31, 3Z. ... 

Encapsulated Flavors. Modified procedures during the past decade have permitted the preparation of encapsulated flavors with flavor levels over twice that of prior available products. Spray drying has been the principal key to this success. First, an oil flavnr is emulsified into an aqueous solution or is dispersed in an edible carrier material, after which the emulsion is pumped through an atomizer into a high-temperature chamber. The water evaporates rapidly, and particles of carrier material are formed around the flavor. However, some of the flavor component reaches the surface of the product. This requires the addition uf antioxidants to suppress oxidative changes in the flavor ingredient. 

An extreme case of covalent binding is cross-linking of enzymes. Instead of fixing the enzyme to a carrier, the enzyme acts as a carrier itself Enzyme aggregates or crystals, enzymes in a spray-dried form, or even enzymes in solution can be cross-linked. The immobilized enzyme is carrier free, that is the material is virtually pure enzyme and the negative effects of carriers can thus be avoided [10, 70]. 

A novel all-aqueous-based system that relies on the thermodynamic incompatibility of biopolymers has been described for the encapsulation of probiotics. A two-phase system comprising of polyvinyl pyrolidone and dextran was used as the carrier material for a probiotic bacterium in the preparation of spray dried preparations of probiotics. The survival of the bacteria Enterococcus faecium E74) was dependent on the composition of the system. Although the survival rate during drying was better when only dextran was used, there were better survival rates of the bacteria during storage with the two-phase carrier system (Millqvist-Fureby et al. 2000). 

Millqvist-Fureby, A., Malmsten, M., and Bergenstahl, B. (2000). An aqueous polymer two-phase system as carrier in the spray-drying of biologieal material. J. Colloid Interface Sci. 225, 54-61. 

The spray drying process is conceptually simple a solution is pumped through an atomizer, a plume of liquid droplets containing solid components is created and subsequently exposed to a suitable gas stream to promote rapid evaporative mass transfer of the liquid carrier into the gas. When sufficient liquid mass has been transformed to vapor, the remaining solid material in the droplet forms an individual dried particle which is then separated from the gas stream. 

The materials to be spray dried, e.g. flavouring concentrates or fmit, have to be prepared into a solution or an emulsion. Flavour concentrates, e.g. essential oils, extracts and/or mixtures of these with other flavouring substances, are emulsified in water with gum arabic and then homogenised with a solution of the dry carrier. Useful carriers are modified starch products, maltodextrin, sugar, modified whey proteins. 

In the process, the active agent (usually water-immisdhle liquid or oil) is dispersed in aqueous solution of the carrier material with the aid of a suitable emulsifier and the resulting oil-in-water emulsion is sprayed into a heated drying chamber where they remain for 30 s or less. The product of this operation is a dry microcapsule powder consisting of small, spherical particles with a typical diameter of 10—40 pm in which the oil phase is dispersed throughout as 1—3 pm size droplets. A small amount of the active agent in the powder, however, remains free or unencapsulated it can only be minimized but not totally eliminated. 

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