Spray drying is the most commonly used technique for the production of dry flavorings. In spray drying, an aqueous infeed material (water, carrier, and flavor) is atomized into a stream of hot air. The atomized articles dry very rapidly, trapping volatile flavor constituents inside the droplets. The powder is recovered via cyclone collectors. Flavor retention is quite satisfactory if dryer operating parameters are properly chosen. Flavor retention is maximized by using a high infeed solids level, high viscosity infeed, optimum inlet (160–210°C) and high exit (>100°C) air temperatures, and high molecular weight flavor molecules. The shelf life of oxidizable flavor compounds is strongly influenced by the flavor carrier.

The spray drying of food flavors

Industrial and pilot plant spray-dried materials were obtained from various manufacturers and qualitatively examined in order to identify structural and morphological features. Three distinct categories of particle morphology were identified. Namely, crystalline, skin forming and agglomerate. A number of unusual morphological phenomena were also noted Selected properties such as powder flowability. particle size and particle friability, were found to be directly related to morphological structure. Single particles were also produced in a convective drying process analogous to spray drying, in which, different solids or mixtures of solids were dried from solutions, slurries or pastes as single suspended droplets. The localised chemical and physical structures were analysed, and the results related to experimental conditions viz. drying air temperature and initial solids concentration. There was a strong similarity between the industrial spray-dried material and those dried experimentally. The morp...

The morphology of spray-dried particles a qualitative view

Single particles were produced in a convective drying process analogous to spray drying, in which, different solids or mixtures of solids were dried from solutions, slurries or pastes as single suspended droplets. The localized chemical and physical structures were analysed, and in some cases, the retention of volatiles monitored. The results were related to experimental conditions, viz.; air temperature, initial solids concentration and the degree of feed aeration. Morphologies of multicomponent mixtures were found to be complex, with the respective migration rates of the solids being dependent on drying temperature. The results are of relevance to dryer optimization and to the optimization of product characteristics, e.g. particle strength or friability, and essential volatiles retention in convective drying.

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The morphology of spray-dried particles

Many aroma compounds, used to flavor food products, are used in a solid state, after encapsulation. Carbohydrates are the most common matrices used to entrap these volatiles. It has been observed that depending on the aroma compound and the carrier, efficiency can vary. This article reviews the influence of physicochemical properties of both the volatiles and the carriers on retention. The latter depends on the functional groups of the aroma compound. Moreover, it increases with molecular weight and decreases with the polarity and relative volatility of the aroma compound. This behavior can be explained by the effect of these properties on the diffusion of the aroma compound through the matrix and on the ability of the volatile to form small drops. The physicochemical properties of the carrier are important too. Retention of the aroma compound increases with the molecular weight of the carrier until an optimum is reached and then decreases for very high polymerization degrees. Viscosity, solubility, and film forming properties improve the retention ability. The effect of these parameters is discussed according to their effect on the diffusion of the volatiles. The state of the carrier has to be taken into account too. The amorphous state provides the highest retention, collapse results in losses of aroma, and crystallization leads to the greatest losses of flavors.

Retention of Aroma Compounds by Carbohydrates: Influence of Their Physicochemical Characteristics and of Their Physical State. A Review

Samples of industrial and pilot plant spray-dried materials were obtained from various manufacturers together with details of drying conditions and feed specifications. The samples were subjected to qualitative and semi-quantitative examination to identify structural and morphological features. The results were interpreted in terms of bulk physical properties and related to drying conditions. Three distinct categories of particle morphology were identified, namely, crystalline, skin-forming and agglomerate. Selected properties such as powder flowability, particle and bulk density, particle size and particle friability were shown to have a direct relationship to morphological structure.

Spray Dried Products—Characterization of Particle Morphology

SUMMARY

—A study has been made of volatiles retention during the drying of aqueous solutions, by putting droplets, fixed on a wire, in an air current. The droplets were of an aqueous solution of malto-dextrin, to which small amounts of acetone had been added. Radioactive labeling permitted quick and accurate measurements of the acetone concentration in a drying droplet. During drying, a film forms on the surface of the droplet. The higher the initial carbohydrate concentration, the quicker the film forms. This film is permeable to water, but impermeable to acetone and to other volatile compounds, such as benzene, ethanol, and ethyl acetate. No satisfactory explanation for the retention can be given. In any case, adsorption is not involved.

L. C. Menting

Papers

Volatiles Retention During the Drying of Aqueous Carbohydrate Solutions