The surface composition of spray-dried powders made from emulsions where the oil content is kept constant (30% of dry weight) but varies in the ratio between whey protein and lactose is presented in Figure 2. The triangular diagram shows the composition of the emulsion before spray-drying, the surface composition of the spray-dried powder and the surface composition of the spray-dried powder after storage in a humid atmosphere (RH 75%, 4 days). Figure 2 shows that the ability of whey protein, together with lactose, to encapsulate the oil phase of an emulsion during spray-drying is relatively low. The fat coverage varies from 45% of the powder surface, when the whey protein content of the emulsion is low, to 60% surface fat when the whey protein concentration is considerably increased (Fig. 2). Apart from fat, the powder surface consists mainly of whey protein. Lactose is not present on the powder surface to any great extent.
Figure 2 Spray-dried emulsions with constant oil content but different ratios of lactose to whey protein. (e) The composition of the spray-dried emulsion (% of dry weight) before spray-drying; (0) the surface composition of the spray-dried powders before storage; (0) the surface composition of the spray-dried powders after storage in a humid atmosphere (4 days, RH 75%).
These findings are somewhat contrary to earlier conclusions drawn from scanning electron microscopic investigations of similar whey protein-containing particles (13-15). These investigations state, on the basis of scanning electron micrographs, that the ability of whey protein to encapsulate milk fat is high when whey protein-stabilized emulsions are spray-dried. However, with ESCA, direct information of powder chemical surface composition is obtained. ESCA measurement clearly shows that a rather large part of the whey protein/fat/lactose powder surface is covered by fat. This is not evident from scanning electron micrographs.
The surface composition of spray-dried powders made from emulsions where the oil content is kept constant (30% of dry weight) but varies in the ratio between whey protein and lactose is presented in Figure 2. The triangular diagram shows the composition of the emulsion before spray-drying, the surface composition of the spray-dried powder and the surface composition of the spray-dried powder after storage in a humid atmosphere (RH 75%, 4 days). Figure 2 shows that the ability of whey protein, together with lactose, to encapsulate the oil phase of an emulsion during spray-drying is relatively low. The fat coverage varies from 45% of the powder surface, when the whey protein content of the emulsion is low, to 60% surface fat when the whey protein concentration is considerably increased (Fig. 2). Apart from fat, the powder surface consists mainly of whey protein. Lactose is not present on the powder surface to any great extent.Figure 2 Spray-dried emulsions with constant oil content but different ratios of lactose to whey protein. (e) The composition of the spray-dried emulsion (% of dry weight) before spray-drying; (0) the surface composition of the spray-dried powders before storage; (0) the surface composition of the spray-dried powders after storage in a humid atmosphere (4 days, RH 75%).These findings are somewhat contrary to earlier conclusions drawn from scanning electron microscopic investigations of similar whey protein-containing particles (13-15). These investigations state, on the basis of scanning electron micrographs, that the ability of whey protein to encapsulate milk fat is high when whey protein-stabilized emulsions are spray-dried. However, with ESCA, direct information of powder chemical surface composition is obtained. ESCA measurement clearly shows that a rather large part of the whey protein/fat/lactose powder surface is covered by fat. This is not evident from scanning electron micrographs.
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