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Whey protein hydrolysate (WPH)-based oil-in-water (O/W) emulsions containing lecithin (0-5%, w/w, oil) were produced and stored at 4°C for 14 days. Surface tension and interfacial tension of these systems were measured for formulation development. Fat globule size distribution (FGSD) analysis and confocal laser scanning microscopy (CLSM) were used to assess the physical stability of emulsions during storage and identify mechanisms of instability. Lecithin decreased interfacial tension between oil and aqueous phases of model emulsions and allowed formation of smaller oil droplets on homogenisation. However, low-intermediate levels (1-3%) of lecithin caused coalescence and shift to bimodal FGSD during storage of emulsions.

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The objective of this study was to compare the drying performance and physicochemical properties of model infant formula (IF) emulsions containing 43, 96 and 192 g L−1 protein, oil and maltodextrin (MD), respectively, prepared using different emulsifier systems. Emulsions were stabilised using either whey protein isolate (WPI), whey protein hydrolysate (WPH; DH 8%), WPH + CITREM (9 g L−1), WPH + lecithin (5 g L−1) or WPH conjugated with maltodextrin (DE 12) (WPH-MD). Homogenised emulsions had 32% solids content and oil globules with mean volume diameter <1 μm. Powders were produced by spray-drying with inlet and outlet temperatures of 170 and 90 °C, respectively, to an average final moisture content of 1.3%. The extent of powder build-up on the dryer wall increased in the order; WPH- MD << WPH ≤ WPI < WPH + LEC ≤ WPH + CIT. The same trend was observed for the extent of spontaneous primary powder agglomeration, as confirmed by particle size distribution profiles and scanning electron micrographs, where the WPH-MD and WPH + CIT powders displayed the least and greatest extent of agglomeration, respectively. Analysis of elemental surface composition of the powders showed that surface fat, protein and carbohydrate decreased in the order; WPH + CIT > WPH + LEC > WPH > WPH- MD > WPI, WPI > WPH > WPH- MD > WPH + LEC > WPH + CIT and WPH- MD > WPI > WPH > WPH + LEC > WPH + CIT, respectively. Additionally, differences in wettability, surface topography and oil globule distribution within the powder matrix and in reconstituted powders were linked to the emulsifier system used. Inclusion of the WPH-MD conjugate in the formulation of IF powder significantly improved drying behaviour and physicochemical properties of the resultant powder, as evidenced by lowest powder build-up during drying and greatest emulsion quality on reconstitution, compared to the other model formula systems