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High shear rheometry was used to investigate the rheological behavior of high internal phase emulsions (HIPEs) stabilized by whey protein isolate (WPI). The physical stability of HIPEs was tested at extremely high shear rates generated by decreasing the gap height between parallel plates. Viscosity and yield stress, at narrow gaps, increased with protein concentration due to tighter packing of smaller droplets. Structural breakdown and recovery of HIPEs were affected by protein concentration and pH. The hysteresis behavior of HIPEs was either thixotropic or anti-thixotropic and was determined by protein concentration, whereas pH affected the magnitude of anti-thixotropy. At pH 3, emulsions showed greater stability against extreme shear and creaming due to higher deformability of oil droplets and increased interdroplet interaction compared to neutral pH. Challenging the physical integrity of concentrated emulsions under high shear is an effective way to characterize microstructural changes and stability of HIPEs in foods.

Accumulation of surface-active compounds may significantly alter the surface composition of food powders compared to the bulk composition of the product and therefore affects the functional properties. Through modification of a commercial contact angle meter surface accumulation of milk proteins and protein hydrolysates could be analysed via surface tension measurements in a time interval relevant for atomisation of emulsions during microencapsulation. The different caseins showed a slower surface occupation compared to industrially processed sodium caseinate and casein hydrolysate with β-casein being more surface-active than α- and κ-casein. In a similar manner, β-lactoglobulin showed a lower surface activity than whey protein isolate and whey protein hydrolysate. It is concluded that molecular weight profile plays an important role for the surface activity of milk proteins, but other factors like surface hydrophobicity, number of ionisable groups and state of aggregation also need to be considered.

Fish oil with 33% omega-3 fatty acids was microencapsulated by spray-drying in a matrix of n-octenylsuccinate-derivatized starch and either glucose syrup or trehalose. Samples showed no difference in physicochemical properties as determined by measurement of particle size, oil droplet size, true density and BET surface. Upon storage at low relative humidity, lipid oxidation was decreased in trehalose containing samples indicating that in the amorphous state trehalose is a more suitable wall material for microencapsulation than glucose syrup. The retarded oxidation of trehalose containing samples may be attributed to the unique binding properties of trehalose to dienes. At 54% relative humidity, a rapid oxidation of the microencapsulated oil was observed upon crystallization of trehalose, which limits the range of applications to products to be stored at low humidity.