Production, Interfacial Behavior, Modification and Functionality of Whey Protein Microgels

The production, interfacial properties, effect of modification and functionality of polymer-based microgel particles as colloidal stabilizers and flavor release agents were evaluated. Microgels were fabricated from β-lactoglobulin with and without pectin by thermal treatment under mildly acidic conditions. The influence of fabrication conditions, including pH, ionic strength, anion type and reducing agents on microgel properties were examined. Low pH and high concentrations of reducing agents increased thermal aggregation of β-lactoglobulin, resulting in the formation of larger microgels. Increased ionic strength also increased thermal aggregation irrespective of anion type, though particle agglomeration was promoted. In contrast, thermal aggregation and size of β-lactoglobulin/pectin microgels were affected by anion type, with thiocyanate anions promoting aggregation to the greatest extent followed by chloride and sulfate anions. The adsorption of β-lactoglobulin microgels to oil-water interfaces was influenced by bulk concentration and particle size, with higher concentration and smaller particles associated with faster adsorption. Microgel adsorption produced dominantly elastic interfaces, with smaller microgels increasing interfacial elasticity faster. As the interface was compressed, surface pressure increased but elasticity did not, potentially due to disruption of interactions within the microgel layer. Monolayer images indicated the presence of small, discrete aggregates at the interface, possibly due to microgel disruption at low interfacial concentrations. Cross-linking and reducing agent treatment had limited impact on the physical and chemical properties of microgels, except for increased chemical stability following glutaraldehyde treatment. Larger microgels were generally able to stabilize flavor oil emulsions to coalescence and flocculation, but not creaming, while smaller microgels generated emulsions susceptible to creaming and flocculation. Release of flavor compounds during storage resulted in the formation on non-spherical droplets, indicating a rigid, irreversibly adsorbed interfacial layer. Glutaraldehyde cross-linking greatly decreased emulsion stability, leading to the formation of large droplet flocs and rapid loss of flavor compounds. Larger microgels were able to slow flavor release from oil droplets, however smaller microgels were not. Overall, monodisperse β-lactoglobulin microgels can be produced by simple processing methods and demonstrate great stability over a wide range of conditions found in food and related products. Larger microgels appear to have greater functionality as interfacial stabilizers due to the formation of a thicker interfacial layer compared to smaller microgels, despite their slower diffusion and less efficient interfacial packing. While β-lactoglobulin microgels showed great promise for preventing coalescence in emulsion systems, their instability to creaming and in some cases flocculation limit their functionality as sole stabilizers in low viscosity, low oil phase systems. β-lactoglobulin microgels may have more value in food systems when employed as controlled release agents, texture modifiers or as structural components of films, or when used in conjunction with other stabilizers or biopolymers