Identification of an optimized ratio of amyloid and non-amyloid fractions in engineered fibril solutions from whey protein isolate for improved foaming

Engineered fibril solutions from whey protein beta-lactoglobulin are known for their excellent foaming capacity. These amyloid aggregates solutions (AAS) usually contain a polydisperse mixture of different protein structures. An optimized ratio of amyloid (AF, fibrils) and non-amyloid fractions (n-AF) in AAS may improve foaming, particularly by interactions at the air-water interface. Foamability, surface activity, and monolayer phase behavior at the air-water interface of isolated AF and n-AF as well as AAS with different AF/n-AF-ratios were investigated using drop tensiometry, Langmuir trough and foam analysis. N-AF exhibited faster migration, twice as fast adsorption and thus faster spreading at the air-water interface than the fibrils (AF). N-AF required less energy to assemble in a liquid-expanded phase in a monolayer, i.e., they were more compressible in the monolayer than AF. This resulted in rapid stabilization of lamellae in foam. High surface hydrophobicity of AF results in faster adsorption and formation of capillary forces between adsorbed fibrils, improving the attraction for additional fibrils. Orientation of semi-flexible and larger fibrils in AF consumes high energy. In combination with n-AF, the energy needed for orientation and assembly of fibrils is equivalent, however, the yield of AF in AAS was only 20 %, indicating the interplay of amyloid and non-amyloid proteins at the air-water interface. N-AF can be incorporated into a fibrillar film, which increase the network's density and stiffness and the interfacial film stability. Consequently, in AAS fibrils and non-amyloid material acted synergistically at the air-water interface, whereby only small amounts of amyloid aggregates are required to stabilize foams.