Influence of seeding and stirring on the structural properties and formation yield of whey protein microgels

The effect of seeding whey protein isolate (WPI) solution with pre-made whey protein soluble aggregates (WPSAs) and stirring on the yield and structural and chemical attributes of whey protein microgels (WPMs) was investigated. Fluorimetry indicated that the heat-exposed hydrophobic amino acids were buried again by WPM formation. Full substitution of WPI with WPSA under non-stirred conditions generated smaller WPMs of ∼200 nm diameter, imaged by atomic force microscopy. Furthermore, full substitution yielded WPMs of a lower percentage proportion of β-sheet structure and a higher proportion of random structures than those of the sample prepared from the 50/50 mix of WPI and WPSA. Stirring increased the hydrodynamic size of WPMs at every ratio of WPI/WPSA. Microgelation under stirring at a WPI/WPSA ratio of 25/75 gave the highest yield (80%) of WPM. Gel electrophoresis indicated that stirring and full substitution of WPI with WPSA caused formation of WPMs rich in β-lactoglobulin monomer.