Rheological properties and microstructure of high protein acid gels prepared from reconstituted milk protein concentrate powders of different protein contents

Milk protein concentrate (MPC) powders were manufactured by pilot-scale ultrafiltration and diafiltration of skim milk to different protein concentration factors, followed by spray-drying. MPC powders were reconstituted at 7.5% (w/w) protein. Suspensions were subsequently standardised to 15% (w/w) total solids with lactose and heated at 90°C for 10min at pH 6.9. Acid gels were prepared from the heated suspensions using glucono-delta-lactone. Protein interactions in the heated dispersions and rheological and microstructural properties of the acid gels were studied. Suspensions from the higher protein MPCs showed no dissociation of κ-casein into the serum phase after heating, whereas elastic moduli at pH 4.6 and the gelation pH of the acid gels were higher and water holding capacity and gelation time was lower in acid gels prepared with high-protein MPCs. Confocal microscopy images revealed an increase in the pore size of the acid gels prepared with high-protein MPCs.