Effect of whey protein aggregates of various sizes on the formation and properties of rennet-induced milk gels

Whey protein (WP) aggregates that ranged in diameter from 41 to 299nm but had the same composition were produced by varying the protein concentration at heating at neutral pH and low ionic strength, followed by dilution. The effect of WP aggregates on the formation and properties of rennet-induced milk gels were evaluated. Whey protein aggregates had no effect on the kinetics of caseinomacropeptide release during renneting but significantly affected the clotting of casein micelles and the properties of milk gels. The maximum clotting rate and the strength of rennet-induced milk gels decreased as the dose of WP aggregates added to milk increased. However, WP aggregates with larger diameter and higher voluminosity had a less detrimental effect on milk clotting than smaller aggregates did. The higher surface hydrophobicity and faster diffusion of smaller WP aggregates could have been responsible for adsorption onto renneted casein micelles, which reduced milk clotting rate and gel strength. The permeability of rennet-induced milk gels decreased as the dose of WP aggregates added to milk increased, but the protein concentration at heating had no effect. Whey protein aggregates reduced the contraction capacity of the gels during cooking (42°C). Drained curd mass fraction and curd moisture increased as the dose of added WP aggregates increased and were affected less by larger WP aggregates. The results of this study suggest that small WP aggregates (<100nm) interact with casein micelles and interfere with rennet gel formation and contraction.