Effect of micellar κ-casein dissociation on the formation of soluble protein complexes and acid gel properties

This study investigated the effect of micellar κ-casein dissociation, caused by cross-linking agent glutaraldehyde, on the formation of soluble protein complexes and the texture of resulting gels. Reconstituted skim milk containing different levels of added glutaraldehyde (SM-GTA) and skim milk without glutaraldehyde (SM) were processed with or without heating, and the structural properties of the prepared acid gel were studied. Acid gel prepared from heated SM (without GTA) had significantly higher firmness (1.40 ± 0.02 N) and water holding capacity (79.0 ± 3.0%) compared to that made from heated SM treated with 0.1, 0.3, 0.5 mmol/L GTA, respectively. Higher storage modulus (G′) and denser microstructure were observed in acid gel prepared from heated SM than those made from heated SM-GTA. Electrophoretic analysis demonstrated that κ-casein levels in the soluble protein complexes of SM was 9.60 ± 0.2 (%) which was decreased to 0.06 ± 0.01 (%) in SM treated with 0.5 mmol/L GTA. This was attributed to GTA decreasing micellar κ-casein dissociation and, therefore, reducing the formation of soluble protein complexes. This reduction in soluble protein complexes in SM-GTA resulted in weaker acid gels compared with those prepared from SM without GTA.