Acid coagulation of milk

Abstract

The acid coagulation of milk is the basis for a wide diversity of cultured dairy products. Acidification directly impacts the stability of casein micelles, reducing their charge, dissolving some of the insoluble calcium phosphate crosslinks and modifying internal bonding between proteins. The formation of aggregates and ultimately gels occurs at some critical point when electrostatic repulsion is reduced and is not sufficient to overcome attractive forces, like hydrophobic interactions. Acid-induced milk gels increase in stiffness with time due to on-going bond formation between casein particles within the network. In gels made from heated milk, an increase in the loss tangent parameter is observed for a short period after gelation; this phenomenon is due to the loss of insoluble calcium phosphate crosslinks within the casein particles that are already forming the gel matrix. The texture and physical properties of acid-induced gels are dependent on the specific conditions used for gel formation including: the rate of acidification, temperature, extent of whey protein denaturation, protein content, and presence of polysaccharide stabilizers. On-going studies are still investigating the exact physicochemical mechanisms involved in the acid coagulation of milk including trying to gain a better understanding of how exopolysaccharides modify yoghurt properties