Effect of pH and time on the quantity of readily available water within fresh cheese curd

Abstract

Some of the textural changes that occur early in cheese maturation may be related to the redistribution of water within the cheese matrix. To examine this, a model cheese curd system was devised and explored. Initially, cheese curd was prepared using starter and chymosin and the curd pH was controlled by varying the draining and salting pH values. The quantity of serum that could be centrifuged from the resultant curd was less for lower pH curd and decreased in volume with time. The curd pH decreased with time. In the protocol finally adopted, milk was acidified with lactic acid and coagulated with Rennilase 46L. After cheddaring, salting and light pressing, the samples of this curd were finely diced and mixed with glucono-δ-lactone to give curd samples with comparable moisture contents, similar casein proteolysis rates but different pH values. The quantity of serum that could be centrifuged from these samples was greater for pH 5·6 curd than for pH 5·2 curd and decreased faster for the lower pH curd. Neither the curd moisture nor the pH changed significantly during curd storage and the casein proteolysis was low. These results for the model curd system are consistent with known water absorption characteristics of casein curd under ‘equilibrium’ conditions and the effects of pH and mineral salts on this absorption. It was concluded that, during the early stages of cheese ripening, there may be a redistribution of moisture within the cheese, related to the basic properties of the protein matrix and the transient effects of curd salting, rather than as a direct consequence of glycolytic and proteolytic changes.