Detection of αs1-I casein in mozzarella Fiordilatte: A possible tool to reveal the use of stored curd in cheesemaking

The assessment of the origin and quality of raw materials is pivotal for the protection and valorization of typical dairy products. Italian high moisture mozzarella cheese, also called “Fiordilatte”, is manufactured by stretching in hot water the curd, which can be produced inside the dairy (fresh curd) or purchased as semi-finished product from specialized companies (pre-made stored curd). The employment of stored curd allows cheese manufacturers to obtain economic profit thanks to the reduction of the production costs. The use of the semi-finished product has not to be mentioned in the label according to the actual EU regulation, and this has given rise to competition between local milk farmers and curd-producing companies causing misinformation among the consumers, and unfair competition to the disadvantage of the traditional dairies. In the present research, a proteomic approach was used to investigate “Fiordilatte” produced with or without the employment of stored curd. The results obtained allowed us to identify a molecular marker which is present in very small amounts in cheese made from fresh curd and at high levels in cheese made from stored curd. The marker is αs1-I casein (fragment 24–199), the main product of primary proteolysis formed by the action of chymosin on αs1 casein. It can be easily detected by electrophoresis in the presence of urea (urea-PAGE) and is measured by image analysis. Even though the kinetic of formation of this proteolytic product has been well known for several decades, in mozzarella it has a peculiar behavior compared to other cheeses. As a matter of fact, it originates during the first part of cheesemaking, and has a very slow increase during storage of the cheese, due to the denaturation of the clotting enzyme by the hot water stretching process. The results obtained demonstrated that the quantification of αs1-I fragment should be recommended to guarantee the production of “Fiordilatte” obtained from fresh milk under normal conditions, and could be the basis for the development of a method able to fully protect the traditional cheesemaking procedure.