Staff PhD

Cheesemaking properties – effect of milk yield and temperature treatment prior to cheese making

Pernille Frederiksen

Background

The coagulation properties of cheese milk reflect its cheese making property as the coagulation process directly influences the time required for coagulation to take place and the cheese yield. Hence, non- or poorly-coagulating milk is unsuited for cheese processing or results in a relatively low cheese yield.

It is known, that the cheese making properties of milk are highly influenced by several components in the milk e.g., protein %, casein %, pH, calcium and fat. Apart from variations inherent of the milk, some technical factors e.g., the storage temperature and duration, as well as temperature treatments before processing affects the cheese making properties. The reports on non-and poorly-coagulating milk from dairy cows of different breeds in the Nordic countries have increased, and the urge to investigate the underlying causes, as well as to establish the extent of this phenomenon is obvious. During the last 20 years the milk yield has increased from the Danish dairy cows due to an intensive breeding programme as well as to improved managements at the farms. The hypothesis is that poorer cheese coagulation properties is caused by changes in the milk composition, and that at least part of this change can be ascribed to genetic factors. If is is true that there has been an increase in the proportion of milk with poor coagulation properties it could have fatal consequences in the future for the competitive position of the Danish milk producers and the dairies, where a great fraction of the milk produced is used for cheese production.

Aim

The aim of the project is to clarify the frequency of poorly coagulating milk among the three main Danish dairy breeds in Denmark, Danish Holstein-Friesian cows (SDM), Red Danish (RDM) and Danish Jersey cows. An insight into the effect of the various milk components on the cheese making properties, as well as the effect of other factors, like e.g., temperature treatments and storage time of the milk before further processing to cheese, will give a better understanding of the significance of these parameters. This will give the information required to optimize the cheese making properties of the cheese milk at an industrial level. It is also the aim to provide the substantial information required for the formulation and development of guidelines for the futures breeding programmes.

Research Outline

Differences in the coagulation properties of the individual cows’ milk will be assessed by rheology measurements. These analyses will also assist in evaluating the effect of storage conditions and the effect of pooling milk with different coagulating qualities.

Candidate cows will be selected based on the coagulating properties and the milk will be subjected to proteomic analyses to elucidate potential differences in the milk composition between good- and poorly-coagulating milk.

The milk samples will be subjected to various analyses e.g., separation, purification and quantification analyses including mass spectrometry, enzyme kinetic measurements, dynamic light scattering analyses. The milk protein profiles will be analyzed by 2D-gel electrophoresis and the casein-genotypes of the cows will be established by PCR-analyses. The contribution of each parameter to explain the differential behaviour in the coagulation properties will be assessed.

The present Ph.D. project is funded by “Arla Foods, Amba, Danish Cattle Organisation and the Danish Innovation Law.