Chemistry Reference
In-Depth Information
7
Dairy Systems
E. Allen Foegeding, Bongkosh Vardhanabhuti and Xin Yang
7.1
INTRODUCTION
Rheological measurements have become essential tools in food com-
panies for characterising ingredients and final products, as well as for
predicting product performance and consumer acceptance. The rheo-
logical properties of dairy products can range from liquids such as milk
to semi-solids or soft gels such as yoghurt and sour cream to hard solids
such as cheddar and Parmesan cheeses. Understanding the rheologi-
cal and mechanical properties of various dairy products is important in
the design of flow processes for quality control, in predicting storage
and stability measurements and in understanding and designing tex-
ture. With the latter, quality attributes such as viscosity, spreadability
and creaminess, or hardness and breakdown properties are extremely
important to the acceptance of liquid, semi-solid, and solid dairy prod-
ucts; therefore, one use of rheological measurements is in determining
which physical properties are associated with the sensory perception
of texture. In rheological tests, a fixed stress or strain (similar to those
occuring during processing and consumption) is applied to a sample
and the relationship among stress, strain, and time scales of foods is in-
vestigated. Selection of an instrumental technique for the determination
of the rheological properties of a dairy product depends on its proper-
ties (i.e. whether the product is liquid, semi-solid or solid) and more
importantly on the purpose of the measurement. This chapter will fo-
cus on the rheological properties of liquid milk, some semi-solid dairy
products and solid cheese to show how rheological techniques have
been and can be used to characterise the mechanical properties of these
materials.
