Rheological Instruments in Food Analysis
Rheology, by name, originated from a combination of two Greek words ‘‘rheo’’ meaning ﬂow and ‘‘logy’’ meaning science. So basically, rheology can be deﬁned as the science of deformation and ﬂow of matters. Food materials can be categorized in three main groups: ﬂuid, visco-elastic, and solid materials. They exhibit ﬂow and deformation under external forces. If the material is an elastic solid, the applied force will not result in a ﬂow but in a deformation; however, if it is a viscous material it will start to ﬂow with the application of a force. To analyze the response of food materials to load deformation, controlled experiments should be carried out. Food materials can be deformed in shear, extension, and bulk compression (Figure 21.1). The tests can be done under steady state or dynamic conditions and ﬁnally the corresponding data can be analyzed by resulting moduli, compliances, and use of various models. The most important and basic concepts of rheology are stress, strain, and strain rate. The rheological response of any material is physically expressed by stress, which is measured by the force concentration on material .