A PHYSICO‐CHEMICAL STUDY OF THE MECHANICAL PROPERTIES OF LOW AND INTERMEDIATE MOISTURE FOODS*

Abstract

A number of textural properties of precooked, freeze-dried beef were examined by a cutting-extrusion test (force) and by a compression test (seven different properties). The tests were performed at different points of the moisture sorption isotherm over the complete range of water activity, A_w . In cutting-extrusion experiments (Allo Kramer Shear Press), a maximum in the force vs. A_w curve was observed at about A_w = 0.85. In compression experiments (Instron Universal Testing Apparatus), important changes of the textural properties were found in the range A_w = 0.15-0.30. These changes were paralleled by changes in the thermodynamic functions of water vapor sorption, especially in the standard differential entropy. Thermodynamic theory and mechanical measurements were used to interpret the textural changes in terms of increased crystallinity and subsequent swelling of the food structure.