IMPACT OF HIGH HYDROSTATIC PRESSURE AND HEAT TREATMENTS ON MILK GEL PROPERTIES: A COMPARATIVE RHEOLOGICAL STUDY

The effects of high hydrostatic pressure (483 and 676 MPa at 20 degrees C for 5 min) and heat treatment (63 degrees C for 30 min and 72 degrees C for 15 s) of milk on the rheological properties of coagulant-induced milk gels were investigated. The rheological properties of gels were determined using a dynamic Physica Rheometer and Texture Analyzer. Milk turbidity was measured by a spectrophotometer. The gels produced from a pressure of 483 MPa had higher storage modulus (G*) and firmer gel at cutting compared to heated milks. Increasing the pressure to 676 MPa caused a reduction in G*, less firm gels, and an increase in milk turbidity compared to 483 MPa and heated milks. The differences between the gels formed from different pressure- and heat-treated milks, suggesting that the structure network of gels were considerably altered by high hydrostatic pressure treatment of milk. Disruption of casein micelles and denaturation of whey proteins caused by high hydrostatic pressure treatments were responsible for most of the effects observed in this study. In general, pressurizing the milk at 483 MPa at 20 degrees C was a promising treatment for the manufacture of coagulant-induced milk gels with good rheological properties; however, pressurization at 676 MPa could not be recommended.