Modelling Stress-Relaxation Curves During the Ripening of Port Salut Argentino Cheese

VERDINI, RA; DE PIANTE VICÍN, D; RUBIOLO, AC

Santa Fe, Argentina

Congreso; 3rd MERCOSUR Congress on Process Engineering – 1st MERCOSUR Congress on Chemical Engineering; 2001

Texture is a subjective attribute of a food however; objective measures, which are concerned with rheology, are widely used in food research. Rheological properties of solid foods can be measured using creep and stress-relaxation tests. In the stress-relaxation test the sample is constrained to deform at a known rate until a certain point, then it is held at constant strain and the stress is followed while the sample relaxes. Physicochemical transformations during cheese ripening, including changes in salt, protein and moisture content, affects textural characteristics. The objective of this work was to study texture changes during the ripening of Port Salut Argentino cheese modeling stress-relaxation curves and to associate rheological parameters with cheese structure. Cheeses were sampled on triplicate at different ripening times: 1, 6, 13, 27 and 56 days. Cubic pieces (25 mm) were obtained from two different cheese zones: central zone (25 mm from the center and 25 mm from the surface) and outer zone (80 mm from the center and 5 mm from the surface). Specimens were compressed on duplicate by a Universal Testing Machine with a 5-kg load cell. Relaxation curves were recorded for 8 minutes. Compression ratios of 40% and 60% were used and crosshead speed was 10 mm min-1. A Visual Basic program was developed for the analysis of the recorded data. Relaxation curves were fitted to exponential decay equations derived from linear viscoelastic models. The obtained coefficients, which are related with the viscous and the elastic moduli, characterized cheese softening and the evolution of the elastic properties. Relaxation curves were also normalized and fitted to a linear equation. The slope of this model, which is related to the asymptotic residual force, denoted the extent of solid behavior of cheeses. Textural parameters established associations between texture and structure during the ripening of cheese.