VISCOELASTICITY OF THE EDAM CHEESE DURING ITS RIPENING Š

NEDOMOVÁ, Š. : Viscoelasticity of Edam cheese during its ripening. Acta univ. agric. et silvic. Mendel. Brun. , 2010, LVIII, No. 4, pp. 183–192 Series of the indentation of the ball (10 mm in diameter) by the constant speed into blocks of Edam cheese has been conducted. The indentation tests were performed at diff erent speeds (1, 5, 10, 20 and 100 mm/min), and the corresponding force–displacement responses were fi tted with an analytical solution to obtain the time-dependent constants and the instantaneous force–displacement response. The measurement has been performed for the cheeses of diff erent stages of their maturity. The dependence of the indentation force on the penetration depth has been evaluated. This dependence can be fi tted by a polynom. The indentation force decreases with cheese fat content. It increases with the loading rate. Its value also decreases with the time of the cheese ripening. The recently proposed method for the indenation of the ball into viscoelastic solids has been used for our data analysis. This procedure, which needs the use of the numeric methods, enables to obtain stress relaxation moduli, which describe the viscoelasticity of the tested materials. The obtained moduli describe the stage of the cheese maturity. Edam cheese, indentation, penetration, depth, relaxation, modulus, viscoelasticity Cheese ripening is a complex process involving many physicochemical changes such as a change in pH, a progressive breakdown of the proteins to smaller polypeptides and the gradual accumulation of amino acids (Fox et al., 1993). Cheese texture may also vary with a change in the physical state of the fats that are already present in the cheese (Dufour et al., 2000; Watkinson et al., 1997). These changes can be described e.g. by the rheological properties of cheese. Rheological characterization of cheese is important as a means of determining body and texture characteristics and also for exa mining how these parameters are aff ected by composition, processing techniques and storage conditions (Konstance and Holsinger, 1992). The most common method employed to study the mechanical properties of cheeses is the uniaxial force-compression: a constant rate of compression is applied to the sample and the resulting stress is continuously recorded. The method is suitable for the study of the rheological parameters of cheese on ripening and has been employed in French cheeses (Antoniou et al., 2000), Cheddar cheese (Hort et al., 1997), Parmigiano Reggiano cheese (Noël et al., 1996), Swiss-type cheese (Bachmann et al., 1999) and Gouda cheese (Spangler et al., 1990). The former tests are used as standards for conventional structural materials because the measured forces and displacements can be converted into the stress– strain properties using simple theories, but they can be tedious and diffi cult when applied to so foods because of the need to prepare specimen of specifi c size and shape. This problem can be solid using of the indentation tests. Tests based on the indentation technique are popu lar in food texture evaluation because they do not require samples with strict shape requirements (Ozkan et al., 2002). However, because of the nonuniformity in the strain distribution, only limited theories that relate the indentation force–displacement response to the stress–strain properties are available (e.g. Sneddon, 1965; Sakai, 2002). As a result, indentation force–displacement measurements for many foods are interpreted empirically (Anand and Scan-