USE OF FOURIER TRANSFORM MECHANICAL SPECTROSCOPY TO STUDY THE MELTING BEHAVIOR OF CHEESE

ABSTRACT

Fourier Transform Mechanical Spectroscopy (FTMS), which employs a complex sinusoidal waveform, was investigated for its applicability in measuring the rheological properties in the cheese system. The complex wave used in FTMS is a superposition of several sine waves whose frequencies are harmonics of a base frequency. FTMS was used to investigate the rheological properties of a 10-month-old Cheddar cheese while the sample was heated from 10 to 90C or cooled from 90 to 10C at the rate of 1C/min or 0.5C/min. The component frequencies of the complex waveform were 0.08, 0.4, 0.8 and 4 Hz. The widely used small amplitude oscillatory shear (SAOS) measurements, which employ only discrete frequencies, were also conducted on separate cheese samples to test the robustness of FTMS results. During heating, the values of the storage modulus (G') and loss modulus (G") decreased by at least four orders of magnitude. In the temperature region from 44 to 55C, there was a shoulder in the G' and G" profiles, which was more pronounced at high frequencies; and in the high-temperature region from 70 to 90C, the dynamic moduli values either reached a plateau or slightly increased. The frequency dependence of the dynamic moduli increased after 40C. The temperature and values of dynamic moduli at the crossover of G' and G" were highly dependent on frequency. Clear maxima were observed in loss tangent (LT) profiles and the temperature of maxima and their values were highly dependent on frequency. Results were similar for both rates of heating, but the heating and cooling curves for G', G" and LT showed hysteresis. The results from FTMS agreed well with the SAOS measurements for all the frequencies tested and indicated that the FTMS technique is a useful method to probe the molecular behavior of cheese systems while undergoing heating or cooling.