Effects of heat treatment and fat reduction on the rheological and functional properties of Gaziantep cheese

Abstract

Gaziantep cheeses with different fat contents (50.4%, 33.4%, and 13.5% w/w) were made and the curds of these were dipped into hot whey at three different temperatures (75°C, 85°C and 95°C) in accordance with the traditional techniques. Cheeses, the curds of which were not dipped into hot whey, were prepared as controls. Cheese samples were analyzed with respect to viscoelastic parameters, meltability and hardness. Reduction in the fat content resulted in significant (P<0.05) increases in protein and moisture contents and decreases in the amount of moisture in non-fat substance (MNFS). Viscoelastic parameters of cheeses were studied using oscillatory dynamic experiments (frequency sweep and temperature sweep tests). A decrease in the fat content and the curd dipping process increased the elastic shear modulus (G′). Temperature sweep test on heating the cheese from 10°C to 70°C showed that reduction of fat content results in a decrease in the magnitude of the phase angle, δ. However, when the curd dipping temperature was increased, the magnitude of the phase angle (δ) increased, at temperatures >35°C. The temperature at which G′=G″, i.e. tanδ equals 1.0, is called as crossover temperature. The crossover temperature was accepted as melting temperature (Tm) and there was a good correlation between Tm and meltability measured with Arnott test for control cheeses. Reduction of the fat content increased the Tm values and decreased meltability. In contrast, increasing the curd dipping temperatures resulted in lowering of both meltability and Tm due to possible structural changes upon heating.