RHEOLOGICAL BEHAVIOR OF DIFFERENT TYPES OF PLAIN YOGURT

Yogurt is a widely consumed food due to its nutritional benefits and pleasant sensory characteristics, with texture being an attribute that directly affects consumer acceptability. In this context, this study aimed to investigate the rheological behavior of 4 types of commercial plain yogurts: full-fat (5.6% fat), skim (0.0% fat), lactose-free, and fat-free (0% lactose and 0% fat), and Greek (5.0% fat) at temperatures of 5 and 25 °C. The rheological properties were determined using a HAAKE MARS oscillatory rheometer equipped with a thermostatic bath, employing a cone-plate sensor (C35/2°Ti) with a 0.105mm gap. The flow curves of the yogurts were obtained by applying an ascending shear rate ramp ranging from 0.01 to 200 s−1, a descending ramp from 200 to 0.01 s−1, and another ascending ramp from 0.01 to 200 s−1, each for 120 s. Hysteresis was calculated as the area between the first two curves. The Ostwald de Waele model provided the best fit for describing the flow behavior of the yogurts at both temperatures (R2>0.99). The yogurts exhibited pseudoplastic behavior (n<1) and thixotropy. At 5°C, Greek yogurt showed the highest hysteresis area (11390 Pa.s-1), while the lactose-free and fat-free yogurt exhibited the lowest value (872.15 Pa.s-1). Greek yogurt displayed the highest consistency index (K), followed by skim, full-fat, and lactose-free and fat-free yogurt: 15.1; 8.6; 4.5; and 2.0 Pa.sn at 5 °C, and 10.0; 4.2; 2.2; and 0.84 Pa.sn at 25 °C, respectively. Thus, it can be concluded that the rheological characteristics of plain yogurt differ significantly, depending on processing type and variations in composition. These findings provide important insights for the dairy industry in developing products with specific rheological properties to meet consumer preferences.