EFFECTS OF TEMPERATURE, SHEAR RATE AND PROCESSING ON THE RHEOLOGICAL PROPERTIES OF SALEP DRINK

Abstract

The effects of shear rate, temperature and processing on the rheological properties of commercial salep drinks (UHT processed in liquid form, powdered forms both instant and traditionally cooked type) are investigated. The empirical power law model is used for the determination of the flow behavior and consistency index. Apparent viscosity of salep drink decreased with increasing shear rate. The salep drink exhibited a pseudoplastic or shear thinning behavior. Processing affected the flow behavior and consistency indices significantly (p <= 0.05). The flow behavior index of samples was in the range of 0.51-0.74 while the consistency index changed in the range of 0.14-2.68 Pa.sn. The lowest flow behavior index and the highest consistency index value are determined with the instant salep drink, while the highest K value was recorded for it. The flow behavior index increased and the consistency index decreased with processing temperature. In sensory analysis, salep drinks were evaluated for flavor, consistency and overall acceptability. A single rheological model is developed to express combined effects of shear rate (by Power law model) and temperature (by Arrhenius equation) on the apparent viscosity of an instant salep drink preferred by the sensory panelists in all samples. This study is expected to standardize the product formulation and facilitate equipment and process design.