## 1 Introduction  
The measurement of rheological properties is one of the most important problems in food engineering. Knowledge of these quantities is necessary for the proper design, modeling and synthesis of optimal control systems. Moreover, knowledge about the rheological properties of food liquids is also important for the proper operation of the installation. Real-time monitoring of rheological properties is very important because of the ability to assess the condition of fluids in a pipeline or mixer [1, 2]. This gives information on the structural changes that occur in the fluid during the transport or mixing process. Continuous monitoring of structural changes in food fluids is important due to the possibility of irreversible damage to the fluid by excessive shear stress. As a result the obtained product is not fully valuable or even obtaining the final product is not possible. There are several options for real-time monitoring of the rheological properties of non-Newtonian fluids through pipelines during flow. The basic method relies on simultaneous measurement of volumetric flow rate and pressure drop over a given length [3]. There are extended variants of this method, in where exist supporting system for velocity measurement based on the Doppler effect (laser or ultrasound) [4, 5]. Alsothere are available commercially solutions of this form of rheometers mounted directly on the pipeline (Schlumberger Technology Corporation) [6]. The cheapest and simplest method of rheological measurement is pressure drop and flow rate monitoring [7]. This method does not require the use of additional equipment on the pipeline, but only the registration of typical process values. This approach can only be used for laminar flow. For the transient and turbulent type of flow, it is possible to monitor only the pressure drop itself in the measuring section. Presented pipeline systems can work in two ways. The first relies on a typical monitoring of process quantities in an actual pipeline system and based on the response of the installation. A decision is made to change the operating parameters, which affect in the number of rotations in the impeller or pump worm or changes in the valve's position. In this case, knowledge of the rheological characteristics of the fluid is required, which has to be learned from an experiment with a capillary or rotary rheometer. Then, obtain characteristic is implemented in the control system. The second method based on using a straight section of the pipeline as a capillary tube rheometer and measure the pressure drop as a function of the volumetric flow rate. Based on the data obtained in this way, it is possible to determine the rheological characteristics of the fluid under laminar flow conditions. For the turbulent range of flow, such tests can be used to determine the flow resistance coefficients. For the measurement data obtained in this way, which form the classic flow curve, it is possible to fit the appropriate rheological models and evaluate the rheological parameters of the fluid. Liquid food systems seldom exhibit [PERSON]'s law properties, most of the food liquids are non-Newtonian liquids. These liquids show very differentiated exceptions from the mentioned law. This is because food largely consists of macromolecular systems and the presence of these molecules in the solutions cause these deviations. That's why, the analysis of the hydrodynamic behavior of food liquids require extensive research due to the variety of rheological phenomena. Currently, non-starch hydrocolloids are important food ingredients. These systems are used in the food industry to create the structure of the product and thus specyfc sensory impressions, or for stabilization in order to minimize, for example the effects of sedimentation of solid particles, syneresis, creaming. Solutions of these biopolymers are also used as stabilisers for metastable systems such as emulsions or foams [8]. They can also act as crystallization inhibitors.