Abstract

When developing new types of dairy products, the formulation of which includes components of both dairy and nondairy origin, it is necessary to study the rheological characteristics of these products. The paper studies the rheological characteristics of concentrated milk products with a complex carbohydrate and protein composition. The study was conducted at the premises of FSBEI HPE "Vologda State Dairy Farming Academy named after N.V. Vereshchagin" (Russia, Vologda Region, Vologda). By using the rotary viscometer "Reotest 2.1" the dependence of shear stress (τ, Pa) and effective viscosity (ηef) on shear rate (γ, s-1) was determined. Freshly made product samples were studied, as well as product samples in the process of storage. In the course of the processing of the obtained data, it was found that freshly made concentrated milk products with sugar, as well as the same products in the process of storage during a period of up to 3 months are classified as "Newtonian" liquids, by virtue of the fact that the dependence of shear stress on shear rate for these samples has a linear character. It is recommended to use a Höppler viscometer for the measurement of viscosity in these samples. Adding starch syrup, malt, or demineralized whey powder to the products results in the deviation of their rheological characteristics from the properties of "Newtonian" liquids. The dependence of shear stress on shear rate for these product samples follows a power-law relationship. On this basis it can be concluded that these products are classified as pseudoplastic bodies. During prolonged storage, consolidation of the structure and an increasing degree of deviation from the properties of Newtonian liquids was observed in all studied samples. This behavior is attributable to the formation of filamentary bridges between the casein micelles, which takes place in the microstructure of concentrated milk products with a complex carbohydrate and protein composition after long storage. These bridges are pseudo-polymers, formed by glucose monomers, and determine the microstructure of the product, its organoleptic and rheological properties. It is recommended to measure the viscosity of the developed products using a rotary viscometer.

Keywords

Rheology, structure, shear stress, effective viscosity, shear rate, "Newtonian" liquids, pseudo-plastic food products

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