THE CLASSIFICATION OF METHODS AND INSTRUMENTS FOR MEASURING

THE CLASSIFICATION OF METHODS AND INSTRUMENTS FOR MEASURING STRUCTURAL-MECHANICAL PROPERTIES OF FOOD PRODUCTS

Structural and mechanical properties (SMP) occur during the approach of mechanical energy to the treated product and characterized by its resistance to externally applied mechanical stress. This group of physical properties provides the most comprehensive view of some essential aspects of product quality. SMP often determines the behavior of products in a variety of processes and energy fields, are the outward expression of the inner nature of the objects, i. e, characterize the state of aggregation, dispersion, structure and type of interaction within the product. SMP are not "pure" constant and significantly depends on the shape and size of product, temperature, etc. .

Viscosity - an indicator of quality of many foodstuff (syrup, mayonnaise, etc. ). It plays an important role in production of many products since actively influences technological processes - hashing, filtering, etc. Viscosity is characterized by coefficient of dynamic viscosity (Pas x c) and coefficient of kinematic viscosity. Values of dynamic and kinematic coefficients of viscosity for each product are individual and pressure, humidity or fat content, concentration of solids depend on temperature. Viscosity of foodstuff decreases at increase of humidity, temperature of fat content and increases with increase in concentration of solutions, degrees of their dispersion. Size, the return viscosity, is called as fluidity. Not less important structural and mechanical properties are plasticity, durability, elasticity, etc.

Plasticity — ability of a product to forming or a current, caused by residual or irreversible deformations. Durability — ability of a product to resist forming under the influence of external forces. It is one of indicators of quality of pasta, refined sugar. Elasticity — ability of products instantly to restore an initial form or volume after cancellation of forces. Elasticity — ability of products gradually to get into condition or volume after cancellation of forces. Shift tension — the product resistance to action of a tangent component of the applied force. It is equal to the relation of this force to a shift surface. The minimum force necessary for shift implementation (movement of layers on squares of shift), is defined by the size of limit tension of shift. The relaxation period — is the major criterion when forming bakery, macaroni and confectionery. For example, when drawing by a stamp of any drawing on dough it will be kept, but won't be tightened provided that duration of influence of a stamp will be not less period of a relaxation.

Creep — property of a product continuously to be deformed under the influence of constant loading. Tiksotropy — ability of some disperse systems spontaneously to restore the structure destroyed by mechanical influence. It is observed at a deposit of sausages, dough at baking of bakery products. Understand the sticking force which arises at contact of surfaces of materials, various on structure, as adhesion (stickiness). Hardness — ability of material to resist introduction in it other more solid body. Hardness is determined at an assessment of quality of fruits, vegetables, grains, sugar. At the same product depending on its state and conditions of loading SMP are shown different. For example, macaroni dough at instant influence of loading behaves as an elastic body, under other conditions of loading viscous and plastic properties are more shown. In the course of technological processing the same product passes from one rheological state into another, often opposite on properties to the first.

According to B. A. Nikolaev, all foodstuff classifies by CMC on three groups: The I group — solid and tverdoobrazny foodstuff; The II group — it is firm - liquid foodstuff; The III group — liquideous and liquid foodstuff.

The minimum of the indicators characterizing adequately the CMC products for each group will be various. Solid and tverdoobrazny foodstuff I of group is characterized generally by elasticity modules, viscosity and the relation of viscosity to the elasticity module, and also critical (limit) tension of destruction. Also limit tension of shift causing the beginning of a current of structure can serve as additional characteristics. The numerous it is firm - the liquid foodstuff II of group having variety of mechanical properties is characterized by the greatest number of indicators: modules of elasticity, rheological curves of dependence of viscosity on tension, viscosity relation to the module, limit tension of shift, relative elasticity (plasticity), and also elasticity and in coefficients of fluidifying (consolidation). Liquideous and liquid foodstuff III of group is characterized by sizes of their limit tension of shift, dependence of structural viscosity on tension, loss of pressure at a current on pipes, the speed limit of a current and, mainly, viscosity.

One of the most important indicators of quality of many foodstuff is the consistence. The existing organoleptic control method of a consistence of foodstuff is subjective. Therefore at examination of foodstuff along with organoleptic by method of an assessment of a consistence apply the tool control method based on definition of one or several objective structural and mechanical characteristics of a product. In it one of the most important values of rheological control methods consists in merchandizing.

Thank for your attention!!!