Lecture+Summary+Week+1+-+Week+6

By Mohamad Iswandi Bin Ishak
 * __Lecture Summary Week 1 – Week 6__**

__OVERVIEW OF ALL ABOUT FOOD RHEOLOGY__

Food rheology is the study of the rheological properties of food that is the consistency and flow of food under tightly specified conditions. The consistency, degree of fluidity, and other mechanical properties are important in understanding how long food can be stored, how stable it will remain, and in determining food texture. The acceptability of food products to the consumer is often determined by food texture, such as how spreadable and creamy a food product is. Food rheology is important in quality control during food manufacture and processing.

__Stress and strain :__

Stress is defined as force per unit area. It has the same units as pressure and in fact pressure is one special variety of stress. However, stress is a much more complex quantity than pressure because it varies both with direction and with the surface it acts on.

Strain is defined as the amount of deformation an object experiences compared to its original size and shape.

__Viscosity :__

Viscosity is a measure of the resistance of a fluid to deformation under shear stress. It is commonly perceived as thickness or resistance to pouring. Viscosity describes a fluid's internal resistance to flow and may be thought of as a measure of fluid friction.

For example, methanol is thin and having a low viscosity, while vegetables oil is thick having a high viscosity.

The variables thatt affect viscosity are : i) Shear rate ii) Time of shearing iii) Temperature iv) Pressure

Water is an example of a Newtonian fluid. In a Newtonian fluid, the relation between the shear stress and the strain rate is linear, the constant of proportionality being the coefficient of viscosity. In simple terms, the size of the drops is directly related to the thickness of the fluid. In a non-Newtonian fluid, the relation between the shear stress and the strain rate is nonlinear, and can even be time-dependent. Therefore a constant coefficient of viscosity can not be defined. Newtonian fluids obey Newton's laws but non-Newtonian fluids does not obey Newton's laws.

Types of flow curve are : i) Bingham ii) Plastic iii) Pseudoplastic iv) Newtonian v) Dilatant

Bingham, Plastic, Pseudoplastic and Dilatant are the non-Newtonian flow curve in time independent while for time dependent, the flow curve are Thixottropic and Rheopectic.

Viscoelasticity is the property of materials that exhibit both viscous and elastic characteristics when undergoing deformation. Viscous materials, like honey, resist shear flow and strain linearly with time when a stress is applied. Elastic materials strain instantaneously when stretched and just as quickly return to their original state once the stress is removed. Viscoelastic materials have elements of both of these properties and, as such, exhibit time dependent strain. Whereas elasticity is usually the result of bond stretching along crystallographic planes in an ordered solid, viscosity is the result of the diffusion of atoms or molecules inside an amourpous material.

There are two type of test to measure viscosity which are empirical test and fundamental test. In empirical test have three way to measure viscosity which are Bostwick Consistometer, Falling ball Viscometer and Glass Capillary Viscometer while Rotational Viscometer use in fundamental test.

Thank You