Min+Ing's+Weekly+summary

Rheology is the study of flow of matter when an "external forces" are subjected .It will cause solid to deform and liquids to flow.We can apply external forces like sucking,pouring,scooping ,pressing and etc.These kind of external forces can initiate flow. 
 * __RHEOLOGY __**
 * What is Rheology **

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 * This picture show the spreading  jam on toast. When we spread jam on toast,the jam will stick on the toast and give us better mouthfeel. **=====



This picture show scooping  ice-cream is the act of applying force to scoop ice-cream.



This picture show pouring  or squeezing <span style="font-family: 'Times New Roman','serif'; font-size: 16px;"> ketchup from the bottle.

<span style="color: #0000ff; font-family: 'Times New Roman','serif'; font-size: 16px;">Rheology in food is important to give us mouthfeel sensation.

<span style="color: #a800ff; font-family: 'Times New Roman','serif'; font-size: 16px;">Rheology is mainly concerned with relationship between stress, strain and time <span style="color: #0000ff; font-family: 'Times New Roman','serif'; font-size: 16px;">.
 * <span style="color: #0000ff; font-family: 'Times New Roman','serif'; font-size: 24px;">Stress and Strain **

<span style="color: #000000; font-family: 'Times New Roman','serif'; font-size: 16px;">a) Stress-Simply defined as force per unit area. (we can think stress as a normalised force or the intensity of force)

<span style="color: #000000; font-family: 'Times New Roman','serif'; font-size: 16px;">b) Strain--Simply a quantitative measure of the extent to which ann element of material has been deformed.

<span style="color: #000000; font-family: 'Times New Roman','serif'; font-size: 16px;">The deformation implies the change of shape. (dimensional change)

<span style="color: #000000; font-family: 'Times New Roman','serif'; font-size: 16px;">Variable that affect viscosity:
 * <span style="color: #0000ff; font-family: 'Times New Roman','serif'; font-size: 24px;">Newtonian and Non-Newtonian fluids **

<span style="color: #000000; font-family: 'Times New Roman','serif'; font-size: 16px;">- Shear rate

<span style="color: #000000; font-family: 'Times New Roman','serif'; font-size: 16px;">- Time of shearing

<span style="color: #000000; font-family: 'Times New Roman','serif'; font-size: 16px;">- Temperature

<span style="color: #000000; font-family: 'Times New Roman','serif'; font-size: 16px;">- Pressure

<span style="font-family: 'Times New Roman','serif'; font-size: 16px;">- Shear viscosity which is independent of the shear rate.
 * __<span style="color: #1a8000; font-family: 'Times New Roman','serif'; font-size: 18px;">Newtonian fluids __**

<span style="font-family: 'Times New Roman','serif'; font-size: 16px;"> - Viscosity in fluid immediately to zero when shearing is stopped.

<span style="font-family: 'Times New Roman','serif'; font-size: 16px;"> -Examples of Newtonian fluids include water, mineral, liquid lecithin, prune concentrate, various syrups, vegetable oils, honey, milk, fruit juices, and wine.

<span style="font-family: 'Times New Roman','serif'; font-size: 16px;">

<span style="font-family: 'Times New Roman','serif'; font-size: 16px;">- Any liquid that show deviation from newtonian behavior.
 * __<span style="color: #008000; font-family: 'Times New Roman','serif'; font-size: 18px;">Non-Newtonian fluids __**

<span style="font-family: 'Times New Roman','serif'; font-size: 16px;"> -Viscosity of fluids depend on shear rate but independent of time of sharing

<span style="font-family: 'Times New Roman','serif'; font-size: 16px;"> -Non-Newtonian materials can be either time independent or time dependent.

<span style="font-family: 'Times New Roman','serif'; font-size: 16px;"> -The terms time “independent” and “dependent” refer to the effect that shearing energy input has on the viscosity of a fluid as it is being sheared.

<span style="font-family: 'Times New Roman','serif'; font-size: 16px;"> -In time-dependent systems, the viscosity changes as shear rate is changed. However, at any given shear rate the viscosity will have a finite value versus time.

<span style="font-family: 'Times New Roman','serif'; font-size: 16px;"> -In time-dependent systems, the viscosity changes with time under a constant rate of shear.

<span style="font-family: 'Times New Roman','serif'; font-size: 16px;"> --Time-independent, non-Newtonian flow includes pseudoplastic, Bingham plastic, and dilatant fluids.
 * <span style="color: #ff0030; font-family: 'Times New Roman','serif'; font-size: 18px;">- Non-Newtonian, Time Independent Fluids **

<span style="font-family: 'Times New Roman','serif'; font-size: 16px;"> a) <span style="color: #00ff00; font-family: 'Times New Roman','serif'; font-size: 16px;">Pseudoplastic <span style="font-family: 'Times New Roman','serif'; font-size: 16px;">—these are fluids which decrease in viscosity as shear rate increases. This type of flow behaviour is reversible and is also known as “shear thinning”.

<span style="font-family: 'Times New Roman','serif'; font-size: 16px;"> b) <span style="color: #008000; font-family: 'Times New Roman','serif'; font-size: 16px;">Bingham Plastic <span style="font-family: 'Times New Roman','serif'; font-size: 16px;">—If the pseudoplastic material has an internal forces which keep it from flowing below some value of shear stress and the material begins to flow above this value.

<span style="font-family: 'Times New Roman','serif'; font-size: 16px;"> c) <span style="color: #1a8000; font-family: 'Times New Roman','serif'; font-size: 16px;">Dilatant <span style="font-family: 'Times New Roman','serif'; font-size: 16px;">—If a material is measured from a low to a high rotational speed (shear rate) and the viscosity increases with increasing speed, the material is classified as dilatant. It is also described as “shear thickening”.


 * <span style="color: #ff0075; font-family: 'Times New Roman','serif'; font-size: 18px;">- Non-Newtonian, Time Dependent Fluids **

<span style="color: #4500ff; font-family: 'Times New Roman','serif'; font-size: 16px;">Thixotropic <span style="font-family: 'Times New Roman','serif'; font-size: 16px;"> – If viscosity is measured from low to high shear rates (rpm) then back to low shear rates and the viscosities coming down are lower than those going up, the material is classified as thixotropic and is time dependent.

<span style="font-family: 'Times New Roman','serif'; font-size: 16px;"> -These fluids lose viscosity under constant shear. When shearing stopped, they regain their original viscosity but require time to do so. Cellulose derivatives (e.g., carboxymethycellulose, CMC), tomato paste, and apple sauce are generally thixotropic.

<span style="color: #808000; font-family: 'Times New Roman','serif'; font-size: 16px;">Corn starch is the example of non-newtonian fluid.


 * <span style="color: #15157a; font-family: 'Times New Roman','serif'; font-size: 18px;">What is yield stress? **

<span style="font-family: 'Times New Roman','serif'; font-size: 16px;"> Yield stress means minimum shear stress that need to be applied to initiate flow. Minimum shear stress needed to be applied to overcome the cohensive force that holds the structure of the material. This means that a critical value of shear stress, below which a viscroplastic material behaves like a solid; above this value, a viscoplastic material flows.

<span style="font-family: 'Times New Roman','serif'; font-size: 16px;">

<span style="font-family: 'Times New Roman','serif'; font-size: 16px;"> The yield stress is the applied stress we must exceed in order to make a structured fluid flow


 * <span style="color: #0000ff; font-family: 'Times New Roman','serif'; font-size: 24px;">Measuring Viscosity **
 * __<span style="color: #008000; font-family: 'Times New Roman','serif'; font-size: 18px;">Empirical test and Fundamental test __**


 * <span style="color: #008080; font-family: 'Times New Roman','serif'; font-size: 18px;">- Empirical test **
 * <span style="font-family: 'Times New Roman','serif'; font-size: 16px;">Test and see
 * <span style="font-family: 'Times New Roman','serif'; font-size: 16px;">Measurement made without changes in product shape, or control of deforming process
 * <span style="font-family: 'Times New Roman','serif'; font-size: 16px;">Examples : Bostwick consistometer, falling ball viscometer,glass capillary viscometer


 * <span style="color: #008080; font-family: 'Times New Roman','serif'; font-size: 18px;">- Fundamental test **
 * <span style="color: #000000; font-family: 'Times New Roman','serif'; font-size: 16px;">'Physics based approach". Use well defined text fixture(geometry) and test condition.
 * <span style="color: #000000; font-family: 'Times New Roman','serif'; font-size: 16px;">units/values are independent of sample geometry and data can be validated with another geometry.
 * <span style="font-family: 'Times New Roman','serif'; font-size: 16px;">Examples : Rotational viscometer


 * __<span style="color: #800080; font-family: 'Times New Roman','serif'; font-size: 32px;">PRINCIPLES OF TEXTURE ANALYSIS __**
 * <span style="color: #0000ff; font-family: 'Times New Roman','serif'; font-size: 24px;">What is Texture **

Benefit

 * 1) Forces applied at a precise rate
 * 2) results are accurate and repeatable
 * 3) Provide an objective measure of customer acceptance
 * 4) cost-effective way to provide repeatable result quickly
 * 5) shorten new product development cycles
 * 6) provide process control feedback

Instrumental Texture Test

 * 1) Fundamental test : measure well define physical properties.
 * 2) Empirical test : developed by observation and experimental
 * 3) Imitative test : test that attempt to imitate the conditions to which the material is subjected in the mouth . (TPA)

= Empirical test =

- Adhension
=__ FOOD COLLOIDS __=

Terminology

 * Colloidal Dispersion (SOL)---Dispersion of 2 or more immiscible materials, containing structural entities in the size range 1nm - 1um.
 * The simplest type of colloidal system consists of a single dispersed phase of particles in a second continuos phase called dispersion medium.
 * Suspension---a system containing particles > 1um, prone to settle under gravity.
 * Emulsion---a dispersion or suspension of liquid droplets in a coontinuos phase.
 * Foam---coarse dispersion of gas bubbles in a liquid/solid continuos phase.
 * Food colloids---dispersions containing large particles.

**Interaction between dispersed droplets** 1. **Van Der Waals attractive forces** - originate from dipole-dipole interaction, closer=stronger 2. **electrostatic repulsive forces** - electrical double layer- the combination of the charged surface and the unequal distribution and counterions near the surface.

** DLVO THEORY **

 * electrical double layer repulsion will stabilise emulsion ( electrolyte concentration phase < certain value)
 * relates stability of emulsifed droplets to two independent potential that come into action when two droplets approach each other

Surface and Interfacial Tension
ΔE = γsΔA
 * Surface tension is the property of liquid in contact with air that makes it behave like it was covered with a thin membrane under tension.
 * **Surface tension (N/m)**---force acting over the surface of liquid per unit length of the surface perpendicular to the force.
 * **Surface tension (γs)**---defined as the amount of energy (ΔE) required to increase the surface area between a liquid and a gas (e.g. air and water) by an amount ΔA.
 * **Interfacial tension ( γ ****i)**---defined as the amount of energy required to increase the interfacial area between two immiscible liquids (e.g. oil & water).

**__Food Emulsion__**
 * Emulsion---consists of 2 immiscible liquids (oil & water), one of the liquid dispersed as small spherical droplets in the other.
 * Water in oil emulsion (w/o)---margerine, butter, spreads.
 * Oil in water emulsion (o/w)---mayonnaise, salad dressing, milk, beverages, cream, soups, sauces.

Homogenization---dispersed phase is broken down into small droplets by high pressure homogenizer (10-100MPa).

Mechanism of Emulsion Breakdown

 * 1) Creaming---the process in which droplets move upwards (droplets density<density of continuous phase).
 * 2) Sedimentation---the process in which droplets move downwards (droplets density>density of continuous phase).
 * 3) Flocculation---the process in which 2 or more droplets “stick” together to form an aggregate (but the droplets still retain their individual integrity).
 * 4) Coalescence---the process in which 2 or more droplets merge together to form a single larger droplet.
 * 5) Phase Inversion---the process in which o/w emulsion changes to w/o emulsion, or vice versa.

**Emulsion Stabilization** **Emulsifier (surfactant)** - compound that facilitate the formation of emulsion by lowering the oil/water interfacial tension and imparting short-term stability by forming a protective film around the droplets. __**Functions:**__ -Ionic emulsifiers form an electrically charged double layer in aqueous solution surrounding each oil droplets. -Thickness of electrical double layer affected by ionic strength.Droplets remain suspended when ionic strength is low, electrical repulsion>van der waals attraction. -With ionic emulsifiers, low salt concentration enhances stability, high salt concentration increases flocculation and/or coalescence. -droplets in an emulsion have a different density to that of liquid which surrounds them - a net gravitational force acts upon them- cause creaming or sedimentation.
 * Stabilizers** - compounds that are not surface active but impart long-term stability to emulsion by restricting interfacial interations.
 * **Adsorption at interface** - amphiphilic, adsorb at the interface between oil and water and form an interfacial film= reduction of interfacial tension.
 * **liquid crystal stabilization (arrange in specific order manner)** - mixture of emulsifier and water - liquid crystals form on the surface of oil droplets in o/w emulsion
 * **ionic stabilization (electrostatic)**
 * **Stabilization via steric hindrance** -hydrocolloids - increase the viscosity - partition into the o/w interface as a physical barrier to coalescence.
 * **Gravitational separation**

Methods of controlling Gravitational Seperation
1. Minimize density difference 2. Reduce droplet size 3. Modify rheology of continuous phase

= __FOAMS__  = Foam Structure
 * Foam is a two-phase system---the gas (air) phase is dispersed in a small amount of liquid (water) continuous phase.
 * Bubbly foam (in ice cream)---formed when the amount of gas incorporated is low enough for bubbles to retain roughly spherical shape.
 * Polyhedral foam (beer foam)---has a large gas-to-liquid ratio, bubbles are pressed against one another in a honeycomb-type structure.



= Foam Formation = ===-3 process involved in foam formation : air has to be injected into the liquid (e.g. using a mixer), large air bubbles have to be broken up into smaller bubbles, the smaller bubbles have to be prevented from fusing during the formation of a foam.===

**Surface active foaming agent** -lower the surface tension of liquid phase-allows expansion of its surface area-form a closely packed film-essential for formation of stable foam. **Protein as surface active agent** - adsorption of protein at the gas-liquid interface.2. surface denaturation3. coagulation of protein (form a network that gives rigidity and stability to the foam) =  **__3 factors affecting foam stability:__**   = 1. **drainage**: the draining of liquid from foam. (under gravity) - as water leaves, faces of film are brought closer together. 2. **disproportionation**: the diffusion of gas from small bubbles into big bubbles 3. **coaslescence**: the fusion of foam bubbles **EGG FOAMS:** -protein-surface active agent-globulins-help to foam gas bubbles-ovomucin- help to stabilize the foam (rapidly denatured at the bubbles surface)