Learning outcomes Physical and Physiochemical aspects of food technology

Function of mesoscopic physics

It acts as a bridge for formulating relationships between properties on a molecular scale and a macroscopic scale.

Categorizations (10 different ones)

1. Milk and dairy

2. Eggs & egg-based products

3. Meat

4. Fruits, vegetables and herbs

5. Grains and nuts

6. Bread and dough

7. Sauces

8. Confectionaries

9. Alcoholic beverages

10. Drinks and juices

Two issues with formulating relations between physical properties on a molecular scale and properties on a consumer relevant scale

• Difference in lengthscale of a factor of a billion

• Structural inhomogeneity

Mesoscopic structures

A structure that has a size between 1 nm and 1 mm

Colloidal systems

Consist of small particles dispersed in a continous medium

• Something that falls in between a homogenous mixture and a heterogenous mixture

• For example Fog is a colloid.

  • It consists of very tiny droplets of water dispersed in air

• The dispersed phase are the water droplets

• The continuous phase is the air where the water droplets are found

What type of flexible structure can result in the rigidity of its system with a low amount of mass?

Platelet-built structure

Order in different states of matter (solids)

• Molecules are arranged in a fixed, regular pattern.

• If you plot the number of molecules at these specific distances, you will observe "peaks" in a graph indicating that there are more molecules present at those discrete distances. The peaks reflect the structural regularity and periodicity typical of solid materials.

Order in different states of matter (liquids)

• The arrangement is less rigid than in solids, yet there are still clusters of correlated molecules.

• This limited extent of order indicates a more disordered and fluid molecular arrangement compared to solids. The peaks in a graph would still exist but would be much less pronounced and only noticeable over short distances, highlighting the transient nature of the interactions.

Order in different states of matter (gases)

• There is no order, molecules are far apart from each other and move freely

• In this state, you'd expect the graph depicting molecular distances to show no significant peaks, indicating a lack of consistent molecular arrangement or correlation at any distance

Relative humidity formula

p/p_max = RH

• p=water vapour pressure

• p_max=the maximum water vapour pressure

Water activity (a_w)

P_product/P_max

• P_product=The water vapour pressure of the product

• P_max=The maximum water vapour pressure

Name 3 principle parameters that affect the physical properties of a system

Concentration, temperature, and pressure

Structure of milk

• Fat globules, embedded in a fluid.

• On a smaller scale one has casein micelles

• These are built up of various proteins, among other constituents.

• Whey proteins: These proteins, dispersed in the liquid surrounding the fat globules and casein micelles, contribute to the nutritional value and also play a role in the structure of dairy products.

Diameter of a fat globule

Range of 1 and 5 micrometers.

What is the thin shell of a fat globule made out of & what is its purpose?

• Proteins

• Phospholipids

• Vitamin A

• Cholesterol

These prevent the globules from coalescing together

Diameter casein micelle and what does it consist of?

• Diameter is 0.1 microns

• Consists of several types of protein aggregated together

• Contains other consituents like calcium and phosphate ions, forming calcium phosphate complexes

What are the hairy regions in casein micelle made of and what is its function?

• Formed by kappa-casein

• These prevent the casein micelles to coagulate together and limit the casein size.

Whey proteins

The class of proteins that are most relevant from a point of view for structure purposes

• they are present in the aqueous fluid surrounding the casein micelles and fat globules

What are the four basic whey proteins

1. Alpha lactoglobulin

2. beta lactoglobulin

3. Bovine serum albumin (BSA)

4. Immunoglobulin

What does the rate of creaming depend on?

• The properties of the fluid surrounding the particle

• If one has syrup, particles cream slower than when the fluid is water (viscosity)

Parameter viscosity of a material

A measure of the difficulty to induce a flow of the material.

• Higher viscosity = more difficult to induce flow, lower the creaming rate of the single fat globules

Colloidal characteristics of mayonnaise

• Continuous phase: Water and vinegar or lemon juice

• Dispersed phase: Oil

Colloidal characteristics of Dough

• Continuous phase: Water

• Dispersed Phase: Proteins (gluten), starch, and fats

Colloidal characteristics of Whipped cream

• Continous phase: Air

• Dispersed phase: Cream (fat globules suspended in water)

Colloidal characteristics of margarine

• Continous phase: Fat

• Dispersed phase: Water, typically around 15-20%

Colloidal characteristics of milk

• Continous phase: Water

• Dispersed phase: Fat globules, proteins (casein and whey), lactose

Colloidal characteristics of Homogenized milk

• Continous phase: water

• Dispersed phase: Smaller, more uniformly distributed fat globules

Colloidal characteristics of butter

• Continuous phase: fat

• Dispersed phase: water

Colloidal characteristics of yogurt

• continous phase: water

• Dispersed phase: milk proteins (casein) coagulated, containing fat and live bacteria.

The spreadability of mayonnaise in terms of physical macroscopic property

• Viscosity: Mayonnaise has a moderate viscosity, which allows it to flow easily without being too runny.

• Texture: The creamy and smooth texture contributes to a pleasant mouthfeel and enhances the interaction between mayonnaise and the spreading tool

The spreadability of mayonnaise in terms of colloidal scale

• The size and distribution of these droplets are crucial for spreadability.

• Smaller, uniformly distributed droplets create a more stable emulsion, leading to improved spreadability.

• This is because smaller droplets have a greater surface area, allowing emulsifying agents, like lecithin from egg yolk, to more effectively coat them and prevent them from coalescing.

The spreadability of mayonnaise in terms of molecular scale characteristics

• Emulsifying agents:

  • Molecules such as lecithin (from egg yolk), are amphipathic.

  • This allows them to stabilize the oil-water interface, preventing separation and contributing to the creamy texture that makes it easy to spread.

• Molecular interactions:

  • Hydrogen bonding and van der Waals forces between water molecules and emulsifying agents help maintain the emulsion's stability.

• Plasticity (adaptibility):

  • The arrangement of fat molecules, especially the length of their fatty acid chains, influences how easily a product deforms and flows, contributing to properties like stiffness and spreadability.

Colloidal structure milk & homogenized milk

• Milk:

  • Composed of fat globules, proteins and lactose dissolved in water. Fat globules are large and naturally rise to the top causing cream separation under gravity.

• Homogenized milk:

  • Fat globules are made smaller. Making the fat globules more dispersed, reducing the tendency to rise, thereby improbing creaming stability.

Creaming milk & homogenized milk

• Milk: Larger fat globules have a higher tendency to coalesce and rise due to buoyancy.

• Homogenized milk: Has reduced creaming due to smaller fat globules and more stable emulsification.

pH stability milk & homogenized milk

• Milk: pH can have a large effect on the stability. A drop in pH can lead to protein denaturation, and destabilization of the emulsion, resulting in sedimentaiton

• Homogenized milk: The process of homogenization can stabilize the pH more than in milk.

Color milk & homogenized milk

• Milk: Color is influenced by the fat content and colloidal dimension of particles such as casein. Larger fat globules scatter light differently compared to smaller ones

• Homogenized milk: Appears whiter and more uniform in color due to the uniform distribution of smaller fat globules that scatter light more consistently.

Browian motion and creaming stability

Smaller fat globules in homogenized milk experience higher levels of Brownian motion, which helps keep them suspended by counteracting gravitational forces. In unhomogenized milk, larger globules have reduced Brownian motion, allowing them to coalesce and rise.

Viscosity milk & homogenized milk

• Milk: Viscosity is higher due to larger fat globules, as the size increases, the resistance to flow increases.

• Homogenized milk: Smaller globule size reduces the viscosity because smaller particles create less resistance.

Newton’s 2nd law and creaming

• According to Newton’s 2nd law (F=ma), the force acting on the fat globules due to gravity (weight) and the viscous drag affects their motion.

• In larger globules, the gravitational force overcomes the drag more easily, causing them to rise, while in homogenized milk, the smaller globules are influenced more evenly by the viscous forces.

Sol in phases + example

• Dispersed phase: solid particles (smaller than one micrometer)

• Continuous phase: Liquid

• Example: gel, starch in water, blood, paint

Hydrosol in phases + example

• Dispersed phase: solid particles or droplets

• Continous phase: Water

• Example: water-based products made from the distillation of fresh flowers, leaves, fruits, and other plant materials

Suspension phases + example

• Dispersed phase: solid particles

• Continous phase: Liquid

• Example: Mixture of flour and water. Mixture of chalk and water. Muddy water

Emulsion phases + example

• Dispersed phase: liquid droplets

• Dispersing phase: Another liquid (usually water or oil)

• Example: mayonaise, butter, milk

Foam phases

• Dispersed phase: Gas bubbles

• Continuous phase: Liquid

Aerosol phases + examples

• Dispersed phase: Solid or liquid particles

• Continuous phase: Gas (usually air)

• Example Sea spray, mineral dust, smoke

Retrieve the meaning of viscosity in terms of molecular interactions

1. Molecular size and shape: larger and more complex molecules can create greater resistance to flow due to their increased surface area and interactions

2. Intermolecular forces: The strength and type of intermolecular forces significantly impacts viscosity.

3. Temperature: Higher temperature, is more kinetic energy, decrease in viscosity

4. Concentration: Higher concentrations can lead to increased viscosity due to more molecular interactions

5. Flow behavior: Non-newtonian fluids exhibit different viscosities depending on the flow conditions.

Analyse in what respect the results of whipping milk and cream differ from one another in terms of the colloidal characteristics of the two products.

• Typically contains about 3-4% fat. This lower fat content limits the amount of fat globules available for stabilizing the air incorporated during whipping.

• The low fat content results in a relatively weak foam that is less stable. The air bubbles tend to coalesce, leading to a quicker breakdown of the foam. Milk can only be whipped to a very limited degree and is not suitable for applications requiring a stiff or stable foam.

• In milk, the smaller and fewer fat globules contribute less to foam stability. The air bubbles lack sufficient anchorage, leading to instability.

• Emulsifiers are less concentrated, reducing the capacity to stabilize the foam formed during whipping

Analyse in what respect the results of whipping milk and cream differ from one another in terms of the colloidal characteristics of the two products.

• Contains around 30-40% fat or more. The higher fat content provides a greater quantity of fat globules necessary to trap air and form stable bubbles.

• Has a higher concentration of proteins, particularly caseins, which enhance the stability of the foam during whipping. The presence of fat globules also supports the protein network that forms.

• The high-fat content allows for the creation of a much lighter and more stable foam. When whipped, the fat globules partially coalesce and form a network that holds air bubbles, producing a thick, stable whipped cream. The foam can maintain its structure for an extended period and can be used in various culinary applications.

• In cream, the larger and more numerous fat globules create a rich network that supports the air bubbles during whipping.

• on the other hand, benefits from a higher concentration of emulsifiers, which promotes better foaming and stabilization of air pockets.

Viscosity Formula for Concentric Cylinder

n = (F x h)/((2pi x r²) x w)

n= viscosity (Pa) (mPa per s to Pa per s you divide by 1000)

F = force (N)

h = height of cylinder (m)

w = angular velocity (rotation speed) (m)

r = radius (m)

How small are fat globules in homogenous milk?

Smaller than one micrometer

Properties of casein micelles

• Proteins

• Exhibit Brownian motion and therefore do not clump

• When pH is lower than 5.3 only then they start to clump

Formula upward force of a particle in a fluid

F = (4/3) x (π) x (g) x (△p) x (R³)

g=gravitational acceleration

△p = The difference in density of the two fluids

R = radius of the particle

10 N = 1 Kg

Formula quantifying thickness of a fluid

F = n x v x A/D

F = Force

N= viscosity (Pa)

A = Surface area A (m)

D= Height (m)

V= velocity

Formula creaming velocity

U = (2a² x Δp x g)/9 x n

a = radius (m)

Δp = Density difference (Kg/m³)

g = Gravitational acceleration (10 m/s²)

n= viscosity = Pa

States of matter in a graph pressure vs. time