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Summary Introduction to Food Technology FPH-10306
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Summary introduction to Food Technology FPH-10306. The FPH, FCH, FHM and FQD part are in English. Only the FPE part is written in Dutch.
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Introduction to Food TechnologyFood physics and physical chemistry
Physics Consumer
Electromagnetism/optics Colour
Mechanics Feel/touch
Mass transport Smell
Mass transport Taste
Mechanics/sound Texture
Mechanics e.o. Satiety
All physical properties of a food in the end bare relations with:
- The type of molecules of the material and their properties
- The mutual interactions of molecules with one another and with light
Two challenges in relating physical material properties to molecular ingredient properties:
- Factor billion difference in length scale (nm > m)
- Food products are usually inhomogeneous
Designing new structures yields new innovations in three areas:
1. New physical understanding
2. New materials
3. New applications
Answering a food related question:
1. Which product?
2. Which ingredients?
3. How are ingredient properties relevant to product properties?
Main ingredients – proteins, fats, polysaccharides, water, air, gases in general
Minor ingredients – salts, preservatives
Mesoscopic domain/colloidal domain – domain in between molecular and macro to formulate relations
between these two
Parameters for material properties:
1. Temperature
2. Pressure/external stress/energy input
3. Concentration/composition
4. (time)
Low fat products: innovation by means of integrating physics (assembly of molecules into platelets and their
interactions leading to a network), application (the low fat product) and structure design (making structures
with the platelets).
Importance of water in food products:
- Sometimes a lot of it is present in the product
- It determines product properties (addition or removal can affect a product quite a lot)
Pmax – maximum vapour pressure at a specific temperature (increasing the temperature increases pmax)
P – pressure when not enough water is present
p/pmax – relative humidity (RH)
pproduct/pmax – water activity product (aw)
, A product loses water if aw>RH and takes up water if aw<RH
The aw is a characteristic of a product at a given temperature. The RH is a characteristic of the air at that
specific place and temperature.
Structure of milk:
- Fat globules, embedded in a fluid containing other ingredients. These fat globules have a think shell
around them (composed of proteins, phospholipids, vit. A and cholesterol) which prevents the globules
from coalescing together.
- Casein micelles, which are built up by various proteins aggregated together, and contain other
constituents like calcium and phosphate ions, forming calcium phosphate complexes.
- Single proteins, which range from ones meant to have nutritional value, to globulins that fight against
disease organisms and enzymes. Whey proteins are the most relevant from a structure point of view.
There are 4 basic whey proteins: alpha and beta lactoglobulin, bovine serum albumin (BSA) and
immune-globulin.
Creaming of milk: because fat globules have a density smaller than water, they rise through the milk towards its
upper surface. The rate of this creaming depends on:
- The size of the globules, and to which extend the globules stick together (the smaller the fat globules,
the smaller the creaming rate)
The viscosity of the fluid surrounding the particle (the higher the viscosity, the lower the creaming rate)
Viscosity – measure of the difficulty to induce flow of the material. The higher the viscosity, the more difficult it
is to induce flow (with the same pressure applied). Another way of looking at viscosity is that it resembles a
measure for the amount of energy which is lost during flow of that fluid. This energy is lost due to friction
between molecules. The higher the viscosity, the higher the energy loss during movement of the fluid
molecules.
Structural difference between raw milk and homogenised milk: homogenised milk has gone through an
apparatus that exerts forces on the liquid, resulting in smaller fat particles. Because of this, creaming in raw milk
occurs more rapidly than in homogenised milk.
When the fat particles are small enough, the milk is non-creaming. If the particles are small enough (< ½ kT
available), there is no (or a too small) gravitational force acting on the particles and the particles will exhibit
Brownian movement, i.e. there will be no preferred direction for the particles to move in, and thus there will be
no creaming nor sedimentation. If a gravitational force is existing (> ½ kT available), there is one direction, i.e.
the direction of the gravitational force, which yields a lower potential energy for the particle when it follows
that direction, i.e. there exists a preferred direction and the milk will cream.
Taste of milk: rather subtle, so minor changes in chemical composition yield detectable changes in taste, usually
perceived as negative. The most important molecules are lactose (sweet) salts, fatty acid molecules with a short
alkyl chain, and sulphur containing molecules.
Optical properties of milk: (close to) white. If one dilutes the milk, the transparency increases upon dilution. The
reason is in the structure of the milk, in combination with what happens with the electromagnetic waves in the
milk as they travel from one part of the milk to the other.
The light scattered at right angles from a diluted milk is blueish, while the transmitted light is reddish. This can
be explained by the fact that blue light scatters more than red light. This can be summarised in Rayleigh’s law,
which states that the scattering intensity of light is inversely proportional to the fourth power of the wavelength
(Intensity = 1/λ4)
The scattering happens because electromagnetic radiation of a certain wavelength hits molecules of a
substance, and the molecules transmit the light again, at the same wavelength. If not too many structures are
present inside a liquid, the red and blue light will move out of the sample at different intensities for a given
angle. When too many structures are present, the red and blue light being scattered from one scattering
structural element will interfere with the red and blue light scattered from another structural element. This will
lead to multiple scattering, and thus fusing of the colours red and blue again, after which we end up with white
light again. This is why undiluted looks white and diluted milk opaque.
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