Ice cream - The four microstructure elements - Anti-freeze proteins
8 important questions on Ice cream - The four microstructure elements - Anti-freeze proteins
What do ice structuring proteins (ISP) do?
In ice cream, ISPs slow down Ostwald ripening dramatically and also change the size and shape of ice crystals.
How can proteins control ice crystals?
What are the consequences of freeze concentration?
- It moves the matrix closer to the glass transition and the viscosity will increase --> decreases rate of recrystallization. It will also provide "body" to the ice cream and provides a certain minimal viscosity to hold the air bubbles within the ice cream during freezing
- Sugar concentration can become so high that the matrix becomes supersaturated and the sugars crystallize out of solution.
- Sucrose recrystallisation --> "white-spot"
- Increase in polysaccharide concentration --> phase separation (when polysaccharides and proteins are both present) --> difference in water distribution
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What are 4 functions of fat in ice cream?
- It has an effect on sensory properties (creamy)
- It holds fat-soluble flavour molecules
- It increases the viscosity of the matrix (they are present as suspended particles)
- It coats the air bubbles and therefore decrease the rate of meltdown.
How can fat be replaced in ice cream?
- Proteins --> stabilise the air bubbles
- Polysaccharides --> increase viscosity of the matrix
What are the 4 main functions of air in ice cream?
- It makes the ice cream soft. The smaller the air bubbles, the smoother the ice cream will be.
- The air bubbles scatter light, so they influence the colour. Aerated ice cream is whiter then unaerated ice cream.
- Help to keep ice crystals from approaching each other. This prevents accretion.
- Heat transfer is slowed down as air is not conductive. It will therefore slow down the rate of melt.
What are the 2 mechanisms for the coarsening of air?
- Coalescence (similar to accretion in the case of ice crystals)
- Disproportionation (similar to Ostwald ripening for ice crystals)
Mention 2 ways to decrease coarsening of air?
- Adsorption of proteins onto the bubble surface. This adsorption of proteins will decrease the surface tension. As the pressure is related to the surface tension, the pressure will decrease and therefore also the gas flow.
- Adsorption of fat droplets. The partially coalesced fat droplets form a three dimensional structure that stabilises the air bubbles and link them into a foam. This is only possible in the case of solid fat, not liquid fat/oil. At low concentrations of fat, the network will not cover the complete surface.
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