Chapter 4 Flashcards
When would be consider applying an edible coat?
- When we want to limit driving force
- When we want to reduce the transfer rate
What is one way to limit driving force?
By having aw be the same everywhere. This can be achieved with the use of sugars and salts.
In an ideal liquid yi equals to?
Equals to 1
What is the influence of the thickness of the film on the mass flux?
Thinner films lead to higher mass flux. However, this is not always linear.
Which are the three heterogeneous film that can be applied?
Parallel (to permeation), series (perpendicular to permeation) and Maxwell model (random distribution of component 1 and 2.
What is the issue of defects in coating?
May lead to much higher permeability
What are some solutions to avoid defects in coatings? And their respective disadvantages.
- Apply thick coatings -> can be expensive, affect taste and appearance and may take long to solidify and must not drain. When thickness double drainage time decrease by 8 times and solidification doubles.
- Using emulsion -> however a relative flexible continuous phase is required which can be given by protein/polysaccharide. These though have high water vapor permeability.
- Applying multiple layer -> Like the first one above, but more thin layer applied on top of each other. Can be time and cost consuming. Can also affect texture.
- Low and high permeable film -> bi-layer. First a lipid layer which is low permeable for water but has defects. A second layer of more permeable but with better mechanical strength is positioned. This has a plugging effect and will penetrate the defect in the lipid layer. This will decrease overall permeability but still have good mechanical and rheological properties. The disadvantage is in making sure that the first layer adheres properly to the second layer.
- Curing -> letting the coat harden so it can close the defects through capillary pressure. Only possible for small defects.
What are the three causes of hysteresis
Relaxation phenomena, glass formation and capillary water in irregular pores.
How can you keep raisins soft at low aw?
By adding glycerol to raisins
Give explanation of biopolymers and their use as coating.
Biopolymers, e.g. protein and polysaccharide, are hydrophilic and have high permeability to water. However, they are good barrier against oxygen and carbon dioxide and lipid components. Good tensile strength and its properties can change with pH. Around pI more hydrophobic and lower mechanical strength.
Give explanation of lipids and their use as coating.
Lipids are good barrier against water. Poor mechanical strength. When crystallized can orient in parallel to surface, so in series, at decrease permeability even more.
Give explanation of emulsions and their use as coating.
Emulsion mixture of lipids and proteins. Better mechanical strength. Must be evaporated at low temp otherwise fat can melt.
Give explanation of additive and their use as coating.
When using biopolymers, plasticizers are added to increase flexibility of film otherwise too brittle. Plasticizer increase moisture permeability and may even diffuse into product.
Dip coating what it is and when is the best suitable and least suitable?
Dip coating is submerging a product on a bath with the melt. If the product temperature is below the crystallization temperature of the melt then the melt will solidify directly and thickness will increase over time. If this is not the case then the product should be blasted with cold air to solidify the product.
Solvent evaporation what it is and when is the best suitable?
Solution of coating material is sprayed or dipped. Only possible when the product is not sensitive for moisture.
