Chapter 6 Flashcards
What is swelling capacity of a biopolymer influence from?
From its hydrophilicity. The more negative X is the more it likes water and the greater swelling capacity. The other factor influencing is crosslink density. The more crosslinking, so the higher the Mw, the lower the swelling capacity.
What is indicated when PDI =1
PDI is the poly dispersity index which indicates the dispersity of the chain length. If all chains have the same length then PDI=1.
What type of biopolymer is protein: a homo polymer, a copolymer or a miscellaneous polymer.
Miscellaneous polymer
A thermoset is a :
A. Heavily crosslinked polymer that does not melt.
B. Linear of branched polymer that melt upon heat and solidify upon cooling.
C. Slightly crosslinking polymer that cannot dissolve but swell.
A. Yes, this is a thermoset
B. No, this is a thermoplastic
C. No, this is a elastomer
Mixing can occur when Gibbs is negative or postive?
Negative
When upon mixing energy is released and product becomes warmer is the enthalpy negative or postive?
Negative
What does X12 when equal to <0, <0.5, >0.5 and >2 represent.
When <0 = exothermic mixing
When <0.5 = polymer is miscible
When >0.5 = partly soluble (proteins, ect.)
When >2 = small molecules are partially soluble.
Between the binodal and spinodal will phase separation occur? And when and how does it occur if it occurs?
No, phase separation will not occur spontaneously in this regime. Phase separation can occur by nucleation and growth.
What does CP line in page 12 chapter 6 represent?
The theoretical phase inversion line
What happens to viscosity as the maximum volume fraction of the dispersed molecules is reached?
Approaches infinity. System becomes a glass.
Why replacing sugar with fibers in chocolate is not easy?
Because when sugar is added to oil viscosity increases while fibers have no effect, only at high concentrations. This increase however is higher in sugars. This is caused by sugars ability to form a network of crystals which ultimately increases viscosity. Fibers do not possess this ability. Therefore substituting sugars with fibers is not an easy task.
What is the effect of a rigid filler on viscosity, yield stress, yield strain and young modulus.
Viscosity increase, yield stress increases, yield strain decrease and young modulus increase. Product becomes more brittle.
A whey/cassava starch gel is made. At low concentration of starch the gel strength is increase while at high concentration the opposite occurs. Explain why?
At low conc. starch absorbs water and increase the effective concentration of whey. However, at high conc. phase inversion occurs which leads to a decrease in gel strength.
Why gelatinizing starch before in a whey/cassava starch gel can be beneficial?
Because cassava is cheaper and performing a gelatinization step prior to mixing would allow the starch to already form a gel.
What is an extruder?
An extruder is a machine with one or two screws inside a barrel house.
Which are the four main reasons why to use extrusion?
- High production rate
- Constant product quality
- Continuous operation/process
- A low moisture process
Why one would not want to exceed 180 C in an extruder when working with proteins?
Because protein at this temperature would start to degrade.
How can one favor fiber formation of protein and what limits are there?
Thermal extrusion has been observed to convert native globular proteins into fibrous insoluble aggregate. A demixed system favors fiber formation. However this is not thermodynamically favorable at high temperature and pressure which reside inside the extrudate.
How can one keep starch from swelling after exiting the dye in the extruder?
One would love the moisture content inside the extruder to about 10 %. This will allow the product to avoid excessive swelling and swell only, e.g., upon frying.
What enzyme can be inactivate by extrusion in protein products.
a-amylase and trypsin inhibitors.
What type of technique is used to produce fibrous proteins to mimic meat?
Spinning is the technique use which align the biopolymer through shear or elongational flow and leading to the formation of anisotropic structures. However, not industrially use for high costs and large waste streams.
What is the difference between single and double extruders?
Single extruder is more simple, cheaper, is mostly used for mixing and shaping and it operates at maximal capacity. E.g. of products made with single extruders include pasta and cereals.
Double extruder on the other hand, allows for more possibilities but is more expensive and its operation capacity is dependent on other machines. E.g used for meat analouges.
Is friction in wall of the extruder a requirement for both single and double extruders?
False. Only single extruder are required to have friction on the wall otherwise material will stick. In double extruders friction is created between the screws.
If a product is high in moisture and fat which screw, single or double, is better for extrustion?
Double as it relies less on friction.
What type of extrusion, cold or hot is used for ready to eat pasta?
Extrusion at high temperatures and pressure is used for RTE pasta. Other products include expanded products like crisps, animal feed and meat analogues. On the other hand, cold extrusion is used for pasta where also low shear is used.
What is the effect of elevated temperature on starch and protein?
Starch will gelatinize, swell and increase viscosity. As temperature further increase a deformable starch past will be made which solidifies upon cooling. On the other hand, proteins tend to behave like a solid a moderate temperature. When temperature is increase, the protein behaves more like a synthetic polymer system which is deformable and suitable for structuring purposes.
Why are plasticizers used in extrusion? And how is water (a plasticizer) removed?
To facilitate deformation. However, water must be removed to set the product but also for microbial purposes and can be performed in two ways. Slow removal, which leaves original structure (spaghetti) and fast removal which leads to a porous structure (crisps).
Why is CO2 a good alternative to commonly used plasticizers?
Because it can evaporate at low temperature and thus is suitable for heat sensitive products.
When is counterrotating and co-rotating used in double extruders?
Counterrotating is used for milder processes while co-rotating is used so that one screw cleans the other as they move in the same direction.
How is the throughput affected in single and double screws.
In single screws, throughput is determine on the screw speed and product properties while in double screws, more pressure will lead to more throughput.
Does the extruder influence the secondary and tertiary structure of proteins?
No, because very high pressure are required which are not reached inside an extruder.
It can be assumed that soy protein isolate consists of proteins only. This makes soy protein isolate mixed only with water an excellent raw material for a meat alternative. Is it true or false.
False. Soy protein isolate indeed only consists of proteins but is therefore not suitable to create the fibrous structure that is desired for meat replacers. A layered and fibrous structure is only created when soy protein isolate is mixed with wheat gluten or when soy protein concentrate is used that still consist polysaccharides.
