Pratice exams - 2011 open questions

7 important questions on Pratice exams - 2011 open questions

In area 4, the lactose in milk can crystallise, but this will not happen in practice. In area 5, the lactose will crystallise, but it will take a long time (more than a day), whereas In area 6, the lactose will crystallise very quickly. Explain these three observations.

The deeper we are located in the supersaturation area, the larger the driving force for crystallisation, and therefore the higher the crystallisation rate. However, it is likely that if we would go very close to the solid line on the right of area 6 (i.e., the glass transition line), the observed rate of crystallisation would decrease again, because the system would become very viscous.

After the evaporation step, the concentrated slurry is now atomised into a spray dryer with air at ambient pressure of 175 °C, in which the droplets quickly lose most of their moisture, and at the end have 97 weight% solids. The particles are now going into a fluidized bed, in which they are contacted with much cooler air, in which the particles dry towards 98.5 wt% solids.
Explain why this cool air is necessary. What would happen to the powder if the fluidized bed would be omitted?

If the temperature would not be decreased by the fluidized bed step, the product would not enter the glassy state, and there would be a risk that the powder particles would clump together.

Give two ways to increase the shelf life of the encapsulates, without adding new ingredients or imposing changes in the environment of storage conditions.

We could:
  1. reduce the oil volume fraction
  2. increase the size of the particles.
Both would lead to a thicker maltodextrin layer.

A manufacturer tries to develop a new meat alternative. Contrary to existing meat alternatives, this company aims at a fat containing product. Fat is used to improve the juiciness and the taste of the product. The final composition of the product is 20% fat, 16% protein, 10% carbohydrates and the rest is water. The protein used is not able to act as surfactant.
Describe the structure of the oil phase. Will this phase be a continuous or a dispersed phase and does oil contribute to the anisotropy of the final product?

Oil will be present as droplets, which are not elongated due to high interfacial tension.

Normally, those products are produced in a production unit consisting of one twin screw extruder combined with a slit die. The manufacture, however, is considering to replace the twin screw extruder with a single screw extruder.
Mention 1 advantage and 1 disadvantage of using a single screw extruder for this application. Consider the composition of the product. Explain your answer.

Advantage: it is cheaper
Disadvantage: more difficult to operate. Especially the presence of fat might lead to slip.

To make a good structure, the product has to be heated to 150°C. At this temperature, the proteins and carbohydrates undergo chemical transitions. Main effect on the carbohydrate phase is molecular breakdown. In other words, the chain length will become much shorter. Proteins can form additional covalent bonds (disulphide bridges)
How will the decreasing chain length of the carbohydrate influence the number and composition of the phases, which you described under question a. Explain your answer.

Decreasing molecular weight implies that phase separation occurs at higher carbohydrate concentration. This could lead merging of phase 1 and 2 into one single phase, though this is not necessary (depends on extent of breakdown and actual protein and carbohydrate concentration).

Test runs are performed on a labscale extruder with a slit die. The dimensions of the slit die used are 350*40*5 mm. The throughput is 15 kg per hour. The temperature of the product entering the die is 100°C. The temperature of the die is 10 °C. The characteristic time τ for heating (or cooling) the product in this die is 30 s.

Why is it necessary to use a cooling die in this application? If you think of more reasons, indicate then which reason you think is most important. Motivate the answer.

Die might influence structuring and solidification. Most likely solidification is most likely effect.

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