These are flashcards an notes made by students on topics like 'crystals', 'fructose' and 'additives', originating from:

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- Wageningen University
ISBN-13 9990002019708
665 Flashcards & Notes
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Study Cards on crystals, fructose, additives

What limits the heat transfer in a plate freezer, and what in a blast freezer?
Plate --> the heat transfer in the plates (outside the product) is limiting (linear line)
Blast --> heat transfer limitation in the product itself (exponential line)
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Give an advantage and disadvantage of both plate freezers and blast freezers?
  • Plate freezer
    • Allow fast cooling, fast freezing
    • Only for plate-shaped products
  • Blast freezer
    • More freedom of shape
    • Slowly freezing, possibly not all products experience same conditions
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What are 2 structural differences between fast and slow frozen meat?
  1. In slowly frozen meat, cells are loose from each other, because crystals are formed in between the cells (intracellular). In fast frozen meat, no such large spaces between cells can be observed.
  2. In slowly frozen meat, cells have collapsed and are dense. In fast frozen meat, there are holes visible where ice has sublimated (intracellular ice formation). Upon thawing these cells may quickly gain their original shape.
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If you store crystalline sugar in an open vessel it will start to form clumps. Explain the formation of these clumps:
Sintering: the moisture from the environment adsorbs on the surface of the crystals. The sugar molecules there become mobile; some dissolve and can then move towards the contact points between sugar crystals. These contact points then form a neck (formed of a very concentrated sugar solution) that becomes stronger with time, and a clump forms.
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If you store crystalline sugar in an open vessel it will start to form clumps. Why is this clumping more pronounced with smaller crystals of sugar?
  • More necks and more contact points per m3, stronger network may form
  • Driving force for sintering is the change in free energy from the decrease in surface area. With smaller crystals, this driving force is higher.
  • The typical path that sugar molecules have to move towards a contact point is smaller, so this process is faster and thus in a given time there is more sugar transport towards the contact points.
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If you store crystalline sugar in an open vessel it will start to form clumps. Why do you not see this clumping so strongly with salt?
In principle, the effect will also be there with salt crystals.

  • A concentrated sugar solution is very viscous, and this concentrated solution will form strong necks between the sugar crystals.
  • A salt solution is not so viscous and the formed bridges will be less strong. Any clumped salt crystals can break up again once you spoon it.
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In the read it is mentioned that the coating on sugar candies is polycrystalline, with the small crystals fused through sintering. However, a glassy coating would perhaps have better barrier properties. Why is this coating not glassy?
The substrate on which the coating is applied, is highly crystalline. Any coating by a concentrated sugar solution will crystallise instantly, because nuclei are present on the surface of the substrate.
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An ice cream manufacturer has been experimenting with different additives. They found that if you add a small sugar such as fructose to the ice cream, that the ice remains more creamy and can be spooned, even when it is deep frozen. Why is this?
Small molecules, such as fructose, are efficient at depressing the freezing point. The effect of adding fructose to the ice cream is therefore that less ice will be formed. The ice cream has thus a more creamy and soft texture.
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An ice cream manufacturer has been experimenting with different additives. With fructose added, the ice crystals under ripening over time, even when it remains frozen to low temperatures. Why is this?
Because of the soft texture (even at low temperatures), molecules can migrate more easily within the ice cream. This makes it easier for disproportionation to occur, i.e. Migration of water molecules from small ice crystals (less stable) and recrystallisation on larger ice crystals.
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An ice cream manufacturer has been experimenting with different additives. If not fructose, but maltodextrin with a higher Mw is used, then the ice crystal size is much more stable over time. Why is this?
Maltodextrin has a higher Mw compared to fructose, for the same added mass, maltodextrin will be less efficient at depressing the freezing point, meaning that more ice will form. This accounts for a harder, more solid texture of ice cream, which also helps limiting molecular diffusion and hence disproportionation of ice crystals.
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An ice cream manufacturer has been experimenting with different additives. What is a disadvantage of using maltodextrin instead of fructose, with respect to sensory properties?
For the same added mass, maltodextrin will bring a less sweet taste compared to fructose. Therefore, the manufacturer will have to compensate for this, for example by adding an artificial sweetener.
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