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Food Processing Technology > 7. Crystallization > Flashcards

7. Crystallization Flashcards

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1
Q

What is crystallization

A

the process by which solid crystals of a solute are formed from a solution

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2
Q

The liquid phase remaining after the formation of crystals is called

A

mother liquor

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3
Q

purpose of crystallization in the food industry

A
  1. recovery of crystalline products (eg sugar, glucose, lactose, citric acid)
  2. removal of undesirable components (eg oils, wax, other high melting point components)
  3. modification of certain food products to obtain desirable structure
  4. confectionery (crystallization of fat in chocolate and margarine, candying of fruits)
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4
Q

undesirable changes in food due to crystallization

A
  1. crystallization of sugar in jams and preserves
  2. crystallization of lactose in ice cream, causing “sandiness”
  3. recrystallization of cocoa butter in chocolate in the form of white crystals (bloom) on the surface
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5
Q

what can be used to trigger crystallization

A

crystal seeds/seed blooms

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6
Q

conditions for crystallization to occur

A

supersaturated solutions

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7
Q

how to bring a solution to supersaturation

A
  • removal of solvent by evaporation, membrane separation or freeze concentratiob
  • cooling of solution
  • changing pH or ionic strength
  • addition of second solvent miscible with solution, to reduce solubilty of solute
  • chemical complexation/precipitation
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8
Q

what is the main methods of crystallization in the food industry

A
  1. removal of solvent by evaporation (concentration)
  2. cooling
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9
Q

two mechanism of the crystallization process

A
  1. nucleation
  2. crystal growth
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10
Q

what is nucleation

A
  • formation of crystalline lattice structure
  • solute molecules dispersed in solvent start to gather into clusters
  • the stable clusters constitute the nuclei, which is stable if the clusters reach a critical size
  • if clusters not stable, they dissolve
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11
Q

what is crystal growth

A
  • formation and continuous addition of crystals until equilibrium stage of solution is reached
  • crystal growth is subsequent growth of nuclei that have achieved critical cluster size
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12
Q

what binds crystals of organic compounds

A

weak forces such as van der waals and weak dipoles

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13
Q

what is polymorphism

A

crystallization of organic comounds in a number of different forms

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14
Q

characteristics of supersaturation

A
  • not thermodynamically stable
  • is temperature dependednt
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15
Q

equation for degree of supersaturation/supersaturation ratio

A

β = C/Cs

C = actual concentration (kg solute/kg solvent)
Cs = saturation concentration

super saturated β >1
saturated β = 1
not saturated β<1

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16
Q

characteristcis of meta stable zone

A
  • crystallization occur if propagated (eg addition of crystal seed)
  • slow growth
  • limited number of crystaks
17
Q

characteristics of labile zone

A

spontaneous nucleation

18
Q

what is magma

A

mixture of crystals and mother liquor, contains crystals with different sizes

19
Q

what is ostwald ripening

A

when very small crystals are at equilibrium with supersaturated mother liquor, causing dissolution of small crystals and growth of large ones

20
Q

undesirable effect of ostwald ripening in ice cream

A
  • changes in texture during storage, destruction of creamy texture
  • fluctuations in storage temperature cause preferential melting of small ice crystals, followed by further growth of larger crystals
21
Q

crystallizers are also called…

A

pans

22
Q

types of pans operation mechanisms

A
  1. batch
  2. contunuous
  3. vacuum/atmospheric
23
Q

what pans are used for large scale vs small scale crystallization

A

large: continuous
small: batch

24
Q

why is agitation important

A

sufficiently vigorous agitation helps facilitate mass transfer and good mixing

25
Q

how to avoid inversion and caramelization in sugar syrup making

A

application of vacuum to lower the boiling temperature

26
Q

principles of crystallization of sucrose

A
  • final step in recovery of sugar from sugar cane or sugar beet
  • requires precise control, skill and experience
  • controlled parameters: temp, pressure, concentration (brix), purity, crysta;/liqui ratio, crystal mean size and shape and flow rates
  • monitored by digital image processing
27
Q

mechanism of crystallization of sucrose in large scale production

A
  1. preparation of seed done in batch process
  2. use both batch and continuous process (mixed process)
28
Q

how can multistage crystallization be beneficial

A
  • as more sugar gets crystallized, the consistency increases; because crystal content increases mixing becomes more difficult, flow channels can get blocked, and crystal rupture due to friction can occur
  • decrease in purity of mother liquor interferes with crystal growth

with multistage fermentation, first crystals separated and mother liquor send to next stage for further concentrating

Food Processing Technology (6 decks)

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