Phase transitions

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Phase transitions

• Phase diagrams
• physical state vs T, P, V at equilibrium
• State diagrams
• simplified phase diagrams
• concentration vs T for equilibrium and
  nonequilibrium states
• time-dependent transitions
• Used in food formulation and design, allow
  evaluation of effects of food composition and
  water content on the physical state and
  physicochemical properties during processing and
  storage

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amorphous -gt rubbery -gt solution change in
specific heat maximum ice formation Tg lt T lt
Tm maximum freeeze concentration stability
related to the temperature difference between the
storage T and Tg. Cg (80)
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Crystallization
water sorption -gt crystallization -gt release of
sorbed water water plasticization and depression
of Tg to below ambient T responsible for
crystallization of amorphous sugars increased
mobility, free volume, decreased viscosity,
enhanced diffusion start at Tg, rate depends on
T-Tg
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At Tg change in enthalpy
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Heat capacity
At Tg Discontinuity in Heat capacity Thermal
expansion coefficient Viscosity Dielectric
coefficient
Tg
Tm
T