CJW-+Chapter+4


 * Phase/ State Transitions in Foods **
 * Refer to changes occurring in the phase and state of materials
 * Common phase and state transitions include melting and crystallization, protein denaturation, starch gelatinization, retrogradation etc

Food materials can be classified into 4 physico-chemical states that characterize movement of water and other solvents in food. They are: It can be redefined in terms of ingredient mobility. Pure ingredient will undergo gradual time-dependent phase changes from liquid to crystalline and  ↑ amorphous forms as temperatures drop and/or conc. ↑ until, they transform themselves into an amorphous glassy state. 
 * Physical states of food **
 * Crystalline
 * Liquid
 * Amorphous rubber
 * Amorphous glass
 * In a crystal, molecules are immobilized in crystalline structures
 * <span style="font-family: 'Times New Roman',serif; font-size: 12pt;">In the amorphous rubbery state, molecules remain mobile but ↑constraint in movement as conc. ↑.
 * <span style="font-family: 'Times New Roman',serif; font-size: 12pt;">In the glassy state, the viscosity is very high that the movement of molecules ceased.
 * <span style="font-family: 'Times New Roman',serif; font-size: 12pt;">Glass transition temperature (Tᵍ) **
 * <span style="font-family: 'Times New Roman',serif; font-size: 12pt;">The condition where the material effects a transformation to the glassy state
 * <span style="font-family: 'Times New Roman',serif; font-size: 12pt;">Refers to change in physical state of amorphous materials between the solid and the supercooled liquid or rubbery states

- <span style="font-family: 'Times New Roman',serif; font-size: 12pt;">removing the solvent/dispersing medium or - <span style="font-family: 'Times New Roman',serif; font-size: 12pt;">from the melt by cooling or  - <span style="font-family: 'Times New Roman',serif; font-size: 12pt;">by rapid supercooling.
 * <span style="font-family: 'Times New Roman',serif; font-size: 12pt;">An amorphous food **is form at non-equilibrium conditions either by

<span style="font-family: 'Times New Roman',serif; font-size: 12pt;">They are not at thermodynamic equilibrium therefore is unstable relative to the crystalline form. <span style="font-family: 'Times New Roman',serif; font-size: 12pt;">-behaves as an extremely viscous glass. In this state, molecular movement Is highly limited. <span style="font-family: 'Times New Roman',serif; font-size: 12pt;">-the glass is in a metastable state, and tends to convert to crystal with a rate depending upon temperature and moisture content. <span style="font-family: 'Times New Roman',serif;"> <span style="color: #7030a0; font-family: 'Times New Roman',serif; font-size: 12pt; line-height: 0px; overflow-x: hidden; overflow-y: hidden;"> <span style="font-family: 'Times New Roman',serif; font-size: 12pt;"> <span style="font-family: 'Times New Roman',serif; font-size: 12pt;">Rapidly cooling a highly concentrated solution causes solidification into the glassy state. <span style="font-family: 'Times New Roman',serif; font-size: 12pt;">By rapid cooling, the sucrose molecules do not have sufficient time to rearrange into crystal lattice structure. <span style="font-family: 'Times New Roman',serif; font-size: 12pt;">The glass transition occurs when the viscosity is so great that no liquid characteristics are observed over the shelf life of the product. <span style="font-family: 'Times New Roman',serif; font-size: 12pt;">Important that the amount and type of corn syrup present determine the characteristics <span style="font-family: 'Times New Roman',serif; font-size: 12pt;">such as sweetness, mouthfeel, hygro <span style="font-family: 'Times New Roman',serif; font-size: 16px; line-height: 24px;">scopicity, and the likelihood of crystallization during storage
 * <span style="color: #7030a0; font-family: 'Times New Roman',serif; font-size: 12pt;">Example 1: Production of hard candy from concentrated sugar syrup **

<span style="color: #7030a0; font-family: 'Times New Roman',serif; font-size: 12pt; line-height: 0px; overflow-x: hidden; overflow-y: hidden;"> <span style="color: #7030a0; font-family: 'Times New Roman',serif; font-size: 14pt;"> <span style="font-family: 'Times New Roman',serif; font-size: 12pt;">Rapidly dry a solution. Small droplets are formed in atomizer and exposed directly to warm, dry air, <span style="font-family: 'Times New Roman',serif; font-size: 12pt;">they dries quickly and rapidly reaches the glass transition point. <span style="font-family: 'Times New Roman',serif; font-size: 12pt;">Importance: to avoid the lactose glass converts to the crystalline form which affects the physical characteristic <span style="font-family: 'Times New Roman',serif; font-size: 12pt;">e.g. the flowability of the powder.
 * <span style="color: #7030a0; font-family: 'Times New Roman',serif; font-size: 12pt;">Example 2: Spray drying **

<span style="color: #7030a0; font-family: 'Times New Roman',serif; font-size: 12pt; line-height: 0px; overflow-x: hidden; overflow-y: hidden;"> <span style="color: #7030a0; font-family: 'Times New Roman',serif; font-size: 14pt;"> <span style="font-family: 'Times New Roman',serif; font-size: 12pt;">Produce a glass from a melt of a material. Sucrose goes through several transitions but ends up as a glass. <span style="font-family: 'Times New Roman',serif; font-size: 12pt;">Crystalline sugar is melt in the spinner and the fluid melt forced out the small holes as the spinner rotates. <span style="font-family: 'Times New Roman',serif; font-size: 12pt;">When the sugar melts contact with air, they cool rapidly and set into a glassy state.
 * <span style="color: #7030a0; font-family: 'Times New Roman',serif; font-size: 12pt;">Example 3: Cotton Candy **


 * <span style="font-family: 'Times New Roman',serif; font-size: 12pt;">Phase and State Diagram **

<span style="font-family: 'Times New Roman',serif; font-size: 12pt;">-used to describe relationship between the equilibrium states and temperature, pressure and volume of pure materials. <span style="font-family: 'Times New Roman',serif; font-size: 12pt;">-show that pressure –temperature dependence of various phases and equilibrium limes for two coexisting phases at equilibrium as 2D-diagram <span style="font-family: 'Times New Roman',serif; font-size: 12pt;">Show temperature-concentration relationship for both equilibrium and non-equilibrium states, as well as time dependent transformations. <span style="font-family: 'Times New Roman',serif; font-size: 12pt;">The glass transition curve can be overlaid on a phase diagram to indicate the regions of stability, metastaility and instability of food. <span style="font-family: 'Times New Roman',serif; font-size: 12pt;">May also show solubility as a function of temperature and information about the various time-dependent changes that due to the metastable of amorphous food solids.
 * <span style="color: red; font-family: 'Times New Roman',serif; font-size: 12pt;">Phase diagram ****<span style="font-family: 'Times New Roman',serif; font-size: 12pt;"> are **
 * <span style="color: red; font-family: 'Times New Roman',serif; font-size: 12pt;">State Diagram **

<span style="color: #000000; font-family: 'Times New Roman',serif; font-size: 12pt;">it may also affect the quality of confectinery products, coating and cookies.
 * <span style="font-family: 'Times New Roman',serif; font-size: 12pt;">Effects of Glass Transition on Physical state of foods **
 * <span style="color: #7030a0; font-family: 'Times New Roman',serif; font-size: 12pt;">Viscosity- **<span style="color: #000000; font-family: 'Times New Roman',serif; font-size: 12pt;">dramatic decrease in viscosity is observed above a critical water content or water activity that depresses the Tg to below ambient temperature
 * <span style="color: #7030a0; font-family: 'Times New Roman',serif; font-size: 12pt;">Stickiness- **<span style="color: #000000; font-family: 'Times New Roman',serif; font-size: 12pt;">food powder may become sticky with an increase in temperature or water content.
 * <span style="color: #7030a0; font-family: 'Times New Roman',serif; font-size: 12pt;">Crispness- **<span style="color: #000000; font-family: 'Times New Roman',serif; font-size: 12pt;"> low moisture food
 * <span style="color: #7030a0; font-family: 'Times New Roman',serif; font-size: 12pt;">Crystallization of amorphous sugar.- **<span style="color: #000000; font-family: 'Times New Roman',serif; font-size: 12pt;">lactose recrystallization in mild powders leads to increased free fat and flavour deterioration