3. Physical Properties
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Do fats have a sharp melting point? why or why not?
No because fat is a complex mixture of TG that each has its own melting point
What is a broad melting range?
composite of individual melting points of all TG in a fat
• fat appears to be solid at room temp but in fact consist of oil trapped in a ___________ ____________ • there can be as little as 10% “solids” in a fat that still retains a ________ (solid or liquid) character
• crystalline matrix • solid
Why can fat have plasticity or spreadability?
because it is made up of a liquid in crystalline matrix
What are the forces that hold fat crystals together? (2) - forces can be broken by shear and reformed? –> hence gives fat ?
• van der Waals & hydrophobic bonds • yes! hence, gives flat plasticity
What is plasticity? IMPORTANT! - Plasticity is a function of what? (2)
• ability to be shaped or molded • function of the solid to liquid ratio, which in turn is a function of temperature
The plastic range of a fat is a function of (2?) VS solid fat content is a function of (1)
• a function of the FA composition of TG and distribution of FA on their glycerol backbones • SFC –> function of temperature
How can solid fat content be determined? (2) IMPORTANT!
• dilatometry • nuclear magnetic resonance (NMR) measurements
Dilatometry is a technique based on what?
• measurement of change in specific volume (inverse of density) per unit temperature • amount of shrinkage/expansion is measured
solid fat index vs solid fat content?
index –> determined by dilatometry content –> determined by NMR
What does it mean that fats have polymorphism?
• they are able to change from one crystal form into another (of the same product)
3 most common polymorphic forms
• alpha • beta prime • beta
How to determine FA crystal structure?
by crystallography
• Tuning fork form –> which 2 FA are parallel to each other/which one is pointing out? • Chair form: which 2 FA are on top of each other?
• 1 and 3 –> 2 is pointing out • 2 and 3
Stearic acid: what groups are facing each other to form a dimer? - is it angled?
• carboxylic group • angle at 63°
4 analytical methods for study of polymorphism?
• x-ray diffraction analyses (crystallography) • microscopic analyses • infrared spectroscopic analyses • thermal analyses
How to convert beta form to beta prime form for lard? (4 ways)
• interesterification • winterization (destearinization) • addition of cottonseed oil • addition of tallow flakes (beta prime)