POLYMORPHISM

Polymorphism

The occurrence of several different crystal forms for a same compound.

Packing Types of Fatty Acids and Position

Fatty Acid Crystal Structure

Cross-Sectional Structures of Triglycerides

Alpha

Beta Prime Beta

Freedom of molecular motion

Hexagonal

Triclinic

Orthorhombic

a

b

c

b c

c

b a

a 120º

Crystal forms

Space Arrangements of Triglyceride Crystals

11

22

33

Tuning fork form Chair form

Double Chain Length Structures of Triglycerides

Alpha Beta-Prime Beta (Vertical tuning fork) (Tilted tuning fork) (Stacked chair)

D

DD

Transformation of Crystal Structures

Simple

Collapse

Cataclysmic

Chain shift

Types of Fatty Acids and Positions for Double Chain Length

Molecular Arrangement in Trilaurin Lattice

Triple Chain Length Structures of Triglycerides

D

D D

Alpha Beta-Prime Beta (Vertical tuning fork) (Tilted tuning fork) (Stacked chair)

Types of Fatty Acids and Positions for Triple Chain Length

sin

= 4

3.76

Å

63º38’

c =

48.

84 Å

63º38’

b = 7.38 Å

a = 5.54 Å

Unit Cell of Stearic Acid

= COOH

= CH3

Crystal Structure of Oleic Acid

Analytical Methods for Polymorphism Study

1. X-ray diffraction analyses

2. Microscopic analyses

3. IR spectroscopic analyses

4. Thermal analyses

Characteristics of Triglygeride Polymorphs Alpha Beta-Prime Beta

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X-ray Diffraction Analyses

Hexagonal Orthorhombic Triclinic

Tuning fork Tuning fork Chair form

Acyl groups oriented Acyl groups are tilted Acyl groups are tiltedat 90 to the plane of 68-70 from plane of about 59 from thethe glyceryl group the glyceryl group plane of the glyceryl

groups

Vertical chain Tilted chain Tilted chainorientation orientation orientation

Longest long Intermediate Shortest longspacing long spacing spacing

Randomly ordered In-between Highly ordered

Most loosely packed More closely packed Most closely packed________________________________________________________________________

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Characteristics of Triglyceride Polymorphs

Alpha Beta-Prime Beta

Microscopic Analyses

Platelet Fine needle Long needle

5 1 25-50

Infrared Spectroscopic Analyses

A singlet at 720 cm -1 A doublet at A singlet at 717 cm -1

719 and 727 cm-1

Characteristics of Triglyceride Polymorphs

Alpha Beta-Prime Beta

Thermal Analyses

Thermodynamically Thermodynamically Most stable formmost unstable unstable

Lowest melting point Intermediate melting Highest meltingpoint point

Color Analyses

Translucent In-between Opaque___________________________________________________________________

Dilatometric Curve of Tristearin Polymorphic Form

Spec

ific

vol

ume

Temperature C

Alpha

Beta

30 50 700.94

0.96

0.98

1.02

1.04

1.06

1.08

1.10

1.00

Formation of Triglyceride Polymorphs

Alpha Beta-Prime Beta

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Rapid cooling Slow cooling Very slow coolingof liquid fat of liquid fat of liquid fat

_ _ _ _ _ _ _ _ Polymorphic Polymorphictransformation of transformation ofthe alpha form beta-prime

Activation Energy of Crystal Nucleation

Factors for Different Crystals Formation

Tristearin

Melt

Drop into dry ice pieces

Solid

Room temperature for 2 weeks

Heat

Heat

Heat

Heat

Heat

Melt at 73 C

Melts at 55 C and Resolidification

Melts at 64 C

Melt at 73 C

and Resolidification

APPLICATION OF POLYMORPHISM IN FOODS

Crystal Form Preference of Oils

Beta-type Beta-Prime Type

Coconut oil Cottonseed oil

Corn oil Herring oil

Olive oil Menhaden oil

Lard Milk fat

Palm kernel oil Palm oil

Application of Polymorphism in Foods

The incorporation of air, plasticity and consistency, and solid-liquid ratio are important characteristics of shortenings.

These physical characteristics in turn depend upon the polymorphic forms of the fats used and the methods of preparation.

Plasticity and consistency, as well as solid-liquid ratio, depends on the melting range, proper tempering is required to form the mixed crystals required for a broad melting range.

Shortening

1. Incorporated Air

Beta-prime crystals large amount of small air bubblesBeta-crystals small amount of large air bubbles

Beta-Prime Crystal ShorteningSmall crystalsWhiter, creamier, more tender, smoother textureUniform and glossy texture

Beta-Crystal ShorteningLarge clustered crystalsA waxy or grainy texture

Beta-prime crystal shortening helps the incorporation of an abundant quantity of small air bubbles in batters for good volume,

texture and tenderness of baked goods.

Natural lard (palmitic acid at 2 position is 64%) -crystal (OPS)

Rearranged lard (palmitic acid at 2 position is 24%) ’crystal (POS)

Lard conversion methods from beta to beta-prime

Interesterification Interesterification and hydrogenation Winterization (destearinization) Addition of cottonseed oil and/or tallow flakes

(beta- prime)

2. Plasticity and Consistency

Plasticity is the changes in consistency as a function of temperature.

Consistency is the apparent hardness at a temperature

Margarine

Spreadability

Plasticity

Water-in-Oil Emulsion:

Scraped surface heat exchanger Partial solidification Crystallizer Crystallization to have desired plastic

properties

Blend of soybean oil () and hydrogenated cottonseed oil (prime) for margarine

Confectionary Fat (Enrobing Fat)

Cocoa Butter – Short melting range at mouth temperature

Melting range of confectionary fat:Fatty acid compositionProper crystallization

Cocoa Butter: 80% of cocoa butter is disaturated triglyceride.

SOS 20%POS 55%POP 5%

Beta-prime beta form Chocolate “bloom” – white spots and dull surface appearance

Small crystal structure a good glossy textureBeta Large clustered crystal structure

POS determines characteristic cocoa butter texture

POS: Alpha form 17.0CBeta-prime form 27.0C

Beta form 35.5C

Tempering

A process which permits transformation to the

proper polymorphic form.

During crystallization, the heat of transformation

must be removed to avoid melting and a later

conversion into large beta crystal.

Melting Points of Triglycerides vs. Chain Length

Fatty Acid Chain Length