136

 

Handbook of Functional Lipids

 

differences in terms of functionality and sensory properties. Other networks, includ-
ing protein, polysaccharide, and ice, may also be present in foods. Each network
and the interactions between ingredients all contribute to the overall sensory impres-
sions of foods. This chapter will review the physical properties of lipids, including
melting, crystallization, phase behavior, polymorphism, microstructure, and rheol-
ogy, and the ways in which the physical properties of fats can be modified.

 

6.2 THE

 

 

 

PHYSICAL

 

 

 

PROPERTIES

 

 

 

OF

 

 

 

LIPIDS

6.2.1 T

 

HE

 

 

 

E

 

FFECTS

 

 

 

OF

 

 

 

C

 

OMPOSITION

 

Molecular composition lays the foundation for a fat’s physical character. Triacyl-
glycerols (TAGs) constitute the bulk of the lipid mass in natural fats and oils,
although minor lipids and other lipid-soluble components may also be present and
can impact on the behavior of fats and oils [1–3]. Considering the large number
of fatty acids (FAs) that exist in nature and the potential for positional variability
along the glycerol backbone, a wide range of TAGs is possible. For example, over
400 different FAs have been identified in milk fat [4]. Fatty acids may be saturated
or unsaturated, branched or linear, and short- or long-chained [5]. Saturated FA
chains tend to adopt a straight-chain configuration, with the long carbon chains
adopting an in-plane zig-zag pattern. In the case of unsaturated FAs, a bend occurs
at the position of the double bond and leads to a decrease in packing density.
Because of their closer packing, saturated FAs have higher melting temperatures
than their corresponding unsaturated FAs in the 

 

cis

 

 configuration. Geometric isom-

erism at sites of unsaturation allows for double bonds to exist in either the 

 

cis

 

 or

 

FIGURE 6.1

 

Levels of lipid structure that determine the rheological properties and texture

of fats and fat-based foods.

Crystal Clusters

Heat, mass,

momentum transfer

Heat, mass,

momentum transfer

Heat, mass,

momentum transfer

Fat

Macroscopic World

>0.2 mm

Crystal Network

Microstructure

0.25–200 

µm

Solid Fat Content

Crystals

Polymorphism

Nanostructure

0.4–250 nm

Molecular Structure

Triacylglycerol Molecules

Rheology

Mechanical Strength

Sensory Impressions

 

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