Chemical and Functional Properties of Food Saccharides

12
CONTENTS
© 2004 by CRC Press LLC
12.1 Introduction
12.2 Pectin Structure
12.3 Extraction of Pectins
12.4 Pectin Modification
12.5 Pectin Conformations
12.6 Pectin Networks
12.7 Concluding Remarks
References
12.1 INTRODUCTION
Pectic Polysaccharides
Alistair J. MacDougall and Stephen G. Ring
In this chapter, we examine the relationship among the structure of pectic polysaccharides,
their physical chemistry, and functional behavior relevant to food use.
Pectins are found in the primary cell wall of higher plants 1–3 where they have a range
of functions, including contributing to the mechanical properties of the cell wall and
its hydration characteristics and acting as a barrier to the invasion of pathogens.
Pectin structure shows variation with botanical origin, cell wall type, and cell wall
development. Extracted pectins find use in the food industry as gelling, thickening,
and film-forming agents. Commercially useful pectins come from a relatively limited
range of materials such as apple pulp or citrus peel. It is inevitable that the extraction
procedure modifies the polysaccharide to some extent, and it may be further modified,
after extraction, by chemical or enzymatic means. Studies on pectin may have
a number of motivations, including trying to explain its role in the plant cell wall
or understanding its behavior as a food ingredient. Cell wall studies often focus on
the complexity of pectin structure and its variation with plant type and cell development.
Food-related studies are often more concerned with the functional behavior
of extracted polysaccharides of somewhat simpler structure. In this chapter, we draw
on literature from both areas, as both are relevant to understanding the relationship
between pectin structure and its functionality. The functionality that forms the focus
of this chapter is the contribution of pectic polysaccharides to mechanical properties
of materials.
A difficulty with establishing structure–function relationships for pectic polysaccharides
is the potential complexity of structure. To put the structural information