Gums and Stabilisers for the Food Industry 14

By Peter A. Williams, Glyn O. Phillips

The Royal Society of Chemistry

Copyright © 2008 The Royal Society of Chemistry
All rights reserved.
ISBN: 978-0-85404-461-0

Contents

The Food Hydrocolloids Trust Medal Lecture,
Giving nature a helping hand G.O. Phillips, NEWI, Wrexham, UK, 3,
1. Novel Hydrocolloid Functionality,
2. Sensory-Texture Relationships,
3. Hydrocolloid Emulsifiers,
4. Hydrocolloids and health,
5. Interactions in mixed hydrocolloid systems,
6. Innovative Applications,
7. Developments in Characterisation,
Subject Index, 578,

CHAPTER 1

GIVING NATURE A HELPING HAND

Glyn O. Phillips

Glyn O. Phillips Hydrocolloids Research Centre The North East Wales Institute, Plas Coch, Mold Road, Wrexham, LL1 1 2AW, Wales

1. INTRODUCTION

There is a considerable appeal for the general public in the concept of “natural” foods. The food producer, therefore, in the current health conscious climate makes every effort to equate “natural” with fitness and good living to promote a “green” image without those nasty chemicals. Into this category come the indigestible plant polysaccharides, which were included by Trowell in the definition of dietary fibre. Previously the term had been used to describe the remnants of plant components that are resistant to hydrolysis by human alimentary enzymes. The impending Codex definition of dietary fibre refers to edible carbohydrate polymers naturally occurring in the food as consumed, and carbohydrate polymers, which have been obtained from food raw material by physical, enzymatic or chemical means. The expectation is that these natural polymers would need to lead to a positive physiological effect, such as: decreased intestinal transit time and increase stools, bulk fermentable by colonic microflora, reduced blood total and/or LDL cholesterol levels or reduced post-prandial blood glucose and/or insulin levels. By association, therefore, food producers can imply that these natural polymers have healthy effects when eaten regularly.

I do not wish to cast any doubt about the beneficial effects of non-starch polysaccharides and indeed there is ample evidence of their effectiveness in promoting a healthy life style . These have undoubted advantages but there are problems to integrate them into industrial production, which demands constant quality and performance Natural polymers are never uniform or simple. Their functionality depends on more than one structural feature. Extraction processes alter the macro- and micro-structures and performance. Their most common feature is their variability which poses a big problem for both the producer and user of natural polysaccharides.

This paper draws attention to this variability in three natural polysaccharide systems: gum arabic, sugar beet pectin and gum Ghatti. The problem we have tried to solve is how can we remove this natural variability and secondly how can we enhance their performance using methods which would not involve the introduction of new chemical groups and so be acceptable to the food industry. In other words can we circumvent Nature and find ways of producing uniform/constant products and if possible with better specific functionalities?

2. GUM ARABIC (GUM ACACIA)

The current WHO/JECFA Specification (1998), which is internationally accepted and has also been approved by Codex Alimentarius (INS No. 414) is: Gum arabic is a dried exudate obtained from the stems and branches of Acacia Senegal (L.) Willdenow or Acacia seyal (fam. Leguminosae). For comparison it is noteworthy that the European Specification (E 414) is slightly broader (2003): Acacia gum is a dried exudation obtained from the stems and branches of natural strains of Acacia Senegal (L) Willdenow or closely related species of Acacia (family Leguminosae).

This paper deals with the gum arabic (A. Senegal (L.) Willd. var. Senegal). This exudate gum is a complex polysaccharide consisting of D-galactopyranose (~44 %), L-arabino- pyranose and furanose (~25 %), L-rhamnopyranose (14 %), D-glucuropyranosyl uronic acid (15.5 %) and 4-O-methyl -D-glucuropyranosyl uronic acid (1.5%). It also contains a small amount (~2 %) of protein as an integral part of the structure. The carbohydrate structure consists of a core of β-(1,3) -linked galactose units with extensive branching at the C6 position. The branches consist of D-galactose and L-arabinose and terminate with L-rhamnose and D-glucuronic acid. Randall et al. fractioned A. Senegal by hydrophobic affinity chromatography and showed that it consists of three components namely arabinogalactan (fraction 1, AG); arabinogalactan protein (fraction 2, AGP) and a glycoprotein (fraction 3, GP). Each fraction contains a range of different molecular weight components which are responsible for the polydispersity of the gum The AG fraction contains 88% of the total gum with small amounts of protein 0.35% which represents 20% of the total protein content, while the AGP fraction comprises 10 % of the total gum with 12 % protein which is 49.5 % of the total protein content. Finally the GP fraction contains 1.24 % of the total gum with 50 % protein, which represents 27 % of the total protein in the whole gum.

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