INTRODUCTION

This review deals with natural products which find use as colourants for foodstuffs or as dyes for textiles and other non-food materials including cosmetics.

The terminology employed for these products is not uniform in commerce or in the published literature and for the purpose of this review the following definitions are used:
 

natural colourants	natural products which are incorporated in foodstuffs to provide a specific colour in the final edible product;
natural dyes/dyestuffs	natural products which are used to impart a desired colour to non-food materials (textiles, wood, leather, etc.) by a process known as "dyeing";
natural pigments	the specific chemical compounds which are responsible for the visible colour in live plant parts.

(Other important terms used in the main text of this review are defined in the glossary.)

SCOPE AND PURPOSE OF THE REVIEW

The review focuses on natural colourants and dyestuffs which are obtained from trees, shrubs, other plant forms and insects present in forestry and agroforestry systems of the tropics and sub-tropics, i.e., non-wood forest products (NWFPs). In view of the enormous number of colourants and dyestuffs found in nature as NWFPs, an exhaustive coverage was not possible and the approach taken was to provide a representative selection of product types. Examples are given of those which enjoy a current major usage and of some others which were formerly important but have suffered from technological or socio-economic developments.

The main purpose of the review, therefore, is to provide information - through the selected examples - which will assist an appraisal of the future developmental opportunities or constraints for the product group. In order to furnish a wider perspective, the review also includes some examples of major natural colourants and dyestuffs which now are mainly produced in horticultural systems; both as an indicator of comparative market demand and production economics and since some are suitable for adaptation within agroforestry systems.

The review does not cover the subject of vegetable tannins because this group of natural products are employed primarily as preserving and softening agents for leather and natural fibres rather than as dyestuffs. Moreover, tannins are an extensive and complex subject area which deserve the attention of a separate review.

FORMAT OF THE REVIEW

The main sections of the review sequentially deal with:

(a) the major natural colourants and dyestuffs which enter
international trade;

Developmental prospects are considered in relation to the local and international markets since demand and competition are the deciding factors for the success of any new commercial venture. The ability to produce in itself is only one element in a developmental appraisal. Competition from synthetic alternatives in particular must be examined for the international market and it is frequently of considerable importance on local markets.

AN OVERVIEW OF THE GLOBAL MARKETPLACE: COMPETITION BETWEEN NATURAL AND SYNTHETIC PRODUCTS AND LEGISLATION ON FOOD COLOURANTS

Up to the latter part of the nineteenth century, the plant and animal kingdoms provided all the colouring materials for dyeing textiles, the preparation of cosmetics and paints, and for making foodstuffs more visually attractive. Cultivation of plants and rearing of animals or gathering the wild resource, together with processing and trading was of enormous socio-economic importance for many communities worldwide. This pattern commenced to change very rapidly following the discovery by chemists of means of synthesising dyestuffs. The initial impact was felt in the textiles sector and major natural dyes, such as indigo, lost most of their market by 1900. Progressively, a wider range of synthetic dyes was manufactured and these displaced many other natural materials in foods and cosmetics. The success achieved by synthetics resulted from a combination of factors: comparative cheapness, reliability of supply, consistency of quality and special quality attributes greater colour fastness with textiles and superior stability in food media.

A few natural dyes have retained a significant position in the textile sector owing to their unique qualities but it must be accepted that the dominance of synthetic dyes is irreversible in the global textile industry.

The food sector, however, is now experiencing a trend back towards natural colourants. This change has not been driven by the food industry but by consumers in developed countries who are concerned over possible health risks associated with synthetic food additives. The new situation presents welcome opportunities in the natural resource sector but also it must be appreciated that there are constraints which relate to legislation on food ingredients.

A discussion of the finer details of legislation on food colourants is not attempted here but interested readers may refer to the specialist texts listed in the bibliography. However, the main points may be summarised as follows. The range of colours of natural origin permitted for use in foods is not extensive in the three major markets, the European Community (which is a different and distinct legal entity to the European Union), USA and Japan; moreover, the three lists are not identical (see Tables 1 to 3). A naturally-derived colour may be a traditional food ingredient which is generally regarded as safe in one of these markets but it can be regarded as new in another. Today, "new" food colours are required by the regulatory authorities to undergo the identical stringent toxicological testing as new synthetics and this is a very expensive process. Some case examples in the European Community are presented in the following main section of this review. Finally, it should be noted that developments in food colour legislation are a continuing process and it is wise for both researchers and exporters to periodically gather an up-date on changes since these can profoundly influence markets.

^a Nature-identical forms only (i.e., synthetically produced material which is
chemically identical in all respects to the naturally occurring compound).