Chemistry

In 1980 the Joint Expert Committee on Food Additives (JECFA) of the Food and Agriculture Organization (FAO)/ World Health Organization (WHO) recommended that further information on the chemical properties of caramel be obtained to establish a suitable classification and specification system. This reaction is common to a number of natural extracts and also to some manufactured colorants. For example, with the colorants from grapes, no manufacturer has attempted to provide a chemical profile of the components of the extract. This is understandable in view of the complexity of the chemical profile. A somewhat similar situation occurs with a synthesized product such as FD&C Yellow No. 5. When it was approved for food use in 1916, the manufacturers wanted to produce as pure a product as possible. The impurities they had to cope with were un-reacted ingredients and about three compounds produced by side reactions. In the usual process of chemical synthesis, the desired reaction does not normally go to 100% completion with no side reactions, and it is the job of the manufacturer to remove the unwanted by-products. But the increasing sophistication of analytical procedures that can routinely detect one part per billion, or even as low as one molecule, has allowed researchers to detect more impurities. Today, FD&C Yellow No. 5 has been shown to have as many as 17 components present, some in exceedingly low concentrations (2). The situation with other FD&C colorants is probably similar. The same situation exists with synthetic /^-carotene. Modern analytical instrumentation has made it possible to identify the impurities in chemicals produced with rigid process control as illustrated with FD&C Yellow No. 5 and /j-carotene. The situation with caramel and colorants produced from grapes is different in that it is not possible to specify in detail the structures of all the compounds present.

The question that arises with knowledge of the impurities is, What do they mean from a safety point of view? It also emphasizes that the chemical profile of a given additive in routine manufacture be the same as that in the batches used for toxicology studies. It is economically unfeasible to remove all impurities in food additives; thus, some form of risk assessment is unavoidable. Fortunately all four products mentioned earlier have been given a clean bill of health.

The JECFA wanted data on caramel for the reasons just described. The International Technical Caramel Committee (ITCA) undertook an extensive research program to provide this information. This resulted in the grouping of the caramel formulations into four classes depending on the net ionic charge and the presence of reactants.

Class Charge

Reactants

I — No ammonium or sulfite compounds

II — Sulfite compounds

III + Ammonium compounds

IV + Both sulfite and and ammonium compounds that moves up or down depending on the concentration. The slope of the line will change according to the hue of the solution. This makes it possible to determine two col-orimetric indices, the Hue Index and the Tinctorial Power, from two simple absorbency measurements. The Hue Index is:

where 0.51 is the absorbency at 0.51 microns, and 0.61 is the absorbency at 0.51 microns. The Tinctorial Power is:

AQ.56 cb where 0.56 is the absorbency at 0.565 microns, c is the concentration (g/L), and b is the cell thickness (cm). Both the Hue Index and the Tinctorial Power should reflect the visual appearance over the whole visual spectrum. The preceding equations are reproduced as they appeared in the original publication, but today the term nanometers would be used instead of microns.

One of the major considerations in this research was the safety aspect of the caramel colorants. This program resulted in 11 papers being published in the same 1992 Vol. 30 issue of the journal Food Chemical Toxicology, and 7 of them were on toxicology. Caramel was given a clean bill of health and the JECFA assigned an Acceptable Daily Intake (ADI) of 0 to 200 mg/kg/day.

It is obvious that heating carbohydrates in the presence of a reactant would produce a wide range of chemical compounds. Complete characterization is not feasible; thus, a series of profiles were developed using 157 samples from 11 manufacturers in seven countries. Since Caramel Color IV accounts for 70% of all caramel colors manufactured, it was chosen as a prototype for this ambitious undertaking. The profiles developed were HPLC screening, size fractionation by ultrafiltration to provide low molecular weight, intermediate molecular weight and high molecular weight groupings, and subfractionation by cellulose chromatography. Each fraction was examined by a series of sophisticated analytical approaches. These data combined with 11 physical characteristics confirmed that the four groupings provided real and reproducible classifications (3).

Color is a physical parameter of interest to the formu-lator. It could, of course, be specified in any of the conventional tristimulus color scales, but it is possible to specify the color accurately by a simpler method (4). The color of caramel is due to a large number of chemical chromo-phores; thus, different formulations do not show markedly different spectral curves and do not change shape with concentration. Curves of different concentrations can be superimposed on each other by plotting log absorbency against concentration. This is the "optical signature" of a colorant. When log absorbency is plotted against wavelength for caramel solutions, the result is a straight line

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