Chapter 16
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Potassium Bromate in Bakery Products: Food Technology, Toxicological Concerns, and Analytical Methodology Gregory W. Diachenko and Charles R. Warner Division of Product Manufacture and Use, U.S. Food and Drug Administration, Washington, DC 20204
Potassium bromate, which has been used since 1916 as a dough conditioner, has been found, in some circumstances, to leave bromate residues in retail bakery products. Studies published in 1983 established potassium bromate as an animal carcinogen. Over the past decade, improvements in analytical methodology have made it possible to detect these residues at levels of 5 µg/kg (ppb). Research within laboratories of the baking industry has established that reducing the amount of added potassium bromate, maintaining higher baking temperatures, and using ferrous salts as the nutritive iron supplement will significantly reduce or eliminate bromate residues. FDA surveys have revealed progress towards the goal of eliminating residues; however, more work is required.
This paper will review the use of potassium bromate in baked goods with emphasis on the regulatory responsibilities of the Food and Drug Administration (FDA), the toxicological concerns regarding potassium
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U.S. government work. Published 2002 American Chemical Society
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219 bromate, the recent developments in analytical methodology that have revealed the presence of bromate residues in finished baked products, and the research program carried out by the baking industry on baking practices that will minimize bromate residues. The results of a mini survey of baked products from commercial outlets within the Washington DC area at two different times will be presented to gauge the progress by the industry. In addition, preliminary exposure data and risk estimates are presented. Future activities by both the baking industry and the Food and Drug Administration will have a profound effect on whether or not potassium bromate will continue to be permitted in baking operations.
The Need for Regulatory Action Potassium bromate and calcium bromate have been used as dough conditioners since 1916 (1). They are additives identified in FDA's food standards for bread, dough, and flour and can be added to the flour or dough in amounts up to 75 ppm (2). In 1982 and 1983 Kurokawa et al. (3,4) published the results of animal tests that demonstrated that potassium bromate, administered in the drinking water, causes renal cancer in rats. More recently Wolf et al. (5) have reported that potassium bromate is a rodent carcinogen and a nephro- and neurotoxicant in humans. However, it was the combination of the initial report by Kurokawa (3) and the development of analytical methods that revealed the presence of residues of bromate in finished baked goods that stimulated regulatory concern in many countries. In 1989, the United Kingdom (UK) banned potassium bromate uses as a dough conditioner in bakery products (6). As a result of the demonstrated carcinogenicity, the findings of bromate residues in retail bakery goods and the regulatory action by the UK, the FDA met with the baking industry in 1991 and requested that they begin phasing out the use of potassium bromate. The industry has studied the optimization of baking parameters to reduce bromate residues (7) and investigated a number of alternative dough conditioners such as potassium iodate, ascorbic acid and azodicarbonamide (8). In addition, analytical methods that were needed to provide the data to accurately assess the prevalence of bromate residues and to monitor the progress of food technological studies, have been developed in industry laboratories. These efforts have yielded data which the industry hopes will convince the FDA that there is no need to ban the use of potassium bromate as was done in the UK and Canada (6,9). Analytical chemistry has played a very important role in the FDA's deliberations.
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Analytical Methodology The evolution of the analytical methodology over the past decade has been very interesting. The methods that initially revealed the presence of bromate residues were based upon the bromate oxidation of bromide to bromine that added across the double bond in styrene to yield a bromoalkyl side chain on benzene that was analyzed by gas chromatography with electron capture detection (10J1). While these methods provided valuable information in the early stages of investigations on potassium bromate residues, an HPLC method that was developed by industry has proven to be the current method-of-choice (22). This method, which was published in 1997 utilizes an ion pairing reverse phase chromatographic method with a post-column derivatization, can be used to detect residues as low as 5 ng/g. This is far lower than previous methodology (10) that was used in the U K to reveal the presence of potassium bromate residues in bakery goods back in the late 80's. Himata et al. (13) successfully completed a rigorous method trial with the FDA laboratory as the peer laboratory. Blind samples with potassium bromate fortifications ranging from 10 ppb to 52 ppb in white bread; multigrain bread and coffee cake were submitted to the peer laboratory. The results were satisfactory and the AOAC International has awarded the method official Peer-Verified® status (13). To achieve a limit of detection (LOD) of ca. 5 ppb the procedure incorporates multiple steps that begin with extracting 10 grams of bread with 50 ml of water in a blender system. This aqueous extract is passed through a 500 mg C-18 solid phase extractor (SPE) to remove lipophilic co-extractives. The chloride, which is typically present in the aqueous extract at concentrations approximately five to six orders of magnitude greater than the concentration of bromate, is removed by passing the extract through a SCX column with an ion exchange capacity of 2.0-2.5 meq/cartridge in the silver ion form. The silver chloride precipitate is removed by filtration. The aqueous extract, which at this stage is essentially water-clear, is subjected to ultrafiltration to remove proteins and polysaccharide extractives with molecular weights in excess of 10K daltons. Some silver ion, which will cause deterioration of the HPLC column, inevitably leaches into the aqueous solution; therefore, further treatment of the aqueous extract with a SCX column in the sodium form is required to remove these traces of soluble silver ions. The extract is ready for HPLC analysis with a 4.6 mm χ 250 mm Zorbax SB-C18 column with mobile phase consisting of 10% methanol in an aqueous solution of 0.05 M tetrabutylammonium acetate at ca. pH6. As previously described for water analysis (14) the bromate in the eluent is detected spectrometrically at 450 nm after a post-column reaction with acidified o-dianisidine. A flow chart of this methodology is shown in Figure 1. The method recoveries of bromate, that was added to unbromated bread, range from about 73 ±11.5% at 5 ng/g to 86.5±5.1% at 100 ng/g (13). The ονα-all mean recovery was 83%±7.6% with a relative standard deviation of 9.6%. This methodology was used by the baking industry to evaluate processing
Figure 1. Analytical Flow-Chart (reproduced with permission from reference 12).
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222 changes that might be implemented to control or, preferably, eliminate bromate residues in bakery products.
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Baking Practices that Reduce or Eliminate Bromate Residues Yamazaki Bakery of Tokyo, Japan and other members of the baking industry have studied readily identifiable parameters that could be controlled to eliminate or at least reduce potassium bromate residues in the final baked products to non-detectable levels, i.e., less than 3 to 6 ppb (7). Thewlis noted that dough seems to have a finite level of reductants and potassium bromate added above 75 ppm leads to very high residues (15). It was found that reducing the added potassium bromate to 25 ppm for loaf bread resulted in elimination of detectable bromate residues (13). To have the same success with rolls and buns it was necessary to reduce the amount of added potassium bromate to 15 ppm because, in contrast to loaves of bread, the internal temperatures of rolls and buns do not reach full oven temperatures. Industry studies have shown that higher baking temperatures effectively reduce bromate residues. The key manufacturing parameters are summarized in Table 1(7).
Table I. Processing Changes to Control Bromate Residues in Bakery Products • • • • • • •
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