Technical profile: Ascorbic acid as a bromate replacement

by Teresa Acklin
Share This:

   Contributed by suppliers, technical profiles feature new technology, products, specific applications or proprietary concepts. This material was prepared by Lutz Popper, research and development department, Muhlenchemie GmbH, Hamburg, Germany;and Klaus Losche, professor and head of Bremerhaven Institute of Food Technology and Bioprocessing, Bremerhaven, Germany.

    For many decades, bromate has been used in flour milling for bleaching and protein strengthening. In the 1950s, investigations were published indicating that a carcinogenic substance may be formed as a result of combining flour ingredients and bromate. Consequently, bromate has been banned in many countries.

   Early in the century, ascorbic acid, a commonly known anti-oxidant, showed surprising oxidative properties in dough. Early in the dough mixing process, it is converted into oxidized form, dehydro-ascorbic acid. Ascorbic acid's effects on dough protein, sulfhydryl and on oxidative gelation of protein-hemicellulose complex are almost similar to bromate, except they happen earlier in the process. Bromate is believed to have a somewhat stronger effect on dough mixing and proofing tolerance as well as on oven rise.

   Since the beginning of its industrial production, ascorbic acid has been used as vitamin C for human nutrition. Unfortunately, patent rights raised its price to a non-competitive level for flour treatment. When the patent rights ran out in 1967, the price of ascorbic acid fell, causing an increase in its use in flour processing.

   Some 20 years ago, hemicellulolytic enzymes, also known as pentosanases or xylanases, were found to strengthen the protein-hemicellulose complex responsible for dough structure. Since then, enzyme compositions combined with ascorbic acid are recommended as a replacement for bromate. Although enzymes probably would also interact positively with bromate, the reaction between enzymes and ascorbic acid yields better results than bromate. Until recently, the price of bromate has been about one-eighth that of ascorbic acid, but unfortunately, bromate's potential health risk is being ignored in some countries.

   Almost since the discovery of the function of oxidizing agents on dough structure, oxidative enzymes have been considered to contribute to dough strengthening. Many scientific investigations have proven the functionality of sulfhydryl oxidase and glucose oxidase. Some are protected by patents that date from 1952. These patents did not prevent flour or bread improver companies from using glucose oxidase in their formulations. Because glucose oxidase also occurs as secondary activity in many enzyme preparations, it had been used long before the patents were filed. Today, it is still being used, but it is masked within these preparations.

   Glucose oxidase is limited by its dependence on oxygen, which is stronger than that for ascorbic acid. Consequently, the effect of glucose oxidase is more pronounced in intensive kneading processes and is most active on the dough surface. Glucose oxidase, and all other enzymes, are only inactivated when heated, making it effective as long as oxygen is available and temperature is below approximately 70°C. Bromate and ascorbic acid are more or less consumed upon reaction with flour components. The results of glucose oxidase addition are not only a very high proofing tolerance, good loaf volume and comparatively fine grain and texture, but also tough, dry dough surfaces causing good machinability. The latter is a clear advantage over ascorbic acid and bromate, while within the dough, the effect is approximately the same as for ascorbic acid.

   Recently, a kneading process including aeration with air or oxygen enriched gas mixtures has been developed, having a very strong effect on ascorbic acid and especially on glucose oxidase function and glucose oxidase-ascorbic acid combinations. Since oxygen is not the limiting factor in this process, ascorbic acid and glucose oxidase addition can be reduced to a necessary minimum with similar performance.

   While 20 ppm to 80 ppm of ascorbic acid are necessary in combination with 200 SKB/kg flour and approximately 60 u/g xylanase (Somogy units) to replace 60 ppm to 80 ppm bromate, half of the ascorbic acid can be used when adding glucose oxidase, approximately 50 ppm or 80 u/kg flour. Ascorbic acid-glucose oxidase can be further reduced to approximately one-third when an oxygen/nitrogen mixture of 60% to 40% is added to the dough for three to five minutes at a flow rate of 90 liters/minute. The resulting dough is superior in most respects and similar to using DATEM bread improver.

   This concept is already being used by small and medium size bakeries. By promoting the use of ascorbic acid, glucose oxidase and other enzymes as bromate replacers, it may find wider distribution in the near future.