Acrylamide is a colorless and odorless chemical compound that is commonly consumed in foods, such as bread and potato chips, among others. Acrylamide was once primarily known as an industrial chemical used as an intermediate for polyacrylamide production.
By Aline Chhun and John Husnik
Acrylamide is a colorless and odorless chemical compound that was propelled into the spotlight in 2002 when the Swedish National Food Administration and the University of Stockholm reported considerably high levels of this WHO Group 2A carcinogen in commonly consumed foods, such as bread and potato chips, among others. Prior to this discovery, acrylamide was known mainly as an industrial chemical used as an intermediate for polyacrylamide production.
Based on various laboratory studies, clear evidence on carcinogenic and genotoxic effects of acrylamide and its metabolite glycidamide have been established, although epidemiological studies of exposure through various foods have not been as clear. Review of all the data convinced numerous scientific committees and regulatory agencies worldwide that exposure to acrylamide by humans should be limited to the lowest possible level. In March, the European Chemical Agency added acrylamide to its list of high-concern substances. Acrylamide was added to the State of California’s Proposition 65 list of carcinogens in 1990.
The main source of acrylamide formation in food occurs when the amino acid asparagine and reducing sugars - such as glucose or fructose - are heated together above 120°C and are transformed into acrylamide. Since asparagine is the limiting precursor for acrylamide and is widely present in many different carbohydrate-rich foodstuffs - grains, potatoes, etc. - reducing its content in food products prior to heating would significantly reduce acrylamide levels.
Harnessing yeast’s natural ability to metabolize asparagine
Numerous approaches have been attempted to reduce acrylamide formation in food. However, no method has yet been accepted as the ideal solution, mainly because major drawbacks exist. The conditions that plague the technologies currently available range from cost, impact on the organoleptic properties (taste, color, odor and feel) of the food and/or ineffective acrylamide reduction under typical food production/processing conditions. Yeast presents a low-cost solution to the acrylamide problem.
Using the natural ability of baker’s yeast to metabolize asparagine, Functional Technologies Corp.’s Phyterra Yeast subsidiary developed bread yeast strains with enhanced asparagine degradation properties. Initial tests show that these proprietary strains can rapidly reduce asparagine in media and food matrices, thereby dramatically reducing acrylamide formation after heating.
Various Functional Technologies’ yeast strains were tested for their acrylamide-reducing (AR) capabilities. The strains were first screened in liquid media for their ability to take up asparagine from the test media. Equal cell numbers of each strain were inoculated into separate test tubes containing YEG (yeast extract, glucose) broth spiked with 0.5 g/L of asparagine. An “aliquot” was taken every hour, and asparagine concentration was determined using an enzymatic kit (Megazyme, K-ASNAM). Three of the AR strains showed enhanced asparagine degradation under these test conditions. In particular, one strain consumed asparagine to undetectable levels after four hours. In comparison, the commercial bread yeast strain reduced asparagine by only 11% in the same time period under the same test conditions.
After determining their ability to reduce asparagine in liquid media, the strains were tested in bread dough. Both the AR and commercial bread yeast strains were grown up simultaneously in two separate fermenters, and the cells were harvested the following day for dough and baking trials. Asparagine was added to the dough in order to monitor asparagine consumption using enzymatic analysis (as above).
99% reduction in asparagine levels
Once the AR yeast was mixed into the dough, it was noted that asparagine levels immediately began to decrease; in contrast, no noticeable decline in asparagine was measured using the control strain (data not shown). After the dough was formed, samples were taken at every 30-minute time point from the addition of yeast to be tested for asparagine concentration. This experiment was performed twice. After three hours, Functional Technologies’ AR strain reduced asparagine concentration in dough by 99.2%; conversely, the control strain reduced the asparagine by just 18.5%.
The dough from this experiment, which contained higher levels of asparagine, was also used to prepare a baked bread sample to determine the acrylamide concentration in the final bread product. Acrylamide results from this experiment reveal that the AR baker’s yeast strain produced bread with approximately 10 times less acrylamide than the control baker’s yeast (under the conditions tested). This result is consistent with the asparagine reduction found in the dough analysis.
Conclusions: No changes in bread texture, color, size or baking process
To reduce acrylamide in food, manufacturers face the challenge of changing their processes and/or product parameters without compromising the taste, texture and appearance of their products. In our latest bread trial, research chefs made various breads using the acrylamide-reducing yeast and the commercial bread yeast control. The final products showed no differences in color, size or texture. Importantly, no changes were required in the baking process to achieve these significant reductions in acrylamide formation in bread.
These early results are encouraging, and more work is being done to create more strains and further enhance existing strains. Furthermore, the acrylamide-reducing yeast technology is not only limited to bread products, research and development also is being conducted to enable this technology to be applied to other types of heat-treated foods, e.g., potato products, biscuits, crackers and other baked snacks.
About the authors:
Aline Chhun is molecular biology supervisor and John Husnik is senior research scientist with Functional Technologies Corp., based in Canada. They can be reached at www.functionaltechcorp.com.
Using Baker's Yeast to Reduce Acrylamide Formation in Foods
October 18, 2010