February 25th, 2013 by James Ayre
Traditionally-made sourdough breads have a good degree of resistance to mold, in contrast with conventionally-made leavened bread. The exact mechanisms for this have been unclear. But now, new research has found that some of the bacteria used in sourdough production convert the linoleic acid that is present in bread flour into a powerfully anti-fungal compound. The researchers, from the University of Alberta, Edmonton, think that this research should eventually allow for the removal of preservatives from conventionally-made bread.
Of course the majority of what is sold (at least in the U.S.) as sourdough isn’t really sourdough though, it’s just conventionally-made leavened bread with an acid, such as lactic acid, added for taste. Traditionally-made sourdough is differentiated from the bread that most people eat now by the inclusion of an extra fermentation step, beyond simple yeast fermentation. This step is mediated by lactic acid bacteria, typically of the genus Lactobacillus.
For the new research, “we offered linoleic acid to lactobacilli and screened for organisms producing potent antifungal activity,” says Michael Gaenzle, lead researcher on the study. The metabolites were then fractionated in order to isolate the compounds and determine which had anti-fungal activity. “The identification was a bottleneck in the research project. In collaboration with analytical chemists, we had to develop novel methods for identifying the compounds.”
“L. hammesii produced substantial quantities of hydroxylated monounsaturated fatty acids which the researchers found strongly inhibited mold formation. A second antifungal fatty acid produced by cereal enzymes contributes to the antifungal activity of sourdough.”
“The two compounds and their formation by cereal or microbial enzymes had been described previously, but their antifungal activity and their generation in food production was unknown,” says Gaenzle. These new research, is “a step towards understanding how and why lactobacilli metabolize fatty acids. This could be useful in the long term to improve our understanding of the biology of these organisms.”
The researchers say that their findings may also lead to new tools to control fungi during malting and plant production.
The new research was just published in the journal Applied and Environmental Microbiology.
Image Credits: Sourdough via Wikimedia Commons
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