Canadian scientists have explained why sourdough bread remains fresher and lasts for longer. The reason is because during sourdough production, bacteria convert the linoleic acid in bread flour to a compound that has powerful anti-fungal activity.
Sourdough is a bread product made by a long fermentation of dough using naturally occurring bacteria called lactobacilli, and yeasts. In comparison with breads made quickly with cultivated yeast, it usually has a mildly sour taste because of the lactic acid produced by the lactobacilli.
Sourdough bread generally resists mold, unlike conventionally leavened bread. For conventional bread, the ‘expiry time’ can be increased through the addition of preservatives. However, the use of preservatives is not popular with everyone. Such techniques include the treatment of seeds with the anti-fungal fatty acids.
With sourdough bread, the bread making process consists of an extra fermentation step, in addition to normal yeast fermentation. This step is uses lactic acid bacteria, which gives the bread its distinctive taste.
The researchers have examined this second step and have isolated a metabolite from the Lactobacillus[/i] bacterium (L. hammesii) involved in the second fermentation. This metabolite was a type of hydroxylated monounsaturated fatty acid.
The implications of the research is that the findings could lead to ways to improve the expiration time for other types of bread and flour based products by using the isolated metabolite in a way which provides resistance to mold but does not change the taste of the other types of bread products.
The research was undertaken by a team led by Michael Gaenzle at the University of Alberta, Edmonton. The study has been published in journal Applied and Environmental Microbiology.