2024-05-08 09:01:03
Sourdough can contain over 20 different types of yeast and 50 types of bacteria. We show you what they look like.
An Ohio State University researcher studied the microbial community in the sourdough his family cooked with. To do this, he used a scanning electron microscope, which allows him to image the surface of samples at the nanoscale. On this subject writes ScienceAlert.
Study characteristics
For comparison, a human hair is between 10 and 150 micrometers thick, and a scanning electron microscope (SEM) can observe features 10,000 times smaller than that.
Because SEM uses electrons instead of light to produce images, there are limits to what can be viewed under a microscope. Samples must be electrically conductive. They must also withstand very low vacuum pressures. A low pressure environment is generally unfavorable for microbes, because under these conditions the water present in the cells evaporates, distorting their structure.
To prepare samples for SEM analysis, a technique called critical point drying is used. During this process, the sample is dried to reduce unwanted artifacts and preserve fine details. It is then covered with a thin layer of metallic iridium.
Sourdough is made from wild yeast and bacteria found in flour. These ingredients create a favorable environment for the development of many types of microbes. Sourdough can contain over 20 different types of yeast and 50 different types of bacteria. The most stable species become the dominant species.
You can visually observe the microbial complexity of a sourdough by viewing the different components that vary in size and morphology, including yeast and bacteria. But for a more detailed analysis of all the diversity present in sourdough, it is impossible to do without sequencing the entire genome.
Sourdough under the microscope
The main component that gives sourdough its texture are the starch grains in the flour. These grains, colored green in the image below, are identified as relatively large spherical structures with a diameter of approximately 8 micrometers.
Red yeast gives rise to leaven. As they grow, they ferment the sugar from the starch grains and produce carbon dioxide bubbles and alcohol as byproducts. They make the dough rise. The size of yeast generally ranges from 2 to 10 micrometers. They have different shapes – from round to elongated. The image shows two different types of yeast: one that is almost round in the lower left corner and one that is elongated in the upper right corner.
Blue-colored bacteria metabolize sugars and produce byproducts such as lactic acid and acetic acid. These byproducts act as preservatives and give sourdough its characteristic sour smell and taste. In the image, the bacteria look like tablets, measuring regarding 2 micrometers.
Now when you eat sourdough bread, you will be able to visualize the rich array of microorganisms that give each bite its distinct flavor.
Previously electron microscope capture “dance” of proteins and lipids.
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