MicrobeHunter.com Microscopy Forum

One of my customers is a small high quality bakery in a small town. It's very hands on and uses a sourdough that they keep a culture of. They gave me a loaf of their sourdough Rye. I'm not particularly a bread eater ( nor much of a bread winner either) but as bread goes it was very good.
I entered into the loaf with a corer and took a small plug from the center, popped it into a 1/2 ounce of water, with an added pinch of sugar, capped it and set it in the warmth for a couple of days. The whole operation took about 5 seconds and everything except the sugar was sterile. The water went cloudy, so obviously some bacterial and or yeast persistors made it through the bake.

Here are a few pictures of the results. Three principal organisms emerged; a lot of a yeast that looks typically like a bread yeast, a leuconostoc looking bacteria, possibly leuconostoc mesenteroides, a lactic acid bacteria that could likely be present in a sourdough culture, and a very long celled type of yeast/fungi that looks more like a fungal hypha than a yeast, probably a cladosporium or a candida. There were also quite a few starch granules, most of which are showing stretch marks from expansion.

All are taken through 60 year old 97X oil immersion phase contrast objectives. AO.

Apochronaut wrote:an oddly symmetrical manner

I naively thought that starch should be amorphous and of a random pattern, but literature data tell that it is semi-crystalline, so it has some order. For example, a fairly modern review in the journal: Agronomy (2017):

Review: Understanding Starch Structure: Recent Progress
Eric Bertoft

Example citation:
"2. The Starch Granule
In view of the great diversity in starch granule morphology, it is remarkable to find that their internal architectural features are shared universally among the plants and regardless the plant organ (endosperm, root, stem, etc.). When observed in cross-polarized light in an optical microscope, a “Maltese cross” is typically seen extending the arms from the so-called hilum, which is believed to be the origin of growth of the granule [42–44]. This birefringence pattern shows that the molecules, or a large part of the molecules, are arranged in a radial fashion and suggests a high degree of order
inside the granules (Figure 1) [45].
2.1. Crystallinity
As mentioned above, starch granules are semi-crystalline, i.e., they contain both crystalline
and amorphous parts. If starch granules are treated in dilute hydrochloric acid, or sulphuric acid,
the amorphous parts in the granules are removed and the crystalline parts remain [46,47]. The “Maltese
cross” also remains [48], which shows that the organized molecular segments are confined to the
crystallites."

The radial development is evident in other granules too but not with such a regular order. It is semi-crystalline so it forms concentric growth rings as a result of amorphous swelling and radial lines as a result of crystalline growth. The theoretical pattern might be symmetrical but it rarely is. This one was unique of the many hundreds that I came across. Here is a picture of another, where you can see the radial pattern of development but not in anywhere near as organized a fashion. The one pictured here is far more typical of a well organized growth pattern. Many had little symmetry at all. Adjacent to the first starch photo, you can see others surrounding it that are little more than gelatinous blobs.

Thanks for the informative post, based on such a simple experiment.