Yeast from a small scale fermentation was heat inactivated and stored in a refrigerator after centrifugation - about 60-70% water content.
The Yeast was planned for lipid/sterol extraction. Sadly i got sick for about a month before i could do the extraction.
Now the refrigerated sample is moldy.
Do you know what influence mold can have on such a sample - if it may be still usable after removing the mold, what the mold may have used/altered as food source to grow?
As to get to this point was quite time consuming I would prefer not to need to repeat the experiment to this point - and maybe find a way to save the sample.
I found a paper investigating the Effect of bug damage and mold contamination on fatty acids and sterols of hazelnut oil (DOI: 10.1007/s00217-016-2778-x)- where the lipids/sterol decreased. Not sure if this is similar in a liquid solution with yeast settled at the bottom.
Do you have any experience and/or advice for such a situation?
Any tip and help is much appreciated
2/8/24
Dear Daryl,
The mold may have grown on residual media from your yeast fermentation. Another possibility is that some of the yeast in the refrigerated sample died and underwent autolysis, releasing cellular metabolites that the mold used as a nutrient source.
My advice to you is to toss out the old refrigerated yeast culture and start over. It will cost you time and effort to do this. However, if you extract the refrigerated yeast culture, your extract will almost certainly be contaiminated by metabolites from the mold. You won't know what you have or where it came from. You'll always have doubts about your results. In the long run, it will be quicker and easier to grow a new, pure yeast culture for the extraction. Then you can be confident of the data you obtain from an uncontaminated culture.
I hope this information helps you.
Bill Colonna
Dept. Food Science & Human Nutrition, Iowa State University, Ames, IA [email protected]
I do not recommend using the mold-contaminated suspension you described to isolate ergosterol.
I remember the industrial production of baker's yeast for ergosterol isolation in the former Czechoslovakia (1965 -1988). Special batches of baker's yeast were produced and transported for ergosterol isolation. The method of culturing the yeast was adapted to ensure that the ergosterol content was as high as possible (the ergosterol content was 3 to 5 times higher than in ordinary baker's yeast).
The cultured baker's yeast was washed and centrifuged on a centrifuge. This produced a yeast cream with a dry matter content of around 16 % w/w. This yeast cream was transported in refrigerated tankers for ergosterol isolation. The transport took approximately 2 hours.
The delay between the production of the yeast cream and the start of the ergosterol isolation never exceeded 6 hours, as the ergosterol content was known to decrease over time.
I recommend producing a new batch of yeast.
Best regards
Vit
Well, you immediately have a problem with reproducibility if you use the samples, so it depends a lot on what you need the lipid for and what types of conclusions you would be making. If you are going to make claims about the fatty acid profile of the yeast, well the month long storage itself may have changed that in addition to whatever changes the fungus has caused. Other factors include which fungus (or fungi) are contaminating the sample, what residual growth substances were in the liquid between the yeast cells (e.g. were the cells washed before storing or are there still medium components present). How much lysis of the yeast occurred during the storage time? If all you need is some microbial lipid and you don't care what sort of profile it has and are not going to make conclusions about the productivity of the yeast it could be okay to extract your cells (might as well just leave the fungus with the yeast and extract everything). Separating the fungus from the yeast would be very challenging. I would expect the total lipid content to have gone down. Otherwise, unfortunately, you need to start over and hopefully utilising what you have learned in the first round, things go more efficiently this time.
