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What concentration of table sugar inhibits bacterial growth?


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#1 Marzfisch

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Posted 14 October 2016 - 09:17 PM

Hello, I am new to this forum, so bare with me.

 

I am working on a project that requires me to ferment sugar water with Lactobacillus Acidophilus. I made a 50% concentration of sugar mixture and it will not ferment. Apparently 50% sugar is too much.

 

Does anyone know what concentration of sugar will allow the bacteria to ferment the sugar?

 

If someone could answer this for me I would be absolutely delighted!


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#2 StringJunky

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Posted 14 October 2016 - 10:29 PM

At 50% sugar you are nearly  into jam making territory which works as preservative by  moving the water out of the bacterial cells osmotically* and dehydrating them. The maximum concentration needs to be lower than the concentration found within the cells to avoid dehydration. From this source , under the chapter called Sugar, a sugar-tolerant strain of acidophillic bacteria can multiply in a 15% sugar concentration.  Probably, 10% would be a better starting point as you won't know if they are sugar-tolerant strains in your sample.

 

*Osmosis - the water will move across a membrane from a low sugar ( or other solute e.g salt)/high water concentration to a high sugar/low water concentration, leading to dessication.


Edited by StringJunky, 14 October 2016 - 10:39 PM.

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#3 Sensei

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Posted 14 October 2016 - 10:29 PM

Anybody making home wine, home alcohol, will tell you "rule 1410".
For 1 kg of sugar, there is needed 4 L of water, and 10g of yeast.
That's 20% by mass. It should not exceed 22%-23% IIRC.
Even saccharimeters that I am using have end of scale at 24°Blg.

If you have extra good turbo yeast, you could try 25%,
or add sugar later, after couple days of fermentation.

This year I am making experiments with turbo yeast (there was promotion in the shop and I bought enough for couple months),
and the fastest one could make 14%-18% of ethanol from 6-8 kg of sugar (plus water enough to 25L of solution), in 48h-72h.

IMHO,
you should prepare couple containers, each one with different sugar proportion, write them down, say 5% more in each than previous,
and add Lactobacillus Acidophilus (or yeast or whatever you're testing).
You will see how they react for various concentrations, and will be able to compare. Or even record it by timelapse camera.

Edited by Sensei, 14 October 2016 - 10:40 PM.

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#4 StringJunky

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Posted 14 October 2016 - 10:49 PM

Anybody making home wine, home alcohol, will tell you "rule 1410".
For 1 kg of sugar, there is needed 4 L of water, and 10g of yeast.
That's 20% by mass. It should not exceed 22%-23% IIRC.
Even saccharimeters that I am using have end of scale at 24°Blg.

If you have extra good turbo yeast, you could try 25%,
or add sugar later, after couple days of fermentation.

This year I am making experiments with turbo yeast (there was promotion in the shop and I bought enough for couple months),
and the fastest one could make 14%-18% of ethanol from 6-8 kg of sugar (plus water enough to 25L of solution), in 48h-72h.

IMHO,
you should prepare couple containers, each one with different sugar proportion, write them down, say 5% more in each than previous,
and add Lactobacillus Acidophilus (or yeast or whatever you're testing).
You will see how they react for various concentrations, and will be able to compare. Or even record it by timelapse camera.

Yeast, fungi and moulds are considerably more sugar tolerant than bacteria, which is what they are using


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#5 CharonY

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Posted 15 October 2016 - 12:20 AM

Depends, actually. Especially among Gram positives there are some very osmostable buggers.


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#6 StringJunky

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Posted 15 October 2016 - 01:00 AM

Depends, actually. Especially among Gram positives there are some very osmostable buggers.

Google does not recognise osmostable. You mean sugar tolerant?


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#7 John Cuthber

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Posted 15 October 2016 - 07:53 AM

Don't forget that you will need other nutrients.

This

https://catalog.hard...lliMRSAgar.html

suggests that 2% dextrose keeps the bugs happy.

 

Cow's milk is about 5% lactose.


Edited by John Cuthber, 15 October 2016 - 07:54 AM.

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#8 CharonY

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Posted 15 October 2016 - 04:08 PM

Google does not recognise osmostable. You mean sugar tolerant?


I meant osmotolerant. If memory serves assays routinely find bugs surviving ca 15% NaCl and 50% sucrose. Some extemophiles may go higher.
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#9 StringJunky

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Posted 15 October 2016 - 06:05 PM

I meant osmotolerant. If memory serves assays routinely find bugs surviving ca 15% NaCl and 50% sucrose. ...

Right. We don't want those little blighters in the marmalade.


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