Autoclaving Dry Yeast Extract Powder - (Nov/06/2007 )
Is it possible to efficiently autoclave a decent amount of yeast extract powder (500g) in a beaker?
Or will this not become fully sterilized due to heat transfer properties? Or will it become one big giant clump or something?
I have a non-sterile 100L fermentation vessel, but I am trying to limit what type of contaminants I am throwing in. So autoclaving the additions may help a bit.
Thanks
Dan
I would not recommend autoclaving dry yeast powder.
Firstly an autoclave uses steam to sterile. Thus, the dry yeast powder will become wet/watery yeast powder after the autoclaving. Secondly powders do not readily sterile as they need to be in contact with steam. Something the centre of a powder does not experience easily.
It would be better to autoclave a solution of yeast powder. However do not make it too concentrated as you will experience significate millard reaction and caramelisation. Both of which reduce the availability of free reducing sugars (glucose, fructose) and the millard reaction has a significate impact on free amino acids, removing as much as half of the free amino acid contant.
Actually, better to just make up a litre of yeast extract with sterile distilled water and filter sterile the lot. (the bottle in use is pre autoclaved.)
Hmm.. since you have 100L fermenter, might you also have a gamma steriliser? That works great on powders.
Firstly an autoclave uses steam to sterile. Thus, the dry yeast powder will become wet/watery yeast powder after the autoclaving. Secondly powders do not readily sterile as they need to be in contact with steam. Something the centre of a powder does not experience easily.
It would be better to autoclave a solution of yeast powder. However do not make it too concentrated as you will experience significate millard reaction and caramelisation. Both of which reduce the availability of free reducing sugars (glucose, fructose) and the millard reaction has a significate impact on free amino acids, removing as much as half of the free amino acid contant.
Actually, better to just make up a litre of yeast extract with sterile distilled water and filter sterile the lot. (the bottle in use is pre autoclaved.)
Hmm.. since you have 100L fermenter, might you also have a gamma steriliser? That works great on powders.
i did some research on the mallaird reaction and it says its the reaction between a reducing sugar and amino acids? the only things I autoclave at high concentrations are pure tryptone and yeast, and sometimes a mixture of both.... There arent any reducing sugars in either... are there?
thanks again guys
there are sugars in yeast extract (total carbohydrate 163mg/g) and a little bit in caesin tryptone (total carbohydrate 4.3mg/g). And consider that the tryptone was made by treatment with HCl and yeast extract by autolysis and concentration of the soluble portion of the lysate.... there is a good chance that all the carbohydrate in trytone consist of simple sugars and a proportion of the carbohydrate are free and small sugar moietoes. Really large complex sugars would probably be preferentially spun down.
And finally there is thermal lysis to consider in regards to the sugars when confronted with an autoclave.
the steam does not have to come in contact with the item being sterilized, the process depends on the transfer of heat to the item. if it required the steam to come in contact then we wouldn't be able to sterilize media without diluting it. also, when you sterilize pipettes (something that most probably don't do anymore) they are sealed in a bag. the heat penetrates to the pipette but the steam never actually touches it.