Hi there,

The darkness of autoclaved YPD is due to Maillard reaction. See below for further details:

https://www.compoundchem.com/2015/01/27/maillardreaction/

Indeed accumulation of products of this complex process may have side effect on yeast growth. See below for further details:

https://www.compoundchem.com/2015/01/27/maillardreaction/

To avoid such reaction you should sterilize YEP and sugar stock separately either as a 10x concentrated stock by filtration (20% solution) or as a 25x concentrated stock by autoclaving (50% solution to avoid caramelization)

I am not sure I understand your question. What was your rationale for removing the lid during autoclaving? Why was the autoclaving done twice? Was that indicated in the manufacturers directions for preparation of the medium? I think sterilization of this medium (Yeast-extract Peptone dextrose) requires autoclaving for just 20 min at 121 deg C. Any other manipulation is entirely your decision. You should be in the best position to tell us how the yeast reacted to the medium. Reference paper is unknown to me and therefore unavailable since no one prepared this medium the way you did.

Dear Maurice Ekpenyong ,

Yes that was completely my decision. And rationale of lid off is not frequent. As medium (Yeast-extract Peptone dextrose) requires autoclaving for just 15-20 min at 121 deg C. But i have observed this activity of media for yeast growth and i don't find any reference paper or discussion anywhere therefore i've ask here.

Hi there,

The darkness of autoclaved YPD is due to Maillard reaction. See below for further details:

https://www.compoundchem.com/2015/01/27/maillardreaction/

Indeed accumulation of products of this complex process may have side effect on yeast growth. See below for further details:

https://www.compoundchem.com/2015/01/27/maillardreaction/

To avoid such reaction you should sterilize YEP and sugar stock separately either as a 10x concentrated stock by filtration (20% solution) or as a 25x concentrated stock by autoclaving (50% solution to avoid caramelization)

Hi Dominique Liger ,

Two things. First, did you intend the second link posted above to be identical to the first? If you didn't and it's not much of a bother, could you post the link you originally intended? There's so much literature on the influence of Maillard products, that I've been unable to find something directly assaying them on laboratory strains of Saccharomyces and/or E. coli after a quick search.

Second, how would you rule out caramelization in the case of the re-autoclaved YPD referred to by the original poster?

Hi Alejandro,

Actually the second link resulted for an unexpected copy/paste from the first one... So I don't have any publication to suggest about the effect of Maillard reaction products on yeast growth. But I already experienced the situation where yeast was unable to growth in an "overcooked" YPD medium. Ever since I always use carbone source as an additive to autoclaved YP to generate full YPD.

To answer your second question, both Maillard and caramelization occur during autoclaving and I can't rule out the possible effect of the latter but my intuition would be that as Maillard reaction can result in carcinogenic molecule accumulation (like acrylamide for instance) it might have a detrimental effect on yeast survival.

Hi Aqib Zafar Khan

The problem you mentioned is pretty common in lab practice. Please find the following reasons:

1. Probably you are lowering the pH of YPD according to your strain.

Sol: Prefer to use 1N HCl or H2SO4 instead of using concentrated one.

2. High glucose concentration is there which may convert into HMF due to presence of high temperature and pressure with concentrated acid (added during pH maintenance) which trigger the molisch reaction.

Sol: I suggest autoclave the YP and Glucose separately followed by mix together.

I am sure this will help you to proceed your research.

Best of luck,

Nilesh

This is because you are adding glucose before autoclaving. Autoclave glucose separately and then add it to YPD after autoclaving.