Try mild acids to make acidic conditions as the solubility of cysteine increases in the acidic pH.

Add Dil. HCL dropwise.

Here is the refernce:

http://www.ncbi.nlm.nih.gov/pubmed/23979510

Dear Saadat

Cysteine is slightly soluble (insoluble in ethanol, ether). it dissolves in dilute hydrochloric acid !

Thank you Abbas,

I want use cysteine in direct contact with food. I think hydrochloric acid has problem for using in direct contact with food, what do you think?

Try with acids permitted by foodlaw in your country (acetic? Lactic? Citric? ...?)

thank you

I will test it with citric acid.

Could check out citrate buffer anywhere between pH 3.0 - 6.2 to see where you get acceptable solubility. Lower pH than 7 will help prevent oxidation while also minimising H2S formation. Heating a solution will produce more H2S, which is the main off odour you might be smelling.

Thank you very much

i will test it.

Dear dr Jeffery,

I used citrate buffer, but cysteine didn't dissolve completely.

Citric acid and heat together dissolve it,but off odor create.

How i can find appropriate solvent for cysteine?

If you use the cysteine fresh and put in 50mM tris, pH 8 it would dissolve if it isn't too high of a molarity. What buffer you use depends on what you want to do next. If it is for tissue culture, then maybe use phosphate buffer. Cysteine should dissolve well at higher pH. I would use pH 8 or a little higher. Oxidation is slow, but I would still use a fresh solution. It also depends on the molarity of the cysteine in terms of solubility. I would not heat the solution.

Try mild acids to make acidic conditions as the solubility of cysteine increases in the acidic pH.

Add Dil. HCL dropwise.

Here is the refernce:

http://www.ncbi.nlm.nih.gov/pubmed/23979510

...practically, by "stoichiometric" approach...

Is the cysteine really more soluble at acidic pH? The only ionizable groups are the carboxylate, the sulfhydryl group and the amine. The carboxyl group and sulfhydryl group become less charged at lower pH making it less soluble, I would think. I think in your link they were talking about solubility of calcium salts and other components in the mixture. Please correct me if I am wrong, but at a higher pH, the sulfhydryl group would start to be negatively charged, and the carboxylate would be negatively charged, and the amine would be positively charged or neutral.

I guess it is counter intuitive to me that the solubility increases in acidic pH.

But if you can keep the pH acidic, that is best.

By adding HCL, as Arvind recommends, you may be just making the salt of cysteine. That salt may dissolve the best at neutral pH and not acidic pH. Remember, the citrate buffer at low pH did not work. It may be that it has to be the HCL salt to dissolve well, but I doubt the pH needs to be very acidic, because less than pH 4, the carboxylate will start to loose its charge.

Nevertheless, I think Arvind' s idea to add HCL, drop wise, is good.

Dear master Maricca,

Thank you for your rich answer,

I am going to use reducing property of cysteine for delaying enzymatic browning in foods.

Let me explain enzymatic browning: a reaction is happen when some fruits and vegetables are cutting; cutting surface is browning (for example apple, potato or banana) .

it due to oxidation of phenolic compound of this food.

Which buffer solution I can use for this propose? Which buffer isn't harmful for human health?

Dear Arvind and Antonia,

Thank you for your answer and attention,

I used different concentration of citric acid; some of them accelerated cysteine dissolving but none of them did not dissolve it completely.

Should be noted cysteine is dissolve in pH higher than 8 or lower than2.

Why cysteine, instead of L-ascorbic acid?

cysteine and L-Ascorbic acid are reducing agents.

I want test cysteine reducing property.

Ascorbic acid, or what is also known as Vitamin C is probably safer. But cysteine is ok too, up to certain concentrations, although I am not sure how high you can go. But given the choice, I would use ascorbic acid.

I cannot understand the problem with cystein solubilisation in water. In my hands with the commecially availiable L-cystein (wich is in the hydrochloride form), it is soluble up to 1 mol.L-1

Dear master

I want test cysteine in 0/1, 0/5, and 1 percent. I think these concentrations are safe for health.

I want test this concentrations for partial my thesis work.

Many research’s have been done in this area, but none of them did not say how dissolved cysteine.

Dear dr Yannis,

I want use cysteine no cysteine hydro chloride.

both cysteine and cysteine hydro chloride are exist.

If you don't want cysteine hydrochloride, then you can pH the water / cysteine to a high or low pH to dissolve it. You can use sodium hydroxide, or any base you want for a higher pH. Maybe even phosphate buffer for higher or lower pH if you are to use it with food.

Cysteine HCL is the salt form of cysteine, and will be more soluble than free cysteine.

It just depends what you want to do.

Yes, You can try to dissolve in mild heating condition with stirrer.

It might be good idea to low down the pH as higher pH may cause disulphide formation within the two molecules. You may try heating, if your results doesn't vary as a function of temperature.

Try to warm the solution but not reach the boiling

Probably your cysteine is oxidazed to cystine which is insoluble in water. Cysteine is a thiol sensible to oxidation and undergoing to disulfide bond formation to produce cystine in the presence of oxidants like molecular oxygen.

If you drop the pH and solubilize Cysteine, you can check the purity of your Cysteine using NMR.

Please note the following:

Sulfur-Containing Amino Acids

The sulfur-containing amino acids (cysteine and methionine) are generally considered to be nonpolar and hydrophobic. In fact, methionine is one of the most hydrophobic amino acids and is almost always found on the interior of proteins. Cysteine on the other hand does ionize to yield the thiolate anion. Even so, it is uncommon to find cysteine on the surface of a protein. There are several reasons. First, sulfur has a low propensity to hydrogen bond, unlike oxygen. A consequence of this fact is that H2S is a gas under conditions that H2O is a liquid. Second, the thiol group of cysteine can react with other thiol groups in an oxidation reaction that yields a disulfide bond. Perhaps as a consequence, cysteine residues are most frequently buried inside proteins. Could not have said it better myself...

Retrieved from: http://www.biology.arizona.edu/biochemistry/problem_sets/aa/sulfur.html

This is why you are getting the 'scent' you are getting. The melting point for this amino acid is:

464°F (240°C)

There really isn't any way that I know of to get rid of the smell, unless you mask it...what are you using it for?

Hope this helps...

James

Dear James,

Thank you very much for your answer and attention,

My problem dissolved; I tried three different brands Cysteine but Cysteine in 1% (w/v) dissolves in water completely. I think problem relate to impurity of Cysteine.

I use Cysteine in 1% and 0.5% for inhibition enzymatic browning in fresh cut vegetables.

Hi Saadat, I should haven mentioned that the raw material that you were using may be the issue. It is unfortunate that the quality of the various sources of raw material isn't always what it should be. In some cases what should be pure USP material is cut with some other contaminant (flow agent, desiccant, inert filler etc.). In many cases this is to cut the costs, and in other cases the impurities are in the material due to improper processing. Did your supplier provide you with a C of A? If you want to ensure that you are going to get the results you want, you may need to get your 'actives' tested by an independent lab as most importer/distributors do not do their own verification testing (quality control). I will be interested to see what your results are...all the best!

Thank you James,

good job

 @saadat: can you please mention which brand cysteine you used to dissolve completely in water, even i am facing the same problem. i will try out options mentioned here as well. Thank you

A low pH of 1-2 will slow the rate of oxidation to cystine in this case, it will also   increase the solubility of cysteine, slightly warming the water may also faciliate this process. Water quality is very important...trace minerals will catalyze the oxidation process, so you will need to obtain and use the cleanest water you can.

Hope this helps...

Hi Tegel,

I would suggest that you use a USP grade of Cysteine, Lab grade would not be practical for commercial applications if that is your intent. You can contact Sigma for lab grade material if you are only doing research. Anything else may taint your results, some companies that claim that their material is water soluble will spray dry the active to a carrier, this will also taint your results.

Hope this helps.

 Dear Tejal 

I used L-Cystein pure whith Applichem brand.  

Thank you James Lembeck & Saadat Azizi for the info.

One other note, the smell...because cysteine is a Sulfur bearing AA this would account for the smell. I am not aware of any way to eliminate this attribute without modifying the structure (and possibly the effect) of this ingredient. Reducing the pH may cause disassociation of the molecules, which again may affect the outcome. If you add an acid to the solution you can check the 'reducing' capabilities by checking the ORP value of the solution before and after the addition. Other than this…I am not sure what you are trying to accomplish so it is difficult to make other suggestions. All the best, James

i have one more query...

if i dissolve L-cysteine in acidic solution, and later if the pH rises (towards neutral or alkaline) will the cysteine precipitate again?

Hi, if my memory serves me...Cysteine is made in the body from homocysteine, which is derived from methionine. Cysteine can be converted to cystine and also taurine. Cystine itself is a disulfide, containing two cysteine molecules. As to the effect that pH has on this process, I would imagine that it is a factor, but we have to remember that (in the body) some of these conversions can occur for more than one reason...enzymes and  the probiotics in the gut will also have an effect. If you are just doing lab work this obviously eliminates a lot of the other factors discussed above. If there is a conversion, then you have to wonder if the reverse conversion will be a complete one.

During the oxidation of two molecules of L-cysteine, the disulfide L-cystine is formed. This reaction is reversible, which means that L-cystine can be converted back to L-cysteine by reduction.

https://www.google.com/patents/US20140141474

Hope this helps...you may need to do more research on this with regards to the pH factor and other causative factors.

James

If you dont want to use L-Cysteine hydrochloride,monohydrate C3H7NO2S.HCl.H2O as this is soluble in watr with high amount also then you can use molar solutions of HCL or NaOH and titrate it.

I have used cysteine in aerobic fermentation media nad autoclaved at 121c for 20 minutes, after several hours the media become white precipitated and produce bad smell or odor, also decrease yeast growth, why? have anyone answer?

you can use the L-Cysteine hydrochloride monohydrate . its is freely soluble in RT water