How it turned turbid? Well... SDS  disrupts non-covalent linkages on proteins and destabilises native conformation.You see, SDS is an anionic surfactant, it imparts net negative charge on proteins... causing repulsion which leads to unfolding and a trend towards linearisation. So yeah maybe thats why...

Why can't we use the same study to other emulsifier? I am not sure i understand that very well... but maybe SDS works if you dont have protein as a stabilizer? i dont know, maybe. Also if you insist on using protein as your stabilizer, SDS can maybe be replaced with a more gentle non-ionic detergent something like dodecyl maltoside... 

SDS denatures proteins, but also keeps them in solution, so a solution of SDS-denatured proteins should not be turbid. If your emulsion contains potassium ions, the SDS will precipitate as potassium dodecyl sulfate. Maybe that is where the turbidity comes from.

Hi! as said above, SDS denaturates proteins by hydrophobic interations at submicellar concentrations, this is a very nice paper about the mechanism involved (http://www.ncbi.nlm.nih.gov/pubmed/19802818).

On the other hand, SDS would form hydrocolloid polymers depending of the ionic concentration, particularly K (I dont know, if you use PBS as buffer). Hope this help!

That has to do with the pH of the solution used to prepare the emulsion. If the protein used in the emulsion is having a positive charge under the experimental conditions, then adding SDS will cause coagulation.

Please try the same experiment with CTAB and triton-X and see whether the turbidity appears or not. Also important is not to use too much of the detergent as that will have other effects.

1% of SDS is ok if the disperse phase is around 5-10% in concentration.

Hi Joseph, I agree with above comments in that if your solution turns turbid immediately after adding SDS, then there has to be something in your solution that precipitates the SDS.

The usual suspects are K+, Ca++ (and many other divalent cations), arginine, guanidinium, and low pH.   

Exactly. Any cation which precipitates SDS is the culprit. I would like to know the solution, Can turbidtiy be prevented by adding EDTA?

Thanks all.. I used PBS buffer as aqueous solution for dissolving protein.. Thats why I turned turbid.. 

Hi Joseph, many PBS preparations use potassium  phosphate and potassium chloride.

• The effect of addition of SDS on protein in solution strictly depends up on the isoelectric point of the particular protein followed by the SDS:protein ratio. SDS is a potential amyloid inducer of protein at below its isoelectric point irrespective to the class it belongs, i.e. whether it is alpha, beta or alpha+beta type of protein. The optimum SDS:protein ratio gives amyloid which show positive results for  all the parameters, used for the amyloid characterization, and increase in turbidity at 350 nm is one of them. pH below pI generates +ve charge on the protein which interacts with the negatively charged SDS and mediate the amyloid fibril formation.

Hello Joseph -

Without knowing your full story of the solution compositions and conditions, my predictions are (a) presence of K+ (as Dr. Shapiro noted above), (b) low temperature of solution when you are mixing with SDS (c) too much ionic strength (salt) in your mixture.

All the best.

Sounds strange that K DS is suspected to be insoluble. As far as I remember kalium soaps have somewhat better solubility than sodium soaps. Further, the original question does not mention presence of kalium ions.

The answer should be quite simple. Stabilization of emulsions by proteins means making the interface between oil and water compatible, due to directed adsorption of the amphiphilic proteins. Adding SDS, will cause adsorption of the dodecyl sulfate to the protein layers at the interface, which makes the interface exposed to water hydrophobic and droplets should flocculate. Same should happen in every case when the interfacial film is made incompatible with the water phase, e.g. adding cationic surfactant to emulsions stabilized by anionic surfactant or anionic polyelectrolyte.

Depending on the specific surface area of oil droplets, further increase in SDS concentration should restabilize the emulsions.