Potassium Sorbate added to cheese with low pH due to the presence of lactic acid; does lactic acid act the same as HCL to convert Potassium Sorbate to Sorbic.
Also, potassium Sorbate added to brine ( saturated water with salt 10% at 4 C degrees)
How you think these conditions will affect the equilibrium between potassium Sorbate to Sorbic acid.
The problem in food industry labs they rely on outside labs to test and analyze samples for all out of ordinary tests and I've been trying to find a lab to analyze Potassium Sorbate separate from Sorbic acid but they only test Sorbate by HPLC which doesn't give an idea how much of each component is in that sample.
Dear Mutasem Z. Bani-Fwaz, I am not really involved in this field, however I found the attached files which I hope they will be usefull. My Regards
From a quick Google at: https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/sorbic-acid it appears that sorbic acid is only 0.15% soluble in water (w/w) while K-sorbate is around 58% soluble @ 20C, and the acid form is biologically active against yeasts but not bacteria. (Probably nothing you don't already know.)
A simple spectrophotometric test for sorbic acid is given here: https://www.ajevonline.org/content/ajev/29/3/217.full.pdf
I expect if you want to distinguish between K-sorbate and Sorbic acid in your samples, you may have to develop the method yourself.
Dear Mutasem,
to a "first order" the equilibrium between Sorbate and Sorbic Acid is given by the pH of cheese.The equilibrium can with known pH ( https://www.cheesescience.org/ph.html) and the pKa of sorbic acid (4.7) be calculated by use of the "Henderson Hasselbalch Equation".
As a tendency I'd expect for "reasonable cheeses (pH>6)" a more than 90% de-protonated Sorbic Acid (-COO-).
I hope this helps
Alfred
Analysis of sorbate is best accomplished by HPLC. Article Determination of Sorbic Acid in Cheese Samples by Rapid HPLC...
A separate analysis needed for the potassium content. The pH of the sample determines the estimated potassium sorbate, which will be in equilibrium with the sorbic acid at that pH. The amount of assumed potassium sorbate in the sample is an estimate. There in no easy way to distinguish sorbate ions from sorbic acid or potassium sorbate.
In Chinese food regulations, sorbate is calculated as sorbic acid, that's why there's no need for food industry lab to distinguish potassium sorbate from sorbic acid directly. And most methods just detect sorbic acid and the extraction is carried on under an acidic condition to make sure all of the sorbates (K+, Na+) transformed into the sorbic acid. And furthermore, even you add potassium sorbates in food, there's still a possibility to have sodium sorbate in food when the condition is suitable. So from a food safety perspective, it's meaningless to separate sorbates and sorbic acid.
Please look at the following below links which may help you in your analysis:
http://downloads.hindawi.com/journals/ijac/2020/6049028.pdf
http://jmp.ir/article-1-269-en.pdf
https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/sorbic-acid
Thanks
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