Organic Acids in Apple Juice

The sample that yielded chromatogram A is the sample of apple juice under scrutiny. The peak at retention time 4.9 min is malic acid and the one at 7.2 min is fumaric acid. The malic acid peak should always be present in a given quantity. The concentration in fumaric acid should not be more than 2 ppm, if otherwise, it is indicative of a juice sample that was submitted to some kind of non-approved treatment or that was adulterated. 

Chromatogram B is the result of the analysis performed on an authentic apple juice. 

Chromatogram D is 100 ppm of a standard of mahc acid. Note that the standard also contains some fumaric acid as a contaminant in it. It is important to note the amount of fumaric acid present in the standard 

Chromatogram E is the sample of apple juice under scrutiny, spiked with 100 ppm of malic acid. The increased concentration of both malic and fumaric acids is due to the presence of these organic acids in the original sample, plus the addition of malic acid contaminated with fumaric acid. The verification of the purity of the standard is very important as contamination will give an erroneous result. Spiking is essential in that it 1) contributes to identify the peak of interest through comparison of retention times, 2) enables the analyst to perform a recovery experiment since the original concentration of the standard is known. From these data, it can be concluded that the sample under scrutiny meet the standards of the authentic apple juice sample. 

---

Coppola, E. and Star, M.S. 1986. Liquid chromatographic determination of major organic acids in apple juice and cranberry juice cocktail Collaborative study. J. Assoc. Off. Anal. Chem. 69 594-597. 

---