Sorbate addition in Dulce de Leche: pH and thermal efect determinate by RP‐HPLC

Abstract:

The method (RP-HPLC ISO 9231| IDF 139) for sorbic acid (H-Sorb) determination in Dulce de Leche (DL) was investigated and fulflled the acceptance criteria: selectivity (single peak), linearity (3.1–50.0 μg/mL; R2=0.9977), precision(CV=0.66–2.04%), accuracy (recoveries=93.6–101.9%), detection limit (0.72 μg/mL) and quantifcation limit (2.17 μg/mL). In DL samples, the accuracy of H-Sorb determination from added K-Sorb before/after heat treatment varied from 88.8 to 96.5%. Addition of K-Sorb before/after evaporation (pH~6.9, 100 min and 120 oC) did not interfere with the fnal H-Sorb concentration. The evaluation of the thermal stability of K-Sorb in aqueous sucrose solutions at diferent pH values showed that H-Sorb losses were pH dependent. At pH≤pKa evaporation losses of H-Sorb occurred. H-Sorb analysis of commercial samples (n=10) showed that their concentrations (265–572 mg/kg) were within Brazilian DL regulations, except for one sample that was mislabeled.

Conclusion:

In the present work, the determination of sorbic acid (from added potassium sorbate) and its thermal behavior in the manufacturing of DL was investigated using an RP-HPLC method. All validation criteria applied (such as selectivity, linearity, precision, accuracy, etc.) were successfully tested and accepted, indicating the adequacy of the method for the determination of H-Sorb in DL. Furthermore, H-Sorb determination results showed that the time of addition of the preservative, either at the beginning of the process (before the concentration step) or at the end of the latter step (evaporation), does not interfere quantitatively in its final concentration. Hence, H-Sorb seems not to evaporate at the normal conditions of pH, temperature and time applied during DL manufacturing. Experiments on model aqueous solutions with diferent pH values showed that at low pH values (≤pKa of H-Sorb), the prevailing acid form seems to be partially lost during the evaporation process. In DL production, the pH of the ingredients blend is close to neutrality (hence K-Sorb is the prevailing moiety) and the processing conditions applied Conclusãoare not able to reduce the pH to values where reactions could occur that would convert K-Sorbate into H-Sorb. To our knowledge, for the frst time RP-HPLC was successfully validated and applied to determine H-Sorb in DL, which can be recommended to be used by the Brazilian food control authorities. Analysis of 10 diferent commercial samples with this method showed that the H-Sorb concentrations declared were within the directives of the Brazilian DL regulation, and also identifed a sample that was not correctly labeled.

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[144] Pinto, C. B. A.; Cunha, C. N.; Da Costa, J. C.; Wolfschoon‐Pombo, A. F.; Perrone, I. T.; Stephani, R. Sorbate addition in Dulce de Leche: pH and thermal effect determinate by RP‑HPLC. European Food Research and Technology, 250:763–770, 2024.