Application of temperature-induced phase partition of proteins for the detection of smoked paprika adulteration by free zone capillary electrophoresis (FZCE)

A procedure for protein extraction was developed for use in the determination, by free zone capillary electrophoresis (FZCE), of smoked paprika “Pimentón de La Vera” adulteration with paprika elaborated from varieties of pepper foreign to the “La Vera” region, in the centre-west of Spain. Two autochthonous varieties of pepper, Jaranda and Bola, and the varieties Papri Queen, Papri King and Sonora, foreign to the “La Vera” region, were used in the study. Several Tris–HCl buffer concentrations and pH values were tested for the extraction of the hydrophilic and hydrophobic protein fractions obtained by temperature-induced phase partition with Triton X-114. On the basis of the results, 0.5 mM Tris–HCl buffer, pH 7.4, with 150 mM sodium chloride, was adopted as the optimal extraction buffer. Five peaks found in the FZCE electropherograms of the hydrophilic protein fraction were investigated as a basis for detecting and estimating the adulteration of smoked paprika. The adulteration detection limits varied from 10% to 40% of paprika elaborated from foreign varieties within a satisfactory working range of admixture (5–80%) sufficiently large to cover the adulteration levels of interest. In addition, a peak of this fraction was identified as a marker for the smoke-drying process. With respect to the hydrophobic proteins, the use of the peak denominated M and the ratio of peaks M and K as markers for determining adulteration gave the best results, with an adulteration detection limit of 5% (w/w), and correlation coefficients greater than 0.965.