Determination of pungency in spicy food by means of excitation-emission fluorescence coupled with second-order chemometric calibration

Capsaicinoids are a family of compounds responsible for the pungency of spicy foods. In this work, the combination of fluorescence and chemometrics was investigated as a novel quantification method of capsaicinoids in spicy food samples. The excitation-emission matrices (EEMs) of the two major capsaicinoids (capsaicin and dihydrocapsaicin) were identical. Hence, the results were presented as the total content of capsaicinoids. The EEMs of a group of paprika, cayenne and chilli peppers, and of another group of spicy sauces were registered. The decomposition of the EEMs of each group was performed by parallel factor analysis (PARAFAC), obtaining three principal components in each case. After the decomposition, the component corresponding to capsaicinoids was identified by comparison with the profile of a standard mixture of capsaicin and dihydrocapsaicin. In addition, the score values of this component were correlated with the Scoville heat units (SHU) calculated by means of an HPLC-FLD method. Good correlations were obtained in both groups (0.998 and 0.992), confirming the assignation of the component to capsaicinoids. Subsequently, a calibration set was built to carry out the calibration in the spectrofluorimeter, using PARAFAC and U-PLS/RBL as second-order calibration algorithms. Good results for SHU determination were obtained in both groups with both algorithms and when the fluorimetric method was validated by means of liquid chromatographic analysis the relative error of prediction was less than 11.3%.