A method named imprint paper spray ionization mass spectrometry (imprint-PSI-MS) has been developed and employed for the determination of pungency of peppers. A pepper fruit was cut into a triangular shape, deposited onto a triangular paper, and compressed by a homemade press tool aiming to imprint and transfer the pepper constituents onto the paper surface. Subsequently, the triangular paper was submitted to conventional PSI-MS analysis. Twelve peppers were analyzed, ranging from highly pungent to lowly pungent taste. Pepper pungency values from the Scoville scale (in Scoville heat units, SHU) were compared with the ion intensities of the capsaicin and dihydrocapsaicin compounds obtained from the imprint-PSI-MS analysis, and a correlation coefficient of 0.97 was achieved. In addition, the ion intensities of a sugar compound were monitored in all peppers, and the results were compared with the Scoville scale. Low sugar ion intensities were detected in pungent peppers, while high ion intensities were achieved in low-pungent peppers, suggesting that the pepper pungency may be determined by inversely relating pungency to sugar contents. This work demonstrates the utility of the imprint-PSI-MS method to perform rapid qualitative analyses of peppers and estimate the pungency by monitoring the pepper metabolites.

Graphical abstract

已经开发了一种称为压印纸喷雾电离质谱的方法（imprint-PSI-MS），并用于测定胡椒的辛辣性。将胡椒果实切成三角形，沉积在三角纸上，然后用自制的压制工具压制，目的是将胡椒成分压印并转移到纸张表面。随后，将三角纸提交给常规PSI-MS分析。分析了十二种辣椒，口味从高辛辣到低辛辣。将Scoville等级的胡椒辛辣度值（以Scoville热单位，SHU）与通过压印-PSI-MS分析获得的辣椒素和二氢辣椒素化合物的离子强度进行比较，得出相关系数为0.97。此外，在所有辣椒中监测糖化合物的离子强度，并将结果与​​Scoville规模进行比较。在辛辣胡椒中检测到低糖离子强度，而在低辛辣胡椒中获得高离子强度，表明胡椒辛辣度可通过将辛辣度与糖含量成反比来确定。这项工作证明了印记-PSI-MS方法可用于对辣椒进行快速定性分析，并通过监测辣椒代谢产物来估算辛辣度。

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