Quantification of rice α‐globulin allergen using liquid chromatography–tandem mass spectrometry combined with cysteine‐specific modifier and extended stable isotope‐labeled peptide

Abstract

An absolute quantification of α-globulin in rice matrices based on the liquid chromatography–tandem mass spectrometry (LC–MS/MS) utilizing extended stable isotope-labeled (SIL) peptides were studied. Two modified signature peptides, derived from the cysteine-specific modification by IAA during the tryptic digestion process, were identified and selected as the surrogates of α-globulin due to the 1.5–4.5-fold enhancement of intensity peak compared with its unmodified form. The digestion efficiency could be improved from 72.3%–98.8% to 94.0%–105.3%, and matrix interference normalized from –26.6% –4.5% to –6.0% –5.5% when the extended SIL peptides were used as ISs. The limit of detection (LOD) and limit of quantification (LOQ) for the α-globulin were 0.25 μg/g and 0.8 μg/g, respectively. The recoveries of α-globulin spiked at three levels were between 82% and 105%. The described method was successfully employed for the determination of α-globulin in rice and food product samples.