Barley malting quality depends on seed characteristics achieved during grain development and germination. One important parameter is protein accumulation in the mature seed， which may vary between cultivars. Here we conducted a protein pattern analysis in the range of pI 4-7 of mature grains from five Mexican barley cultivars， commonly used for malt and beer production. Reproducibly distinct protein spots， separated by 2D SDS PAGE， were identified by mass spectrometry and considered as potential markers for cultivars with distinct seed protein accumulation. The expression patterns of glutamate decarboxylase (GAD) and protein disulfide isomerase (PDI1-1) were followed at transcript level during grain development for three independent growth cycles to establish whether differences between cultivars were reproducible. Quantitative determination of PDI1-1 protein levels by ELISA confirmed a reproducibly， distinctive accumulation and post-translational modifications between cultivars， which were independent of plant growth regimes. According to its impact on differential storage protein accumulation， we propose the PDI1-1 protein as potential biomarker for Mexican malting barley cultivars.