Protein extraction method for the proteomic study of a Mexican traditional fermented starchy food

Pozol is a traditional fermented maize dough prepared in southeastern Mexico. Wide varieties of microorganisms have already been isolated from this spontaneously fermented product; and include fungi, yeasts, and lactic- and non-lactic acid bacteria. Pozol presents physicochemical features different from that of other food fermentation products, such as a high starch content, in addition to a low protein content. It is these qualities that make it intractable for protein recovery and characterization. The aim of this study was to develop a methodology to optimize the recovery of proteins from the pozol dough following fermentation, by reducing the complexity of the mixture prior to 2D-PAGE analysis and sequencing, to allow the characterization of the metaproteome of the dough. The proteome of 15 day fermented maize dough was characterized; proteins were separated and analyzed by mass spectrometry (LC–MS/MS). Subsequent sequence homology database searching, identified numerous bacterial and fungi proteins; with a predominance of lactic acid bacterial proteins, mainly from the Lactobacillus genus. Fungi are mainly represented by Aspergillus. For dominant genera, the most prevalent proteins belong to carbohydrate metabolism and energy production, which suggest that at 15 days of fermentation not only fungi but also bacteria are metabolically active.