Changes in Green Coffee Protein Profiles during Roasting

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Abstract
To reveal its flavor, coffee has to be roasted. In fact, the green coffee bean contains all ingredients necessary for the later development of coffee flavor. It is now widely accepted that free amino acids and peptides are required for the generation of coffee aroma. However, the mechanisms leading to defined mixtures of free amino acids and peptides remain unknown. Information pertaining to the identification of precursor proteins is also lacking. To answer some of these questions, two-dimensional polyacrylamide gel electrophoresis (2D-PAGE) was used to follow the fate of green coffee proteins. Two conditions were considered: roasting and incubation of green coffee suspensions at 37 °C. Coffee beans were observed to acquire the potential to spontaneously release H2O2 upon polymerization of their proteins during roasting. Fragmentation of proteins was also observed. Conversely, H2O2 was found to control polymerization and fragmentation of green coffee proteins in solution at 37 °C. Polymerization and fragmentation patterns under the two conditions were comparable. These observations suggest that the two conditions under study triggered, at least to some extent, similar biochemical mechanisms involving autoxidation. Throughout this study, a unique fragmentation cascade involving the 11S coffee storage protein was identified. Generated fragments shared an atypical staining behavior linked to their sensitivity to redox conditions. Keywords: Green coffee; roasting; storage protein; autoxidation; hydrogen peroxide; two-dimensional polyacrylamide gel electrophoresis