Microstructural and conformational changes of gluten proteins in wheat-rye sourdough

Changes in the microstructure and secondary structure of sourdough gluten proteins were studied. Four strains of lactic acid bacteria (LAB) were used in fermentations, Lactobacillus delbrueckii subsp. bulgaricus (LB), Lactobacillus fermentum (LF), Lactobacillus plantarum (LP), and Pediococcus pentosaceus (PP). LAB fermentative profiles were performed by potenciometric measurements, microstructural analyses by scanning electron microscopy (SEM), and conformational changes by Raman spectroscopy. Gluten proteins experienced different degree of depolymerisation into defined microstructures, as fibril networks and laminar-like structures, and their occurrence was associated to an increase in beta-sheets structures. These changes were dependent upon the distinctive acidifying kinetics of each strain. Gluten proteins of LF and LP sourdough were preferably arranged into laminar structures, and, in both cases, parallel beta-sheet was the predominant conformation. Meanwhile for LB and PP sourdough, the development of three-dimensional fibril networks prevailed and it was accompanied by an increase of antiparallel beta-sheets. LAB fermentative activity also lead to modifications in disulphide bonds and in the microenvironment concerning aromatic amino acids.