Disulfide exchange reactions in wheat dough impact the polymerization of gluten and the volume of bread. In wheat sourdoughs fermented with Lactobacillus sanfranciscensis, glutathione reductase activity accumulates thiols. This study investigated the role of glutathione reductase and NADH oxidase of L. sanfranciscensis on disulfide exchange reactions, peroxide levels, and gluten polymerization in type I wheat sourdoughs. Fermentation with L. sanfranciscensis DSM20451 Δ gshR lacking glutathione reductase activity reduced the thiol levels in dough when compared to the wild type strain L. sanfranciscensis DSM20451. Fermentation with any strain reduced peroxides in wheat doughs when compared to a chemically acidified control. The impact of baker's yeast on thiol and peroxide levels was greater than the impact of lactobacilli. The depolymerization of gluten proteins was dependent on the free thiol content and dough acidification. Bread produced with the glutathione reductase deficient mutant strain had the highest specific volume compared with all the other groups.
Keywords: L. sanfranciscensis; NADH oxidase; glutathione reductase; gluten macropolymer; type I sourdough.