Abstract
The effect of redox reactions catalysed by lactobacilli on properties of wheat gluten was followed during sourdough fermentations. Thiol levels in doughs remained high in doughs fermented with Lactobacillus sanfranciscensis or in chemically acidified doughs to which 10 μmol g –1 glutathione were added. In chemically acidified doughs or sourdoughs fermented with L. sakei or L. perolens, the thiol levels decreased during fermentation. Thiol-groups in gluten proteins were estimated by RP-HPLC separation of DAC-maleimide-labeled, propanol-soluble proteins extracted from wheat doughs. An increase of the SH groups in gluten proteins was observed in protein fractions from sourdoughs fermented with L. sanfranciscensis but not from chemically acidified doughs. A glutathione-reductase was expressed in L. sanfranciscensis and during its growth in sourdough resulted in the reduction of extracellular GSSG to GSH. It was concluded that in addition to the pH-dependent activity of cereal proteases, redox reactions catalysed by lactobacilli determine gluten quality during sourdough fermentations. The formation of thiols by L. sanfranciscensis interferes with gluten polymerisation. Due to differences in their central carbon metabolism, homo- or facultative hetero-fermentative lactobacilli have opposite effects on redox-reactions in wheat doughs.
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