Model studies for wheat sourdough systems using gluten, lactate buffer and sodium chloride

Model studies were conducted in order to study the influence of acid and NaCl, as occurring in wheat sourdough bread, on fundamental rheological properties of wheat gluten. Gluten was divided into pieces and subjected to a swelling period in lactate buffer of pH 3.9, with or without added NaCl (3 g/100 ml). The respective controls were unbuffered NaCl solution and pure water. The microstructure of the gluten pieces was studied by laser-scanning confocal microscopy and the recombined pieces were examined using fundamental rheology. The combination of buffer (pH 3.9) and NaCl in comparison to unbuffered NaCl solution caused a denser, but partially dissolved fibrillar microstructure. Further to this, swelling of the gluten was reduced (62.0% versus 65.9% moisture) and an increase in firmness and elasticity was observed: in comparison with unbuffered NaCl solution, the absolute value of the complex dynamic modulus (IG*I) was higher, while the phase angle was lower in dynamic oscillatory measurements at 30degreesC and dynamic temperature sweeps (30-95degreesC), while in creep tests at 30degreesC and 95degreesC strain values were lower and relative recovery higher. In contrast, pH 3.9 buffer without added NaCl caused softer rheological behaviour than water and a film-like microstructure.