Water dynamics in white bread and starch gels as affected by water and gluten content

Three levels of water (180, 220 and 260 g/345 g flour) and three levels of gluten (giving 11.2, 13.0 and 14.2 g protein/100 g flour) were used to study the effects of water and gluten on water mobility in white bread using ¹H nuclear magnetic resonance (NMR) relaxometry. Changes in the transverse relaxation time (T₂) were related to water mobility. The three water levels resulted in three different moisture contents in the finished bread (0.55-0.77 g H₂O/g solids). Distributed exponential analysis showed two distinct regions of T₂ (30-600 μs and 1-60 ms), associated with multiple domains of water in the bread crumb. There was no significant difference in peak T₂ values with different gluten content, but significant differences were observed with different moisture content. The results suggested that the mobility of water associated with starch decreased dramatically because of gelatinization. To further investigate the effect of gluten on starch gelatinization, NMR measurements were made directly on model systems containing starch and various gluten amounts. The starch-gluten gels had higher T₂ values than pure starch gels, indicating less swelling of starch granules and absorption of water. This was attributed to less water available to starch in the presence of gluten.