Effects on Gluten of Heating at Different Moisture Contents. I. Changes in Functional Properties

Drying is regarded as being the most critical step in the commercial production of vital wheat gluten. To study the drying process, the effects were determined of heating gluten at 80°C for 30 min at moisture contents ranging from 6 to 60%. The breadmaking quality of flour containing 3% (w/w) of added gluten was severely impaired when the gluten had been heated at moisture levels greater than 20%. At this level, the water activity was greater than 0·9. The Brabender Extensograph extensibility and maximum resistance ( R m) of doughs made from flour containing 4% gluten decreased sharply for gluten that had been heated at moisture contents between 20 and 25%; outside this moisture content range, R m increased, and, over the whole range of moisture contents, the resistance after 50-mm paper transport ( R 1) increased. An increase in apparent viscosity at a deformation rate of 0·001 rad/s was observed for doughs from flour containing 4% gluten heated at a moisture content greater than 20%. The extractibility of different protein classes in sodium dodecyl sulphate solution showed a decrease in low M r glutenin aggregates (< 1 × 10 6) and an even larger decrease in the high M r glutenin aggregates (> 1 × 10 6). No significant change in extractibility was observed for gliadins, albumins and globulins. This indicates that changes in glutenin aggregation are responsible for the observed changes in functional properties. Differences in R 1 , R m and glutenin extractability between glutens heated at an intermediate moisture content (20-25%) and those that were fully hydrated (> 55%) indicated differences in the nature of the heat damage.