(262e) Agglomeration and Rheological Properties of Different Wheat Millings

In cereal industry, different millings from common and durum wheat are used to produce a large scale of human and pet foods. In many manufacturing processes, stages of hydration and mixing take place allowing structuring and texturing of end products. The aim of this study is to understand the impact of water addition and the contribution of physical and biochemical characteristics on agglomeration ability and rheological properties of different wheat-based powders. The measurement of the forces produced by a twisted blade on a powder as it progresses in helical fashion through the powder, has been shown to give sensitive and reproducible results.

The study is carried out on very different wheat millings, such as common wheat flours, durum wheat flours, durum wheat groats and durum wheat semolinas. Wheat millings were characterized according to physical (particle size distribution) and biochemical (contents of ash, damaged starch, protein, soluble and insoluble pentosans) parameters. Wheat-based powders and water are mixed in an experimental 1 kg mixer. Powder agglomeration properties are characterized by measurements of weight distribution of three classes according to particle size (isolated particles, agglomerates, and dough pieces) after mixing. A powder rheometer is used to compare cohesion behaviour (depending on compaction rate) and flow stability (related to attrition effects) of different wheat millings at different water contents (13.8 to 30%).

The water content has shown an important impact on agglomeration ability and rheological properties of wheat powders. Low water contents are characterized by weak cohesion between particles and changes due to attrition effects (flow stability index below 1). As water content increases, the content of isolated particles decreases as they form agglomerates and dough pieces. Conversely, high water contents are characterized by high cohesion between particles and no changes due to attrition effects. Different wheat millings have presented specific rheological properties. At low water content, common wheat flour and durum wheat semolina have lower cohesion than durum wheat flour and groat. The common wheat flour is less cohesive at the end of the test, the cohesion of durum wheat semolina is not affected during the test and durum wheat flour and groat are more cohesive at the end of the test At high water content, only the durum wheat semolina has a weak cohesion and is still not be affected by attrition effects. Common wheat flour and durum wheat flour are less cohesive at the end of the test when durum wheat groat is not sensitive to attrition. The cohesion behaviour at low and high levels of water content seems to be linearly correlated (R² from 0.44 to 0.55). Cohesion behaviour of different wheat millings at low water content seems to be correlated to initial particle size distribution (R² from 0.42 to 0.63) and wheat protein fractions (R² from 0.45 to 0.71).

The study of agglomeration and rheological properties of different wheat millings has a great interest to understand structuration mechanisms during manufactoring processes. Powders properties could permit the prediction of end product qualities.