Effect of puffing on ultrastructure and physical characteristics of cereal grains and flours

Puffed cereals are commonly used as ready-to-eat breakfast foods or as ingredients in snack formulations. Few investigations have been made on the ultrastructure and physical characteristics of puffed cereals; the properties of the flours milled from them have been even less investigated. The changes associated with the gun puffing process were evaluated for six different grains: common wheat, emmer wheat, rye, barley, rice and buckwheat. The results demonstrate that the effect of the puffing treatment is strongly influenced by the morphology and composition of the kernel. Puffed rye and rice have a very porous matrix, made up of numerous cavities of different sizes separated by a very thin ‘wall’ puffed wheat, emmer wheat and barley on the other hand show a much more compact, homogeneous and less porous structure; puffed buckwheat is characterised by a large number of small and regular cavities. Moreover, puffing induces significant changes in the structure and physical properties of the starch and an increased water holding capacity of both the grains and the flours.