EXTRUSION-COOKING OF PEA FLOUR - STRUCTURAL AND IMMUNOCYTOCHEMICAL ASPECTS

Pea flour was submitted to extrusion-cooking under various conditions. The progressive structural transformation was investigated by light microscopy and immuno-gold transmission electron microscopy. Each of the three major compounds, i.e., starch granules, protein bodies, and cell wall fragments, develop a specific, independent structure. Protein bodies aggregate and fuse giving a protein matrix. Starch granules swell, deform, come into contact with each other, and ultimately also fuse together. The resulting gel expands giving honey-combed structure. Consequently, the protein matrix is arranged into dense strata, i.e., protein fibers in cross or longitudinal sections, disrupted by the expanded starch gel. Cell wall fragments are clustered together and seem to be intact. This structural segregation is shown to be related to the fact that protein bodies fuse before starch granules. The use of pressure and heating models in conjunction with scanning electron microscopy confirm this observation. On the other hand, immuno-gold labelling has shown that the legumin fraction was localized in the protein bodies as well as in the protein fibers. This indicates that, during extrusion-cooking, some of the antigenic determinants of this protein were not affected.