ÉVALUATION DE DIVERS TRAITEMENTS TECHNOLOGIQUES DES CÉRÉALES II. — ÉTUDES HISTOLOGIQUES ET CYTOCHIMIQUES DES CARYOPSES DU MAÏS ET DE L'ORGE. EFFETS DES TRAITEMENTS D'EXPANSION ET DE FLOCONNAGE

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Abstract
Using complementary techniques (light and scanning electron microscopy), the histological and cytochemical characteristics of barley and maize grains before and after popping and steam flaking are described. The localization of the biochemical cell constituents of the grain was done by means of the most specific staining methods. Popping of maize grains caused heterogenous reactions according to the constitution and localization of the different tissues within the cereal grain. From the outer to the central part of the latter, different zones could be differentiated. In the unpopped peripheral zones, starch granules were little or not at all swollen and the protein matrice was stretched. Near the popped zones, starch granules were partly swollen and a bubble was found in their center (a "soap-bubble" like structure). The inner part of the endosperm showed an alveolar structure where starch was completely gelatinized and pushed against the remnant cell walls. The reaction was more homogeneous for barley: starch granules were generally slightly swollen, and the protein matrice was stretched. Steam flaking, especially with maize, produced a disorganization of the cell structure: the cell walls were broken and the cell content was more or less dispersed. In details, the starch granules were very slightly deformed. They showed a beginning of gelatinization and their surface was always fissured (revealing a moist-heat treatment in 2 steps). The protein matrice seemed to be reticulated and fragmented. These 2 moist-heat treatments brought about a more or less pronounced disorganization of the endosperm of the grains, but resulted in a good protection of the outer layers (aleuron and adjacent layers). A critical study of the staining treatments and a comparison of the results obtained by light and scanning electron microscopy allowed to differentiate the cellular and tissular changes imputable to moist-heat treatments from those depending on preparation artefacts.

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