129 Spatial distribution of protein and phenolics in wheat grain as probed by confocal Raman spectral imaging.

O. Piot (1), M. Manfait (1), and J. C. AUTRAN (2). (1) Laboratoire de Spectroscopie Biomoléculaire, Université de Reims, 51 Rue Cognacq Jay, 51096 Reims cedex, France; (2) Unité de Technologie des Céréales et des Agropolymères, 2 Place Viala, 34060 Montpellier Cedex 2, France.

Improved control of fragmentation and dry fractionation of cereal grains lies on better understanding of mechanisms of grain fracture on a molecular level at: aleurone layer/starchy endosperm and starch granule/protein matrix interfaces. Microstructure of wheat kernel was first explored by microspectrofluorimetry to study spatial distribution of phenolics (Saadi et al, 1998). In a second phase, we explored the potential of confocal Raman spectroscopy. Principles of confocality and Raman spectroscopy were pointed out. Wheat samples were selected for their various hardness levels, and aptitudes for separation of outer layers during industrial milling. Identification of characteristic vibrations of Raman spectra was possible using standard components (protein fractions, arabinoxylans, ferulic acid). Information was obtained on component conformation and location at the various interfaces of the wheat kernel. Effects of chemical pretreatments prior to grain milling were followed. Respective interests of fluorescence, infrared and Raman techniques were discussed. New assumptions were formulated about physicochemical bases of endosperm fragmentation in hard or soft wheat types, and of separation between endosperm and outer enveloppes.