Microstructural changes to proso millet protein bodies upon cooking and digestion

Cooking results in a drastic decline in digestibility of proso millet proteins, panicins. Scanning electron and confocal microscopy were used to observe morphological changes in proso millet protein bodies upon cooking and digestion that could be associated with the loss in digestibility. Spherical protein bodies (1-2.5 μm) were observed in proso millet flour and extracted protein. Cooking did not result in any noticeable change in the size or shape of the protein bodies. However, upon digestion with pepsin the poor digestibility of cooked proso millet protein was clearly evident from the differences in microstructure of the protein bodies: large cavities were observed in the uncooked protein bodies while cooked protein bodies had only tiny holes. When proso millet was cooked in 8 M urea and then digested, the protein bodies appeared similar to uncooked digested protein bodies. The morphological changes observed in proso millet protein upon cooking and digestion did not show any visible aggregates, but the inability of pepsin to digest cooked protein bodies was clearly evident under microscopy and is in agreement with the chemical analyses reported previously.