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Heat treatments reduce in vitro protein digestibility of proso millet (Panicum miliaceum) flour
P. GULATI (1), D. J. Rose (2). (1) Univ of Nebraska-Lincoln, Lincoln, NE, U.S.A.; (2) University of Nebraska-Lincoln, Lincoln, NE, U.S.A.
The storage proteins in proso millet (<i>Panicum miliaceum</i>) are similar to sorghum. Because sorghum protein digestibility is greatly affected by heating, the objective of this study was to determine the effect of heating on protein digestibility of proso millet. De-hulled proso millet flour was subjected to various heat treatments, including heating at different temperatures (0-100°C) in excess water; dry heating in an oven or autoclave in closed containers at different moisture contents (10-30%); and extrusion (17% moisture content, 210 rpm and 120°C); and then subjected to <i>in vitro </i>protein digestion using pepsin. Sorghum and wheat flours were treated under the same conditions for comparison. Wet heating resulted in a reduction in proso millet protein digestibility from 80% in the raw flour to 35% when flour was heated at 100ËšC for 20 min prior to digestion. Sorghum flour exhibited a similar reduction in protein digestibility under the same conditions (from 77 to 48%), while no change was observed for wheat flour. Reductions in protein digestibility were also observed for dry heating of millet flour using an oven or autoclave (34% digestibility) regardless of moisture content; extrusion also reduced protein digestibility. These results suggest that the protein digestibility of proso millet decreases upon subjecting the flour to dry or moist heat treatments above 60°C. Further investigations on structure of proso millet protein may help explain the observed changes.
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