FTIR and solid state 13C NMR spectroscopy of proteins of wet cooked and popped sorghum and maize

Fourier transform infrared (FTIR) and solid state (13)C NMR spectroscopic methods were used to investigate changes in maize and sorghum proteins on wet cooking and popping. FTIR spectra indicated that wet cooking led to proteins in two normal sorghums, namely NI( 283 a red hybrid) and KAT 369 (a white variety), two sorghum mutants (P850029 and P851171) and a maize hybrid (PAN 6043) assuming more antiparallel intermolecular beta -sheet character, possibly at the expense of some alpha -helical conformation. Solid stale (13)C NMR, using the technique of Cross Polarisation Magic Angle Spinning show ed shifts of the protein carbonyl carbon and alpha -carbon resonances upfield on M et cooking in all samples, also indicating a change in protein secondary structure from alpha -helical to beta -sheet conformation. The extent of secondary structural change on wet cooking seemed to be greater in sorghum than in maize and may have a bearing on the inferior protein digestibility of wet cooked sorghum compared to maize. Popping produced the same secondary structural change as observed for wet cooking in both sorghum and maize. However, the extent of change on popping was less than on wet cooking in sorghum and maize. (C) 2001 Academic Press.