INFLUENCE OF STORAGE ON PEPTIDE SUBUNIT COMPOSITION OF RICE ORYZENIN

Peptide subunits of oryzenin preparation from postharvest and stored rice grains of the two typical U.S. rice varieties (long and medium grain) have been studied by SDS-PAGE. Both studied varieties of the postharvest and/or stored rice had similar qualitative peptide subunit compositions. The subunits which occurred in the reduced denatured oryzenin had molecular weights 12 300,14 200,22 000-23 000 (double spot), 32 000-37 000 (double spot), 56 000, 79 200, 83 000, 91 300, 104 000, 141 000, 169 000, 181 000, and 202 000. The results revealed differences not only between the rice varieties but also between the postharvest and stored rice grains of the same variety. The low molecular weight peptide subunits decreased and the high molecular weight peptide subunits increased during storage. The average molecular weight of oryzenin increased during storage. This increase was caused not only by the cystine bridges but also by more complex changes in peptide composition.