82 Application of the BCA assay to identify sorghum with high protein digestibility.

A. ABOUBACAR and B. R. Hamaker. Dept. of Food Science, Purdue Univ., W. Lafayette, IN 47907.

Recently, we developed a quick electrophoresis-based protein digestibility assay that can be used by breeders to identify highly digestible sorghum cultivars. The assay consisted of a 1-hour pepsin-digestion of sorghum flours followed by SDS-PAGE of the undigested proteins and densitometric measurement of the alpha-kafirins band intensity. Very high correlation coefficients were obtained between the assay and standard procedures of protein digestibility determinations. Here we report on an even quicker colorimetric procedure that uses the bicinchoninic acid (BCA) protein assay to quantify the undigested sorghum proteins. Using ninety sorghum samples, we found a correlation coefficient of r = 0.92 between the BCA assay and the electrophoresis-based assay. More importantly, two distinct populations of normal and highly digestible sorghum cultivars were obtained when the results of the BCA assay were compared to those of the electrophoresis-based assay. With this assay, highly digestible sorghum cultivars were defined at an absorbance cut-off. We estimate that about 120 samples can be assayed in a day using the BCA assay as compared to 60 samples with the electrophoresis-based assay.