Turbidity assay for rapid and efficient identification of high protein digestibility sorghum lines

ABSTRACT Recently, our laboratory reported a protein digestibility assay based on SDS-PAGE that distinguishes mutant high protein digestibility from wild-type sorghum lines. Using that assay, high protein digestibility sorghum lines were identified both qualitatively (visual observation) and quantitatively by measuring the SDS-PAGE band intensity of the undigested α-kafirin protein. Here, we report on a new turbidity assay that can be used for an even quicker quantitation of the undigested proteins with much higher throughput for screening purposes. Proteins remaining after 1 hr of pepsin digestion were extracted with a buffer of SDS, 2-mercaptoethanol, and borate and an aliquot of the extract was precipitated using 72% trichloroacetic acid (TCA). Absorbance of the resulting turbid solution was then read at 562 nm. Lower readings corresponded to more digestible lines. The turbidity of the suspensions developed quickly and reached a plateau at ≈5 min for high protein digestibility lines and 10 min for wild...