A rapid protein digestibility assay for identifying highly digestible sorghum lines

Protein digestibility in sorghum (Sorghum bicolor (L.) Moench) lines was de termined using two standard procedures (pepsin digestibility and pH-stat) a nd compared with a newly developed, rapid electrophoresis-based screening a ssay. The new assay was based on the rate of alpha -kafirin disappearance a fter pepsin digestion. alpha -Kafirin, the major sorghum storage protein, m akes up approximate to 60-70% of the total protein in the grain. In the new assay, samples were first digested with pepsin for 1 hr, and undigested pr oteins were then analyzed by SDS-PAGE. The intensities of the undigested a- kafirin bands were measured. Higher band intensity indicated lower protein digestibility. The new assay was significantly correlated with the standard pepsin digestibility assay (r = -0.96, n = 16) after which it was patterne d. The same was true of the pH-stat procedure (r = -0.85, n = 16). This imp lies that the new assay is comparable to existing procedures and can be use d for screening sorghum lines for protein digestibility. Two groups consist ing of high-protein digestibility and wild-type sorghum lines were identifi ed when the new assay was tested on 48 sorghum lines derived from crosses o f wild-type and mutant high protein digestibility lines, indicating that th e new assay was efficient in differentiating between the two groups. Advant ages of the new assay over the standard procedures include considerable red uction in analysis time and sample size required for the analysis. For exam ple, analysis time was reduced by 20% and sample size by 10% when the new a ssay was used as compared with the pH-stat procedure. We estimate that appr oximate to 60 sorghum lines can be screened in a day by a single operator u sing the new assay.