Qualitative assessment of 'highly digestible' protein mutation in hard endosperm sorghum and its functional properties

Sorghum mutants with altered protein body structure have improved protein nutritional quality; however, practical methods to accurately track heritability of the trait are lacking. We evaluated suitability of the in vitro pepsin assay, and a new high-resolution field emission electron microscopy (FE-SEM) method to detect the mutation (HD) in hard-endosperm sorghum; and compared the physicochemical properties of experimental HD sorghums to wild type (LD) lines. FE-SEM reliably resolved sorghum protein body structure, allowing for qualitative classification of sorghum as HD or LD. The pepsin assay was less reliable, with significant variations across environments. Nevertheless, HD lines averaged higher protein digestibility (69.4% raw, 57.6% cooked) than LD lines (61.7% raw, 45.6% cooked). The HD lines also had better water solubility and starch pasting profiles than LD lines. FE-SEM, but not pepsin assay, reliably detects HD nutation in sorghum. The HD trait may improve food-use functionality of sorghum.