Sorghum grain is an important cereal that thrives under arid growing conditions less tolerated by wheat and corn. Sorghum is utilized as an animal feed and human food in various parts of the world. However, sorghum grain protein is known for having reduced in-vitro protein digestibility (IVPD) compared to other cereals limiting sorghum nutritional quality. Previous research has identified high digestible sorghum mutants in which misshapen protein bodies were responsible for increased protein digestibility. However, significant variation in IVPD of wild-type sorghum lines exists and little research has been done to determine what factors govern digestibility in non-mutant sorghum populations. A genetically diverse sorghum association mapping population was analyzed for several factors hypothesized to be related to IVPD. As expected, tannin content decreased protein digestibility. Non-tannin sorghums averaged 58% digestibility while tannin containing sorghums averaged only 46%. The tannin containing sorghum lines exhibited a strong negative correlation between tannin content and IVPD (r= -0.82) as expected. However, within the non-tannin sorghum population, total non-tannin phenolics did not correlate to digestibility. Physical grain traits including kernel weight, diameter, and hardness did not correlate to IVPD in the non-tannin sorghum population. Protein cross-linking was analyzed on a subset of non-tannin samples using selective extraction and size exclusion chromatography. This analysis revealed that the degree of protein cross-linking negatively correlated to IVPD (r= -0.61). The presence of protease inhibitors also decreased IVPD in sorghum. Phytic acid levels did not correlate with IVPD in a subset of the non-tannin samples. Further work will include developing biochemical methods to unlock the latent nutrient potential of sorghum grain to attain increased value of cultivated natural resources through elevated bioavailability.

Factors related to reduced in-vitro protein digestibility in a diverse sorghum population

249th National Meeting (2015)

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