Genotype and grain pretreatment effects on digestibility of sorghum proteins in the Ethiopian fermented bread

Authors: BELAINEH, YEMANE - Kansas State University; Bean, Scott; Aramouni, Fadi; Wu, Xiaorong; LIU, SANZHEN - Kansas State University; TESSO, TESFAYE - Kansas State University

Submitted to: Cereal Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/26/2024
Publication Date: 1/2/2025
Citation: Belaineh, Y.G., Bean, S.R., Aramouni, F.M., Wu, X., Liu, S., Tesso, T.T. 2025. Genotype and grain pretreatment effects on digestibility of sorghum proteins in the Ethiopian fermented bread. Cereal Chemistry. 102(1):102-116. https://doi.org/10.1002/cche.10821.
DOI: https://doi.org/10.1002/cche.10821

Interpretive Summary: Sorghum is an important source of calories and protein for vulnerable populations, especially in Sub-Saharan Africa and Southeast Asia. However, the low digestibility of sorghum proteins can lead to protein malnutrition when sorghum is consumed as a primary staple food product. While cooking sorghum generally reduces protein digestibility, the digestibility of foods made from fermented sorghum tend to not be as impacted as other food types. Therefore, the objective of this study was to investigate the impact of grain processing treatments on protein digestibility of fermented flat bread. Four sorghum varieties were subjected to three processing treatments, decortication, sprouting, and roasting, as well as ground into two particle sizes of flour. Sprouting sorghum before making it into fermented bread significantly increased the protein digestibility compared to all other treatments. Grinder samples into finer particle size also tended to improve digestibility. Sprouting grain before making fermented foods and grinding grain to small particle sizes is a low-cost, simple method to improve the nutritional quality of sorghum-based foods.

Technical Abstract: Sorghum is the principal food source for smallholder farmers in Sub-Saharan Africa. Animal proteins are beyond economic reach, and only few food legumes are well-adapted in major sorghum-growing regions. Hence, sorghum serves as the primary source of protein and calories. However, the low digestibility of its proteins renders the communities vulnerable to protein malnutrition. Several factors, including genotypes and processing methods, have been shown to affect the digestibility of proteins in sorghum food products. The objective of this study was to investigate the impact of grain pretreatment on the protein digestibility of Ethiopian fermented flatbread. Findings: The effect of four grain pretreatment processes: decortication, sprouting, parching, and untreated control was compared using four diverse sorghum genotypes milled to medium (2 mm) and fine (0.5 mm) particle sizes. The in-vitro protein digestibility (IVPD) was significantly lower in the parched samples compared to the unprocessed control, while sprouting significantly increased IVPD. Decortication appears to have no impact on IVPD. Finer particle size tended to enhance IVPD in all genotypes and for all pretreatement methods. The treatments had no significant effect on protein content except the sprouting consistently but marginally increased total protein. Conclusions: Sprouting sorghum grains can significantly improve the protein digestibility of fermented breads. Given that it involves little cost, the process can be readily adopted by the local community, provided that they are educated about the impact of protein deficiency on the health and productivity of the community. Significance and Novelty: Low-cost grain pretreatment procedures such as sprouting can have a significant impact on the availability of nutrients, especially protein, the most limiting nutrient in smallholder communities. Combining the procedure with genetically enhanced varieties and improved cropping systems that integrate food legumes can significantly enhnace protein nutrition for smallholder farmers.