The effect of genotype and traditional food processing methods on in-vitro protein digestibility and micronutrient profile of sorghum cooked products

Authors: WEERASOORIYA, DILOOSHI - Kansas State University; Bean, Scott; NUGUSU, YOHANNES - Ethiopian Institute Of Agricultural Research; Ioerger, Brian; TESSO, TESFAYE - Kansas State University

Submitted to: PLOS ONE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/29/2018
Publication Date: 9/7/2018
Citation: Weerasooriya, D.K., Bean, S.R., Nugusu, Y., Ioerger, B.P., Tesso, T.T. 2018. The effect of genotype and traditional food processing methods on in-vitro protein digestibility and micronutrient profile of sorghum cooked products. PLoS One. 13(9):e0203005. https://doi.org/10.1371/journal.pone.0203005.
DOI: https://doi.org/10.1371/journal.pone.0203005

Interpretive Summary: Uncooked and processed food samples from 15 sorghum varieties, one variety of maize and one teff sample were investigated for nutritional composition and quality. Grain quality and nutritional traits measured included protein digestibility, phytic acid concentration, phytase levels, trypsin inhibitor activity, and iron and zinc content. The results revealed a highly significant interaction between genotype and food processing methods where, occasionally, genotypes with highest protein digestibility under one processing method ended up with the lowest under another. Mineral contents of the samples were also impacted by food processing methods, possibly through the degradation of phytic acid. These results showed that the nutritional quality of sorghum foods varied widely depending on the food processing method used as well as the sorghum variety used. Identification of specific varieties for a specific food product may help improve the nutritional quality of sorghum foods.

Technical Abstract: Uncooked and processed food samples from 15 sorghum (Sorghum bicolor (L.) Moench) varieties, and one variety of maize (Zea maize) and teff (Eragrostis tef) all of Ethiopian origin were investigated for nutritional composition and quality. Traits including in-vitro pepsin digestibility (IVPD), phytic acid concentration, phytase levels, trypsin inhibitor activity, and iron and zinc content were measured on all samples. Kafirin composition of genotypes was also determined using uncooked samples via reverse phase high performance liquid chromatography (RP-HPLC). Upon cooking, sorghum showed a greater reduction in IVPD as compared to maize but was not different from teff. Results revealed a highly significant interaction between genotype and food processing methods where, occasionally, genotypes with highest IVPD under one processing method ended up with lowest under another. Trypsin inhibitor levels had a significant and negative correlation with IVPD (r2=0.1), while changes to phytic acid concentration and intrinsic phytase levels during processing followed opposite trends to each other. Processing increased mineral levels by 20-44% for iron and 4-29% for zinc possibly owing to degradation of phytic acid. Results demonstrated that protein digestibility behavior and anti-nutritional factor concentrations of sorghum varied widely depending on the food processing method used. Identification of specific genotypes for a specific food product may help improve the nutritional quality of sorghum based food products.