Effect of Grain Structure and Cooking on Sorghum and Maize in vitro Protein Digestibility |
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| Affiliation: | 1. University of Pretoria, Department of Food Science, Pretoria, Pretoria 0002, South Africa, Department of Chemistry, Aveiro, 3810-193 Aveiro, Portugal, Norwich Research Park, Colney, Norwich, NR4 7UA, UK;2. Department of Food Science, Pretoria, Pretoria 0002, South Africa, University of Aveiro, Department of Chemistry, Aveiro, 3810-193 Aveiro, Portugal, Norwich Research Park, Colney, Norwich, NR4 7UA, UK;3. Department of Food Science, Pretoria, Pretoria 0002, South Africa, Department of Chemistry, Aveiro, 3810-193 Aveiro, Portugal, Institute of Food Research, Norwich Research Park, Colney, Norwich, NR4 7UA, UK;1. Department of Food Science, Institute for Food, Nutrition and Well-being, University of Pretoria, Private Bag X20, Hatfield 0028, Pretoria, South Africa;2. Department of Anatomy, Faculty of Health Sciences, University of Pretoria, Private Bag X323, Arcadia 0007, Pretoria, South Africa;3. Biotechnology and Nuclear Agriculture Research Institute, Ghana Atomic Energy Commission, P.O. Box LG 80, Legon, Accra, Ghana;1. Department of Food and Nutrition, Faculty of Food Engineering, University of Campinas – UNICAMP, Rua Monteiro Lobato, 80, Cidade Universitária Zeferino Vaz, CP 6121, CEP 13083-862 Campinas, SP, Brazil;2. Department of Food Technology, Faculty of Food Engineering, University of Campinas – UNICAMP, Rua Monteiro Lobato, 80, Cidade Universitária Zeferino Vaz, CP 6121, CEP 13083-862 Campinas, SP, Brazil;3. Embrapa Maize & Sorghum, Brazilian Agricultural Research Corporation, Rodovia MG 424, Km 65, P.O. Box 151, 35701-970 Sete Lagoas, MG, Brazil;1. Department of Food Technology, Universitat de Lleida, Av. Rovira Roure, 191, 25198 Lleida, Spain;2. Departament de Mathematics, Universitat de Lleida, Carrer Jaume II, 69, 25001 Lleida, Spain |
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| Abstract: | Uncooked and cooked sorghum showed improvement in in vitro protein digestibility as the structural complexity of the sample reduced from whole grain flour through endosperm flour to protein body-enriched samples. This was not the case for maize. Cooking reduced protein digestibility of sorghum but not maize. Treating cooked sorghum and maize whole grain and endosperm flours with alpha -amylase to reduce sample complexity before in vitro pepsin digestion slightly improved protein digestibility. The reduction in sorghum protein digestibility on cooking was not related to the total polyphenol content of samples. Pericarp components, germ, endosperm cell walls, and gelatinised starch were identified as possible factors limiting sorghum protein digestibility. Electrophoresis of uncooked and cooked protein-body-enriched samples of sorghum and maize, and prolamin fractions of sorghum under non-reducing conditions showed oligomeric proteins with molecular weights (Mr) 45, 66 and >66 kDa and monomeric kafirins and zeins. Protein-body-enriched samples of sorghum had more 45–50 kDa oligomers than those of maize. In cooked sorghum, some of these were resistant to reduction. Pepsin-indigestible residues from protein-body-enriched samples consisted mainly of α-zein (uncooked and cooked maize) or α-kafirin (uncooked sorghum), whilst cooked sorghum had in addition, β- and γ-kafirin and reduction-resistant 45–50 kDa oligomers. Cooking appears to lead to formation of disulphide-bonded oligomeric proteins that occurs to a greater extent in sorghum than in maize. This may explain the poorer protein digestibility of cooked sorghum. |
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