Abstract
Kafirin, the hydrophobic prolamin storage protein in sorghum grain is enriched when the grain is used for bioethanol production to give dried distillers grain with solubles (DGGS) as a by-product. There is great interest in DDGS kafirin as a new source for biomaterials. There is however a lack of fundamental understanding of how the physicochemical properties of DDGS kafirin having been exposed to the high temperature conditions during ethanol production, compare to kafirin made directly from the grain. An understanding of these properties is required to catalyse the utilisation of DDGS kafirin for biomaterial applications. The aim of this study was to extract kafirin directly from sorghum grain and from DDGS derived from the same grain and, then perform a comparative investigation of the physicochemical properties of these kafirins in terms of: polypeptide profile by sodium-dodecyl sulphate polyacrylamide gel electrophoresis; secondary structure by Fourier transform infra-red spectroscopy and x-ray diffraction, self-assembly behaviour by small-angle x-ray scattering, surface morphology by scanning electron microscopy and surface chemical properties by energy dispersive x-ray spectroscopy. DDGS kafirin was found to have very similar polypeptide profile as grain kafirin but contained altered secondary structure with increased levels of β-sheets. The structure morphology showed surface fractals and surface elemental composition suggesting enhanced reactivity with possibility to endow interfacial wettability. These properties of DDGS kafirin may provide it with unique functionality and thus open up opportunities for it to be used as a novel food grade biomaterial.
Highlights
Kafirin, the hydrophobic prolamin storage protein in sorghum grain is enriched when the grain is used for bioethanol production to give dried distillers grain with solubles (DGGS) as a by-product
A detailed comparison of physicochemical characteristics of sorghum, grain kafirin and sorghum Dried distillers grain with solubles (DDGS) kafirin identified differences between the two types that likely arose from heat induced molecular changes to the DGGS kafirin during the bioethanol production process
The primary and quaternary structures of the two kafirins appeared similar through electrophoretic examination
Summary
The hydrophobic prolamin storage protein in sorghum grain is enriched when the grain is used for bioethanol production to give dried distillers grain with solubles (DGGS) as a by-product. There is a lack of fundamental understanding of how the physicochemical properties of DDGS kafirin having been exposed to the high temperature conditions during ethanol production, compare to kafirin made directly from the grain. The structure morphology showed surface fractals and surface elemental composition suggesting enhanced reactivity with possibility to endow interfacial wettability These properties of DDGS kafirin may provide it with unique functionality and open up opportunities for it to be used as a novel food grade biomaterial. The high hydrophobic to hydrophilic ratio is the principal characteristic that allows selfassembly of kafirin into various mesostructures such as spherical particles, films and fibres[4] This hydrophobic nature is due to the large number of hydrophobic amino acid residues, for instance proline and amide nitrogen from glutamine ( it belongs to the class of proteins called prolamins). A complete structural and/or surface elemental analysis with regards to material functionality has not been studied yet, hindering the potential use of these proteins for development of new value-added biomaterials
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