Physicochemical characterisation of kafirins extracted from sorghum grain and dried distillers grain with solubles related to their biomaterial functionality

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.

Advances in Extraction, Structure, and Physiochemical Properties of Sorghum Kafirin for Biomaterial Applications: A Review

“…An early method used for laboratory-scale sorghum protein isolation was sequential (Osborne) extraction [27], in which water-soluble proteins (albumins) and salt-soluble proteins (globulins) are extracted by water and salt solutions, respectively, followed by extraction of prolamins by aqueous alcohol at room temperature. Other early methodologies for extracting kafirin include the Landry-Moureaux method, which extracted kafirin fractions with different molecular weights, either with alcohol or aqueous alcohol and reducing agents like sodium metabisulphite.…”

“…In these binary systems, the more polar solvent, e.g., water, interacts with polar amino acids. In contrast, the less polar organic compound interacts with the non-polar amino acids to give effective dissolution [27].…”

“…Tertiary solvent systems are those with a combination of water, low aliphatic alcohol, and other components. Examples reported for kafirin extraction include water + lower aliphatic alcohol + acetone, ethylene glycol, formaldehyde, or nitromethane [27]. The different extraction systems used for kafirin will now be reviewed in more detail.…”

Propiedades nutricionales, funcionales y bioactivas de alimentos a base de sorgo: Avances y oportunidades para su aprovechamiento integral

“…Los cuerpos proteicos de las kafirinas poseen una capa externa compuesta principalmente de βy γ-kafirinas entrecruzadas mediante puentes disulfuro y un interior comprendido predominantemente de α-kafirinas (Labuschagne, 2018;Shah et al, 2021). Este rearreglo que adoptan las kafirinas entre sí y las interacciones que establecen con el almidón determinan su baja digestibilidad y pobres propiedades funcionales, ya que las α-kafirinas, que son la forma más digerible y abundante, quedan atrapadas en una red polimérica que las vuelve poco accesibles (Labuschagne, 2018).…”

Proteínas do sorgo

“…Suas proteínas apresentam baixa digestibilidade, devido principalmente ao alto conteúdo de prolaminas e taninos (DUODU, 2003;BUTLER et al, 1984;TAYLOR et al, 2007). As prolaminas do sorgo apresentam características únicas, como alta hidrofobicidade e baixa solubilidade em água, e por isso são consideradas potenciais biomateriais food-grade (SHAH et al, 2021). Entretanto, apesar de suas proteínas serem majoritariamente prolaminas, o sorgo apresenta também albuminas, globulinas e glutelinas.…”