| Abstract
| - Various extraction and drying conditions for the isolation of kafirin from dry-milled, whole grain sorghumhave been investigated, with a view to optimizing extraction of the protein for commercial food coatingsand packaging films. The addition of sodium hydroxide to an aqueous ethanol extractant increasedthe yield and solubility of kafirin. Subsequent heat drying at 40 °C was shown to cause the kafirin toaggregate as indicated by an increase in intermolecular β-sheets. Extraction of the flour using ethanol(70%, w/w) with 0.5% (w/w) sodium metabisulfite and 0.35% (w/w) sodium hydroxide at 70 °C followedby freeze-drying of the protein was found to produce a yield of 54% kafirin with good film-formingproperties. The kafirin films were assessed for their sensory properties, tensile strength, strain, andwater vapor permeability. Fourier transform infrared spectroscopy was used to study the secondarystructure of the extracted kafirins. The best films were made with kafirin containing a large proportionof nativelike α-helical structures with little intermolecular β-sheet content as indicated by the Fouriertransform infrared reflectance peak intensity ratios associated with these secondary structures. Theprincipal factor affecting the secondary structure of the protein appeared to be the temperature atwhich the protein was dried. Heat drying resulted in a greater proportion of intermolecular β-sheets.Any industrial-scale extraction must therefore minimize protein aggregation and maximize nativeα-helical structures to achieve optimal film quality. Keywords: Kafirin; biofilm; sorghum; protein secondary structure; FT-IR
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