Effect of Preparation Conditions on Protein Secondary Structure and Biofilm Formation of Kafirin

• Published in: Journal of agricultural and food chemistry Vol. 53; no. 2; pp. 306 - 312
• Main Authors: Gao, Chunli, Taylor, Janet, Wellner, Nikolaus, Byaruhanga, Yusuf B, Parker, Mary L, Mills, E. N. Clare, Belton, Peter S
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 26.01.2005
• Subjects: biofilm; Biological and medical sciences; Cereal and baking product industries; drying; edible films; ethanol; extraction; Flour - analysis; Food industries; Food Packaging - instrumentation; Fundamental and applied biological sciences. Psychology; grain sorghum; heat treatment; kafirins; packaging materials; Plant Extracts - chemistry; Plant Proteins - chemistry; Plant Proteins - isolation & purification; protein secondary structure; Protein Structure, Secondary; sodium hydroxide; Sorghum - chemistry; Zein - chemistry; Monocotyledones; Fourier transformation; Sorghum; FT-IR; Secondary structure; Protein; Infrared spectrometry; protein secondary structure; Gramineae; Preparation; Kafirin; Angiospermae; Biofilm; Cereal; Spermatophyta; Sorghum (food)
• ISSN: 0021-8561; 1520-5118
• DOI: 10.1021/jf0492666

Various extraction and drying conditions for the isolation of kafirin from dry-milled, whole grain sorghum have been investigated, with a view to optimizing extraction of the protein for commercial food coatings and packaging films. The addition of sodium hydroxide to an aqueous ethanol extractant increased the yield and solubility of kafirin. Subsequent heat drying at 40 °C was shown to cause the kafirin to aggregate 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 followed by freeze-drying of the protein was found to produce a yield of 54% kafirin with good film-forming properties. The kafirin films were assessed for their sensory properties, tensile strength, strain, and water vapor permeability. Fourier transform infrared spectroscopy was used to study the secondary structure of the extracted kafirins. The best films were made with kafirin containing a large proportion of nativelike α-helical structures with little intermolecular β-sheet content as indicated by the Fourier transform infrared reflectance peak intensity ratios associated with these secondary structures. The principal factor affecting the secondary structure of the protein appeared to be the temperature at which 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 native α-helical structures to achieve optimal film quality. Keywords: Kafirin; biofilm; sorghum; protein secondary structure; FT-IR