Structure, Morphology, and Assembly Behavior of Kafirin

Abstract

Prolamins from grains have attracted intensive attention in recent years due to their potential in satisfying the demand for environmentally friendly (biodegradable), abundantly available (sustainable), and cost-effective biomaterials. However, for kafirin, the prolamin from sorghum, its composition, structure, morphology, and self-assembly behaviors have not been fully characterized. In this paper, kafirin was extracted from the whole sorghum grain and found to contain 68, 14, 6, and 12% of α-, β-, and γ-fractions and cross-linked kafirin, respectively. Freeze-dried kafirin contained ∼49% α-helix in the solid state. When dissolved in 65% (v/v) isopropanol, 60% (v/v) tert-butanol, and 85% (v/v) ethanol aqueous solvents, the relative α-helix content in kafirin increased with the decrease of solvent polarity. Structural analysis using small-angle X-ray scattering (SAXS) indicated that kafirin (2 mg/mL) took stretched and extended conformations with dimensions of 118 × 15 × 15 and 100 × 11 × 11 Å in 60% tert-butanol and 65% isopropanol, respectively. More elongated conformation of individual kafirin with high-order assembly was observed in 85% ethanol. Protein aggregation occurred as protein concentration increased in its good solvent. The morphology of kafirin assemblies captured by atomic force microscopy (AFM) revealed that kafirin protein took uniform particle morphology at low concentration, and disk-like or rod-like structures resulting from solvent evaporation induced particle interactions emerged at high concentrations. These results suggest that both protein concentration and solvent polarity can effectively regulate kafirin assemblies from thick rod-like to slim rod-like structures, a convenient way to tune the fibrillation of prolamin-based biomaterials.

Comparison of formation of visco-elastic masses and their properties between zeins and kafirins

“…All the prolamin preparations exhibited higher and more distinct αhelical peaks ( Figure 5C). This is in agreement with the findings of Xiao et al (2014), who found that the α-helical content of kafirin increased in solution and was dependant on solvent polarity. As the solvent polarity decreased the amount of α-helical structure increased.…”

Assembly of kafirin/carboxymethyl chitosan nanoparticles to enhance the cellular uptake of curcumin

“…Kafirin protein with a purity of 90% was extracted from whole sorghum grain in our lab and its properties were reported in our previous work (Xiao et al, 2015). Na-form carboxymethyl-chitosan was purchased from Nantongxingcheng Biological Product Inc. (Nantong, Jiangsu Province, China), with a deacetylation degree of 99%.…”

Encapsulation and protection of resveratrol in kafirin and milk protein nanoparticles

“…Kafirin was extracted from sorghum by using ultrasound-assisted tert-butanol extraction method (Xiao et al, 2015a). Briefly, sorghum flour was defatted with n-hexane and washed with water and 0.5 mol L À1 NaCl to remove albumin and globulin proteins, respectively.…”