Extraction, identification and characterization of the water-insoluble proteins from tobacco biomass

BACKGROUND: Tobacco leaves are a potential candidate for plant proteins, yielding fourfold more protein per acre than soybeans. However, more than 60% of these proteins are water-insoluble and remain in the residue (referred to as tobacco biomass) after aqueous extraction. Efficient extraction of tobacco biomass proteins (TBPs) could boost the development of value-added products from tobaccos. RESULTS: TBPs were resistant to salt extraction at pH2.0-12.0, but theywere readily extracted by organic solvents. A simplified extracting method, including mechanical homogenization, a first extraction with a methanol-water mixture (40/ 60, v/ v) and a second one with water at pH 6.0, recovered at most 68% of the TBPs. Analysis by sodium dodecyl sulfate-polyacrylamide gel electrophoresis indicated the presence of both the water-soluble tobacco F1 protein and the less soluble cell wall proteins in TBPs, while Fourier transform infrared spectra suggested the coexistence of TBPs with polysaccharides (especially pectin). Meanwhile, a higher content of hydrophobic amino acids was found in TBPs compared with water-extractable tobacco proteins. The amino acid score of TBPs was 0.71, with cysteine and methionine being the primary limiting amino acids. CONCLUSION: Satisfying recovery of TBPs was achieved using a two-step organic solvent extraction. The hydrophobicity and protein-pectin interaction of TBPs explained for this result. (C) 2011 Society of Chemical Industry