title: Extraction, identification and characterization of the water-insoluble proteins from tobacco biomass.
abstract: 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 pH 2.0-12.0, but they were 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 F(1) 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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Nutrition and Food Science, University of Maryland, College Park, MD 20742, USA.
authors.forename: Zi
authors.initials: Z
authors.lastname: Teng
authors.forename: Qin
authors.initials: Q
authors.lastname: Wang
mesh_terms: D000596:Amino Acids / Q000032:analysis*; D018533:Biomass; D002473:Cell Wall; D057927:Hydrophobic and Hydrophilic Interactions; D010368:Pectins / Q000032:analysis; D018515:Plant Leaves / Q000737:chemistry*; D010940:Plant Proteins / Q000737:chemistry / Q000302:isolation & purification*; D012995:Solubility; D014026:Nicotiana / Q000737:chemistry*; D014867:Water
chemical_list: D000596:Amino Acids; D010940:Plant Proteins; D014867:Water; D010368:Pectins