Determination of Protein in Lupin Using Liquid Chromatography Coupled with Organic Carbon Detector and Organic Nitrogen Detector (LC-OCD-OND): Validation of a New Method

The Kjeldahl or Dumas methods used to estimate the crude protein in foods measure total organic nitrogen of foods. The limitation of these methods is that the estimated nitrogen is not solely derived from proteins. This is the first study to determine the protein content of Australian sweet lupin using size-exclusion chromatography interfaced with organic carbon detector and organic nitrogen detector (LC-OCD-OND), a method that is widely used in water research. Protein was initially extracted into 10 mM phosphate buffer saline, filtered and diluted prior to analysis. Measured protein in the lupin flour and the lupin protein isolate were 1.6 g and 6.1 g per 100 g, respectively, in agreement with results obtained from Bicinchoninic assay. The coefficients of variation for both intra and inter-variability studies were 5%. The work presented here introduces a fast and simple protein extraction from solid state prior to LC-OCD-OND analysis that specifically measures only soluble protein in lupins.