Simple and Robust Approach for Determination of Total Protein Content in Plant Samples

The determination of total protein in plant samples is a difficult task, as classical nitrogen-based methods are not selective for the nature of nitrogen, and the results of biochemical methods are influenced by both associated compounds and the complex composition of the protein matrix. Using electrophoretic separation of three commercial sunflower protein samples, it was determined that the studied proteins are a mixture of salt-soluble globulins and water-soluble albumins of different molecular weights. The total protein content of the studied samples was determined using five spectrophotometric methods: direct spectrophotometry, bicinchoninic acid assay, and Benedict's, Bradford's, and Lowry's methods. After comparing the results obtained, it was concluded that, for the determination of protein in these plant materials, the use of the Dumas nitrogen-based method in tandem with Lowry's spectrophotometric method is the most suitable.