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Spectrophotometric methods for total protein analysis are generally simple, rapid and sensitive. Such sensitive protein assays may have applications in forensic science, in the detection of protein contaminants in drugs and in a number of other applications of research interest. Biuret reaction with proteins and peptides is widely used in clinical and biological laboratories. In this work, instead of copper sulphate, sodium hydroxide and Seignette salt, we used insoluble copper phosphate, potassium or sodium hydroxide and ethyl alcohol for the preparation of the biuret reagent. Absorbance of the biuret complex was recorded both at 219-230 nm (after dilution) and around 550 nm against a reagent blank. Amino acid interference was investigated around 550 nm at the same concentration as proteins. The sensitivity of the method at 226 nm was greater than those of other spectrophotometric assays (old biuret method, Lowry, and BCA) with a LOD of about 0.5 μg mL-1 BSA. The new variants of the biuret method for total protein analysis eliminate the need for precise reagent addition and vortexing inherent in the widely used Lowry method, providing flexibility of application. The method developed, which uses an alkaline-alcoholic reagent and insoluble copper phosphate, is simple, rapid, reproducible and sensitive; it is not influenced by detergents, solvents and buffers containing ammonium and is flexible enough to change the analytical protocol when necessary. A discussion was made on the applications of protein and peptide determination with the new biuret assay. [ABSTRACT FROM AUTHOR]

Zein proteins belong to the class of prolamin proteins which, in maize, represent more than 60% of the total endosperm protein. Based on their molecular weight, sequence and solubility, zeins are classified into four different zein structures (α, β, γ, δ). The major maize seed storage proteins, zeins, are deficient in lysine and tryptophan content, which contribute to the poor nutritional quality of corn. Therefore, we report here on an original and novel process, which consists in successive grinding and sieving of corn seeds to bring about different maize flours, with chemical compositions and protein contents depending on particle hardness. In addition, zeins extracted from maize flours have wide application in: (i) refining food products, such as candies and nuts; (ii) microspheres filled with pesticides are produced out of zein proteins for controlled release of the biologically active substances to provide a safer working environment; (iii) “zein films” are used as a controlled release matrix of active components, such as salicylic acid, lysozyme and EDTA; (iv) coating of tablets and in zein-coated chitosan /tripolyphosphate nanoparticles for oral delivery of selenite. Moreover, the most defining characteristic of zein proteins refers to their insolubility in water and their high solubility in aqueous high percentage alcoholic solutions, such as from 65% to 95% ethanol. Due to the vast genetic polymorphism of the starting material and to the extraction conditions, the consistency of the “zein product” varies substantially; therefore analysis of protein compositions in biological samples of high complexity requires a combination of the latest and modern analytical methods such as SDS-PAGE, 2D gel electrophoresis and mass spectrometry. We have also investigated zein extraction using 65-95% aqueous ethanol under ultrasound conditions from dry-ground whole corn as well as meals with different grain sizes. Besides, the extracted zein and the commercial zein protein were used for different conjugates synthesis. Protein determination was made by UV-Vis spectrophotometry. We have applied modern methods such as MALDI ToF mass spectrometry and FT-IR spectroscopy to characterize the synthesized zein conjugates. [ABSTRACT FROM AUTHOR]