The Lowry Protein Assay For Determination Of Total Proteins

Lowry introduced this colorimetric total protein assay method. It offered a significant improvement over previous protein assays, and his paper became one of the most cited references in the life-science literature Lowry, 1951 . The Lowry assay is easy to perform, since the incubations are done at room temperature and the assay is sensitive enough to allow the detection of total protein in the low microgram per milliliter range. It is one of three copper chelation...

Net Protein Utilization Npu And Biological Value Bv To Determine Protein Quality

An NPU assay can be conducted in conjunction with a PER assay. NPU is used as a means of predicting the biological value of a protein. For NPU assays, the protein content of the animal carcasses is determined. Biological value BV measures the efficiency of the utilization of nitrogen by the animal. The biological value of a test protein is the proportion of nitrogen that is retained for maintenance and for growth, corrected for metabolic and endogeneous losses of nitrogen BV N retained N...

Direct Manometric Determination of Vapor unit a24 Pressure

Diagram Pressure Chemistry

Water activity aw is the ratio of the partial vapor pressure of water above a solution to that of pure water at the same specific temperature. It plays an important role in evaluating the microbial, chemical, and physical stability of foods during storage and processing. The vapor pressure in the headspace of a food sample can be measured directly by a manometer. A manometer has one or two transparent tubes and two liquid surfaces where pressure applied to the surface of one tube causes an...

The Biuret Assay For Determining Total Protein

Biuret Reagent Standard Curve 540

All proteins are composed of amino acids joined by peptide bonds in a linear sequence. There are 20 naturally occurring amino acids found in proteins. The amino acids are joined to each other by peptide bonds formed by a condensation reaction that occurs between the terminal amine of one amino acid and the carboxyl end of the next. Peptides containing three or more amino acid residues will form a colored chelate complex with cupric ions in an alkaline environment containing sodium potassium...

Commentary Background Information

Although the exact mechanism of color formation reaction in the Lowry protein assay remains poorly understood, it is known that the color producing reaction with protein occurs in two distinct steps. As seen in Figure B 1.1.1, protein is first reacted with alkaline cupric sulfate in the presence of tartrate during a 10-min incubation at room temperature. During this incubation, a tetradentate copper complex forms from four peptide bonds and one atom of copper. The tetradentate copper complex is...

Dew Point Method for the Determination of Water Activity

Chilled Mirror

The single most important property of water in food systems is water activity aW Taoukis et al., 1988 . Throughout history the importance of controlling water in food by drying, freezing, or addition of sugar or salt was recognized for preserving and controlling food quality. Water activity is a measure of the energy status of the water in a system or the degree to which the water is bound , and hence of its availability to act as a solvent and participate in chemical or biochemical reactions...