Protein digestibility in vitro
Protein quality determination is important in the production of nutritionally improved varieties of cereals and pulses. The nutritive value of a protein depends primarily on its capacity to supply needs of nitrogen and essential amino acids. Although the chemically determined amino acid composition is used to measure the quality of a protein, the biological availability of these amino acids is the real measure of the quality of the proteins. The availability of amino acids depends on the extent of digestibility of proteins by the proteolytic enzymes of the alimentary tract.
Digestibility of a protein can be assessed using rats which is termed in vivo digestibility. It can also be measured using proteolytic enzymes and called in vitro protein digestibility. The results obtained with the later procedure agreed well with in vivo protein digestibility as measured in the rats.
The procedure described here is that of Hsu et al1 which was later modified by Satterlee et al2.
Four proteolytic enzymes are used to digest the protein and the pH changed due to the release of amino acids at a fixed time interval is measured. By using the formula - % digestibility = 234.84 – 22.56 X, where X is the pH after 20min incubation, the in vitro digestibility is arrived at.