EVALUATION OF PROTEIN QUALITY BY ENZYMATIC AND CHROMATOGRAPHIC METHODS

A method is described for evaluating nutritional quality of food proteins via enzymatic hydrolysis and analysis of enzymatically released amino acids using gas-liquid chromatography. Prior to proteolysis, presolubilization of the proteins was achieved in 0.05N HCl. Of over 30 different proteins analysed, more than 90% of the total N was recovered by using a combined but sequential action of papain-pronase E enzyme system. This showed that maximal hydrolysis was achieved without destruction of chemically sensitive amino acids. The enzymatic process was used in measuring protein digestibility by a colorimetric reaction of (alpha)-amino nitrogen with trinitrobenzene sulfonic acid (TNBS). The developed in vitro digestibility predicted (r = 0.77) the in vivo rat-digestibility. Predictive models of protein quality, Enzymatic-PER and modified essential amino acid indexes (MEAII) were developed from enzymatically released amino acid profiles and were utilized in assessing the nutritional quality of animal, plant and mixed protein sources.