Use of the o-Phthalaldehyde and N-Acetyl-L-Cysteine the Evaluation of Milk Proteins

¹ Departamento de Química Analítica, Facultad de Química, Universitat de Valencia, 46100 Burjassot (Valencia), Spain

o-Phthalaldehyde and N-acetyl-Lcysteine are used in the determination of milk proteins. Three procedures are proposed and compared. One of them is based on reaction of o-phthalaldehyde and N-acetyl-Lcysteine with the intact proteins and the two others on reaction of the reagents with the released amino acids after total acid hydrolysis of the protein samples. When the protein sample is hydrolyzed, calibration is performed either with a hydrolyzed protein standard or with isoleucine. A procedure for the measurement of the degree of enzymatic hydrolysis of milk proteins without separation of the unhydrolyzed protein, which makes use of the same reagents, is also described. In all cases absorbance is measured at 335 nm.

Key Words: milk proteins determination • o-phthalaldehyde • N-acetyl-L-cysteine • proteolysis degree

Submitted on May 16, 1990
Accepted on December 18, 1990