Microparticle-Enhanced Nephelometric Immunoassay. 3. Application to Milk and Dairy Products

¹ Laboratory of Applied Biochemistry, Associated with Institut National de la Recherche Agronomique, Faculty of Sciences, BP 239, 54506 Vandoeuvre les Nancy, France
² Laboratory of Immunology, Faculty of Medicine, BP 184, 54505 Vandoeuvre les Nancy, France
³ Sanofi Research, Montpellier, France

A microparticle-enhanced nephelometric immunoassay (NEPHELIA®) has been developed for the measurement of milk, whey, and curd proteins (_s-casein, -casein, -lactalbumin, and ß-lactoglobulin). This new method was applied to measure milk protein variations in a year-long study. The protein levels and their chronological evolution agree with other published data. The effects of some technological treatments on these measurements were studied: -lactalbumin and -casein were not modified during freezing-thawing cycles; ß-lactoglobulin and _s-casein measurements were strongly influenced by freezing; the determination of heat-processed ß-lactoglobulin in the presence of -casein was also altered; the technological treatments applied to raw milk for pasteurization and fat standardization of milk had no influence on the proteins' measured values. The ß-lactoglobulin: -lactalbumin ratio was determined as a good indication of heat denaturation. It was unmodified in standardized milk as well as in whey. The -casein level in milk was correlated with some cheese-making parameters, particularly with soft and pressed cheese yield, which could be a good predictive factor in cheese making.

Key Words: nephelometric immunoassay • milk technology • dairy products

Submitted on February 13, 1991
Accepted on June 19, 1991