DETECTION OF ADULTERATION OF BUTTERMILK POWDER BY GEL-ELECTROPHORESIS

Six commercial samples sold as buttermilk powder were compared with an authentic sample by SDS-PAGE, using either large gels (13.5 x 18 x .3 cm) with a manual system or precast miniature gels (4.3 x 5.0 x .045 cm) with an automated system. After being stained with Coomassie blue R, protein bands were quantitated by densitometry. Two unique fat globule membrane proteins, in addition to the caseins and whey proteins, were clearly visible in authentic buttermilk powders, but densities of fat globule membranes were reduced or absent in commercial nonfat dry milk and adulterated powders. The extent of adulteration was estimated by comparison of the relative percentage of fat globule membrane proteins in a suspect sample with their percentage in an authentic sample. The limit of detection for significant fat globule membrane protein bands was 12 mug of a 229-mug sample applied to a large gel and 420 ng of ''a 5-mug sample on a miniature gel. Although large gels facilitated visual observation of results, several days were required to cast a gel, separate the proteins, stain, and destain. In contrast, SDS-PAGE on miniature gels with the automated system required less than 3 h and offered a rapid screening procedure for detection of adulterated buttermilk powders.