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1 Eastern Regional Research Center, ARS, USDA, 600 East Mermaid Lane, Philadelphia, PA 18118
2 Eastern Regional Research Center, ARS, USDA, 600 East Mermaid Lane Philadelphia, PA 18118
3 Eastern Regional Research Center, ARS, USDA ,600 East Mermaid Lane, Philadelphia, PA 18118
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 µg of a 229-µg sample applied to a large gel and 420 ng of a 5-µg 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.
Key Words: buttermilk powder fat globule membrane proteins nonfat dry milk whey
Submitted on January 25, 1993
Accepted on March 16, 1994
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