14A-9 |
Plasmin, plasminogen, and plasminogen activator levels in milk supernatant vs. cheese whey as influenced by heifer stage of lactation and number of offspring |
C. A. SCHAUL, K. McPherson, K. D. Hayes, and S. S. Nielsen. Dept. of Food Science, Purdue Univ., 745 Agriculture Mall Dr., West Lafayette, IN 47907-2009 Historically, liquid whey has been referred to as the by-product in cheese manufacturing. Recently, whey has begun to gain value in the food industry as a functional ingredient with many food applications. Plasmin is the native serine proteinase in milk and has been shown to be released into the whey fraction during the cheesemaking process. Plasmin system activities include the active enzyme plasmin (PL), the zymogen form, plasminogen (PG), and plasminogen activators (PA), which convert PG to PL. Cow stage of lactation and number of offspring (i.e. lactation number) has been reported to influence the levels of PL, PG, and PA in milk. The effects these factors have on plasmin system components in whey are unknown. To determine what effect stage of lactation and number of offspring have on PL, PG, and PA levels in milk supernatant and cheese whey. Milk from 36 cows was collected and pasteurized. Compositional analysis of the milk was conducted along with total bacterial and somatic cell counts. Cheese whey samples were prepared by following a standard cheese procedure. Milk supernatant fractions were prepared by ultracentrifugation of each milk sample. All supernatant and whey samples were tested for PL, PG, and PA activities using synthetic substrates. Stage of lactation had an effect on the PL levels in milk supernatant fractions but did not in cheese whey. Supernatant fractions from later stages of lactation contained higher levels of PL. Number of offspring did not have an effect on PL and PG levels in milk supernatant fractions or in cheese whey. Milk supernatant PL levels were substantially higher than cheese whey. PA content was undetectable in both supernatant and cheese whey samples. Controlling the milk source, specifically cow’s stage of lactation and number of offspring, does not seem to control the plasmin content found in cheese whey.
Session 14A, Dairy Foods: General developments in dairy technology I
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