Effect of Mastitis on Proteolytic Activity in Bovine Milk

Abstract

Proteolytic activity of milk was studied before, during, and after experimental-induced mastitis. An inoculum of Streptococcus agalactiae was infused into one quarter of each udder of six cows to elicit an infection. Bacteriological cultures and SCC of milk were used to monitor infection status. Sodium dodecyl sulfate-PAGE was used to measure proteolytic activity of milk. Inhibitor 6-amino-n-hexanoic acid was used to determine the relative proportion of plasmin and nonplasmin proteolytic activity of milk. Somatic cell count, total milk proteolytic activity, and nonplasmin proteolytic activity were higher in infected quarters than in quarters preinfection. After elimination of infections, SCC and nonplasmin proteolytic activity decreased to preinfection amounts. Total proteolytic activity of milk decreased after infections were cured but remained significantly higher than preinfection activity. This postinfection proteolytic activity in milk may be due to an increase in milk plasmin activity. Our data suggest that detrimental effects of mastitis on milk quality can continue after infection has been eliminated and milk SCC have returned to low values.

Effect of Plasmin, Milk Somatic Cells and Psychrotrophic Bacteria on Casein Fractions of Ultra High Temperature Treated Milk

“…These results indicate that somatic cell proteinase hydrolyse mainly β-casein, followed by α s-casein and lastly κ-casein. The same findings were reported by Saeman et al (1988), Leroux et al (2003) and Kahina et al (2005). Leroux et al (1995) observed a decrease of 2% in β-caseins and 1.6% in α s-caseins when SCC exceeded 250,000 cells/mL in raw milk.…”

“…In contrast DeRham and Andrews (1982) reported that only one-third of the proteinase activity in mastitic milk was due to plasmin. Similarly, Saeman et al (1988), Leroux et al (1995) and Somers et al (2003) showed that plasmin was not the only enzyme responsible for degradation of casein in milk from cows with mastitis, and concluded that proteinases from somatic cells and blood may also play a significant role in casein hydrolysis in mastitic milk. High SCC predispose raw milk to hydrolysis of α s-and β-casein by proteases, resulting in a reduction in the concentration of these milk proteins (Verdi et al, 1987;De Noni et al, 2007).…”

Effect of somatic cell count on dairy products: a review

“…The proteolysis has been attributed to both the natural milk proteinase and proteinases produced by psychrotrophic bacterial contaminants of raw milk. The proteolytic activity associated with SCC in fluid milks has been extensively studied (Senyk et al, 1985;Saeman et al, 1988;Ballou et al, 1995). Grufferty and Fox (1988) reported that proteolysis of casein caused by milk proteinase is responsible for gelation of UHT milk during storage.…”

Avaliação do iogurte produzido com leite contendo diferentes níveis de células somáticas.

“…O aumento da CCS associado à deterioração na qualidade da proteína (GRANDISON & FORD, 1986) ocorre devido ao fato de, no leite mastítico, ocorrer aumento na atividade proteolítica em conseqüência à presença de altos níveis de proteases, que podem ter origem na plasmina (Enzyme Commission -3.4.21.7), nas células somáticas (DE RHAM & ANDREWS, 1982;ANDREWS, 1983;VERDI et al, 1987;SAEMAN et al, 1988) ou nas bactérias (GRIEVE & KITCHEN, 1985).…”

“…A atividade proteolítica pode estar associada em grande parte à CCS (SENYK et al, 1985;VERDI et al, 1987;SAEMAN et al, 1988;BALLOU et al, 1995), o que predispõe o leite a uma substancial hidrólise da α S -e β-caseína por proteases, havendo diminuição nos níveis destas frações no leite ANDERSON & ANDREWS, 1977;DE RHAM & ANDREWS, 1982;ANDREWS, 1983;VERDI et al, 1987).…”