Mastitic milk

Bovine blood serum is lipolytically active, but cows producing milk which goes rancid quickly do not have sera that are more lipolytically active than those producing normal milk. Leukocytes, which are present in large numbers in milk, are especially high in mastitic milk they are the source of milk catalase but are apparently not the source of milk lipases (Nelson and Jezeski 1955). 

Figure 10. DEAE-cellulose chromatography of casein from mastitic milk containing M-ff-C.

The results on the hydrolysis of partially methylated /3-casein by plasmin indicate that proteins radiomethylated to a low level can serve as substrates for trypsin-like enzymes and probably for proteinases in general. Because it is likely that methylation will interfere with enzymatic attack at lysine residues, the complete hydrolysis of /3-casein probably would not be possible. Studies on mastitic milk demonstrate the usefulness of 14C-methyl proteins for qualitative examination of protein hydrolysis in complex multiprotein systems where resolution and characterization of individual protein fragments is difficult. The requirements in such studies are the availability of pure samples of the proteins under investigation and a suitable technique for separating the radio-labeled protein from hydrolytic products. 

Arylesterase has received considerable attention because of its elevated level in colostrum and mastitic milk (Forster et al., 1959 Marquardt and Forster, 1965). Since its level in mastitic milk correlates well with other indices of mastitis (Luedecke, 1964), it has been suggested as a sensitive indicator of the disease (Forster et al., 1961 Downey, 1974). The enzyme is believed to originate from blood, where its activity is up to 2000 times that in milk (Marquardt and Forster, 1965). 

Carboxylesterase activity is elevated in mastitic milk and colostrum (Fitz-Gerald et al., 1981) and may correspond to that of the reported lipases from somatic cells (Gaffney and Harper, 1965 Azzara and Dimick, 1985a) and colostrum (Driessen, 1976), respectively. The retinyl esterase activity that co-purifies with, but can be separated from, LPL may also be due to a carboxylesterase (Goldberg et al., 1986). It is of interest that the BSSL in human milk that has been shown to be identical with pancreatic carboxylesterase, has retinyl esterase activity (O Connor and Cleverly, 1989). 

The data of Gudding (1982) suggest that the elevation of FFAs may depend on the cause of mastitis, as relatively higher levels of FFAs were observed in milk from quarters infected with Staphylococcus aureus. When mastitis is induced experimentally by intramammary infusion of endotoxins or bacteria, the increases in FFAs correspond closely with the increases in SCC and other indices of mastitis (Salih and Anderson, 1979 Fitz-Gerald et al., 1981 Ma et al., 2000). Murphy et al. (1989) concluded that the increased lipolysis in mastitic milk is due to increased susceptibility of the milk fat. 

The leucocytes in milk contain a lipase (Gaffney and Harper, 1965 Azzara and Dimick, 1985a) or carboxylesterase (Deeth, 1978), which may contribute to lipolysis in mastitic milk. When suspensions of these cells are added to milk, the level of FFAs increases, almost linearly up to a cell count of ca. 2 x 106/ml (Salih and Anderson, 1978). More lipolysis is observed if the cells are disrupted prior to addition to milk (Jurczak and Sciubisz, 1981). 

Gudding, R. 1982. Increased free fatty acid concentrations in mastitic milk. J. Food Prot. 45, 1143-1144. 

During intramammary infection, the somatic cell count (SCC) in mastitic milk increases, and the concentrations of plasma components, including bovine serum albumin (BSA) and immunoglobin, are higher in comparison to normal milk. Several components in mastitic milk are... 

Figure 9.3.2 illustrates the relation between log SCC data obtained by the reference method and the respective values predicted by NIR regression based on smoothed log (1/r) data. The equations obtained with multiple scatter correction or first-derivative spectral data transformation had similar accuracy. The obtained standard error of prediction of 0.382 and variation coefficient of validation of 7.63% allow screening of milk samples and differentiation of healthy and mastitic milk samples. These results present better standard errors of prediction than the value of 0.60 reported by Whyte et al. (24) for the spectral region from 400 to 1100 nm. 

Mastitis is well known to decrease lactose content. This fact explains the relation between lactose content and determination of log SCC (4). This emphasizes the possibilities of detecting changes with lactose when analyzing milk spectra and proves its strong relation with SCC. Factors 5, 6, 8 and 10, which showed high correlation with regression coefficients, had the highest correlation with protein content. This is consistent with the fact that mastitis causes alteration of protein fractions in milk. Mastitic milk has more proteolytic activity than normal milk, due to increase of proteinase plasmin, which hydrolyzes the casein (25, 26). Harmon (6) and Urech et al. (25), have reported decreased ccs-casein and (3-casein content and elevated whey proteins and y-casein in the total protein of mastitic milk. 

The accuracy of SCC determination in composite cow s milk by NIR spectroscopy has allowed health screening of cows and differentiation between healthy and mastitic milk samples. It has been found that SCC determination by NIR milk spectra is based on the related changes in milk composition. The most significant factors that influence NIR spectra of milk are the alteration of milk proteins and changes in ionic concentration of mastitic milk. 

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