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Fleminger G.,Tel Aviv University | Heftsi R.,Tel Aviv University | Uzi M.,Institute of Technology and Storage of Agricultural Products | Nissim S.,Institute of Animal Science | Gabriel L.,Kimron Veterinary Institute
International Dairy Journal | Year: 2011

Milk-clotting parameters are highly affected by hydrolysis of casein. Previously, it was shown that products of the hydrolysis of casein impair milk clotting, affecting both clotting time and curd firmness. One of these fractions is of particular interest since it is produced exclusively by enzymes of Streptococcus dysgalactiae. The present study aims to further investigate the chemical and structural properties of this fraction in an attempt to understand its influence on milk clotting. Preparations of this fraction, obtained from either S. dysgalactiae-infected glands or ex vivo inoculations with the same bacteria, were found to be identical. Mass spectrometry and Edman degradation analyses indicate that it comprises primarily β-CN 83-209, generated by cleavage at a Val-Val peptide bond, presumably by bacterial thermolysin- or elastin-like proteases. A model offering a putative mechanism for interference with milk-clotting parameters through production of this fraction is presented. © 2011 Elsevier Ltd.


Leitner G.,Kimron Veterinary Institute | Merin U.,Institute of Technology and Storage of Agricultural Products | Silanikove N.,Institute of Animal Science
International Dairy Journal | Year: 2011

Effects of glandular bacterial infection and stage of lactation on milk quality were compared among cows, goats and sheep. These parameters affected milk quality in all three species: sheep were most affected by bacterial infection and goats by stage (particularly end) of lactation. The study highlighted the effectiveness of lactose level as a predictor of milk quality; in all three species, the correlation between lactose level and curd firmness (CF) was higher than those between casein as a percentage of total protein and CF, or between somatic cell count and CF. In all three species, lactose concentrations ≤4% were associated with non-clotting milk. A model that describes the simultaneous and close association between reductions in lactose concentration and milk yield, on the one hand, and reductions in lactose concentration and milk quality on the other hand, is presented. © 2010 Elsevier Ltd.


Fleminger G.,Tel Aviv University | Ragones H.,Tel Aviv University | Merin U.,Institute of Technology and Storage of Agricultural Products | Silanikove N.,Institute of Animal Science | Leitner G.,Kimron Veterinary Institute
International Dairy Journal | Year: 2013

Previously it was shown that a low molecular mass fraction isolated from the proteose-peptone preparation of milk, fraction E, inhibited milk coagulation. Here, the composition and molecular mass of fraction E, and its effect on milk clotting parameters, was investigated to better understand its mechanism of action. Fraction E comprised casein-derived peptides of 1-3 kDa rich in phosphorus residues. Fraction E content increased substantially in milk from glands infected with Escherichia coli and Streptococcus dysgalactiae, and during storage of the milk. However, the specific activity of fraction E on milk clotting parameters was the same whether sampled from healthy, infected or stored milk. The inhibitory effect was reversible on adding 0.75 mm CaCl2, suggesting that chelation of Ca by fraction E was involved in the inhibitory mechanism. However, only partial recovery was achieved and an excess of Ca was required, suggesting the involvement of additional pathways in the process. © 2013 Elsevier Ltd.


Silanikove N.,Institute of Animal Science | Merin U.,Institute of Technology and Storage of Agricultural Products | Leitner G.,Kimron Veterinary Institute
Small Ruminant Research | Year: 2014

Bulk milk is the mixture of all the milked udders in a given herd. Nowadays, about 15-40% of the udders in most herds are intramammary infected by different bacteria species, mainly coagulase negative staphylococci. The presences of bacteria in the lumen of the mammary gland induce impairment of milk quality and increase the number of somatic cells. A positive relationship between % casein (casein/total protein) and curd firmness (CF) and negative relationship between lactose, or somatic cell count (SCC) and CF are associated with bacterial infection and with late lactation milk, and therefore with reduction in cheese yield and quality. On the other hand, in milk of goats with intramammary infection, the correlation between the levels of fat, protein, casein and curd yield is minor compared to milk of uninfected animals. Thus, gross milk composition is an insufficient predictor of milk quality for cheese production, since a high percent of the bulk milk originates from subclinically infected glands. Research carried out in the past few years highlighted the effectiveness of lactose as a predictor of milk quality. The correlation between lactose and CF was higher than that for % casein and SCC. Lactose concentration of ≤4% is associated with non-coagulating milk and therefore, such milk is unsuitable for making cheese, but still meets the criterion for consumption as pasteurized milk. A model that describes the simultaneous and close association between reduction in lactose concentration and milk yield on the one hand and reductions in lactose concentration and milk quality on the other hand is presented. The physiological and biochemical basis for deterioration of milk quality in subclinically infected and in late lactation animals is reviewed and suggestions to improve the quality of milk produced by farmers and acquired by dairies are presented. © 2014 Elsevier B.V.

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