Fleminger, G., Department of Molecular Microbiology and Biotechnology, The George Wise Faculty of Life Sciences, Tel-Aviv University, Tel Aviv 69978, Israel
Heftsi, R., Department of Molecular Microbiology and Biotechnology, The George Wise Faculty of Life Sciences, Tel-Aviv University, Tel Aviv 69978, Israel
Uzi, M., Department of Food Science, Institute of Technology and Storage of Agricultural Products, A.R.O., The Volcani Center, P.O. Box. 6, Bet Dagan 50250, Israel
Nissim, S., Biology of Lactation Laboratory, Institute of Animal Science, A.R.O., The Volcani Center, P.O. Box 6, Bet Dagan 50250, Israel
Gabriel, L., National Mastitis Reference Center, Kimron Veterinary Institute, P.O. Box 12, Bet Dagan 50250, Israel

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-CN83-209, 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.