Type

PhD Thesis

Authors

Alan L. Kelly

Subjects

Agriculture & Food Science

Topics
proteinases milk analysis cheese plasmin somatic cells polymorphonuclear leucocyte levels pmn late lactation milk leucocytes somatic cell counts scc proteolysis of milk

Variations in total and differential milk somatic cell counts and plasmin levels and their role in proteolysis and quality of milk and cheese (1995)

Abstract Increased plasmin and plasminogen levels and elevated somatic cell counts (SCC) and polymorphonuclear leucocyte levels (PMN) were evident in late lactation milk. Compositional changes in these milks were associated with increased SCC. The quality of late lactation milks was related to nutritional status of herds, with milks from herds on a high plane of nutrition having composition and clotting properties similar to, or superior to, early-mid lactation milks. Nutritionally-deficient cows had elevated numbers of polymorphonuclear leucocytes (PMNs) in their milk, elevated plasmin levels and increased overall proteolytic activity. The dominant effect of plasmin on proteolysis in milks of low SCC was established. When present in elevated numbers, somatic cells and PMNs in particular had a more significant influence on the proteolysis of both raw and pasteurised milks than plasmin. PMN protease action on the caseins showed proteolysis products of two specific enzymes, cathepsin B and elastase, which were also shown in high SCC milk. Crude extracts of somatic cells had a high specificity on αs1-casein. Cheeses made from late lactation milks had increased breakdown of αs1-casein, suggestive of the action of somatic cell proteinases, which may be linked to textural defects in cheese. Late lactation cheeses also showed decreased production of small peptides and amino acids, the reason for which is unknown. Plasmin, which is elevated in activity in late lactation milk, accelerated the ripening of Gouda-type cheese, but was not associated with defects of texture or flavour. The retention of somatic cell enzymes in cheese curd was confirmed, and a potential role in production of bitter peptides identified. Cheeses made from milks containing high levels of PMNs had accelerated αs1-casein breakdown relative to cheeses made from low PMN milk of the same total SCC, consistent with the demonstrated action of PMN proteinases. The two types of cheese were determined significantly different by blind triangle testing.
Collections Ireland -> University College Cork -> College of Science, Engineering and Food Science - Theses
Ireland -> University College Cork -> College of Science, Engineering and Food Science - Doctoral Theses
Ireland -> University College Cork -> Food and Nutritional Sciences - PhD Theses
Ireland -> University College Cork -> College of Science, Engineering and Food Science
Ireland -> University College Cork -> UCC Theses
Ireland -> University College Cork -> Food and Nutritional Sciences
Ireland -> University College Cork -> Doctoral Theses

Full list of authors on original publication

Alan L. Kelly

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Alan L. Kelly
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Total Publications: 63