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

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dc.contributor.advisor Foley, John en Kelly, Alan L. 2014-08-26T09:17:03Z 2014-08-26T09:17:03Z 1995 1995
dc.identifier.citation Kelly, A. L. 1995. Variations in total and differential milk somatic cell counts and plasmin levels and their role in proteolysis and quality of milk and cheese. PhD Thesis, University College Cork. en
dc.description.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. en
dc.format.mimetype application/pdf en
dc.language.iso en en
dc.publisher University College Cork en
dc.rights © 1995, Alan L. Kelly en
dc.rights.uri en
dc.subject Late lactation milk en
dc.subject Polymorphonuclear leucocyte levels (PMN) en
dc.subject Somatic cell counts (SCC) en
dc.subject Proteolysis of milk en
dc.subject Proteinases en
dc.subject.lcsh Milk--Analysis en
dc.subject.lcsh Somatic cells en
dc.subject.lcsh Leucocytes en
dc.subject.lcsh Plasmin en
dc.subject.lcsh Cheese en
dc.title Variations in total and differential milk somatic cell counts and plasmin levels and their role in proteolysis and quality of milk and cheese en
dc.type Doctoral thesis en
dc.type.qualificationlevel Doctoral en
dc.type.qualificationname PhD (Food Science and Technology) en
dc.internal.availability Full text available en No embargo required en
dc.description.version Accepted Version
dc.description.status Not peer reviewed en Food and Nutritional Sciences en
dc.check.type No Embargo Required
dc.check.reason No embargo required en
dc.check.opt-out Not applicable en
dc.thesis.opt-out false
dc.check.embargoformat Not applicable en

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