Diagnosing the Cause of Proteolysis in U.H.T. Milk

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Datta, Nivedita and Deeth, H. C (2003) Diagnosing the Cause of Proteolysis in U.H.T. Milk. Lebensmittel-Wissenschaft und-Technologie (LWT) - Food Science and Technology, 36 (2). pp. 173-182. ISSN 0023-6438


Proteolysis of UHT milk during storage at room temperature is a major factor limiting its shelf-life through changes in its flavour and texture. The latter is characterised by increases in viscosity leading in some cases to gel formation. The enzymes responsible for the proteolysis are the native milk alkaline proteinase, plasmin, and heat-stable, extracellular bacterial proteinases produced by psychrotrophic bacterial contaminants in the milk prior to heat processing. These proteinases react differently with the milk proteins and produce different peptides in the UHT milk. In order to differentiate these peptide products, reversed-phase HPLC and the fluorescamine method were used to analyse the peptides soluble in 12% trichloroacetic acid (TCA) and those soluble at pH 4.6. The TCA filtrate showed substantial peptide peaks only if the milk was contaminated by bacterial proteinase, while the pH 4.6 filtrate showed peptide peaks when either or both bacterial and native milk proteinases caused the proteolysis. Results from the fluorescamine test were in accordance with the HPLC results whereby the TCA filtrate exhibited significant proteolysis values only when bacterial proteinases were present, but the pH 4.6 filtrates showed significant values when the milk contained either or both types of proteinase. A procedure based on these analyses is proposed as a diagnostic test for determining which type of proteinase—milk plasmin, bacterial proteinase, or both—is responsible for proteolysis in UHT milk.

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Item type Article
URI https://vuir.vu.edu.au/id/eprint/2395
DOI 10.1016/S0023-6438(02)00214-1
Official URL http://dx.doi.org/10.1016/S0023-6438(02)00214-1
Subjects Historical > FOR Classification > 0908 Food Sciences
Historical > Faculty/School/Research Centre/Department > School of Biomedical and Health Sciences
Keywords ResPubID18312, plasmin, bacterial proteinase, proteolysis, Fluorescamine, RP-HPLC
Citations in Scopus 120 - View on Scopus
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