title: Electrophoretic characterization of protein interactions suggesting limited feasibility of accelerated shelf-life testing of ultra-high temperature milk.
abstract: Accelerated shelf-life testing is applied to a variety of products to estimate keeping quality over a short period of time. The industry has not been successful in applying this approach to ultra-high temperature (UHT) milk because of chemical and physical changes in the milk proteins that take place during processing and storage. We investigated these protein changes, applying accelerated shelf-life principles to UHT milk samples with different fat levels and using native- and sodium dodecyl sulfate-PAGE. Samples of UHT skim and whole milk were stored at 20, 30, 40, and 50°C for 28d. Irrespective of fat content, UHT treatment had a similar effect on the electrophoretic patterns of milk proteins. At the start of testing, proteins were bonded mainly through disulfide and noncovalent interactions. However, storage at and above 30°C enhanced protein aggregation via covalent interactions. The extent of aggregation appeared to be influenced by fat content; whole milk contained more fat than skim milk, implying aggregation via melted or oxidized fat, or both. Based on reduction in loss in absolute quantity of individual proteins, covalent crosslinking in whole milk was facilitated mainly by products of lipid oxidation and increased access to caseins for crosslinking reactions. Maillard and dehydroalanine products were the main contributors involved in protein changes in skim milk. Protein crosslinking appeared to follow a different pathway at higher temperatures (≥40°C) than at lower temperatures, making it very difficult to extrapolate these changes to protein interactions at lower temperatures.
authors.affiliation: Advanced Food Systems Research Unit, Victoria University, Melbourne, VIC 8001, Australia.
authors.forename: Manpreet Kaur
authors.initials: MK
authors.lastname: Grewal
authors.affiliation: Advanced Food Systems Research Unit, Victoria University, Melbourne, VIC 8001, Australia.
authors.forename: Jayani
authors.initials: J
authors.lastname: Chandrapala
authors.affiliation: Advanced Food Systems Research Unit, Victoria University, Melbourne, VIC 8001, Australia.
authors.forename: Osaana
authors.initials: O
authors.lastname: Donkor
authors.affiliation: Immunology in Chronic Diseases Program, Centre for Chronic Disease, College of Health and Biomedicine, Victoria University, Melbourne, VIC 8001, Australia.
authors.forename: Vasso
authors.initials: V
authors.lastname: Apostolopoulos
authors.affiliation: Advanced Food Systems Research Unit, Victoria University, Melbourne, VIC 8001, Australia. Electronic address: todor.vasiljevic@vu.edu.au.
authors.forename: Todor
authors.initials: T
authors.lastname: Vasiljevic
mesh_terms: D000818:Animals; D002364:Caseins / Q000032:analysis; D004591:Electrophoresis, Polyacrylamide Gel; D005511:Food Handling; D006358:Hot Temperature; D008892:Milk / Q000737:chemistry*; D008894:Milk Proteins / Q000032:analysis*
chemical_list: D002364:Caseins; D008894:Milk Proteins
keywords: aggregation; protein interactions; storage; ultra-high temperature; whole and skim milk