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Time-dependent aggregation of casein micelle concentrates.
Pulari Krishnankutty Nair1, Milena Corredig2
1Department of Food Science, University of Guelph, Guelph, ON, Canada N1G 2W1.
Journal of Dairy Science
|November 15, 2020
Summary
Concentrated milk proteins undergo changes over time, with viscosity increasing due to casein micelle aggregation. Heat treatment reduces proteolysis, while protease inhibitors prevent these viscosity changes.
Area of Science:
- Food Science
- Dairy Chemistry
- Protein Chemistry
Background:
- Milk protein concentrates are vital in food manufacturing.
- Understanding their physical and chemical stability is crucial for product quality.
- Osmotic stressing offers a non-invasive method for milk concentration.
Purpose of the Study:
- To investigate the physical and chemical changes in concentrated skim milk over time.
- To determine the role of proteolysis and heat treatment in these changes.
- To elucidate the mechanisms of casein micelle aggregation during storage.
Main Methods:
- Concentration of skim milk using osmotic stressing.
- Addition of protease inhibitors to selected samples.
- Monitoring apparent viscosity, casein micelle size, and proteolysis.
- Microstructural analysis using field emission scanning electron microscopy (FESEM).
Main Results:
- Apparent viscosity significantly increased in concentrated milk over 9 days at 4°C.
- Protease inhibitors prevented viscosity increase, indicating a role for enzymatic activity.
- Unheated milk showed increased casein micelle diameter, while heated milk exhibited heat-induced aggregation.
- Heated milk demonstrated reduced proteolysis compared to unheated milk.
Conclusions:
- Proteolysis drives viscosity increase and casein micelle aggregation in concentrated skim milk.
- Heat treatment mitigates proteolysis and alters aggregation mechanisms.
- Milk protein stability is influenced by both enzymatic activity and processing conditions.
