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Microstructural changes in casein supramolecules during acidification of skim milk
D J McMahon1, H Du, W R McManus
1Western Dairy Center, Utah State University, Logan 84322, USA. donald.mcmahon@usu.edu
Journal of Dairy Science
|November 20, 2009
Summary
This study reveals how acidification temperature affects milk gelation. Lower temperatures create finer gel structures, while higher temperatures result in coarser networks due to protein dissociation and aggregation.
Area of Science:
- Food Science
- Dairy Science
- Biochemistry
Background:
- Acid-induced gelation is crucial for dairy products.
- Understanding the microstructural changes during milk acidification is key to controlling gel properties.
Purpose of the Study:
- To investigate the effect of acidification rate and temperature on the microstructural changes and gelation process of skim milk.
- To propose a model for acid-induced milk gelation based on observed changes.
Main Methods:
- Skim milk was acidified using glucono-delta-lactone at various temperatures (10-40°C).
- Milk coagulation was monitored via turbidity and curd firmness measurements.
- Microstructural changes were observed using transmission electron microscopy on fixed samples.
Main Results:
- Acidification temperature significantly influenced casein supramolecular appearance and aggregate formation.
- All milks gelled at pH 4.8, but turbidity increases began around pH 5.2-5.4.
- Higher temperatures (40°C) promoted larger protein aggregates, suggesting hydrophobic interactions.
- Lower temperatures (10°C) resulted in ragged casein structures and fine-stranded gel networks, while 40°C yielded coarse-stranded networks.
Conclusions:
- A 3-phase model for acid-induced milk gelation is proposed, involving protein dissociation, aggregate formation, and final gel network aggregation.
- Temperature plays a critical role in protein dissociation and subsequent aggregation, influencing the final gel microstructure.
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