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Changes in salt solubility and microstructure of proteins from herring (Clupea harengus) after pH-shift processing
Sofia K Marmon1, Annika Krona, Maud Langton
1Department of Chemical and Biological Engineering, Food Science, Chalmers University of Technology, Gothenburg, Sweden. sofia@marmon.se
Journal of Agricultural and Food Chemistry
|July 4, 2012
Summary
Herring muscle protein solubility is significantly affected by pH changes during isolation. Precipitating proteins at pH 6.5, closer to their native state, preserves more salt solubility and improves gel quality compared to pH 5.5.
Area of Science:
- Food Science
- Protein Chemistry
- Marine Biology
Background:
- Understanding the impact of pH on fish muscle protein functionality is crucial for food processing.
- Herring (Clupea harengus) proteins are valuable but their solubility can be altered during isolation.
Purpose of the Study:
- To investigate how pH shifts affect the salt solubility and microstructure of isolated herring muscle proteins.
- To compare the effects of different precipitation pH values on protein interactions and gel properties.
Main Methods:
- Proteins were solubilized at alkaline pH (11.2) and then precipitated at different pH values (5.5 and 6.5).
- Salt solubility was measured, and microstructure was analyzed using transmission electron microscopy (TEM).
- Gel deformability and lipid oxidation were also assessed.
Main Results:
- Precipitation at pH 5.5 drastically reduced salt solubility (78% to 17%), while precipitation at pH 6.5 retained higher solubility (59%).
- The pH range between 6.5 and 5.5 had a greater impact on solubility than the full pH cycle (6.5 → 11.2 → 6.5).
- Precipitation at pH 6.5 resulted in hydrophobic interactions only, whereas pH 5.5 involved hydrogen bonds, hydrophobic interactions, and S-S bridges, leading to a finer microstructure and more deformable gels with less lipid oxidation.
Conclusions:
- The pH of precipitation critically influences the salt solubility, microstructure, and functional properties of isolated herring proteins.
- Precipitating at a pH closer to the native state (pH 6.5) yields a superior protein isolate with better gel properties and reduced lipid oxidation.
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