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Conformational changes in serum pectins during industrial tomato paste production
Jerome V Diaz1, Gordon E Anthon, Diane M Barrett
1Department of Food Science and Technology, University of California, Davis, California 95616, USA. jeromevdiaz@gmail.com
Journal of Agricultural and Food Chemistry
|August 26, 2009
Summary
Tomato paste production causes irreversible serum viscosity loss. This study shows pectin conformational changes, not depolymerization, are key. Pectin becomes more compact, reducing viscosity during concentration.
Area of Science:
- Food Science
- Polymer Science
Background:
- Industrial tomato paste production involves concentrating juice, leading to an irreversible decrease in serum viscosity.
- This viscosity loss has been attributed to pectin depolymerization caused by high processing temperatures.
Purpose of the Study:
- To investigate the role of pectin conformational changes versus depolymerization in the loss of serum viscosity during tomato paste production.
- To analyze the molecular weight and conformation of pectin polymers in tomato serum at different processing stages.
Main Methods:
- Tomato juice, intermediates, and paste were collected and diluted to 5 degrees Brix.
- Tomato serum was isolated by centrifugation.
- High-performance size-exclusion chromatography with multi-angle laser light scattering and refractive index detectors (HPSEC-MALLS-RI) was used to determine pectin's weight average molecular weight (M(w)) and root-mean-square (rms) radius.
Main Results:
- Serum viscosity decreased significantly during concentration, particularly at later stages (90-95°C).
- Pectin molecular weight (M(w)) remained largely unchanged (2.62 x 10^5 g/mol to 2.61 x 10^5 g/mol), indicating minimal depolymerization.
- Pectin's root-mean-square (rms) radius decreased, signifying a more compact conformation (shape factor from ~0.40 to ~0.25) as concentration increased.
Conclusions:
- Pectin conformational changes, leading to a more compact structure, are the primary cause of irreversible serum viscosity loss in tomato paste production.
- Increased polymer-polymer interactions due to concentration likely drive this conformational change.
- Findings challenge the sole reliance on depolymerization as the explanation for viscosity reduction.
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