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Phase Segregation and Microstructural Changes in Starch - Protein Systems

Quiroga, Carla LU (2007)
Abstract
This thesis presents the study of the phase behavior of starch ? protein systems in relation to their microstructure and mechanical properties.



To study the complexity of this multicomponent system, the main components of starch (amylopectin and amylose) were studied separately in presence of a protein (ß-lactoglobulin or patatin). The two-component systems in aqueous media or dry state were: amylopectin - ß-lactoglobulin, amylose - ß-lactoglobulin and, amylopectin - patatin.



The influence of certain parameters on the phase segregation--such as heat treatment, total macromolecular concentration, polysaccharide to protein ratio and type of the molecular structure (branch or linear polysaccharide and... (More)
This thesis presents the study of the phase behavior of starch ? protein systems in relation to their microstructure and mechanical properties.



To study the complexity of this multicomponent system, the main components of starch (amylopectin and amylose) were studied separately in presence of a protein (ß-lactoglobulin or patatin). The two-component systems in aqueous media or dry state were: amylopectin - ß-lactoglobulin, amylose - ß-lactoglobulin and, amylopectin - patatin.



The influence of certain parameters on the phase segregation--such as heat treatment, total macromolecular concentration, polysaccharide to protein ratio and type of the molecular structure (branch or linear polysaccharide and gel-forming or precipitating protein)--and therefore changes in the structure and mechanical properties were evaluated by spectroscopy (Fourier Transform Infrared), microscopy (Atomic Force Microscopy, Transmission Electron Microscopy), rheology, X-ray diffractometry and calorimetry (Differential Scanning Calorimetry).



Aqueous systems with the branch polysaccharide (amylopectin) have shown to phase segregate at high total macromolecular concentrations (above of 20 %), if the protein was ß-lactoglobulin. The segregated phases were one phase rich in protein (upper layer) and one phase rich in polysaccharide (lower layer), and a third layer (metastable phase) was seen in some samples. True phase equilibrium was not attained after 6 weeks though the amylopectin content in the lower layer increased drastically during that time and the polysaccharide showed signs of retrogradation. When the system was heat treated above 60 °C the incompatibility between polysaccharide and protein was enhanced and the threshold concentration for phase segregation dropped to around 8 %. At temperatures close to the temperature of denaturation of the protein, the samples displayed only two layers which were inverted. At protein concentrations higher than about 7 %, phase segregation was hindered by the gelation of the protein.



Dry mixtures of polysaccharides and proteins prepared from solutions displayed a range of even to uneven structures with different degrees of coarsening. For the amylopectin - ß-lactoglobulin system, all the samples have been shown to phase segregate, and exhibited two types of morphologies: domains wetting the air-water surface and domains appearing to be immersed in the solid film. The size of the domains varied widely from about some nanometers to about a few micrometers which was determined by kinetic reasons or by restrictions given by the film structure of the sample. At polysaccharide to protein ratios above about of 1:3, amylopectin was the continuous phase; and at ratios below about of 1:6, ß-lactoglobulin was the continuous phase. Between these ratios the systems appeared more or less bicontinuous. On the contrary, for the other polysaccharide-protein systems not all the samples were phase segregated; some of them displayed uniform structures and other rougher structures. Phase segregation has been shown for amylose to ß-lactoglobulin ratios below 1:1 and for amylopectin to patatin ratios equal or below 1:1. Phase segregated samples exhibited protein and polysaccharide irregular domains with sizes ranging from nanometers to few micrometers. The phase segregation was enhanced when the samples were heat treated; samples with even structures displayed unevenness after heat treatment. The degree of coarsening depended on the protein concentration. At the same concentration and with the same polysaccharide, samples with patatin displayed rougher structures than with ß-lactoglobulin.



The rheological studies in the region of incompatibility of the amylopectin - ß-lactoglobulin ? water system confirmed that phase segregation and phase inversion control the mechanical properties of the system. (Less)
Please use this url to cite or link to this publication:
author
supervisor
opponent
  • PhD Conde-Petit, Béatrice, ETH, Zurich, Switzerland
organization
publishing date
type
Thesis
publication status
published
subject
keywords
Patatin, ß-Lactoglobulin, Amylopectin, Phase Segregation, Amylose, Macromolecular chemistry, Makromolekylär kemi
publisher
Food Technology, Lund University
defense location
Lecture hall B, Centre for Chemistry and Chemical Engineering, Getingevägen 60, Lund University, Faculty of Engineering
defense date
2007-10-23 13:00
ISBN
978-91-976695-3-5
language
English
LU publication?
yes
id
d8321e20-fac4-4e05-8c82-fe35aa440554 (old id 599019)
date added to LUP
2007-11-13 08:52:57
date last changed
2016-09-19 08:45:13
@phdthesis{d8321e20-fac4-4e05-8c82-fe35aa440554,
  abstract     = {This thesis presents the study of the phase behavior of starch ? protein systems in relation to their microstructure and mechanical properties.<br/><br>
<br/><br>
To study the complexity of this multicomponent system, the main components of starch (amylopectin and amylose) were studied separately in presence of a protein (ß-lactoglobulin or patatin). The two-component systems in aqueous media or dry state were: amylopectin - ß-lactoglobulin, amylose - ß-lactoglobulin and, amylopectin - patatin.<br/><br>
<br/><br>
The influence of certain parameters on the phase segregation--such as heat treatment, total macromolecular concentration, polysaccharide to protein ratio and type of the molecular structure (branch or linear polysaccharide and gel-forming or precipitating protein)--and therefore changes in the structure and mechanical properties were evaluated by spectroscopy (Fourier Transform Infrared), microscopy (Atomic Force Microscopy, Transmission Electron Microscopy), rheology, X-ray diffractometry and calorimetry (Differential Scanning Calorimetry).<br/><br>
<br/><br>
Aqueous systems with the branch polysaccharide (amylopectin) have shown to phase segregate at high total macromolecular concentrations (above of 20 %), if the protein was ß-lactoglobulin. The segregated phases were one phase rich in protein (upper layer) and one phase rich in polysaccharide (lower layer), and a third layer (metastable phase) was seen in some samples. True phase equilibrium was not attained after 6 weeks though the amylopectin content in the lower layer increased drastically during that time and the polysaccharide showed signs of retrogradation. When the system was heat treated above 60 °C the incompatibility between polysaccharide and protein was enhanced and the threshold concentration for phase segregation dropped to around 8 %. At temperatures close to the temperature of denaturation of the protein, the samples displayed only two layers which were inverted. At protein concentrations higher than about 7 %, phase segregation was hindered by the gelation of the protein.<br/><br>
<br/><br>
Dry mixtures of polysaccharides and proteins prepared from solutions displayed a range of even to uneven structures with different degrees of coarsening. For the amylopectin - ß-lactoglobulin system, all the samples have been shown to phase segregate, and exhibited two types of morphologies: domains wetting the air-water surface and domains appearing to be immersed in the solid film. The size of the domains varied widely from about some nanometers to about a few micrometers which was determined by kinetic reasons or by restrictions given by the film structure of the sample. At polysaccharide to protein ratios above about of 1:3, amylopectin was the continuous phase; and at ratios below about of 1:6, ß-lactoglobulin was the continuous phase. Between these ratios the systems appeared more or less bicontinuous. On the contrary, for the other polysaccharide-protein systems not all the samples were phase segregated; some of them displayed uniform structures and other rougher structures. Phase segregation has been shown for amylose to ß-lactoglobulin ratios below 1:1 and for amylopectin to patatin ratios equal or below 1:1. Phase segregated samples exhibited protein and polysaccharide irregular domains with sizes ranging from nanometers to few micrometers. The phase segregation was enhanced when the samples were heat treated; samples with even structures displayed unevenness after heat treatment. The degree of coarsening depended on the protein concentration. At the same concentration and with the same polysaccharide, samples with patatin displayed rougher structures than with ß-lactoglobulin.<br/><br>
<br/><br>
The rheological studies in the region of incompatibility of the amylopectin - ß-lactoglobulin ? water system confirmed that phase segregation and phase inversion control the mechanical properties of the system.},
  author       = {Quiroga, Carla},
  isbn         = {978-91-976695-3-5},
  keyword      = {Patatin,ß-Lactoglobulin,Amylopectin,Phase Segregation,Amylose,Macromolecular chemistry,Makromolekylär kemi},
  language     = {eng},
  publisher    = {Food Technology, Lund University},
  school       = {Lund University},
  title        = {Phase Segregation and Microstructural Changes in Starch - Protein Systems},
  year         = {2007},
}