title: How micro-phase separation alters the heating rate effects on globular protein gelation.
abstract: This study was conducted to determine how the combination of heating rate and pH can be used to alter viscoelastic properties and microstructure of egg white protein and whey protein isolate gels. Protein solutions (1% to 7% w/v protein, pH 3.0 to 8.5) were heated using a range of heating rates (0.2 to 60 °C/min) to achieve a final temperature of 80 °C. The gelation process and viscoelastic properties of formed gels were evaluated using small strain rheology. Single phase or micro-phase separated solution conditions were determined by confocal laser scanning microscopy. In the single phase region, gels prepared by the faster heating rates had the lowest rigidity at 80 °C; however, a common G' was achieved after holding for 4 h at 80 °C . On the other hand, under micro-phase separation conditions, faster heating rates allowed phase separated particles to be frozen in the network prior to precipitation. Thus, gels produced by slower heating rates had lower rigidities than gels produced by faster heating rates. The effect of heating rate appears to depend on if the solution is under single phase or micro-phase separated conditions.
  
  
  CONCLUSIONS
  The effect of heating rate and/or time on protein gel firmness can be explained based on protein charge. When proteins have a high net negative charge and form soluble aggregates, there is no heating rate effect and gels with equal firmness will be formed if given enough time. In contrast, when electrostatic repulsion is low, there is a competition between protein precipitation and gel formation; thus, a faster heating rate produces a firmer gel.
authors.affiliation: Department of Food, Bioprocessing and Nutrition Sciences, North Carolina State University, Raleigh, NC 27695-7624, USA.
authors.forename: Phanin N
authors.initials: PN
authors.lastname: Leksrisompong
authors.forename: Edward Allen
authors.initials: EA
authors.lastname: Foegeding
mesh_terms: D055598:Chemical Phenomena; D004044:Dietary Proteins / Q000032:analysis*; D004527:Egg Proteins / Q000737:chemistry* / Q000648:ultrastructure; D004529:Egg White / Q000032:analysis; D004548:Elasticity; D005511:Food Handling; D005782:Gels; D006358:Hot Temperature / Q000009:adverse effects*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D055595:Mechanical Phenomena; D018613:Microscopy, Confocal; D008894:Milk Proteins / Q000737:chemistry* / Q000648:ultrastructure; D008956:Models, Chemical; D009391:Nephelometry and Turbidimetry; D017510:Protein Folding; D012212:Rheology; D055672:Static Electricity; D014783:Viscosity; D000067816:Whey Proteins
chemical_list: D004044:Dietary Proteins; D004527:Egg Proteins; D005782:Gels; D008894:Milk Proteins; D000067816:Whey Proteins