title: Initial Droplet Size Impacts pH-Induced Structural Changes in Phase-Separated Polymer Dispersions.
abstract: The effect of pH change on the morphology of whey protein isolate (WPI)-pectin dispersions obtained from phase-separated systems after mild shear was studied. The purpose of this study was to examine the impact of mixing speed on the initial particle size of biopolymer complexes and their structure morphology after sequentially changing the pH. Therefore, solutions of WPI and pectin were combined at pH 6.1, allowed to phase separate and were then mildly homogenized at 50, 100, and 150 rpm, respectively, to form a dispersion containing differently sized WPI droplets in a surrounding pectin-rich phase. Each dispersion was then subjected to a pH change, such as 6.1 to 5.2 and 3.2, by slowly adding hydrochloric acid. The systems morphology, size, appearance, rheology, and storage stability was then characterized by optical microscopy, static light scattering, visual inspections, and steady shear rheometry to gain insights into the structural rearrangements. Results indicated substantial changes in the structure of the dispersion when the pH was changed. Formation of core-shell structures from the WPI droplets was observed at an intermediate pH. There, initial droplet size was found to affect structures formed, that is, core-shell type particles would only form if droplets were large (>1.5 μm) prior to pH change. Insights gained may be of importance to food manufacturers intending to create new structures from mixtures of proteins and carbohydrates.
authors.affiliation: Dept. of Food Physics and Meat Science, Inst. of Food Science and Biotechnology, Univ. of Hohenheim, Garbenstrasse 25, 70599 Stuttgart, Germany.
authors.forename: Chutima
authors.initials: C
authors.lastname: Thongkaew
authors.affiliation: Dept. of Food Physics and Meat Science, Inst. of Food Science and Biotechnology, Univ. of Hohenheim, Garbenstrasse 25, 70599 Stuttgart, Germany.
authors.forename: Benjamin
authors.initials: B
authors.lastname: Zeeb
authors.affiliation: Dept. of Food Physics and Meat Science, Inst. of Food Science and Biotechnology, Univ. of Hohenheim, Garbenstrasse 25, 70599 Stuttgart, Germany.
authors.forename: Monika
authors.initials: M
authors.lastname: Gibis
authors.affiliation: Dept. of Soft Matter Science and Dairy Technology, Inst. of Food Science and Biotechnology, Univ. of Hohenheim, Garbenstrasse 21, 70599 Stuttgart, Germany.
authors.forename: Jörg
authors.initials: J
authors.lastname: Hinrichs
authors.affiliation: Dept. of Food Physics and Meat Science, Inst. of Food Science and Biotechnology, Univ. of Hohenheim, Garbenstrasse 25, 70599 Stuttgart, Germany.
authors.forename: Jochen
authors.initials: J
authors.lastname: Weiss
mesh_terms: D004040:Dietary Carbohydrates; D004044:Dietary Proteins; D004655:Emulsions / Q000737:chemistry*; D005524:Food Technology; D006863:Hydrogen-Ion Concentration; D027845:Malus / Q000737:chemistry; D008894:Milk Proteins / Q000737:chemistry; D010316:Particle Size; D010368:Pectins / Q000737:chemistry*; D011108:Polymers / Q000737:chemistry*; D012212:Rheology; D012996:Solutions; D013314:Stress, Mechanical; D000067816:Whey Proteins / Q000737:chemistry*
chemical_list: D004040:Dietary Carbohydrates; D004044:Dietary Proteins; D004655:Emulsions; D008894:Milk Proteins; D011108:Polymers; D012996:Solutions; D000067816:Whey Proteins; D010368:Pectins
keywords: electrostatic attraction; hydrophobic interactions; pH; particle size; pectin; structure; water-in-water dispersion; whey protein isolate