title: Compositional fingerprint of soy sauces via hydrophobic surface interaction.
abstract: In this work, the interaction of soy sauces with hydrophobic surfaces has been analyzed. Hydrophobic self-assembled monolayers on gold or silicon dioxide were used to harvest conditioning layers from soy sauce products with varying amounts of additives. The data was compared to adsorption of soy protein and glutamic acid as common ingredients. Spectral ellipsometry revealed that all tested sauces led to the formation of thin overlayers on hydrophobic surfaces. Products with less additives yielded adlayers in the same thickness range as pure soy protein. In contrast, sauces with more ingredients create distinctly thicker films. Using water contact angle goniometry, it is shown that all adlayers render the substrate more hydrophilic. Infrared spectroscopy provided a deeper insight into the adlayer chemistry and revealed that the adlayer composition is dominated by protein rich components. X-ray reflectivity on selected films provided further insight into the density profiles within the adlayers on the molecular scale.
authors.affiliation: Analytical Chemistry - Biointerfaces, Ruhr-University Bochum, Universitätsstr. 150, 44780 Bochum, Germany. Electronic address: Victoria.Jakobi@rub.de.
authors.forename: Victoria
authors.initials: V
authors.lastname: Jakobi
authors.affiliation: Fakultät Physik/DELTA, Technische Universität Dortmund, 44221 Dortmund, Germany. Electronic address: Paul.Salmen@tu-dortmund.de.
authors.forename: Paul
authors.initials: P
authors.lastname: Salmen
authors.affiliation: Fakultät Physik/DELTA, Technische Universität Dortmund, 44221 Dortmund, Germany. Electronic address: Michael.Paulus@tu-dortmund.de.
authors.forename: Michael
authors.initials: M
authors.lastname: Paulus
authors.affiliation: Fakultät Physik/DELTA, Technische Universität Dortmund, 44221 Dortmund, Germany. Electronic address: Metin.Tolan@tu-dortmund.de.
authors.forename: Metin
authors.initials: M
authors.lastname: Tolan
authors.affiliation: Analytical Chemistry - Biointerfaces, Ruhr-University Bochum, Universitätsstr. 150, 44780 Bochum, Germany. Electronic address: Axel.Rosenhahn@rub.de.
authors.forename: Axel
authors.initials: A
authors.lastname: Rosenhahn
mesh_terms: D005504:Food Analysis; D005511:Food Handling; D006046:Gold / Q000737:chemistry; D057927:Hydrophobic and Hydrophilic Interactions; D012822:Silicon Dioxide / Q000737:chemistry; D045730:Soy Foods / Q000032:analysis*; D017550:Spectroscopy, Fourier Transform Infrared; D013499:Surface Properties; D014867:Water / Q000032:analysis; D014965:X-Rays
chemical_list: D014867:Water; D006046:Gold; D012822:Silicon Dioxide
keywords: ATR-FTIR; Hydrophobic self-assembled monolayer; Protein adsorption; Soy protein; Soy sauce; Spectral ellipsometry; X-ray reflectivity