title: Reactions between β-lactoglobulin and genipin: kinetics and characterization of the products.
abstract: In this paper, we present the first detailed study of the reaction kinetics and the characterization of the products from the endothermic reactions between β-lactoglobulin and genipin. The effects of the concentration, temperature, and pH were investigated. In the temperature range studied, the reaction was approximately a pseudo-first-order with respect to genipin and 0.22-order and -0.24-order with respect to β-lactoglobulin for pH 6.75 and 10.5 with corresponding activation energy (E(a)) estimated to be 66.2 ± 3.8 and 9.40 ± 0.36 kJ/mol, respectively. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis studies, validated by matrix-assisted laser desorption ionization-time of flight mass spectrometry, showed the presence of oligomeric, i.e., di-, tri-, quadri-, and pentameric, forms of cross-linked β-lactoglobulin by genipin at neutral but not alkaline pH; however, an extensive cross-linked network was not observed, consistent with the atomic force microscopy images. It was demonstrated that the reaction temperature and the concentration of genipin but not that of β-lactoglobulin positively affected the extent of the cross-linking reactions.
authors.affiliation: Dairy and Functional Foods Research Unit, Eastern Regional Research Center-ERRC, Agricultural Research Service-ARS, United States Department of Agriculture-USDA, 600 East Mermaid Lane, Wyndmoor, Pennsylvania 19038, USA. phoebe.qi@ars.usda.gov
authors.forename: Phoebe X
authors.initials: PX
authors.lastname: Qi
authors.forename: Alberto
authors.initials: A
authors.lastname: Nuñez
authors.forename: Edward D
authors.initials: ED
authors.lastname: Wickham
mesh_terms: D002152:Calorimetry, Differential Scanning; D003432:Cross-Linking Reagents; D006863:Hydrogen-Ion Concentration; D039823:Iridoids / Q000737:chemistry*; D007700:Kinetics; D007782:Lactoglobulins / Q000737:chemistry*; D018625:Microscopy, Atomic Force; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D013696:Temperature; D013816:Thermodynamics
chemical_list: D003432:Cross-Linking Reagents; D039823:Iridoids; D007782:Lactoglobulins; C007834:genipin