Covalent labelling of β-casein and its effect on the microstructure and physico-chemical properties of emulsions stabilized by β-casein and whey protein isolate. (December 2016)

• Record Type: Journal Article
• Authors: Li, Meng; Auty, Mark A.E.; O'Mahony, James A.; Kelly, Alan L.; Brodkorb, André
• Is Part Of: Food hydrocolloids. Volume 61(2016:Dec.)
• Page Start: 504
• Page End: 513
• Publication Date: 2016-12
• Subjects: β-Casein -- Whey proteins -- Emulsion stability -- Confocal laser scanning microscopy -- Covalent labelling techniques; Hydrocolloids -- Periodicals; Food additives -- Periodicals; Colloïdes -- Périodiques; Aliments -- Additifs -- Périodiques; Colloids; Food additives; Periodicals; Electronic journals; 664.06
• DOI: 10.1016/j.foodhyd.2016.05.029
• Languages: English
• ISSNs: 0268-005X

Abstract

Abstract: The objective of this work was to investigate the effect of covalent labelling on the physico-chemical properties of β-casein (β-CN) in solution and in emulsions stabilized by β-CN and whey protein isolate (WPI). β-CN was covalently labelled by 5-(and 6)-carboxytetramethylrhodamine, succinimidyl ester (NHS-Rhodamine). The effect of conjugating β-CN with NHS-Rhodamine on the spectroscopic properties of labelled β-CN (β-CNlabelled ) was examined. No significant difference in interfacial tension (p > 0.05) was found between mixture of WPI and β-CNlabelled (0.5% w/w WPI/β-CNlabelled ) and of WPI and β-CN (0.5% w/w WPI/β-CN) in 10 mM phosphate buffer (pH 7.0) at 20 °C. Oil-in-water emulsions stabilized with either WPI/β-CN or WPI/β-CNlabelled (0.5% w/w) were also investigated using laser-light scattering, analytical centrifugation, rheometry and CLSM. It was shown that labelling had no significant effect on the physico-chemical properties of emulsions (p > 0.05) in terms of droplet size, creaming stability, viscosity or zeta-potential. Confocal micrographs of emulsions made with WPI/β-CNlabelled showed that both β-CN and whey proteins could be observed simultaneously, and were co-localized at the surface of fat globules. Furthermore, it was found through image analysis that β-CN produced a thicker interfacial layer than WPI. Graphical abstract: Highlights: β-Casein was covalently labelled by NHS-Rhodamine. Labelled β-casein was evaluated in terms of spectroscopic and emulsification properties. Covalent labelling had no negative effect on the properties of the emulsions. Whey protein isolate could be distinguished from labelled β-casein at the interface of emulsions.