Spectroscopy characterization of acid and rennet camel milk caseins using XRD, XPS, and SEM and effects on their emulsifying properties

Abstract

Casein, the main protein in milk, is a viable protein source for natural emulsifiers, which are frequently utilized in food emulsions. Camel milk casein powders obtained by acid and rennet coagulation were investigated and characterized using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). These methods gave extensive information regarding crystal structure, surface composition, and secondary and microstructures of the camel caseins, respectively. Therefrom new acknowledgements on morphology and surface composition have emerged, which is necessary to better understand functional characteristics such as emulsifying behaviour (i.e., emulsion’s stability over time and the oil droplet size). The O and C atomic proportions of camel casein surfaces generated by acidification were greater than those obtained through rennet-induced coagulation, whereas the percentage of N atomic was lower, according to XPS measurements. The oxygen to carbon (O/C) ratios on the surface of camel caseins produced by the two coagulation techniques were comparable. But, the enzymatic coagulation method yielded a high (N/C) ratio. ‎The findings suggested that rennet-induced coagulation might influence the C, O, and N components on the surface of camel milk caseins. Furthermore, SEM and XRD data revealed that acid aggregation affected casein micelle’s morphology, resulting in more β-sheet and smooth structures. Rennet camel caseins, on the other hand, have a porous colloidal surface. ‎A correlation between the casein surface composition and the emulsifying stability of the casein powders was observed, whereas the droplet size and stability of emulsions were strongly improved by the rennet-induced coagulation method.