Citrus Oil Emulsions Stabilized by Citrus Pectin: The Influence Mechanism of Citrus Variety and Acid Treatment.

Citrus pectin and citrus oil are the main functional components of citrus residuals in the processing industry. In this study, citrus oil emulsions were fabricated for the first time using four different citrus pectins (orange, mandarin, grapefruit, and commercial citrus pectins) as the emulsifier. The influence mechanism of citrus variety and acid treatment (pH 1, 2, 3, 4, 5, 6, and 7) on the emulsifying capacity of citrus pectins was systematically investigated by understanding the relationship between molecular structure, solution property, interfacial property, and emulsion property. The results suggest that citrus variety and acid treatment can significantly influence the emulsifying capacity in relation to the molecular structure and molecular state of citrus pectins. A smaller molecular size of citrus pectin and lower pH between 2 and 7 produced a reduction in aggregate size, which improved the interfacial capacity and emulsifying ability by promoting their distribution at the interface. Although hydrolyzed citrus pectins at pH 1 with a lower molecular size exhibited better interfacial capacity, citrus oil emulsions were unstable due to electrostatic attraction caused by partially positive charged citrus pectins. Fine stable citrus oil emulsion was prepared using mandarin pectin with a relative high methyl ester content and small molecular size at pH 2. Our results provide a scientific basis for the fabrication of citrus oil emulsion based on citrus pectin and facilitate the application of citrus residuals in the food industry.