Effects of hydrosoluble calcium ions and organic acids on citrus oil emulsions stabilized with citrus pectin

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Citrus fruits are rich in nutritional substances, including various hydrosoluble and liposoluble components, and many of these are subject to enormous waste in the food industry. To make full use of these components and produce novel, high value-added citrus products, an emulsion-based delivery system containing both hydrosoluble (Ca2+, citric acid, ascorbic acid, and citrus pectin) and liposoluble (citrus oil) components was fabricated. In this paper, we investigated the effects of hydrosoluble calcium ions and organic acids on the properties and stability of citrus oil emulsions stabilized by citrus pectin. The effects of varying the adding order of Ca2+ and organic acids were analyzed for the first time. Ca2+ can interact with citrus pectin, resulting in large emulsion droplets. Adding Ca2+ prior to emulsification resulted in an emulsion that was stable with respect to phase separation for 20 days, due to the enhancement of the continuous phase viscosity. The addition of organic acids (citric acid and ascorbic acid) reduced the droplet size and improved the emulsion stability, and the benefits were more evident when acids were added prior to emulsification (from 1.47 to 0.83 μm with 1 wt% ascorbic acid added), due to the enhancement of the emulsifying capacity caused by the acidic environment. Notably, the degradation of d-limonene was reduced by adding 1 wt% ascorbic acid to the citrus oil emulsion. Furthermore, the large droplets formed due to the addition of Ca2+ can be avoided by the simultaneous addition of organic acid. This study details a novel emulsion product prepared using endogenous citrus nutrient components, which may improve the utilization and added value of citrus fruits.