Understanding the different emulsification mechanisms of pectin: Comparison between watermelon rind and two commercial pectin sources

In this work, an advanced approach combining small angle X-ray scattering (SAXS) experiments, rheology and confocal laser scanning microscopy was used to explain the different emulsification mechanisms of three pectin sources (pectin extracted from watermelon rind -WRP- and commercial citrus -CP- and apple pectin -AP). Very interestingly, three different emulsification mechanisms were identified, related to the structure and composition of the pectin extracts. WRP had significantly greater emulsifying capacity than commercial CP and AP. This enhanced emulsification ability was mainly ascribed to a combination of its relatively high protein content (mainly acting as the surface-active material), combined with the presence of longer sugar side chains in pectin, further contributing to stabilizing the oil droplets in the emulsions. All these structural features resulted in a reduction in the mean droplet size as the concentration increased, thus, hindering flocculation and coalescence during the short-term storage conditions at 4 °C. In contrast, AP had the lowest emulsification capacity, which was only related to its viscosifying effect (provided by its greater Mw), while CP, having the greatest homogalacturonan content, greatest linearity and a more balanced hydrophilic/hydrophobic character (reflected in the degree of esterification), was able to form a better adsorbed layer at the o/w interphase, although it could not avoid flocculation and creaming at low pectin concentration during refrigerated storage.