Structure characterization and calcium ions induced emulsion gel properties of pectic polysaccharide from Fructus aurantii

A novel pectic polysaccharide was extracted from Fructus aurantii using ammonium oxalate extraction, whose primary structure and emulsification properties were investigated for the first time. Fructus aurantii ammonium oxalate-extracted pectin (FAOP) was a highly methyl-esterified pectin with a 60.36% methyl-esterification degree and a relative weight-average molecular weight (M-w) of 1.30 x 10(6) Da. The backbone of FAOP was composed of a 2:3 molar ratio of -> 4)-alpha-GalpA-(1 -> and -> 4)-alpha-GalpA-6-O-methyl-(1 -> linkage, which contained an similar to 57.04% linear homogalacturonan (HG) structural domain. In addition, neutral sugar side chains, such as arabinan and galactan belonging to the rhamnogalacturonan I (RG-I) region, were identified. Subsequently, the effects of Ca2+ on the properties of oil-in-water emulsions were investigated by droplet size, zeta potential, rheological properties and emulsion stability. Results indicated that FAOP formed a solid-like gel emulsion and exhibited excellent emulsion stability when the Ca2+ concentration was 5 mM. At this concentration, the droplet size was the smallest, the backscatter signal (BS) was almost unchanged; the Turbiscan stability index (TSI) value was the lowest, and tan delta (G ''/G') was less than 1. These findings indicated that the improved emulsion stability of FAOP by the introduction of Ca2+ was related to the emulsion gel network structure. These results indicated the potential application of Fructus aurantii pectin as a food stabiliser and thickener.