Preparation and properties of ferulic acid-sugar beet pulp pectin ester and its application as a physical and antioxidative stabilizer in a fish oil-water emulsion.

A ferulic acid-sugar beet pulp pectin complex (FA-SBPP) was prepared using an immobilized enzyme (Novozym 435®) as the catalyst at 60 °C in a vacuum-controlled system. The structure of FA-SBPP was characterized by FT-IR and NMR (H and C). In addition, the antioxidant activity of FA-SBPP was evaluated according to the DPPH free radical scavenging ability and ORAC values. Moreover, the physical and oxidation stability of the emulsion was evaluated by particle size distribution, cream index (CI), peroxide value (POV), and 2-thiobarbituric acid reactive substance (TBARS) formation. The results showed that esterification between FA and SBPP was confirmed, and the reaction mainly occurred at the C-2, C-3, and C-6 positions. When the concentration was 1.0 mg/mL, the DPPH scavenging activity and total antioxidant activity of FA-SBPP-3 were 80.03% and 355.72 μmol TE/g, respectively. Compared with SBPP, FA-SBPP-stabilized emulsions exhibited significant smaller droplet sizes and lower CIs, POVs and TBARS amounts. Thus, the introduction of FA changed not only the chemical reactivity but also the polarity of SBPP, thereby improving its antioxidant ability and affinity for the oil-water interface. Thus, we provide a multifunctional stabilizer that can reduce the dose of antioxidants or even replace them in oil-in-water emulsions.