Optimization Conditions for Ultrasound-Assisted Emulsification of Anthocyanins from Grape Peel Extract

This study investigated the effect of PGPR emulsifier and ultrasonic treatment on the properties and stability of water-in-oil (W/O) emulsion of grape peel extract. Different PGPR concentrations (0%, 3%, 4%, and 5%), sonication times (4 min and 6 min), and power (160 W and 200 W, corresponding to 40% and 50% of power amplitude in relation to the nominal power of the ultrasonic probe) were used. PGPR proved to be effective in the kinetic stability of the emulsions, for an optimal concentration of 4%. The findings showed that the ultrasound treatments improved the emulsifying properties at different levels. The treatment W/O-200W-4min showed lower particle size (3.15 ± 1.86 µm) and polydispersity index. The US treatments increased the viscosity of the emulsions. The ultrasound treatment affected the anthocyanins and phenolic compounds levels, with values of 119-113 mg malvidin-3,5-diglycoside /100 g, and 287-205 mg GAE / 100g on a dry weight basis, respectively. The antioxidant activity of the emulsions was also affected by the US, with values of 75-68%. FTIR analysis indicated no changes in the molecular structure of the palm oil and palm fat after ultrasonication. The US-treated emulsions had a longer half-life (49-56 days) when compared to the control treatment (41 days). The accelerated stability test of the emulsions at 65°C for 120 hours showed that the US increased the stability, provided a controlled release of anthocyanins in the grape peel extract, and reduced the lipid oxidation and the color changes during storage, which is desirable for its application in food systems.