Emulsions prepared by ultrahigh methoxylated pectin through the phase inversion method.

Abstract

Ultrahigh methoxylated pectin (UHMP) was prepared by esterification of citrus pectin in absolute methanol at 60 °C for 12 h, whereby its methoxylation degree was increased from 63.18 ± 0.08% to 91.20 ± 0.13%, and its molecular weight was reduced from 64,400 g/mol to 15,000 g/mol. Structural modifications improved UHMP solubility by over 5%(w/v) and resulted in a flat reduced viscosity profile that was slightly affected by pectin concentration increase and pH change. Interfacial activity of UHMP was improved since most of the galacturonic acid (GalA) units had one methyl group and two hydroxyl groups. Dynamic interfacial tension analysis indicated that UHMP was adsorbed at O/W interface faster than mother pectin with a better capacity to reduce the initial interfacial tension. UHMP emulsions prepared by phase inversion method at different solid-to-oil ratios (20-50%) had a small Z-average size of approximately 400 nm with a creaming index (CI) of 17-20%. During long-term storage (56 days), droplet size and CI were monitored every 7 days, and results suggested that UHMP emulsions were stable. UHMP emulsions showed good pH stability after 14-days storage in a wide pH range of 2-8 without droplet coalescence. Thermal treatment at 85 °C accelerated the flotation of large droplets but did not break droplets.