Emulsion stabilizing properties of depolymerized pectin

Emulsifying properties of depolymerized citrus pectin of 70% esterification and differing molecular weights in the range 48–146 kg mol−1 have been investigated in systems containing rapeseed oil (RSO) and D-limonene at pH values 4.7 and 7. Emulsion stability was followed by determining changes in average droplet size and extent of serum separation with time, with gum arabic chosen as the reference emulsifier. At pH 4.7, it has been found that a relatively low concentration (4 wt%) of pectin of molecular weight 70 kg mol−1 give fine RSO emulsions (20 vol% oil) with excellent long-term stability. Emulsion stability was reduced: (a) at pH 7, (b) with pectin of higher or lower molecular weight and (c) in the presence of added ionic calcium. Changes in particle-size distribution on storage were inferred to arise, at least in part, from droplet flocculation by pectin bridging. Analysis of the aqueous serum layer after centrifugation indicated that only about 25% of the pectin becomes associated with the oil droplets, and that this adsorbed material contains almost all the protein fraction present in the hydrocolloid. The fraction remaining in the serum phase was found not to be effective for subsequent emulsification.