Effect of methylcellulose on the stability of oil-in-water emulsions: influence of the disperse phase

Abstract

The influence of nature of the disperse phase on the stability of oil-in-water emulsions containing nonionic emulsifiers and methylcellulose 4000 as an auxiliary emulsifier was investigated. One stable and three unstable base emulsions each of olive oil and of mineral oil were formulated with an emulsifier blend of Tween® and Span®. The stable emulsion (SE) contained 2% emulsifier blend optimized for maximum stability. Three unstable emulsions were formulated from the SE formulation: one with 0.5% emulsifier blend as of the SE formulation (UE1), one with excessive hydrophilic emulsifier (UE2) and one with excessive lipophilic emulsifier (UE3). A series of emulsions was prepared containing increasing amounts of methylcellulose 4000 for each base emulsion. The particle size of all olive oil emulsions was reduced (UE2>SE>UE3) and the viscosity was increased (UE2>SE>UE3) on addition of methylcellulose. The stability of these emulsions improved in the presence of methylcellulose. However, the addition of the polymer caused instability in mineral oil emulsions containing lower concentrations of the hydrophilic emulsifier (Tween®). These results suggest that: (i) methylcellulose and the hydrophilic emulsifier associate to form a complex; (ii) this complex when present at the mineral oil-water interface would be dislodged from the interface due to less interaction between the non-polar oil and the polyoxyethylene (POE) chain of the hydrophilic emulsifier; and (iii) this complex when present at the olive oil-water interface would stabilize emulsions due to higher interaction between the polar oil and the POE chain of the hydrophilic emulsifier.