EFFECT OF METHYLCELLULOSE ON THE STABILITY OF OIL-IN-WATER EMULSIONS - INFLUENCE OF THE DISPERSE PHASE

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 thre e unstable base emulsions each of olive oil and of mineral oil were fo rmulated with an emulsifier blend of Tween(R) and Span(R). The stable emulsion (SE) contained 2% emulsifier blend optimized for maximum stab ility. Three unstable emulsions were formulated from the SE formulatio n: one with 0.5% emulsifier blend as of the SE formulation (UE1), one with excessive hydrophilic emulsifier (UE2) and one with excessive lip ophilic emulsifier (UE3). A series of emulsions was prepared containin g increasing amounts of methylcellulose 4000 for each base emulsion. T he particle size of all olive oil emulsions was reduced (UE2 > SE > UE 3) and the viscosity was increased (UE2 > SE > UE3) on addition of met hylcellulose. The stability of these emulsions improved in the presenc e of methylcellulose. However, the addition of the polymer caused inst ability in mineral oil emulsions containing lower concentrations of th e hydrophilic emulsifier (Tween(R)). These results suggest that: (i) m ethylcellulose and the hydrophilic emulsifier associate to form a comp lex; (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 hydrophi lic emulsifier; and (iii) this complex when present at the olive oil-w ater interface would stabilize emulsions due to higher interaction bet ween the polar oil and the POE chain of the hydrophilic emulsifier. (C ) 1997 Elsevier Science B.V.