ASIAN JOURNAL OF CHEMISTRY ASIAN JOURNAL OF CHEMISTRY http://dx.doi.org/10.14233/ajchem.2014.16287 INTRODUCTION Emulsions are a class of dispersed systems that consist of two immiscible liquids, with one of the liquid dispersed as small droplets in the other called continuous phase 1 . Among important emulsion properties are emulsion stability and rheological behaviour. Emulsions are thermodynamically unstable and have tendency to break down overtime due to the difference in specific gravity between the oil droplets and medium usually water 2 . In many commercial emulsion formu- lations, polymers are often incorporated into the emulsions systems to modify the rheology of the continuous phase and to confer viscosity and yield value on the continuous phase 3 thereby slowing down the gravitational separation of the droplets 2,4 . A fast growing area in food emulsion technology research is finding new natural alternatives for improving the stability and rheological properties of emulsions. This is because consumers are demanding more natural products. Contributions of green banana pulp, okra extracts, flax seed and soybean to stability and rheology of oil-in-water emulsions have been documented 5-7 . Like other legumes (e.g. flax seed and soybean) bambara groundnut has recently been shown to Emulsion Stability and Steady Shear Characteristics of Concentrated Oil-in-Water Emulsion Stabilized by Gelatinized Bambara Groundnut Flour O. ADEYI 1,* , D. IKHU-OMOREGBE 1 and V. JIDEANI 2 1 Department of Chemical Engineering, Cape Peninsula University of Technology, Cape Town 7530, South Africa 2 Department of Food Technology, Cape Peninsula University of Technology, Cape Town 7530, South Africa *Corresponding author: E-mail: adeyioladayo350@yahoo.com Received: 5 September 2013; Accepted: 29 January 2014; Published online: 28 July 2014; AJC-15618 Effect of sunflower oil and bambara groundnut flour concentrations on the stability and steady shear flow behaviour of concentrated sunflower oil-in-water (o/w) emulsion stabilized by gelatinized bambara groundnut flour dispersions was studied. Emulsion stability was studied using Turbiscan MA 2000 by observing changes in the average Δ-backscattering flux (%) at 20 °C. The steady shear flow behaviours were also modeled by two rheological equations. Both bambara groundnut flour and sunflower oil concentration affected the emulsion stability and rheological behaviour. Increase in oil phase fraction and bambara groundnut flour concentration improved emulsion creaming and led to increase in the emulsion viscosity. Kinetics of destabilization showed that increase in sunflower oil and bambara groundnut flour concentration has profound effect on emulsion destabilization. For the steady shear flow models, both of the rheological models tested were found to predict the rheological behaviour of the emulsions. Herschel-Bulkley (H-B) predicted an increase in consistency index, yield stress and decrease in flow behaviour index with increase in the oil and bambara groundnut flour concentrations while Casson model revealed that all emulsions studied possessed yield stress and plastic viscosity which increased as sunflower oil and bambara groundnut flour concentration increased. However, high value of coefficient of determination (R 2 ) coupled with low root mean square error and standard error made Casson model a better predictor. Keywords: Rheology, Bambara groundnut flour, Oil-in-water emulsion, Rheological model, Non-newtonian fluids. possess stabilizing and emulsifying properties 8 and has been reported to stabilize oil in water emulsions 9 . Bambara groundnut (Vignasubterranea (L.) Verdc) is an underutilized indigenous African legume grown primarily by subsistence farmers. Many researchers have studied the proximate compositions of this legume and on the average the bambara groundnut seeds contain 63 % carbohydrate, 19 % protein and 6.5 % oil 10 . The seed is regarded as a balanced food because it is rich in iron and the protein contains high lysine and methionine 11 . It was also reported that bambara groundnut flour contained 11.51 % moisture content, 7.90 % fat, 15.48 % protein, 4.19 % ash, 2.54 % fiber and 58.38 % carbohydrate 12 . In another study conducted to determine the functional properties of bambara groundnut, it was unveiled that oil absorption capacity (OAC) of bambara groundnut flour was high which could be due to high content of hydrophobic proteins. The foaming capacity (FC) of bambara groundnut was reported as 72 % and high emulsion capacity of 83 g/oil protein, respectively 13 . Oil-gelatinized bambara groundnut flour emulsion is a novel "green" emulsion system that has potential applications in food industries but whose stability and rheological data have never been reported in the literature. Asian Journal of Chemistry; Vol. 26, No. 16 (2014), 4995-5002