Water-in-oil and oil-in-water emulsions stabilized by octenylsuccinic anhydride modified starch and adsorption of modified starch at emulsified oil/water interfaces

Abstract

Emulsions are utilized to help control phase separation and are found in many products ranging from food to pharmaceuticals. Because of the hydrophobic properties of its functional group, octenylsuccinic anhydride (OSA) modified starch is commonly used in oil in water (o/w) emulsions. The first objective of this study was to investigate if OSA modified starch could be used in water in oil (w/o) emulsions. Experiments were designed to determine the effects of concentrations of OS starch, mineral oil and water on the stability of emulsions. High shear homogenizers and a microfluidizer were used to create stable o/w and w/o emulsions. The stability of the emulsions was examined by optical microscopy, gravitational separation, and electrical conductivity. The microfluidized samples always had a longer stability (days), no gravitational separation and did not exceed three microns, compared to the unmicrofluidized (o/w and w/o) samples. Stable (over 100 days of stability) o/w emulsions could be made without a microfluidizer if the emulsion was made of 2, 60, 38% (w/w) oil, water, starch, respectively. Stable o/w emulsions prepared with a microfluidizer were stable for over 100 days. The o/w emulsion prepared by 8, 66, 26% oil, water, and starch, respectively, was stable for over 600 days. The most stable w/o unmicrofluidized sample was made of 52, 22, 26% oil, water, starch, respectively, with a stability of 240 days. For the w/o emulsions from the microfluidizer, the most stable emulsion was made of 52, 34, 14% oil, water, starch, respectively, with a stability of 250 days. The most stable emulsion that could flow (under the 30,000 cP) was 56, 38, 6% oil, water, starch, respectively, with a stability of 150 days. The statistical mixture experiments models successfully predicted the stability for other ratios of oil, water, and starch for o/w and w/o emulsions. The second objective of the study was to determine the concentration of modified OS starch adsorbed to the mineral oil and the water phases for oil-in-water (o/w) emulsions. The percentage of the starch adsorbed at the mineral oil phase was determined and compared when different ratios of starch to oil and water were used. When the ratio of oil:starch was decreased, the emulsion particle size decreased. As the starch content increased, the percent starch adsorbed onto oil based on total oil increased. The adsorption yield and the level of starch in the emulsion did not show a trend. The surface load ranged from 1.6 to 6.98 mg/m². The sample with the highest concentration of starch (26 g/ml) had the highest surface load (6.98 mg/m²) and samples with low concentrations of starch (0.84 and 1.68 g/ml) had the second and third highest surface loads (6.82 and 4.70 mg/m², respectively). The ratio of oil:starch was increased to determine the emulsifying capacity. A high emulsifying capacity was achieved. Samples with an oil:starch ratio of 3:1 were stable for over 80 days while other samples with oil:starch ratios of 5:1 and 6:1 could be stable for one week.