Effect of sweet potato pectin on multilayer emulsion stability

Abstract

Sweet potato (Ipomoea batatas) is a good alternative source of pectin which has the potential for stabilization of emulsion. This study aimed to optimize the extraction of pectin from sweet potato peels, and to investigate the effect of sweet potato pectin on multilayer emulsion stability. Response surface methodology was employed to optimize pectin extraction from sweet potato peels using citric acid. The factors included in the experimental design were temperature (60 - 100 °C), time (40 – 100 min) and pH (1 – 2). The yield of pectin was calculated on the basis of the sweet potato cell wall material. The degree of esterification (DE) of the pectin was analyzed using Fourier transform infrared spectroscopy. The extracted sweet potato pectin was incorporated in oil-in-water emulsion after homogenization using microfluidizer producing whey protein isolate-pectin multilayer emulsion. The effects of environmental conditions on the multilayer emulsion were studied by subjecting the emulsions to various conditions namely: 0 – 1.2 wt % pectin, pH 3 - 7 and 0 – 400 mM salt solution. The emulsion stability was characterized by determination of particle size, zeta-potential and creaming index (CI). The optimum conditions to extract the maximum yield of pectin of 65.8% were at extraction temperature 76°C, time 64 min and pH 1.2. The pectin was categorized as highmethoxyl pectin with DE of 58.5%. Decreasing of zeta-potential (+2.38 to –14.8 mV) showed the adsorption of pectin layer around the emulsion droplets. CI was the lowest (3.64%) at the highest pectin concentration (1.2 wt%) which showed great stability against creaming. Multilayer emulsion showed better stability at high pectin concentration and wide range of salt concentration compared to primary emulsion. Pectin addition largely improved the stability of emulsion especially at pH 4 and 5. Multilayer emulsion prepared using sweet potato pectin can be utilized to produce food emulsion with good stability against environmental pressure (pH and salt content) and can be further applied for controlled release of active ingredients in functional food and beverages.