Stabilization of emulsion of olive oil in water by ultrasound treatment

There is an increasing trend for using novel technologies instead of conventional techniques because current technology is not sufficient to meet expectations from food products in terms of formulations, nutritional and sensory properties and cost. Stabilization of emulsions of oil in water is important for shelf life of product. High intensity ultrasound (HIUS) technology has been used in food industry for producing homogeneous and stable emulsions via ultrasound waves. The aim of this study was to determine effects of ultrasound amplitude and application mode on stabilization of olive oil-in-water emulsion. In this study, olive oil was preferred as a dispersed phase because of both its nutritional value and sensory attributes in food emulsions. It is more resistant to the effects of ultrasound treatment than other edible oils such as corn oil or sunflower oil, due to its composition with high amounts of monounsaturated fatty acids. It shows better oxidative stability and minimum off-flavor after sonication. It is also a component of salad dressings which are emulsions. Whey Protein Isolate (WPI), Butter Milk (BM) and Na-Caseinate (NaCS) solutions were used as protein emulsifiers. They contribute to the stability with their amphiphilic structure and they also provide nutritional value. Emulsions were prepared at an olive oil concentration of 25% (v/v). Protein solutions were prepared at a concentration of 3% (w/v) in phosphate buffer at pH 7. Olive oil and protein solutions were mixed at two stages. In the first stage, a probe-homogenizer was applied for 2 min at a rotation speed of 15500 rpm. In the second stage, high- power ultrasound was applied at a frequency of 24 kHz for 2 min by using 13-mm diameter cylindrical titanium probe. Ultrasound was applied at amplitude of 20 or 50% in continuous or pulsed mode. In the pulsed mode, ultrasound was applied as 0.5 s on/0.5 s off cycle for 2 min. Control samples were treated with two-stage probe homogenization for 2 min. Samples were kept in ice-water bath during ultrasound treatment to prevent temperature elevation. While EAI and SSA of droplets were increasing, CI, droplet size and span values decreased by ultrasound applications when compared to those of homogenized sample. Temperature of the emulsions was increased after ultrasound depending on amplitude and mode application. Increase in amplitude values and continuous mode resulted in higher increase in temperature values. The highest temperature increase was observed when ultrasound was applied at 50% amplitude in continuous mode. Emulsion samples containing NaCS and WPI and treated with ultrasound at 50% amplitude in continuous mode displayed higher EAI values compared to those of the other ultrasound-treated samples.. The lowest EAI value was measured in the sample treated with ultrasound at 20% amplitude in pulsed mode for among these samples. Lowest EAI value was observed in the sample treated with ultrasound at 50% amplitude in continuous mode among BM containing emulsion. On the other hand, CI, mean droplet size, span and SSA of droplets of emulsions were not affected by amplitude and mode of application of ultrasound treatment.Pseudoplastic flow behavior with thixotropy was observed for all emulsions. Rheological properties of emulsions were not changed after ultrasound treatments compared with those of conventionally homogenized sample.High power ultrasound treatment was found to be an effective method for creating more stable emulsions compared to conventional homogenization. Applied ultrasound amplitudes (20 or 50%) and mode of applications (continuous or pulsed) were found to be feasible for increasing stability of olive oil-in-water emulsion. Pulsed mode can be preferred in ultrasound treatments to reduce adverse effect of temperature elevation on emulsions.