Changes in the surface tension and viscosity of fish oil nanoemulsions developed by sonication during storage M. Nejadmansouri 1 , S. M. H. Hosseini* 2 , M. Niakosari 3 , Gh. H. Yousefi 4 , M. T. Golmakani 5 Received: 2017.03.14 Accepted: 2017.09.11 Abstract Adequate consumption of ω-3 essential fatty acids (EFAs) has a positive impact on human health. EFAs- enriched functional foods may be used for this purpose. Nanoemulsion is a promising delivery system for incorporating EFAs into a variety of foods and beverages. In this work, fish oil nanoemulsions developed by sonication method were subjected to various analyses as a function of hydrophilic lipophilic balance (HLB) and surfactant to oil ratio (SOR). Analyses were performed upon production and during 1-month storage at two temperatures (4 and 25 ˚C) in the presence (100 ppm) or absence of α-tocopherol. Increasing in HLB and SOR decreased the particle size and surface tension; while, increased the refractive index and viscosity. During storage, the particle size of α-tocopherol-loaded nanoemulsions decreased; whereas, that of α-tocopherol-free nanoemulsions increased in a temperature-dependent manner. Irrespective of the storage temperature, surface tension values of antioxidant-loaded nanoemulsions remained constant. However, their viscosity values increased. Antioxidant incorporation fairly increased the nanoemulsions stability likely due to partitioning at the interface. TEM micrographs confirmed the results obtained by static light scattering. The results of this study may help the rational design of functional foods using nanoemulsion-based delivery systems. Keywords: Fish Oil, High Intensity Ultrasound, Viscosity, Surface Tension, Nanoemulsion 1 Introduction Recently, nanoemulsions, as a sub-group of emulsion-based systems, have gained particular attention due to simple fabrication method, high kinetic stability and bioavailability (McClements, 2011; Walker et al., 2015). The droplet radii of nanoemulsions (<100 nm) results in the formation of semi- turbid or even optically transparent systems particularly at sufficiently small particle sizes (<50 nm) (Mason et al., 2006; Tadros et al; 2004). High- or low-energy methods can be used to fabricate nanoemulsions. In high- energy approaches, mechanical devices such as microfluidizer, high pressure valve homogenizer and high intensity horn sonicator are usually applied to create fine droplets 1, 2, 3 and 5. PhD student, Assistant Professor, Professor and Associate Professor, Department of Food Science and Technology, Shiraz University 4. Associate professor, Department of Pharmaceutics, Shiraz University of Medical Sciences * Corresponding author email:(hhosseini@shirazu.ac.ir) DOI: 10.22067/ifstrj.v1396i13.63073 (McClements, 2011; McClements & Rao, 2011). These methods do not have any limitations on the types of the oils and surfactants. Moreover, low surfactant to oil ratio (SOR) is typically needed. As determined in previous works (Nejadmansouri et al., 2016; Kumar Dey et al., 2012; Ghosh et al., 2013), the application of sonication for the formation of nanoemulsions may lead to promising results without any requirement for coarse emulsion. The increasing awareness about the biological roles of ω-3 polyunsaturated fatty acids (PUFAs) in human health has prompted significant researches to find appropriate methods for incorporating fish oil (or its essential fatty acids) into functional foods and beverages, while preventing them from oxidation and off-flavor development. Natural antioxidants, such as α-tocopherol, are used for this purpose. They act as chain-breaking electron-donor antioxidants (Shimajiri et al., 2013). The antioxidant activity depends on the chemical structure of antioxidant molecules and interactions in the emulsions. The “polar paradox” theory describes that lipophilic ﻧﺸﺮﯾﻪ ﭘﮋوﻫﺸﻬﺎي ﻋﻠﻮم و ﺻﻨﺎﯾﻊ ﻏﺬاﯾﯽ اﯾﺮان ﺟﻠﺪ13 ، ﺷﻤﺎره6 ، ﺑﻬﻤﻦ- اﺳﻔﻨﺪ13 96 ، ص.116 - 105 Iranian Food Science and Technology Research Journal Vol. 13, No.6, Feb. Mrch. 2018, p. 105-116