Physical and antimicrobial characteristics of thyme oil emulsified with soluble soybean polysaccharide

There is a great need of essential oil emulsions as antimicrobial delivery systems to enhance microbiological safety of food products. In the present study, thyme oil was emulsified by soluble soybean polysaccharide (SSPS) at different SSPS-to-oil mass ratios (SORs) and physical and antimicrobial properties of emulsions were characterized. Particle dimension generally decreased with an increase in SOR and reached a constant at a SOR ≥5. For emulsions prepared with SORs ≥5, SSPS adsorbed at a greater amount on droplet surface at a higher SOR, ranging from 80 to 140 mg/m2, and no creaming was observed. The particle mean diameter (about 300 nm) and distribution of emulsions with SORs of ≥5 were stable during 60-day storage at 21 °C, indicating the absence of Ostwald ripening. The thyme oil emulsion had similar or slightly better antimicrobial properties than thyme oil pre-dissolved in ethanol when tested against Listeria monocytogenes Scott A, Salmonella Enteritidis and Escherichia coli O157:H7 in microbial growth media. Findings from the present study indicate that SSPS is a feasible polymeric surfactant to prepare emulsions of essential oils with promising physical and antimicrobial characteristics to improve the microbiological safety of foods.