Comparative Evaluation of Antioxidative and Antibacterial Activities of Erythorbyl Laurate in Oil-in-Water Emulsions with Different Emulsifiers and Droplet Sizes

Abstract

Erythorbyl laurate (EL) is a multi-functional emulsifier with antioxidative and antibacterial activities for simultaneously controlling the lipid oxidation and microbial contamination in emulsion-based food. In the previous study, the antioxidative activity of EL in emulsion was enhanced since EL was located in the interface where lipid oxidation occurred in the emulsion. In addition, EL showed no inhibitory effect in aqueous system, but showed the inhibitory effect in emulsion against gram-negative bacteria. Hence, it was expected that emulsifying properties could affect the antioxidative and antibacterial activities of EL. Emulsions were prepared with different emulsifiers and droplet sizes. Tween-series emulsifiers were used and sonication time was controlled to prepare emulsions with different droplet sizes. Then the antioxidative and antibacterial activities of EL in the emulsions were compared. Concentrations of lipid peroxides in Tween 20-, Tween 40-, Tween 60-, and Tween 80-stabilized emulsions with EL after 9 days were determined to be 35.95±4.05, 49.17±4.55, 51.74±9.18, and 70.79±0.59 mmol/kg oil, respectively. The result could be explained in terms of the quantity of EL caused by different packing of EL in the interface according to type of emulsifier. EL could be densely packed in the interface of Tween 20-stabilized emulsion since Tween-20 has lauric acid as a fatty acid with the same as EL. In contrast, EL could not be packed densely in Tween 80-stabilized emulsion due to a double bond kink structure in fatty acid of Tween 80. Concentrations of lipid peroxides in Tween 20-stabilized emulsions with EL containing droplet sizes of 261.80, 430.67, and 688.55 nm after 12 days were found out to be 65.97±3.23, 51.92±2.16, and 35.79±5.71 mmol/kg oil, respectively. It was reported that interfacial area of emulsion increased by reduction of droplet size and consequently oxidation occurs rapidly. Thus, there was no effect of droplet size on antioxidative activity of EL in emulsion. Minimum bactericidal concentrations of Tween 20-, Tween 40-, Tween 60-, and Tween 80-stabilized emulsions with EL after treatment for 12 h were 0.040±0.000, 0.057±0.006, 0.087±0.012, and 0.090±0.010%, respectively. EL in Tween 20- and Tween 80-stabilized emulsions showed the highest and the lowest antibacterial activity, respectively, due to the different amount of EL in the interface. Effect of droplet size on antibacterial activity of EL in emulsion was difficult to investigate due to micelle formation formed by the remaining emulsifiers in the continuous phase. Consequently, this study revealed that the antioxidative and antibacterial activities of EL in emulsion were affected by hydrophobic tail length and double bond of the emulsifier mixed with EL. Therefore, when applying EL to emulsion-based food, hydrophobic tail length and double bond of the emulsifier mixed with EL should be considered. When EL mixed with an emulsifier structurally similar to EL, such as Tween 20, which composed of the lauric acid (12:0), the functionality of EL can be improved.