Date Published: March 8, 2019
Publisher: Public Library of Science
Author(s): Yujie Li, Dong Xiang, Stuart Prescott.
Emulsifiers are added to enhance product stability to obtain a satisfactory shelf-life. For this reason, stable emulsions that do not form peroxides nor change the fatty acid composition of food, as well as safe treatments to obtain them, are aspects of utmost importance. High-pressure homogenization is a conventional approach to prepare emulsions because of its high efficiency. In addition, the beneficial effects of ultrasound on the processing efficiency are known. Therefore, the impact of high-pressure homogenization (30 MPa, 50M Pa) or ultrasound power (270 W) on the emulsion stability and emulsifying properties of 5% coconut oil-in-water emulsion were discussed in this study. The complexes (3:7and 4:6, by weight) of propylene glycol alginate and xanthan gum were selected as emulsifier. The apparent viscosity, particle size and distribution, emulsifying properties and ζ–potential of 5% coconut oil-in-water emulsion before and after ultrasound treatment or high-pressure homogenization were investigated and compared. The micro structure of the emulsion was observed under the fluorescence microscope. The experimental results showed that both high-pressure homogenization and ultrasonic treatment effectively reduced the apparent viscosity, average droplet size and narrowed the distribution range of the emulsion, compared with the pre-emulsion. However, aggregation in the emulsion appeared only after being subjected to high-pressure homogenization, while the emulsion made by the ultrasound treatment remained stable during 30 days storage. In conclusion, this study provides valuable information regarding emulsion preparation methods that can be feasible in food and beverage industries, demonstrating a better performance of ultrasound in optimizing and extending food shelf-life in food and beverage industries.
Oil-in-water emulsions are conventionally defined as a thermodynamically unstable systems which include two immiscible liquids (generally water and oil), in which oil is distributed into the water. Emulsions maybe divide into two phases over time through creaming, coalescence, flocculation or Ostwald ripening. The stability of emulsions is the most important parameters for the shelf life of the food products. The preparation method is great influencing on the stability of o/w emulsion. Currently, some ways were used to prepare emulsions such as mechanical, ultrasound (US) treatment and high-pressure homogenization.
High-pressure homogenization and US treatment are two commonly used emulsification method[8,17]. In the previous experiment, the average droplet size of 5% coconut oil-in-water emulsions prepared by 270W ultrasound treatment was smallest compared to that prepared by other ultrasound intensities.(S1 and S2 Figs). In the storage process, the oil-in-water emulsion prepared by 270W ultrasonic treatment did not show phase separation and maintained good stability.(S3 Fig) In this study, comparing the effects of 270W ultrasound treatment on the stability and emulsifying properties of 5% coconut oil-in-water emulsions with 30MPa and 50MPa high-pressure homogenization. The results showed that the pre-emulsions after US treatment and high-pressure homogenization had a larger reduction in apparent viscosity, which consistent with Zhang et [9,30,31]. The average particle size of o/w emulsions prepared by high-pressure homogenization and 270W US treatment were smaller compared to pre-emulsions. The aggregation occurred in the o/w emulsions prepared by 30MPa and 50MPa high-pressure homogenization, resulting in larger average particle size and a wide particle size distribution of the o/w emulsions during storage time. The hydrophobicity of the polysaccharide treated by 270W ultrasound treatment enhanced. so the complexes of PGA-XG treated by 270W US treatment can form relatively thick hydrophilic coating around the coconut oil droplets which can generate strong steric repulsion. This result is consistent with Matos conclusion.