Stability of oil-in-water emulsions performed by ultrasound power or high-pressure homogenization

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.

乳化剂（Emulsifiers）的添加旨在提升产品稳定性，以获得令人满意的货架期（shelf-life）。正因如此，不产生过氧化物、不改变食品脂肪酸组成的稳定乳液，以及制备此类乳液的安全工艺，均为至关重要的研究方向。高压均质（High-pressure homogenization）因高效性成为制备乳液的常规手段；此外，超声（ultrasound）在提升加工效率方面的有益效果也已得到证实。因此，本研究探讨了高压均质（30 MPa、50 MPa）或超声功率（270 W）对5%水包油椰子油乳液的稳定性及乳化性能的影响。本研究选用质量比分别为3:7及4:6的海藻酸丙二醇酯与黄原胶复配物作为乳化剂。对超声处理或高压均质处理前后的5%水包油椰子油乳液，分别对其表观黏度、粒径与粒径分布、乳化性能及ζ电位（ζ–potential）进行了检测与对比。通过荧光显微镜（fluorescence microscope）观察了乳液的微观结构。实验结果表明：相较于预乳液，高压均质与超声处理均能有效降低乳液的表观黏度与平均液滴粒径，并缩小其粒径分布范围。但仅经高压均质处理后的乳液中出现了聚集现象，而超声处理制备的乳液在30天储存期内始终保持稳定。综上，本研究为食品及饮料工业中可行的乳液制备方法提供了有价值的参考信息，证实超声在优化食品加工、延长食品货架期方面表现更优，适用于食品与饮料工业。