Liposomal vesicles-protein interaction: Influences of iron liposomes on emulsifying properties of whey protein

Highlights

• Ferrous sulfate liposomes (FL) interacted with whey protein (WP) by electrostatic and hydrophobic forces, hydrogen bonds.

• WP secondary and tertiary structures were changed by the interactions between FL and WP.

• FL improved the emulsifying properties of WP.

Abstract

In this study, whey protein (WP) was used as a model protein to interact with ferrous sulfate liposomes (FL). The interaction between FL and WP was researched using circular dichroism, intrinsic fluorescence, surface hydrophobicity, free sulphydryl groups, Fourier transform infrared spectroscopy, zeta potential, particle size, and interfacial tension. These observations indicated that FL interacted with WP via electrostatic force, hydrophobic force, and hydrogen bonds. WP secondary structure and tertiary structure could be changed by the interaction between FL and WP. The emulsifying properties of WP were improved by the interaction between FL and WP. Emulsifying activity index and emulsifying stability index of WP in the presence of FL increased from 39.69 to 65.63 m²/g, from 28.63 to 101.55 min, respectively. And the WP-stabilized emulsion droplet size decreased from 1.64 μm to 0.78 μm in the presence of FL. However, the emulsifying properties of WP were also influenced by liposomal composition, pH, and temperature. The changes of WP emulsifying properties could be attributed to the effects of liposomes on WP secondary structure and tertiary structure, zeta potentials, and particle size. This work provides new insights into the application of liposomes in food.

Introduction

Iron deficiency is one of the most common nutritional deficiency in the world today. It often leads to anemia which may be the main cause of disability, especially in children of 0–14 years old (Vos et al., 2016). It is usually the result of insufficient dietary intake of iron, poor utilization of iron from ingested food, or a combination of the two (Gaucheron, 2000). It might be an effective method for increasing iron intake that iron salts are used to fortify fluid milk or dairy products. However, iron salts commonly utilized to fortify food, such as ferrous sulfate, may reduce the quality of food due to potential oxidized off-flavors, color changes, and metallic flavors (Jackson & Lee, 1991). However, the iron salts microencapsulated into microcapsules could be kept from direct contact with the food vehicles, and the undesirable interactions also could be prevented that occurred when conventional iron salts was used (Kosaraju, Tran, & Lawrence, 2006).

At present, liposome technology as a special kind of microencapsulation technique has been extensively investigated and used in functional foods as a delivery system (Chen, Wu, Yang, & Wang, 2017; Gomez-Mascaraque, Casagrande Sipoli, De La Torre, & Lopez-Rubio, 2017; Vélez, Perotti, Zanel, Hynes, & Gennaro, 2017). Ferrous sulfate, one of the most common iron supplements, had been microencapsulated with liposomes and applied in dairy product (Xia & Xu, 2005). Whey protein (WP) widely exists in dairy products (20% of total protein in milk), and it is also a model protein for studying the interactions between proteins and food ingredients (such as gum Arabic, citrus pectin, Persian gum, and almond oil) (Lam & Nickerson, 2015; Smithers, 2015). WP has been extensively utilized in various food products due to its functional properties and nutritional value (such as cake, milk drink, bread, beverage) (Zhang, Sun, Wang, & Cao, 2017). Meanwhile, ferrous sulfate liposomes (FL) have also been adopted to prevent iron deficiency through food fortification. The potential interactions between liposomes and WP may exist in FL-fortified dairy products.

At present, the interactions between WP and food ingredients, such as pectins, proteins, and phenols, have been extensively investigated (Genovese, Caporaso, De Luca, Paduano, & Sacchi, 2015; Li & Zhao, 2018; Qi, Xiao, & Wickham, 2017). As a common nanocarrier system, liposomes have also been widely applied to carry functional food ingredients in the food industry. However, the effects of the interaction between active ingredient-loaded liposomes and proteins on protein functional properties, such as emulsifying ability, are still unclear.

The objective of this study was to research the interactions between FL and WP. Furthermore, the effects of the interactions on WP emulsifying properties were to estimate. This work could enhance our understanding of the interactions between proteins and active ingredient-loaded liposomes in food formula, and provide a scientific basis for the effective application of liposomes as a nanocarrier for functional ingredients in protein-rich food, such as FL-fortified fluid milk.