# Effect of Food Emulsifiers on Aroma Release
## 1 Introduction  
Flavour plays a very important role in the preference for and consumption of foods [1]. Among sensory evaluation components such as colour, rheological properties, or texture, flavour plays an important role during eating [2]. Allowing a controlled release of aroma from food systems has often been a top priority for manufacturers. Food flavourings are important food additives that have become essential in almost all processed foods. To improve the aroma and the unique flavour of food, natural or synthetic flavours are often added during food production. However, a lot of the aroma compounds in food is lost during transport and storage, which affects the quality of food [3; 4]. Emulsifiers, thickeners, other additives in food systems, and even food itself are emulsions. In order to preserve the maximum amount of aroma, the effect of emulsifiers on aroma release was studied. Many studies have been performed to understand the theory of aroma release from food, which delays the release of aroma compounds and enhances the flavour of food [5; 6]. The binding interactions among aroma compounds, emulsifiers and partition ratios among different phases are of great importance on the aroma release of foods. This determines the correlative release of flavour compounds during processing, storage and consumption [7; 8; 9]. The changes of the concentration of the released aromas result from the binding between flavours and polymer molecules and from the system viscosity. The reduction of flavour release is caused by hydrogen bonding, formation of inclusion compounds, or hydrophobic interactions, according to previous studies [10]. A food emulsifier may be defined as a heterogeneous system of two non-mixing liquid phases, where one of the liquids is dispersed into the other phase [11]. As the surface contact between oil and water is unfavourable, kinetically stable emulsions can be produced by the addition of emulsifiers [12]. Emulsifiers can be used to overcome the activation energy of a system by reducing the interfacial tension between the two layers, and thus enhancing its stability over a long time [13]. Food emulsifiers are also a type of surfactant that can effectively reduce the interfacial tension of the system; these emulsions can stabilize two phase or multiphase systems, including liquids, gases, and particles, which are generally immiscible. The most important functions of food emulsifiers include emulsification, stability, dispersibility, and foaming. Emulsifiers control the retention or release of aroma during food processing and storage, which thereby ensures the flavour and taste of food. Adding different emulsifiers to different aroma compounds can effectively improve product quality. Emulsifiers are categorised into natural and synthetic emulsifiers based on their HLB values (hydrophilic and lipophilic) [14], which in turn depend on the molecular composition of the emulsifier. The HLB value is also called the hydrophilic-lipophile balance value, indicating the equilibrium relationship between the hydrophilic groups and the lipophilic groups in the surfactant molecules. The greater the HLB value is, the stronger the hydrophilicity is, the lower the HLB value is, the stronger the lipophilicity is. Emulsifiers show strong hydrophilicity when the HLB value is high, and a large quantity of hydrophilic groups (such as -OH functions) is present in emulsifier molecules. The following paragraphs give examples of relevant food emulsifiers. Soybean lecithin is a byproduct from the production and processing of soybean oil. Specifically, it is viscous crude phospholipid with a high oil content and is mainly used as an emulsifier, moisturizer, and thickener in industrial applications. Soybean lecithin is a natural emulsifier that is not only used as a food additive with external activity, but also has important physiological functions. Phospholipids have both hydrophilic and hydrophobic properties because of their special structure.