In today's society, people's living standards have improved. While addressing basic dietary issues, there is a greater emphasis on the appearance, color, aroma, sensory characteristics, and diversity of food. To meet consumer demands, safe and high-quality food emulsifiers can be used.

The market demand for emulsifiers is continuously rising, and research on food emulsifiers has become a hot topic. Its application prospects are quite broad, with uses in baking, beverages, desserts, and more. Emulsifiers can interact with various components in food, thereby improving food quality.

Different types of emulsifiers have different properties and emulsifying effects. These characteristics promote the widespread application of emulsifiers in food processing.

01. Food Emulsifiers

Food emulsifiers are active substances that are evenly dispersed by physical methods to form a mixture of two or more immiscible phases (such as oil and water). They play a significant role in the food industry, improving food quality, preventing spoilage, extending shelf life, and enhancing the taste and appearance of food, thus stimulating consumer demand. The emulsifying properties depend on the hydrophilic-lipophilic balance (HLB) value of the emulsifier; the higher the HLB value, the stronger the hydrophilicity, and vice versa.

I. Emulsification Mechanism of Emulsifiers

Emulsifiers are essential components that promote the stability of emulsions and play an important role in the stability of emulsions. The use and selection of emulsifiers are also crucial for forming stable emulsions with very small dispersed droplets.

Emulsifiers primarily work by reducing interfacial free energy and forming a stable emulsifying film to create stable emulsions. By lowering interfacial free energy, droplet particles form spherical shapes to maintain minimal surface area. The process of forming an emulsion from two different liquids involves creating a large number of new interfaces between the two liquid phases. The smaller the droplets, the larger the new interface, and the greater the free energy on the surface of the droplet particles.

Emulsifiers adsorb onto the surface of droplets, effectively reducing surface tension or surface free energy. Emulsifiers arrange themselves around the droplets, forming a film that reduces the oil-water interfacial tension and effectively prevents droplet aggregation. The more orderly the arrangement of emulsifiers on the droplet surface, the stronger the emulsifying film, and the more stable the emulsion.

The goal of emulsification is to reduce the energy consumed in preparing emulsions. To maintain the stability of the emulsion, emulsifiers should possess strong emulsifying capabilities, form stable emulsifying films, and have properties that are safe, non-irritating, stable, and minimally affected by external factors.

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II. Functions of Food Emulsifiers

Emulsifier molecules generally contain both hydrophilic and lipophilic groups, which determine the emulsifier's hydrophilicity and lipophilicity. By adding an appropriate amount of emulsifier to immiscible oil and water phases and processing it, a homogeneous dispersion system can be formed.

(1) Emulsifying Action

Adding small molecule emulsifiers to the system can reduce the surface tension of the system, thereby lowering its interfacial energy and improving the stability of the emulsion, such as in juices and protein drinks.

Additionally, when surfactants adsorb at the droplet interface, they can act as a barrier to prevent droplets from aggregating. When charged ionic surfactants are added, the emulsion droplets will repel each other due to the same charge, enhancing emulsification.

(2) Solubilizing Action

When the concentration of small molecule emulsifiers in the system exceeds the critical micelle concentration, surfactant molecules aggregate to form micelles, dividing the solvent system into hydrophobic and hydrophilic regions. At this point, the surface tension of the solution decreases rapidly, allowing dissolved substances to gradually adsorb onto the hydrophilic region of the micelles, achieving the purpose of solubilization.

(3) Anti-aging Action

Food emulsifiers are generally used as anti-aging agents in grain products. They can react with linear starch in foods like bread and steamed buns to form insoluble substances, thereby reducing the water absorption and swelling capacity of starch, preventing starch from recrystallizing, thus preventing aging and improving the softness of flour products like bread and steamed buns.

(4) Foaming and Defoaming Action

Emulsifiers containing saturated fatty acid chains can act as foaming agents by generating bubbles within food, giving it a fluffy appearance, and can be used in pastries and bread. In contrast, emulsifiers with unsaturated fatty acid chains can act as defoaming agents, suppressing or eliminating bubbles without affecting the product's taste, and are widely used in dairy products and beverages.

02. Classification of Food Emulsifiers

Currently, there are dozens of commonly used food emulsifiers in China, and different emulsifiers can be selected based on different purposes.

Emulsifiers can be classified into ionic surfactants (anionic surfactants such as carboxylic acids, sulfate esters, etc., and cationic surfactants such as polyacrylamide, fatty amine salts, etc.) and non-ionic surfactants (such as Tween, Span, etc.) based on whether they contain hydrophilic groups.

Additionally, there are amphoteric surfactants such as amino acid-based surfactants and composite surfactants, etc. Based on their source, they can be divided into natural surfactants (such as lecithin, certain proteins, etc.) and synthetic surfactants (such as polyacrylamide, polyglycerol esters, etc.).

Based on the size of the HLB value of emulsifiers, they can be classified into lipophilic surfactants (HLB value less than 10, such as Span) and hydrophilic surfactants (HLB value greater than 10, such as Tween).

The properties of emulsifiers vary, and in today's food processing industry, to improve the functionality of food emulsifiers, different emulsifiers are often used in combination.

A common method is to adjust the hydrophilic-lipophilic balance (HLB) of the emulsifiers, changing their hydrophilicity and lipophilicity to determine the type of emulsifier, thus providing broader practical adaptability. For example, different mixing ratios of Span 20 and Tween 80 result in different types of emulsions. A ratio of 1:3 of Span 20 to Tween 80 forms an O/W type emulsion, while a ratio of 1:6 forms a W/O type emulsion.

I. Span 80

Sorbitan monostearate (Span 80) is a commonly used emulsifier in food processing, classified as a low molecular weight polyol non-ionic surfactant, and is an oil-loving emulsifier widely used in the food industry.

Generally, Span 80 is produced through the esterification reaction of sorbitan after dehydration with oleic acid. This production method is widely applied and is a relatively mature production method.

Span 80 has good emulsifying and dispersing properties, is odorless, easily volatile, and non-irritating, making it widely used in the processing industries of medicine, food, cosmetics, etc.

II. Tween 80

Tween 80 is the abbreviation for polyoxyethylene 20 sorbitan monostearate. It is a hydrophilic and lipophilic non-ionic surfactant commonly used as an additive in industries such as food and medicine, and is soluble in water, ethanol, and other solutions. It can be used as an emulsifier, stabilizer, dispersant, etc., and is widely applied in the production and processing of medicine, food, cosmetics, textile dyeing, and petroleum industries.

III. Whey Protein

The soluble proteins remaining after removing casein, which has an isoelectric point of 4.6, are collectively referred to as whey protein, accounting for about 18% to 20% of milk protein. Whey is a byproduct of cheese and casein production, and can be processed into other products after special concentration techniques. Whey protein concentrate (WPC) and whey protein isolate (WPI) are currently common whey protein emulsifiers.

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In the past 20 years, the modification of whey protein has become a research hotspot for scholars both domestically and internationally. For example, high-pressure homogenization can effectively improve the emulsifying stability of proteins, partially unfolding whey protein molecules, exposing hydrophobic groups, and facilitating interactions between protein molecules to achieve the desired effect.

However, among these modification methods, enzymatic hydrolysis is relatively costly, and most chemical methods require the addition of chemical reagents, which limits the development of modified whey protein. Moreover, conventional techniques do not significantly improve the modification effects on whey protein.

Therefore, in-depth research on composite modification techniques for whey protein, such as the effects of microwave and ultrasound on the physicochemical and functional properties of whey protein, is an effort to enhance the application of whey protein in food processing and provide a solid theoretical basis for its utilization.

IV. Lecithin

Lecithin is a commonly used charged amphoteric surfactant. The lecithin used in the food industry is often extracted from soybeans, egg yolks, milk, sunflower seeds, and rapeseeds. Soy lecithin is generally used in chocolate and ice cream, with less application in emulsions.

Lecithin can be compounded with other natural emulsifiers (such as proteins) to prepare mixed emulsifiers to stabilize emulsions. So far, there has been more research on the use of mixed emulsifiers synthesized with other emulsifiers, while studies on the use of lecithin alone as an emulsifier and its emulsifying performance are relatively few.

V. Monoglyceride

Monoglycerides belong to fatty acid glycerides and are currently the most widely used non-ionic emulsifiers in food processing. The HLB value is about 3.8, making it an oil-loving emulsifier with emulsifying, foaming, and anti-staling properties.

Monoglycerides have developed rapidly, not only due to their low cost but also because they are easy to use and store. As a mainstay food emulsifier, they are primarily used in bread, ice cream, pastries, and tofu manufacturing for defoaming.

VI. Sucrose Fatty Acid Esters

Sucrose fatty acid esters are composed of hydrophilic sucrose and lipophilic fatty acids. Sucrose esters generally have no special odor and are easily soluble in ethanol. Due to their HLB value of 7 to 15, they can serve as both hydrophilic and lipophilic emulsifiers, with a wide range of applications, typically used in combination with other lipophilic emulsifiers. They play roles in anti-aging, emulsifying, and foaming in starch, ice cream, and hydrophilic products. Research on sucrose esters in China is still not very complete and is currently in a research phase.

03. Applications of Emulsifiers in Food

I. Application in Plant-Based Whipped Cream

Whipped cream generally refers to natural animal whipped cream, but plant-based whipped cream is now also widely used in food processing. Plant whipped cream is made primarily from vegetable oils, combined with other ingredients, and emulsifiers can emulsify the vegetable oils to form a stable structure. Typically, hydrogenated vegetable oils with higher saturation, such as coconut oil, palm oil, palm kernel oil, corn germ oil, and sunflower seed oil, are used, which are refined and oxidized to obtain plant hydrogenated oils.

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Hydrogenated vegetable oils are solid at room temperature, have a good taste and plasticity, and possess texture characteristics similar to dairy fat. Plant-based whipped cream is a versatile product, widely used in cake decoration, sandwiching in bread, mousse cakes, and baked goods.

II. Application in Candies and Chocolates

Common candies, such as cream candies, toffees, and chocolates, contain a large amount of fat. Adding emulsifiers (such as molecular distilled monoglycerides) during processing can emulsify the fats in the candies, forming an emulsified system with other substances, preventing fat separation in candies, stabilizing the shape of candies, inhibiting fat crystallization in chocolates, and improving the texture of chocolates and candies.

III. Application in Ice Cream

Emulsifiers can ensure that the fat molecules in ice cream are of uniform size and evenly distributed, effectively preventing the formation of ice crystals that can affect the smooth texture of the product, and improving the stability of the emulsion. Certain emulsifiers (such as whey protein and glycerol monostearate) can also replace some of the fat in traditional ice cream without significantly altering the unique texture of the ice cream product, thereby reducing the calorie content and promoting the development of low-fat ice cream.

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IV. Application in Beverages

Some beverages (such as soy milk, peanut milk, cocoa milk, etc.) also contain a large amount of fat. Emulsifiers (such as whey protein, molecular distilled monoglycerides, sodium caseinate, etc.) can emulsify the fat in the beverage, forming a stable emulsion system, preventing the beverage from separating, ensuring good sensory properties and taste.

The emulsifiers used in beverages should meet the following basic conditions: safety, acid resistance, good hydrolysis, ethanol resistance, and high HLB value.

5. Application in Meat Products

The application of food emulsifiers is also very common in many meat products, with common emulsifiers including soy protein, serum protein, etc. The main function is to emulsify and disperse the fatty substances in the meat product raw materials, suppress the exudation of moisture from the raw materials, and prevent the raw materials from shrinking and hardening, thus having a water-retaining effect. This improves the color, aroma, taste, and shape of meat products, making their properties more stable and enhancing the taste, while promoting the rapid development of meat products.

6. Application in Fermented Foods

The production of bread and pastries generally requires fermentation, and the shelf life of the food is not long. Emulsifiers can act on the dough itself, suppressing the aging of starch to achieve preservation. Emulsifiers can also increase the gelatinization temperature, increase the maximum viscosity, and reduce the minimum viscosity. By utilizing the foaming properties of emulsifiers, the appearance of bread and pastries can be maintained during expansion, acting on the dough to improve fermentation ability and enhance food texture.

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Source: Zhu Die, Hu Lan, Wang Shishuai. Classification, function, and application of emulsifiers in the food industry. Wuhan Business College.

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