Food emulsifiers are one of the most important additives in food, not only have typical surface activity, but also can combine with starch to prevent aging, work with protein to enhance dough network structure, improve moisture resistance of products, increase the lubrication of starch and protein, promote liquid dispersion, reduce surface tension of liquids and solids, stabilize air bubbles, and can improve fat crystals.

Due to the complexity of food components, food emulsifiers involved in the formation of emulsions are often required to be safe for human consumption and have good compatibility with other food components.

The starch molecule is a natural organic polymer compound composed of dehydrated glucose units, and enzymatic modifications (e.g., glucosyltransferases) and chemical modifications (e.g., esterification and etherification) can alter the hydrophilic and hydrophobic properties of starch, giving it potential for use as an emulsifier.

With the advantages of low cost and good compatibility, the development of starch-based emulsifiers has catered to the demand for nutritious and versatile foods to a certain extent, and has been widely used as emulsifiers, stabilizers and thickeners in the food industry.

Classification and properties of starch-based food emulsifiers

1、Etherized starch
1）Sodium carboxymethyl starch
Sodium carboxymethyl starch is a kind of anionic starch ether generated by etherification reaction of starch with monochloroacetic acid or its sodium salt under alkaline condition.

Carboxymethyl starch contains hydrophilic carboxyl group and has a negative charge, starch molecules and water molecules to enhance the binding force, with better water solubility. High viscosity sodium carboxymethyl starch is a cold water-soluble anionic starch derivative with excellent properties such as thickening, emulsification, dispersion, adhesion, etc. It has good miscibility with many hydrophilic polymer compounds.

Since high viscosity sodium carboxymethyl starch can be used as raw material for the production of octenyl succinate starch ester, with a view to introducing carboxymethyl to enhance the hydrophilicity of octenyl succinate starch ester.

2) Hydroxypropyl starch
Hydroxypropyl starch is a nonionic modified starch produced by etherification of starch with propylene oxide under strong alkaline conditions.

The introduction of hydrophilic hydroxypropyl destroys the internal structure of starch granules, weakens the intermolecular hydrogen bonding force, and enhances the hydrophilic and water retention capacity of starch, which makes the starch easier to paste and increases the paste transparency and stability.

Due to the better pH tolerance, the addition of hydroxypropyl starch can make acidic food have better stability, and have good water retention in the low-temperature storage process.

2、Esterified starch
(1) Octenyl succinic acid starch ester
Octenyl succinic acid starch ester is starch and octenyl succinic anhydride after esterification reaction to generate a starch ester, usually in the form of starch ester or sodium starch, is an emulsifying thickener with excellent performance.

Octenyl succinic acid starch ester is white powder, non-toxic, odorless, tasteless, soluble in cold water, has good stability in acid and alkaline solution, large molecular mass, has excellent free-flowing hydrophobicity, and other surfactants have a good synergistic effect.

Due to the good emulsification stability, starch octenyl succinate will not have a negative impact on oil droplet size and suspension effectiveness even in a small amount, and inhibit precipitation, oil separation or delamination phenomenon, and has good foaming and foam stability.

2）Starch acetate
Starch acetate is a non-ionic starch ester generated by esterification reaction between starch and acetic anhydride. Starch as raw material after acetylation reaction in the starch molecular chain introduced a hydrophilic acetyl group, increasing the starch molecule spatial site resistance, can maintain the stability of the starch system, expanding the starch system of the fluid volume, and reduce the molecular chain of the hydrogen bonding force, which increases the viscosity, solubility, transparency and freeze-thaw stability of the starch paste, the obtained product water solubility, stability and safety, in food main products, and the product can be used in the food industry. The products obtained have better water solubility, stability and safety, and are mainly used as stabilizers, film-forming agents, thickening agents and shape-keeping agents in food.

Research shows that starch acetate can reduce the interfacial tension between cetyl hydrocarbon and water, can be used as some emulsifiers and polymer coatings more economical biodegradable alternatives.

(3) Sodium starch phosphate
Sodium starch phosphate is an anionic starch ester generated by esterification reaction of starch and sodium phosphate, with dispersion of transparent, high viscosity, strong anti regrowth and other characteristics, and has good water retention properties, freeze-thaw stability, cold water solubility and anti-aging stability, especially for frozen food, is a good emulsifier for vegetable oil dispersed in water, instead of gelatin used as stabilizers, instead of gum arabic as a It can be used as stabilizer instead of gelatin and thickening agent instead of gum arabic.

3、Beta-cyclodextrin
β-CD is a cyclic oligosaccharide with external hydrophilic and internal hydrophobic structure composed of 7 glucose unit molecules, which is produced by cyclodextrin glucosyltransferase modification of starch molecules.

β-Cyclodextrin as a food emulsifier is different from commonly used food surfactants in that it has a hydrophobic internal cavity and a hydrophilic external cavity, which can be used for molecular recognition according to the size of its cavity using van der Waals forces, hydrogen bonding and hydrophobic forces, and combines with a variety of organic substances in food to form cyclodextrin inclusion complexes, thereby improving the properties of the inclusion.

In the food industry, cyclodextrins are mainly used as: carriers of flavor substances; protective agents for food components; masking or reducing off-flavors; improving the physical properties of food; carriers of preservatives to prolong the preservative effect; emulsifiers and foaming agents: β-CD can keep the emulsion stable.

Application of starch-based emulsifiers in the food industry

Starch-based emulsifiers can be used in rice and noodle products, frozen foods, beverages, dairy products, jams, cocoa products, chocolate and chocolate products, canned meat, condiments and jellies and other food products, to play the role of emulsification, thickening, stabilization and so on, of which rice and noodle products, frozen foods and beverages, starch-based emulsifiers are the most widely used.

1、The application of starch-based emulsifier in rice and noodle products
Rice and noodle products are mainly composed of starch and protein, which are easy to lose their commodity properties due to the aging of natural starch. The addition of emulsifiers can not only form hydrophobic spiral complexes with straight-chained starch to slow down the aging of starch, but also increase the volume of fermented noodle products and improve their freeze-thaw stability and mechanical resistance.

Octenyl amyl succinate is used in baked goods to emulsify, preserve and moisturize.

Sodium carboxymethyl starch used in bread and pastry can improve the shape, flavor and color of the finished products by improving the thickening, stability and water retention of the pasta products, improving the elasticity and powder power of the flour.

Sodium starch phosphate is used in pasta products to improve their baking properties, increase freshness and improve texture.

Starch acetate can improve the gluten strength of instant noodles, yield and rehydration without paste soup, enhance the crispness and extensibility of noodles and improve the texture, used in non-dry instant wet noodles can reduce the degree of starch regrowth and maintain a good taste.

2、Application of starch-based emulsifier in frozen foods
Adding emulsifier in ice cream can make the oil-water interface form an interfacial membrane with certain mechanical strength, improve the fat dispersion and air bubble stability, make the ice crystals fine particle size, smooth texture. Adding emulsifier in frozen fermented noodle products can make the dough form a good network structure, improve the dough’s air-holding properties, mechanical endurance elasticity of freeze-thaw stability, and can give the dough a soft texture, preventing and controlling the aging of the dough.

Sodium carboxymethyl starch can be used in ice cream to increase its expansion rate and improve its taste and appearance, can replace food glue to reduce production costs, and can be used in noodle products to improve its freeze-thaw stability.

Sodium starch phosphate can form a complex with trace metal ions to protect the oil from oxidation, can be used in frozen food to shorten the aging time and can replace part of the oil and gelatin and gum arabic to reduce production costs.

Hydroxypropyl starch paste viscosity stability, low-temperature storage with good water retention, suitable for frozen food and convenience foods.

3, starch-based emulsifiers in beverage applications
Emulsifiers in non-alcoholic beverages can play a role in reducing the effect of interfacial tension, and can form interfacial film to prevent the aggregation of dispersed phase particles due to mutual collision, in order to achieve the effect of stabilizing the system.

Low viscosity octenyl amyl succinate stabilizes flavoring agents in non-alcoholic beverages and can replace gum arabic to reduce costs.

The emulsifier will have a certain aroma strength of the flavor oil emulsified dispersion in the aqueous phase and the formation of emulsified flavors are mainly used in turbid beverages, in which the role of the emulsifier is mainly to reduce the floating oil and precipitation, and can make the product to obtain a uniform and stable turbidity.

Octenyl amyl succinate can be used in orange emulsified flavors to produce a more stable emulsion system, in alcohol-free beverages can be stabilized flavors, in carbonated beverages instead of gum arabic stabilizing effect, and can be used as a microcapsule wall material to encapsulate the flavor seasoning, aromatics and vitamins.

β-CD with its special structure of hydrophobic inside and hydrophilic outside can be used in the food industry as a carrier of flavor substances and preservatives, food components of the protective agent, emulsifier and foaming agent, and can improve the physical properties of food and masking or reduction of off-flavors, applied to tea drinks can play a role in improving the degree of clarification, masking off-flavors and preventing the color of the product from browning, etc., but also for the protection of peppermint oil and cinnamon oil components of light and heat. It can also be used to protect the light and heat unstable substances and volatile substances in the components of peppermint oil and cinnamon oil.

Hydroxypropyl starch is less affected by electrolyte and pH changes, which gives acidic beverages (e.g., orange juice) better fluidity and stability.

Phosphate starch can be used as an emulsifier in place of gum arabic in the production of orange juice beverage coloring.

Problems and Prospects of Starch-based Food Emulsifiers

Although starch-based food emulsifiers have achieved a relatively wide range of applications, problems in the production and application of existing starch-based emulsifiers have limited their further development in the food industry.

Carboxymethyl starch, which has disadvantages such as harsh synthesis conditions, poor stability (not resistant to acids and high temperatures, poor shear resistance), and lack of lipophilicity, is often used as a raw material to improve its surface activity through further hydrophobic modification by etherification and esterification.

Hydroxypropyl starch is prone to toxic and carcinogenic chloropropanol residues during the production process, which have certain toxic effects on human blood, liver, kidney and nervous system.

Sodium starch phosphate will have phosphate residue in the preparation process, medical research shows that the optimal calcium-phosphorus ratio in the human body is l:1, long-term intake of excessive phosphorus may change the bone structure and lead to osteoporosis.

The raw material (octenyl succinic anhydride) of starch ester acetate mainly relies on imports, and the production process route is complex, the reaction efficiency is low and the side reaction is more, so it has a higher production cost.

Due to the large influence of raw material differences on the properties of acetate starch pastes, the limited acetyls produced by food-safety-approved preparation methods and the lack of research related to emulsification properties limit the application of acetate starch as a food emulsifier.

The poor water solubility leads to a poor quantity-effect relationship of β-CD in the application process, and the high price and the harm to human body caused by overconsumption limit its wide application in the food industry.

In summary, the relatively low production cost and good compatibility enhance the potential of starch-based emulsifiers in the food field, and it is of great practical significance and value to solve the problems of the existing starch-based food emulsifiers in the process of production and application, and to further develop low-cost, easy-to-prepare starch-based food emulsifiers with good water solubility, safety and storage stability.