This post will provide a comprehensive review of why emulsifiers are used in ice cream. In addition, it will cover the most commonly used synthetic (namely mono- and diglycerides, polysorbate 80, and glycerol monooleate) and natural (namely egg yolk and sweet cream buttermilk) emulsifiers, as well as their recommended quantities in ice cream. If you’re short on time, you can skip to the summary 🙂
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- A blend of 20% polysorbate 80 and 80% mono- and diglycerides at 0.2% – 0.3% of the total mix weight produces better functional properties than when either emulsifier is used separately.
- Distilled unsaturated monoglycerides (glycerol monooleate) at the optimum dosage of 0.3% promotes more partial coalescence and shows better meltdown performance than a mono- and diglyceride and polysorbate 80 blend.
- Glycerol monostearate at 0.3% can be used to advantage in low fat ice cream to provide similar textural qualities as regular ice cream.
- 1% – 2% egg yolk is required to induce sufficient partial coalescence.
Table of Contents
- 1. Why are emulsifiers used in ice cream?
- 2. Which emulsifiers are used in ice cream?
- 2.1 Mono- and diglycerides
- 2.2 Distilled monoglycerides
- 2.3 Polysorbate 80
- 2.4 Egg Yolk
- 2.5 Buttermilk
- 3. Summary
- 4. References
1. Why are emulsifiers used in ice cream?
Emulsifiers are used in ice cream to produce a drier ice cream with smoother body and texture, to increase the resistance to rapid meltdown during consumption, and to increase the resistance to shrinkage during storage (1). These beneficial effects result from the enhancement of partial coalescence of fat globules during the whipping and freezing stage.
1.1 The enhancement of partial coalescence
Ice cream is an oil-in-water emulsion. An oil-in-water emulsion consists of two immiscible liquids (oil and water), with one of the liquids (oil) being dispersed as small spherical droplets in the other (water) (2). All food emulsions are thermodynamically unstable systems, meaning that, after a while, the oil and water will separate. Creaming, flocculation, coalescence, and Ostwald ripening are the four main types of instability. In an ice cream mix, this instability, or creaming, is seen as the milk fat globules rising to the top during the ageing stage of production.
To create a stable emulsion, it is necessary to include a substance known as an emulsifier. Emulsifiers are molecules that adsorb to the surface of freshly formed fat droplets during the homogenisation and ageing stages, forming a protective layer that prevents the droplets from coming close enough together to flocculate and/or coalesce. (2).
The most commonly used emulsifiers in the food industry are small molecule surfactants (e.g. monoglycerides, diglycerides, and polysorbates), phospholipids, proteins, and polysaccharides (2). In an ice cream mix, it is primarily the milk proteins that adsorb to the surface of the fat globules to enhance their stability, so emulsifiers are not needed for fat emulsification in the classic sense (3). Instead, they are added to displace proteins from the surface of the fat globules, thereby rendering them more susceptible to controlled destabilisation, or partial coalescence (3 4).
1.1.1 What is partial coalescence?
During the freezing and whipping stage, some of the fat globules in the mix stick together during collisions caused by the rotating dasher blades, forming clumps and clusters of fat globules. This process is known as partial coalescence. Partially coalesced fat globule clusters are responsible for surrounding and stabilising air cells and for creating a semi-continuous network or matrix of fat throughout the ice cream, resulting in the beneficial properties of dryness when the ice cream is extracted from the ice cream machine, smooth and creamy mouthfeel, resistance to shrinking during storage, and resistance to meltdown or good shape retention (necessary for soft-serve operations) (3 5 6).
Studies have consistently shown that ice cream mixes containing an emulsifier have higher rates of partial coalescence and, consequently, drier, smoother, and creamier texture, a slower melting rate during consumption, and better shape retention (7 8 9).
2. Which emulsifiers are used in ice cream?
As previously mentioned, the most common emulsifiers used in the food industry are small molecule surfactants (e.g. monoglycerides, diglycerides, and polysorbates), phospholipids, proteins, and polysaccharides (2).
2.1 Mono- and diglycerides
Mono- and diglycerides are the most widely used synthetic food emulsifiers accounting for about 70% of world production (10). They are made by reacting fats of either plant or animal (important for certain religious, ethnic, or dietary considerations) origin with glycerol, yielding a mixture of monoglycerides, diglycerides, triglycerides, fatty acids, and glycerol (2). The content of monoglycerides in the mixture may vary from 10% to 60%, depending on the glycerol/fat ratio (10). For ice cream use, mono- and diglycerides usually contain more than 40% monoglycerides as this is the form that is most functional (1). Typical concentrations in regular ice cream are 0.1-0.2% mono- and diglycerides (1), 0.5% mono- and diglycerides with 60% monoglycerides content in low fat (3%) ice cream, and 0.6% mono- and diglycerides with 60% monoglycerides content in 0% fat ice cream (11).
2.1.1 Saturated or unsaturated monoglycerides
The degree of unsaturation of the fatty acids present in monoglycerides influences the level of fat destabilisation. Most dietary fats contain three fatty acid molecules linked to a glycerol molecule (12). Monoglycerides, however, have just one fatty-acid molecule linked to the glycerol molecule. This fatty acid can be saturated or unsaturated, with unsaturated fatty acids encouraging higher rates of protein displacement and, consequently, higher rates of partial coalescence (3 4 13 14). Typically, mono- and diglycerides are saturated in terms of their fatty acids.
2.2 Distilled monoglycerides
The monoglyceride content can be increased to more than 90% by distillation, producing an ingredient referred to as distilled monoglycerides. Distilled unsaturated monoglycerieds (glycerol monooleate) and distilled saturated monoglycerides (glycerol monostearate) can be used rather than the more random form of mono- and diglycerides, although they tend to be more expensive.
2.2.1 Use in low-fat ice cream
Milk fat contributes to the smooth and creamy texture of ice cream by lubricating the palate, thereby reducing the perception of coarseness due to large ice crystals. Low-fat ice creams are generally associated with harder and colder texture, faster melting, and lower creaminess.
Unsaturated glycerol monooleate can be used to advantage in low fat ice cream to provide similar textural qualities as regular ice cream. Zeng et al. (15) investigated the use of unsaturated glycerol monooleate in low (4%) fat and regular (10%) fat ice cream. Sensory and physical properties such as mouthfeel, overrun, firmness, and melting resistance of each ice cream were compared. The researchers found that the use of unsaturated glycerol monooleate in low-fat ice cream at 0.3% of the total mix weight provided a similar sensory effect as regular ice cream.
2.3 Polysorbate 80
Polysorbate 80, also known as Tween 80, is another synthetic emulsifier made by reacting fats of either plant or animal origin with sorbital rather than glycerol. Typical concentrations in ice cream are 0.02% to 0.04% of the total mix weight (1). Overuse can lead to off flavours, especially during storage.
Research shows that polysorbate 80 is much better than mono- and diglycerides at promoting fat destabilisation, due to its ability to displace more protein from the fat globules’ surface, but only when used in combination with mono- and diglycerides. Chavez-Montes et al.(16) studied different combinations of emulsifiers (0.2% mono- and diglycerides only, 0.2% polysorbate 80 only, and a blend of 0.1% mono- and diglycerides with 0.1% polysorbate 80) in ice cream. The researchers found that only the ice cream mixes containing a blend of mono- and diglycerides and polysorbate 80 had a significant degree of destabilisation. The mix containing mono- and diglycerides only showed moderate destabilisation, and the mix containing polysorbate 80 only did not reveal significant amounts of destabilisation. Furthermore, the blend containing mono- and diglycerides and polysorbate 80 exhibited high resistance to meltdown and good shape retention, whereas the mix containing mono- and diglycerides only or polysorbate 80 only had poor resistance to meltdown and poor shape retention. Research done by Chang & Hartel(17) also showed that ice cream emulsified with only mono-and diglycerides had significantly less destabilisation than the ice cream emulsified with an emulsifier blend containing polysorbate 80 and mono- and diglycerides.
2.3.1 How much of an emulsifier blend to use?
Blends of 20% polysorbate 80 with 80% mono- and diglycerides at 0.1% – 0.3% of the total mix weight are frequently used in ice cream production. Research shows that fat destabilisation, iciness values, and meltdown rates are dependent on emulsifier amount, with an 80/20 blend of mono- and diglycerides and polysorbate 80 at 0.3% producing a higher rate of partial coalescence, better iciness values, and better melt down rates than at 0.2% and at 0.1% (7 17).
Lee et al.(18) investigated whether unsaturated monoglycerides could perform as well as an emulsifier blend of 80% mono- and diglycerides with 20% polysorbate 80. The researchers found that at the optimum dosage of 0.3%, unsaturated monoglycerides promoted more destabilisation and showed better meltdown performance compared to a mono- and diglyceride and polysorbate 80 blend.
2.4 Egg Yolk
Natural emulsifiers can be used in ice cream formulations where synthetic emulsifiers are not desirable. These natural emulsifiers include egg yolks and buttermilk. The major egg yolk constituents, apart from water, are proteins (15.7-16.6%) and lipids (32-35%). The lipids fraction is made up of about 66% triglycerides, 28% phospholipids, 5% cholesterol, and 1% other lipids (19). Consequently, egg yolk is used as an emulsifier in ice cream, although it is not as efficient at promoting partial coalescence of the fat as are mono-and diglycerides and polysorbate 80 (1). 1-2% yolk is required to induce sufficient structure similar to monoglycerides (20).
Churning cream during butter making produces both butter and an aqueous liquid byproduct known as buttermilk (21). There are two types of buttermilk. Sweet cream buttermilk is the aqueous liquid byproduct released when cream is churned to produce butter. Sweet cream buttermilk has, however, been replaced almost entirely by cultured, or fermented, buttermilk. Cultured buttermilk is skim milk fermented by a mixture of mesophilic lactic acid bacteria. It has a mild acidic taste with an aromatic didcetyl flavour and a smooth viscous texture (22).
2.5.1 Milk fat globule membrane
Sweet cream buttermilk contains a large fraction of fat globule membrane components comprised predominantly of phospholipids and proteins. This high fraction of phospholipids and protein provides enhanced emulsifying properties, improved whipping properties (23) (results in more air being whipped into the mix), and an increased water-holding capacity (24) (important for texture).
The composition of cultured buttermilk differs from that of sweet cream buttermilk. It contains no, or hardly any, proteins and phospholipids derived from the milk fat globule membrane (22). Cultured buttermilk does not, therefore, have the same functional properties as sweet cream buttermilk .
2.5.2 Functional Properties of sweet cream buttermilk
Sweet cream buttermilk and sweet cream buttermilk powder can be used as a substitute for milk and skim milk powder, especially in ice cream made without added emulsifiers or low in fat, to improve texture, appearance and colour, and whippability, prolong shelf-life, reduce meltdown rates, and contribute richness of flavour.
Szkolnicka et al(25) investigated the quality characteristics of ice cream made using sweet and cultured buttermilk. Three kinds of ice cream were prepared: 1. ice cream made from skimmed milk, cream, skimmed milk powder, and sucrose (the control sample); 2. ice cream made from sweet buttermilk, cream, buttermilk powder, and sucrose; and 3. ice cream made from cultured buttermilk, cream, buttermilk powder, and sucrose. The researchers found that the ice cream made with sweet cream buttermilk and sweet cream buttermilk powder had a higher air content (overrun) (55.5%) compared to the control (47.3%) sample, a lower hardness value, a higher creaminess value, and a higher ‘stickiness’ value after storage, most likely as a result of the improved water-holding capacity and subsequent reduction of ice crystal growth rates.
El-Kholy et al.(26) compared buffalo skim milk with sweet buttermilk in low fat (2%) ice cream production. The researchers found that the sample containing 100% sweet buttermilk had higher flavour, body and texture, and appearance and colour scores, as well as a lower meltdown rate.
Emulsifiers are used in ice cream to produce a drier ice cream with smoother body and texture, to increase the resistance to rapid meltdown during consumption, and to increase the resistance to shrinkage during storage. Emulsifiers are not needed in ice cream to emulsify the mix (i.e. make a stable emulsion) as there is sufficient protein present to do this, but are, in fact, used to make a more unstable emulsion that is more susceptible to controlled destabilisation, or partial coalescence. Partial coalescence has a significant influence on dryness, smooth and creamy mouthfeel, resistance to shrinkage during storage, and resistance to meltdown during consumption.
The most commonly used synthetic emulsifiers in ice cream are mono- and diglycerides and polysorbate 80. Due to the improved functional properties when used together, these two emulsifiers are frequently used as a blend of 20% polysorbate 80 and 80% mono- and diglycerides at 0.2% to 0.3% of the total mix weight. Research has found that distilled unsaturated monoglycerides at the optimum dosage of 0.3% of the total mix weight promotes more partial coalescence and shows better meltdown performance than a mono- and diglyceride and polysorbate 80 blend.
The most commonly used natural emulsifiers are egg yolk and sweet cream buttermilk. 1-2% yolk is required to induce sufficient partial coalescence, although it is not as efficient at promoting partial coalescence as a mono-and diglyceride and polysorbate 80 blend. Sweet cream buttermilk and sweet cream buttermilk powder can be used to replace milk and skim milk powder, respectively, especially in low fat formulations, to improve texture, appearance and colour, and whippability, prolong shelf-life, reduce meltdown rates, and contribute richness of flavour.
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