Blends of stabilizers & emulsifiers have a profound influence on ice cream qualities and thus their selection & mechanisms are of critical importance .
An Introduction :
Stabilizers, usually polysaccharides, make the water that is not frozen thicker and prevent it from moving around in the product. This makes the ice cream chewier. Ice cream without stabilizers would get rough and frosty soon because the free water would move and make the ice crystals bigger. Some ice cream products are good with only the natural substances in milk that stabilize and emulsify, like milk proteins and phosphates. But adding more stabilizers and emulsifiers can also be helpful.
Emulsifiers make the ice cream drier when it comes out of the machine, with a smoother feel and look and less melting. The most common emulsifiers in ice cream are mono and diglycerides & polysorbate-80, polyoxyethylene sorbitan monooleate. Milk has some natural substances that help make ice cream too. These are milk proteins, phosphates and citrates. Egg yolks can also work as an emulsifier because they have a lot of lecithin.
Stabilizers
Stabilizers help ice cream have body or ‘substance’ and creaminess, make it smooth and resist melting. But too much of the stabilizer/s can make it sticky, melt badly and affect the taste. The main role of stabilizers is to keep the product texture steady i.e. to avoid or reduce damage from heat shock when storing and moving.
Importance of heat shock : Heat shock means the harm that ice cream gets from temperature changes. Ice cream can lose its quality, texture, and taste when it gets warmer or colder than its best storage condition. For example, heat shock can make ice cream melt and refreeze, forming big and rough ice crystals that ruin its smoothness and creaminess . Heat shock can also make ice cream shrink, form lactose crystals, and lose air . Heat shock can occur at any point of the cold chain, from the factory to the customer. To avoid or reduce heat shock, ice cream makers need the right ingredients, equipment, packaging, and temperature control.
Selection considerations
While choosing a stabilizer one must consider :
- Ease of incorporation in mix
- Effect on viscosity & whipping properties in mix
- Ease of dispersibility in cold & hot mix
- Type of body produced in the ice cream
- Effect on meltdown characteristics
- Ability to retard ice crystal growth
- Quantity required to produce the stabilization
- Cost
- Vegetarian source
- Flavor stability
Understanding mechanism of action
Stabilizers can soak up a lot of water and still stay mixed in water and make colloidal solutions. They are also called hydrocolloids because of this. These compounds that make the liquid thicker are mostly polysaccharides but gelatin, a well-known stabilizer, is a protein. The most obvious effect of stabilizers is that they make the liquid phase more viscous. The stabilizers affect the viscosity in a complex way with milk parts. For example, the basic thickness of stabilizer solution does not change much by heat treatment without milk solids, but with more milk solids, the stabilizer makes the system thicker when heated.
When ice cream gets hard, it has less water and more stabilizer in the liquid part. More stabilizer and lower temperature make the liquid thicker, so it does not move or mix much in the frozen product. The stabilizer also makes gel in the mix, which stops the liquid from moving. The water cannot move well because of the hydrogen bonds that hydrocolloids make. So, when water melts and freezes again because of temperature changes, it does not make big ice crystals. But, making the liquid thicker alone may not keep the ice structure stable. Making a 36% TS mix thicker by adding 5% polyethylene glycol did not change the ice crystal size in the frozen dessert.
TS means total solids in ice cream. It is the total of all the solid parts in the ice cream mix, like fat, protein, sugar, stabilizers, and water. The TS amount changes the quality, texture, and taste of the ice cream. Usually, more TS means more rich and creamy ice cream, but also more expensive and caloric. The TS amount of ice cream is different based on the kind and class of the product.
Some stabilizers like guar gum make the liquid thicker but do not make gel. Also, the stabilizers change how the frozen ice cream feels and looks because of their shape and position and their ability to make gel or thicker liquid. But, it is hard to apply the results from simple systems to ice cream because ice cream is complicated with a lot of salt, sugar and stabilizers, which mix with other parts, like protein.
Stabilizer effects on mix & ice cream
Effect on texture
Stabilizers make the ice cream smoother by controlling the ice crystal size after it freezes and hardens. When the ice crystals are made, the stabilizers do what they say… keep the ice crystals from getting bigger because of temperature changes (heat shock). The ice crystals get bigger on average when the temperature changes. Stabilizers help make a situation where more water that melts when it gets warmer freezes again as small crystals. This happens because of a system (with thicker liquid and/or gel) that stops the melted water from moving and sticking to the existing ice crystals when it freezes again. The result is to make the ice crystals grow slower when heat shock happens.
- Effect on body characteristics
This is an important function at that time when the product is drawn, during hardening & when it is eaten. It depends on the stabilizer ingredients which dictate the cohesiveness of the ice cream expressed by words like chewy, sticky, weak, gummy, and so on. - Effect on whipping & overrun retention
The structure that forms when water freezes and stabilizer and its mixes get more dense helping make the air cell wall stronger. Stabilizer affects how much air goes in and their stability - Effect on melting rate & properties of melted product
The structure that forms when gums mix with water and other ingredients affects how fast it melts and how it looks when melted.
The stabilizer helps keep the serum and fat from separating and making the melted product look curdy thus making the melt visually appealing. - Effect on sandiness
Sandiness happens because of lactose which was a common problem 50-60 years ago but not now. This is because of the stabilizers of today use sodium CMC, natural gums, etc. Their function is in controlling ice crystal size by making unfrozen water less movable during heat shock. In super saturation stage, sugars that cause sandiness tend to form crystals in frozen desserts at temperature when one uses a lot of stabilizer. This makes the lactose crystals spread over many small crystals instead of fewer big crystals. Microcrystalline cellulose is very good at this, maybe by making more small crystals grow. - Effect of stabilizer during ageing
Ageing of ice cream mix helps the stabilizer work better. The stabilizer gets more hydrated as it ages, but some stabilizers do not need ageing to be fully hydrated. Ageing makes gelatin stabilizers work better, and the ice cream and freezing get better as the ageing time goes from 4 to 12 h or more. Even mixes with stabilizers that do not need ageing for full activation get better from some ageing because of milk protein hydration and fat crystallization. - Readymade Stabilizer blends
Ice cream makers use different readymade stabilizer blends to get what they want. One stabilizer cannot do everything. For example, sodium CMC makes ice cream short & chewy. Guar gum makes it gummy. Sodium alginate makes it light. Some common stabilizer mixes are: guar gum and xanthan gum, locust bean gum and xanthan gum; locust bean gum and carrageenan; alginates and pectin. To make ice cream that is a little short and chewy, but not too much they need to use CMC and alginate or CMC and guar gum. Mixing different hydrocolloids can also make the stabilizer cheaper. But changing the stabilizer mix too much can be bad because the frozen dessert properties can change profoundly. So, they need to choose the stabilizer mix based on what it does, not how much it costs. - Emulsifiers
Emulsifiers are agents that make the ice cream feel better by helping the whipping, spreading the air cells and making it resist heat shock. They also make the product look dry and stiff when it comes out of the freezer. These effects are because of how emulsifiers act on the surfaces. They lower the surface tension and make more and smaller air cells. Emulsifiers in ice cream mainly work by breaking the fat globule membrane made during homogenization. This breaking happens when the fat globule membranes freeze and makes the fat globules stick together and churn out some fat. The stuck fat globules keep the air cells stable. So, emulsifiers make the ice cream whip better by making smaller ice crystals and air cells, which make the ice cream smoother and drier and stiffer. Usually, a mix of high and low HLB emulsifiers, like mono- and diglycerides and polysorbate 80 are used. HLB is a concept developed by Griffin in 1949. HLB number is from 0 to 20. The HLB number can be found by calculating the hydrophilic proportion of molecular weight of the emulsifying molecule & dividing by 5. The HLB system can help describe an emulsifier’s general features; but, it is not exact enough to find an exact HLB number for a specific emulsion need.
Selection considerations
While choosing an emulsifier one must consider the following :
- Percentage & type of fat in the mix
- Type of frozen dessert
- Effect on flavour of product
- Cost
- Compatibility with stabilizer & other ingredients
- Type of freezer used
- Method of processing – homogenization
Understanding mechanism of action
The emulsion has two parts and is kept stable by casein micelles that stick to the fat globule serum border in the ice cream mix. But when an emulsifier like a monoglyceride is used, the fat globules have an emulsifier coat and the milk proteins make an outer coat. Monoglycerides compete with protein if they make crystals at the border. So, the outer protein coat is pushed away from the fat globules. This makes the emulsion easy to break by movement during freezing. This breaking & destabilizing effect, with other factors, helps to decide what sort of product structure that is wanted.
Ice cream looks dry when it comes out of the freezer because of some things. One thing is that emulsifiers make fat globules stick together at the liquid air border. Also, emulsifiers make more and smaller air cells that foam and make more surface for the liquid. This means the liquid covers a larger area & more space.
Paradoxically, de-emulsification is done by emulsifiers themselves and depends on how much emulsifier & fat is present in the mix. More emulsifier breaks more fat and makes too much butter in the freezer. This makes the product greasy and short. More fat makes this worse. So, they need enough emulsifier to churn some fat, but not too much. High-fat ice cream needs less emulsifier than low-fat one. Too much emulsifier can make the product melt slowly and look awfully curdy & lumpy on melting.
Emulsifier effects on mix & ice cream
- Effect of type of an emulsifier
Emulsifiers have different 3-dimensional molecular shapes & work differently in ice cream. So, they need different amounts of emulsifier for different types. Mono- and diglycerides are used together, but the first one is better. When there is oleic acid in the molecule, these emulsifiers make the product drier when it comes out of the freezer.
The fat destabilization that makes the frozen mix stiff is more for monolaurate, monooleate, and monostearate in that order at 0.1-0.2% levels. Mono- and diglycerides do not churn much. But they are not as good at drying and whipping as polysorbates which dissolve in water and come from sorbitol. Polysorbate 80 (polyoxyethylene sorbitan monooleate) dries well & resists heat shock, but the fatty acid can oxidize and impart a bad taste, especially when too much is used. Usually used at 0.02 to 0.06%, Polysorbate 80 can churn too much in soft serves and high fat ice creams. Polysorbate 65 (polyoxyethylene sorbitan tristearate) dries a bit less than Polysorbate 80 but whips very well. It has a stable flavour, so it can be used at higher levels (e.g. 0.1%) without affecting the product’s taste.
Different polysorbates break fat in the following order :
Polysorbate 80> Polysorbate 40 (polyoxyethylene sorbitan monopalmitate) > Polysorbate 60 (polyoxyethylene monostearate)> Polysorbate
- Mix processing in relation to emulsifier action
Emulsifiers work better in ice cream mix when it is homogenized. Milk protein, especially casein, makes fat globules smaller by homogenization. Emulsifiers make them more even in size. For example, mix with a monoglyceride has a very small size range (about 1µ) as compared to mix without it (1-5 µ). Homogenization of ice cream mix keeps the oil-in-water emulsion stable. This stability and the emulsifier’s breaking effect make the texture quality good. The smaller fat globules and the emulsifier’s-controlled breaking make the right structure and texture in ice cream.
Milk fat in ice cream mix becomes crystals, mostly in the first hour of ageing process. Emulsifiers make more extensive fat crystals. The emulsifier makes protein leave the fat globules over time during ageing. Also, the protein leaves the fat globule surface as a whole layer, not as single casein parts. The breaking of fat goes on in the freezer to make the desired body and texture good. Emulsifiers and stabilizers help make the body and texture of ice cream and frozen desserts good. Their actions & roles at each process have been researched profoundly & have been explained by many people. Definitively, a mix of two or more emulsifiers/stabilizers is better to avoid the problems & drawbacks of individual ingredients in terms of processing & final product characteristics.