Emulsifier Applications-Aplicaciones de los emulsionantes

[Jorge B]

Hola a tod@s. He visto que se ha hecho mas que notable que cada dia usamos mas emulsificantes, y es necesario nutrirnos de buena bibliografia tecnica para tener un mejor panorama de lo que estamos haciendo al mezlar "X" emulsificante con "Y" emulsificante o "Z" co-emulsificante. me parecio mas que interesante compartirles la siguiente informacion la cual saque textualmente de su autor. Scott Hegenbart es uno de los editores principales de la web Food Design. Sin mas que decir espero que disfruten de la información-

Saludos.


Emulsifier Applications

October 1995 -- Design Elements
By: Scott Hegenbart
Editor*
*(April 1991 - July 1996)
Ask a group of product designers what emulsifiers do and most will answer that they help oil and water remain in stable emulsions. While this characteristic is useful in products such as salad dressings, it is not the limit of emulsifier functionality. In fact, industry sources indicate that only about 15% to 20% of emulsifiers are used to stabilize emulsions. Because of their unique molecular structure, emulsifiers have many diverse functions that can improve the quality of a wide variety of food products.
Structural foundation

Emulsifier functionality is the direct result of their chemical structure, which consists of two parts. The first is a hydrocarbon chain that is lipophilic. The other part is a hydrophilic polar group. Many substances exhibit this combined hydrophilic/lipophilic nature. One of the most common is monoglyceride.
Fats and oils are the raw material for monoglycerides. The glycerin backbone of a fat triglyceride is hydrophilic, but the three fatty acids attached to it make the entire molecule lipophilic. Once the triglyceride is chemically broken into monoglycerides, however, the functional balance tips. Here, the single fatty acid "tail" on the molecule remains lipophilic, but it is now more evenly matched by the hydrophilic properties of the glyceride "head."
Many chemical variations of the basic emulsifier structure exist. Some are chemical modifications of monoglycerides -- such as ethoxylated monoglycerides, or organic acid esters of monoglycerides -- while others are totally different substances. One such group of emulsifiers is the stearoyl lactylates made by combining either calcium or sodium with stearic and lactic acids.
Still other emulsifying ingredients occur naturally. An example is lecithin derived from soybean oil. The functional component of lecithin is a mixture of phospholipids. Like the basic emulsifier structure, these phospholipids have a hydrophilic polar head. The lipophilic portion of the molecule, however, has two fatty acid tails. The various phospholipids can be separated out through fractionation to give specific functional properties to the lecithin. In addition, the lecithin can be modified in many other chemical ways similar to the way monoglycerides are altered.
Class identification

With so many different emulsifiers and their variations each producing different functional properties, food designers can select an emulsifier that provides the performance best-suited to the needs of a product. At the same time, this variety of selection can make the selection process confusing. Fortunately, emulsifiers can be classified in many ways, and these classifications give a general guide to the emulsifier's performance.
HLB. An often-cited way to classify emulsifiers is by their hydrophilic/lipophilic balance, or HLB. Ranging from zero to 20, this scale indicates an emulsifier's relative overall attraction to either oil or water. A low HLB indicates a strongly lipophilic emulsifier, while a high HLB indicates one that is strongly hydrophilic.
In the past, the HLB was one of the primary criteria for selecting an emulsifier. Its effectiveness is, unfortunately, pretty much limited to simpler food systems. Still, it can be very important in applications that require basic emulsification, such as salad dressings. It also is useful as a general indicator of the emulsifier's solubility.
Ionic charge. When dispersed in an aqueous medium, certain emulsifiers will exhibit a negative (anionic) charge. These ionic emulsifiers -- including the stearoyl lactylates and diacetyl tartaric acid esters of monoglycerides -- have a carboxylic acid group on the molecule's ester ("head").
Crystal stability. Like the fats many emulsifiers are made from, emulsifiers have polymorphic properties that allow them to exist in different crystal forms -- ( (alpha), ( (beta) and (( (beta prime). Like fats, most emulsifiers will crystallize in the ( form initially, then transform to one of the ( forms. But, certain emulsifiers are "(-tending" and are stable in the ( form. This group includes acetic acid esters, lactic acid esters, polyglycerol esters, propylene glycol esters and sorbitan esters.
Visible functional spectrum

The basic structure and classification of an emulsifier form the basis of its observed functional effects. For food applications, these functions can be broken down into seven primary areas.
Emulsification. As previously stated, emulsifiers help maintain emulsions. As obvious as this sounds, some confusion in the industry exists.
"Emulsifiers do not create emulsions, mechanical energy creates emulsions," says John Wyatt, director of innovation, Danisco Ingredients, New Century, KS. "Emulsifiers lock the emulsion that's been created. People get into trouble with this all the time. They add an emulsifier and complain that it didn't form an emulsion."
Emulsions are fundamentally the dispersion of two liquids that aren't ordinarily miscible, such as oil and water. On a microscopic level, an emulsion will appear as small droplets of one material dispersed into a continuous phase of the other.
The dual affinities of an emulsifier molecule cause these molecules to orient themselves at the interface between the droplets and the continuous phase -- the lipophilic part of the molecule in the oil, the hydrophilic portion in the water. This prevents the droplet from coalescing with other droplets and breaking the emulsion.
The emulsifier selected will depend largely on which substance is the dispersed phase and which is the continuous phase. If oil is the continuous phase, the emulsifier must be more lipophilic; a more hydrophilic emulsifier is required when water is the continuous phase.
For this reason, emulsification is the one application where the HLB is somewhat useful. Although this is not exact nor does it apply to complex foods, the higher the proportion of oil as the continuous phase, the lower the HLB number should be. Again, the opposite is true when water is the continuous phase -- the higher the percentage of water, the higher the HLB.
For oil-in-water emulsions, an ionic emulsifier may be able to provide even more stability. Because of negative charge on the hydrophilic portion of the molecule, the oil droplet will be covered with a negatively charged surface once the emulsifiers are in place. This negative charge will help repel other oil droplets and further stabilize the emulsion.
Starch complexing is possibly the most widespread application of emulsifiers.
Starch granules contain both amylose, a linear molecule; and amylopectin, a branched molecule. When starch is dispersed in water and heated, these granules absorb water and swell. The fully swollen granules are said to be gelatinized. At this stage, the starch molecules have either built maximum viscosity or have associated to form a gel. Either way, once gelatinization is complete and heat is removed, the starch molecules gradually associate more closely with one another, forcing the absorbed water out until the starch recrystallizes. This is called retrogradation.
When bread and other yeast-raised products are made, the starch from wheat flour is gelatinized. Although the exact mechanism is still being studied, the retrogradation of this starch is believed to play a role in staling. Emulsifiers can retard this retrogradation and maintain softness in these products.
When gelatinized, the linear amylose molecule forms a helical structure. The inside of this helix has mild lipophilic tendencies. Emulsifiers complex with the amylose by "docking" their lipophilic tails inside the helix. This physically inhibits the amylose molecule from retrograding.
Different emulsifiers complex starch to different degrees, depending on the molecule's shape.
"The fatty acid must either be fully saturated or a trans oleic fatty acid," says Wyatt. "If it's in the cis form or a polyunsaturate, there will be an optical bend on the fatty acid and it won't fit into the helix. The molecule must be straight."
The twin tails of lecithin phospholipids also prevent them from being effective starch complexors. They can, however, be modified by selectively cleaving one of the fatty acids with a phospholipase enzyme.
"The increase in dispersibility and its ability to complex with starch are enzyme-modified lecithin's main advantages," says Lance Colbert, manager of lecithin technical services, ADM Lecithin, Decatur, IL. "It's used in some applications for water dispersibility, but mainly in the bakery industry to complex starch."
Foam stabilization/aeration. Air is an important part of many baked goods and dairy products. Although emulsifiers improve the way air is incorporated and retained in both product categories, the mechanism by which they do so is very different.
To provide the correct finished texture in a cake, air must be mixed into the cake batter. Air cells in the batter are subsequently expanded by carbon dioxide gas from the leavening system to form the structure of the finished cake. Aeration must be efficient because over-mixing the batter can make the cake tough.
Emulsifiers increase the whipping rate of cake batters by reducing the surface tension of their aqueous phase. This allows mixer blades to more easily break the surface and incorporate air. Although the mechanism is less understood, emulsifiers also help to increase overall cake volume and to make the cell structure more even.
In ice cream and whipped toppings, emulsifiers stabilize the foam by actually de-stabilizing the product's emulsion. In these products, naturally occurring dairy proteins stabilize the emulsion. The proteins do so by binding themselves through hydrophobic interactions to the triglycerides on the surface of fat globules. This prevents the fat from agglomerating into clusters. These clusters, however, are necessary for building foam because they coat the surface of air cells and stabilize them.
The emulsifiers that can destabilize this emulsion and promote agglomeration are the (-tending emulsifiers. According to Wyatt, the theory behind this functionality is that the (-tending emulsifiers displace the protein from the fat globule surface to the aqueous phase. This increases the liquid cream's viscosity and allows the fat globules to agglomerate. The increased viscosity promotes aeration, while the agglomerates stabilize the air cells once the air is incorporated.
Other emulsifiers, such as monoglycerides, also can help improve aeration in these products. Keep in mind, though, that ionic emulsifiers will not. The mechanism behind this is the same one that makes ionic emulsifiers so effective at maintaining emulsions -- that is, the dispersed fat globules will have a negatively charged surface that repels other globules and prevents agglomeration.
At the same time, an even dispersion of smaller fat globules is desirable in coffee whiteners. Here, agglomeration would be a detriment to a smooth creamy mouthfeel. This is why ionic emulsifiers like sodium stearoyl lactylate are so common in these products.
Protein interaction. Although the destabilizing of protein in aerated dairy products just discussed is technically a protein interaction, this section will focus on interactions with gluten protein in baked products. When water is added to flour and mixed to make a dough, gluten forms an elastic network which gives structure to the dough and helps contain leavening gasses. If this network is weak, however, leavening gasses may be lost and the finished product's volume will not be optimal.
Two reasons account for weak network formation. First, not all gluten is of the same quality; some has a weaker potential to associate into this network. Even with the same flour from the same supplier, the potential may vary from year to year. Second, even high quality gluten can have its functionality diminished by the rigors of mechanical handling in the plant.
Emulsifiers can interact with these proteins to build a stronger gluten network. Many emulsifiers can perform this function, but the ionic ones, such as the stearoyl lactylates, are believed to be the most effective. Although this application is probably the second most common use of emulsifiers -- behind starch complexing -- the mechanism behind protein interaction is the least understood emulsifier function.
Perhaps the emulsifier helps the proteins associate with one another in some way -- possibly through hydrophobic interactions, hydrogen bonding or ionic reactions. Present research hasn't revealed which of these interactions may be the crucial one or if some combination of the interactions is required. Other research suggests an entirely different theory involving the hydrophobic and hydrophilic interaction between lipids and gluten proteins. This dual effect is thought to be enhanced by emulsifiers' lipophilic/hydrophilic qualities.
Crystal modification. As previously discussed, fats -- including many fatty-acid emulsifiers -- exhibit polymorphism. The (-tending emulsifiers, however, have less of a polymorphic quality and tend to stay in the ( configuration. This property can be used to control crystallization in fat-based systems.
Chocolate, for example, is tempered specifically to promote the formation of the more stable ( and (' crystals in the cocoa butter. Yet, some ( crystals may still be present. Another way ( crystals can emerge is if the chocolate is exposed to heat during transport, then cooled. These ( crystals will tend to convert to a more stable form. As they do, small amounts of the cocoa butter will migrate to the surface of the chocolate and appear as a grayish-blue haze known as bloom.
Fat crystals can be used to "seed" a fat-containing system. By adding an (-tending emulsifier to chocolate, the a cocoa butter crystals that may appear will be inhibited from converting. This slows the appearance of fat bloom.
Outside the United States, emulsifiers also are used to modify fat crystals in margarine. Fully hardened canola and sunflower oils are ( crystal stable. These ( crystals can become so large that they contribute a gritty mouthfeel. Adding an emulsifier will inhibit the large crystal formation to yield a much smoother product.
When using an emulsifier for crystal modification, first select one that is not polymorphic. It must go into a specific crystal form and stay there. The emulsifier also should be lipophilic enough to be fully soluble in the food product's fat system. Remember, too, that the emulsifier's crystals must be available to seed the fat. Make sure that the emulsifier has a higher melting point and crystallizes more rapidly than the product's fat does.
Instantizing. Consumers want their powdered mixes to disperse rapidly and completely. This isn't always the case in mixes that contain significant amounts of fat. Again, the dual affinity of the emulsifier comes to the rescue.
A fat-containing mix often will have fat on the surface of the individual particles. This, naturally, will resist dissolution in water. When an emulsifier is applied to the particle's surface, the lipophilic portion of its molecules will align with this fat, leaving the hydrophilic portion exposed. This gives the particle a greater affinity for water and aids dispersion.
For other reasons, lower fat powders can resist dispersion and clump when added to water, too.
"A good example is a protein that absorbs water quickly," says ADM's Colbert. "Because it hydrates so fast, it absorbs water on the surface and encapsulates the internal powder, forming a lump."
An oil applied to the surface of such powders will slow the water absorption and reduce clumping. An emulsifier applied with that oil will improve the dispersion even more because it counteracts the oil's hydrophobic nature.
Instantizing requires emulsifier levels ranging from 0.3% to 0.7%. Government regulations limit some emulsifiers to 0.5%. For this reason and for cost considerations, lecithin is possibly the most common emulsifier for instantizing. It's inexpensive compared with other emulsifiers, and its use level regulation is defined by Good Manufacturing Practice.
Release agent. For smooth plant operation, food products must not stick to equipment. In a bread bakery, for example, product sticking can occur at many points during the operation -- on forming equipment, in pans, and on slicing machines. Using edible oils as a lubricant helps curb sticking, but emulsifiers -- either alone or added to the oil -- can be more effective.
Theoretically, emulsifier molecules have a slight attraction to process equipment surfaces. Although the attraction is slight, it is enough to improve how the emulsifier or emulsifier/oil blend clings. Better cling means more effective anti-sticking.
As with instantizing, cost and use level restrictions guide emulsifier selection in this application. This is again why lecithin is so common in bakery pan oils and other commercial food lubricants. Still, other emulsifiers do have specialized application in this area. Acetylated monoglyceride, for instance, has been shown to work well for lubricating bread slicer blades.
The unique molecular structure of emulsifiers indeed provides many functional properties. These are useful in a range of food applications that goes far beyond maintaining salad dressing emulsions. Now, if only someone could invent an emulsifier that would make R&D and marketing more miscible...

[Azimut]

Gracias, Jorge. Una aportación, como todas las que haces, muy interesante.