The Art of Suspending Particulates

Product development blends art and science. It requires equal parts aesthetics and technical know-how to create a visually appealing product. Yet formulators must also have a bit of prescience to anticipate the life of the product. How will the product look after processing? What about warehousing and transport? Extended shelf life?

When the product contains spices, herbs, certain flavorings, vegetables or fruit pieces, and the like, will these particulates sit uniformly throughout the product, or settle randomly and unappealingly on the bottom of the container? Learning how best to suspend these particulates is an essential element in many formulations.

Physics 101

Maureen Akins, food scientist, TIC Gums, Inc., Belcamp, MD, reminds us the biggest enemy is gravity. We have to think of that first, she says. If you increase your viscosity, you know youre going to slow down the ability of something to settle or fall out of solution simply because you made a physical barrier and it cant move around in the solution anymore.

Some products, such as yogurt, may be inherently viscous enough to support ingredient suspension without the addition of a stabilizer. Others require intervention.

The mechanisms for suspending particulates in food can be divided into three categories, according to Firth Whitehouse, Ph.D., senior applications scientist, Cargill Texturizing Solutions, Wayzata, MN. In the first category of ingredients, suspension is achieved by specific electrochemical interactions. An example of this would be the stabilization of casein micelles by pectin in an acid milk drink such as a smoothie, he says.

Here, the net negatively charged pectin chains will be attracted to the net positively charged casein micelles. The attraction will cause the casein to remain suspended in solution, instead of clumping and precipitating to the bottom of the container.

The second category of ingredients will stabilize and suspend particulates by increasing the viscosity of the food system, such as the suspension of blueberries in a muffin batter. In this case, a xanthan gum and guar gum blend develops a synergistic relationship that creates a weak gel in the batter, says Whitehouse. This enables the blueberries to remain suspended and more evenly distributed throughout the batter. This makes a more-consistent and more-attractive finished product.

The third category of ingredients stabilize and suspend particulates by forming a strong gel network. An example of this would be the suspension of strawberry pieces in strawberry preserves, Whitehouse elaborates. In this case, a strong gel is formed through cross-chain interactions between pectin molecules. Through the use of proper formulation and processing conditions, the strawberry pieces will be evenly distributed throughout the jar of preserves.

Dairy dilemmas

Many hydrocolloid specialists agree that dairy systems can be among the most challenging to work with. One reason is the low number of hydrocolloids that are compatible with milk protein.

One of the food industrys most-ubiquitous suspending aids, xanthan gum, makes a poor choice for milk systems. Because of the structure of the xanthan and because it has a charge on it, it destabilizes the structure of the milk protein, cautions Akins. Youll see what we call whey off, meaning youll see serum separation of the whey protein on the surface.

Other gums provide better results. For example, carrageenan is used extensively for suspending cocoa solids in chocolate milk. It works on a gelnetwork principle, says Akins. Most of the time, you are going to find people using kappa carrageenan, but youll also find people using iota carrageenan. Additionally, a lot of times youll see phosphates used as a buffering agent. It helps further maintain pH. If the pH gets too low, carrageenans are not effective. Milk systems are generally neutral in pH, so its not really an issue, but if you tried suspension using carrageenan in an acidified beverage like a yogurt smoothie drink, youd end up having problems.

For suspending cocoa in milk, Alan Harpell, senior research scientist, FMC BioPolymer Princeton, NJ, suggests carrageenan, microcrystalline cellulose or combinations of the two, depending on what type of storage conditions the milk needs. If its a pasteurized milk where its going to be refrigerated, carrageenan works very well by itself in ranges of 200 to 400 ppm, he says. However, if its going to be a UHTprocess milk where it may see elevated temperatures during distribution and storage, microcrystalline cellulose is recommended in combination with carrageenan. The microcrystalline cellulose forms a heat-stable three-dimensional matrix that complements high-temperature processing and improves the stability of the product through a range of storage and distribution temperatures.

Knowing the details about the end application is critical. If Im making a chocolate milk beverage thats UHT and its going to sit on the shelf for six months and the chocolate has to be suspended throughout, Im going to have to come up with a really bulletproof system, says Akins. The enduse conditions and the processing conditions are always important. If Im UHTing it, then my heat conditions are two times higher than it was; and maybe my homogenization pressures are going to be different. I have to take those processing conditions under consideration to make sure that I dont destroy the stabilizer that Im trying to use during my processing, she says.

Designers must also think about shear. Too much shear after the carrageenan gel matrix has been established can result in the disruption of the matrix that provides suspension, Harpell cautions. If sufficient heat is applied after the matrix is set up, without cooling the system under low shear conditions, the cocoa will settle out. The carrageenan matrix reforms as it cools, and if the cocoa has settled due to elevated temperature, the reformed carrageenan matrix will not entrap the settled cocoa.

Like most hydrocolloids, proper carrageenan use level is important: Too much carrageenan will over-stabilize the milk and cause gelation, and too little can cause settling. During processing, if we have a customer that is filling chocolate milk into a bottle above its gelling temperature, during the slow process of cooling it is possible that not all the cocoa particles have been fully entrapped in the gel matrix, Harpell says. This can cause dusting or settling of the cocoa. Conversely, if they set a gel matrix in their balance tank and then fill into a milk bottle or the finished container at too low a temperature with too much shear, they can also break that matrix down.

Its important to consider the pH of the product, as well as the solids content. Were seeing lots of dairy-based smoothie beverages and soy-based protein drinks, says Akins. Its critical to make sure you know all the parameters that youre working on so that you can determine which is going to be the best stabilizer system for your product. Remember that every system will be slightly different, especially those with proteins.

Unlike beverages, the very structure of yogurts can provide some suspension. Because its a very viscous solution, Akins says, It doesnt really take a lot more to keep fruit suspended, because we already have so many solids and so much viscosity built in. In that same breath, there are stabilizers that you use in yogurt to make sure that they do maintain stability. Some companies use gelatin. Were going to tell you to use agar or pectin to stabilize your yogurt to make sure you dont have syneresis. Since you gain viscosity, youll gain additional suspension.

Some stand-alone ingredients that can be used for fruit-piece suspension in yogurt preps are low-methoxyl low-esterpectin, gellan gum or modified starch, according to Whitehouse. Blend systems that can be used include low-methoxyl pectin and locust bean gum, pectin and modified starch, and xanthan gum and modified starch. Using the appropriate suspension ingredient and proper processing conditions can ensure that the fruit prep will remain pumpable, but will still have enough of a gel network to evenly suspend the fruit pieces.

Saucy applications

Modified food starches thicken, stabilize and suspend particulates in sauces, according to Tonya Armstrong, senior applications scientist, food, pharmaceutical and personal care service, Grain Processing Corporation, Muscatine, IA. Both pre-gelatinized modified food starches and modified food starches are used, she says. Modified starches can be used alone in these applications, but gums can be added for certain textural properties.

Harpell suggests that use of starches in sauces and marinades is cost-driven. Gums can fine-tune certain desirable characteristics We found that microcrystalline cellulose will complement the functional properties of starches in sauces and marinades, especially where you want viscosity over a wide range of temperaturefor example, in marinades if you want to maintain a certain viscosity for cling even when youre cooking, he says. If you use microcrystalline cellulose with starch in the marinade, youd have a very similar viscosity as its going on cold as well as when its being cooked.

Xanthan gum suspends without adding significant viscosity. Xanthan is comprised of a cellulose backbone b-1,4-linked D-glucose unitswith trisaccharide side chains linked on every other glucose unit, Akins explains. The gum interacts with itself and forms a helical conformation. This structure is what actually suspends the ingredients, and so, she says, allows for it to suspend particulates when theres not a great amount of viscosity in the system.

Xanthan gum creates a pseudoplastic solution that suspends particulates while at rest. When the sauce or marinade is poured onto vegetables or meat, its viscosity decreases and it becomes pourable, says Shay Bustamante, applications specialist, Cargill Texturizing Solutions, Atlanta. Once at rest on top of the vegetables or meat, the viscosity increases again, allowing the spices and the sauce to cling to the food.

The beauty of xanthan gum is that it can withstand very extreme conditions, such as very low pH, or very low or very high salt concentrations. This lends itself toward soups, salad dressings and sauces. The downside of using xanthan is that its texture can be on the gloppy side, Akins notes. For this reason, xanthan is sometimes combined with other gums, such as guar, which adds viscosity. It has a beautiful rheology, she says. Its very smooth in terms of its flow properties, so in combination it provides you with additional viscosity. You get the suspension benefits from the xanthan. Xanthan and guar are synergistic, so xanthan achieves the same suspension. Guar, by itself, is a poor suspending agent.

Carrageenans can also suspend particulates by providing viscosity to a sauce. Another choice is propylene glycol alginate, which has emulsifying properties and can act as a thickening agent in sauces, thereby helping to suspend spices and herbs, Bustamante says.

Propylene glycol alginate is an esterified alginate where the carboxyl groups on the alginate backbone have been substituted with propylene oxide, Harpell explains. Through processing, we control the reactivity with proteins and calcium, he says. This creates a very stable gum system for use in lower-pH protein systems.

Product designers need to be careful when increasing viscosity for suspension purposesadding too much viscosity can often impart a negative mouthfeel to the product. In soups, thickening carrageenans, guar gum and locust bean gum can help suspend particulates by adding viscosity, says Bustamante. Xanthan gum offers a lot of suspension power due to its helical structure, but you have to be careful not to use too much or it will give a slimy mouthfeel. It is helpful to blend the xanthan gum with a thickening carrageenan, guar gum or locust bean gum, because these ingredients will add viscosity, which supports particulate suspension.

In dressings or marinades high amounts of acidic vinegar or lemon juice can reduce the ability of guar gum or locust bean gum to suspend particulates due to degradation. For a low pH, it is better to use propylene glycol alginate, xanthan gum or a combination of the two, because these products remain stable in low-pH conditions, says Bustamante.

Emulsification aids particulate suspension by increasing viscosity. In conjunction with my suspension aid, xanthan, I may have a true emulsifier in there, like propylene glycol alginate, says Akins. That will actually maintain the emulsification of the product giving me viscosity, and then I have additional suspension characteristics of my xanthan as a secondary source to keep my particulates uniformly dispersed throughout.

Stabilized emulsions often contain suspended ingredients, for example herbs in a bottled salad dressing. If the emulsion breaks, this can cause problems. When they are warehoused in hot conditions, jostled during transport, or just stored over a long period of time, emulsions that make up sauces and dressings naturally want to separate back into oil and water phases, Bustmante says. This can cause the herbs and spices to float to the top or fall out to the bottom of the separated phases. She recommends adding hydrocolloids such as xanthan gum, propylene glycol alginate, guar gum and thickening carrageenans to sauces and marinades as a way of stabilizing their emulsions and suspended ingredients.

Particulates in tomato-based salsas are usually suspended by the very weak gel network or water-organizing ability of the pectin naturally present in the vegetables contained in the salsa recipe. If the natural pectin levels are too low or a thicker salsa is desired, small amounts of pectin can be added to the formula in order to achieve greater water control and improved particulate suspension, but at a higher cost, says Whitehouse.

In salsa, food starches thicken, stabilize and suspend particulates. Because most salsas are hot processed, the modified food starch needs to be heat, shear and acid stable, Armstrong says. Gums can be added along with the starch for certain textural properties or used alone, depending on the texture and viscosity desired.

Starches dont usually retrograde, but Harpell cautions that if consumers practice double dipping, sometimes the saliva enzymes will degrade the starch. Youll have salsas break down and start syneresing, he warns.

No matter what type of system you are working with, Akins advises, you have to make sure whatever your gum system you chose is stable enough for the environment youre going to put it in.

And dont forget shelf life. The food scientist must foresee the future life of the product and predict any unsettling developments.

Cindy Hazen, a 20-year veteran of the food industry, is a freelance writer based in Memphis, TN. She can be reached at [email protected].