July 1, 1999

17 Min Read
Dressing for Success

Dressing for Success
July 1999 -- Applications

By: Ann Juttelstad
Associate Technical Editor

  Sometimes a little government interference can do a lot of good. The newest national health guidelines urge consumers to gobble "five-a-day" - five servings of fruits and vegetables a day, that is. And for many, this is easiest and tastiest when at least some of the servings come as a bowl of greens topped with a creamy, vinegary, cheesy or sweet blend of oils, acids and herbs - i.e., salad dressing.

Salad days

  Indeed, toppings really do dress up greenery. The piquancy of the dressing heightens the interest of the salad, elevating mere lettuce to new levels of taste. However, a good salad dressing never overpowers its substrate, but rather complements and rounds out the flavor of greens (or punches up a pile of pasta).

  Americans consumed 60 million gallons of salad dressing in 1997 - almost double the consumption from 1970, according to the Atlanta-based Association for Dressings and Sauces (ADS). The category continues to grow, as the quest for lighter eating, fast fixes and five-a-day pushes the public to grab for the greens. Bagged salads and prepared vegetables have also made an impact on the salad-dressing industry, helping increase sales as salad preparation time has been cut to a minimum.

  Even kids are being introduced to salad dressings at earlier ages, with products aimed directly at their developing tastes and interests. Packages of pre-cut carrots and celery featuring cartoon characters contain ranch-style dressings to dip the veggies in. Formulated with kids in mind, these dressings are a bit sweeter than their adult-targeted counterparts, but still contain typical ranch ingredients - a buttermilk base with garlic, onion and herbs.

Flavor finesse

  According to the ADS, ranch-style dressings are number one in popularity in the United States, followed by Italian, creamy Italian, Thousand Island, French and Caesar.

  Originally, salads were dressed with a sprinkle of salt - the word "salad" is derived from the Latin sal, which means salt - but soon the salt was joined by oil and vinegar, soy sauce or a dash of Worcestershire. Nowadays, the array of available dressings also includes offerings made with walnut, hazelnut and macadamia oils; balsamic, raspberry and champagne varieties of vinegar; mangos, kiwi or citrus fruits; and poppy seeds, spices or herbs.

  Flavoring components can indeed set one salad dressing apart from the others on the market. A dressing might obtain elements of its flavor from the oil used in the formula; acidifying agents such as vinegar, lemon juice or lime juice; or other ingredients such as salt, spices, monosodium glutamate, tomato products and eggs. Various herb and spice blends, mustards and oleoresins can also lend unique flavors to a dressing.

  Cheese and other dairy ingredients are some of the common flavorings used in dressings. For example, NZMP Key Ingredients, Hummelstown, PA, produces Supernatural cheese ingredients, which are blends of natural, standard-of-identity cheeses with intensities three-to-five times that of regular cheese. Says Steve King, vice president of manufactured ingredients for the company, "bleu, Parmesan and Romano types are most commonly used in dressing applications." The various cheese ingredients can be tailored to the specific needs of any application, and are designed for high-acid products and/or products not requiring further heat processing, such as dressings.

  "A new development is our enzyme-modified cheeses, which have no bitter or soapy notes," says King. Essential to any dressing formulation is that the product maintain a balance of flavors that neither overpowers the entire system, nor is dominated by it. "A system high in fat, such as a creamy oil- or mayonnaise-based dressing, tends to mask flavors," continues King. In this case, microbiologically stable, concentrated cheese ingredients can provide economic savings when replacing regular cheeses in a dressing, because of the reduced usage levels possible.

Pour on the oil

  The oil used in pourable salad dressings provides a base for the rest of the ingredients. Highly flavored oils, such as olive and nut oils, lend distinctive characteristics to the flavor profile of the finished product. However, most salad dressings are made with refined, bleached and deodorized (RBD) and winterized vegetable oil. The most commonly used oil is soybean, because of its cost effectiveness.

  Salad-dressing oil should have a minimum cloud point of 5.5 hours. The cloud point is defined as the amount of time an oil remains liquid at refrigeration temperatures. Cloudiness is undesirable in salad dressings, not only because it looks bad, but also because it contributes a waxy mouthfeel. Winterizing significantly reduces clouding. In winterizing, the processor removes high-melting-point triglycerides from the oil by chilling and filtering it.

  Crystallization inhibitors can also help inhibit clouding. With a molecular structure similar to that of triglycerides, says Clyde Stauffer in Fats and Oils (Eagan Press 1996), crystallization inhibitors settle on the face of growing fat microcrystals and interfere with their growth by preventing the further deposition of fat molecules. Those allowed by the FDA include, but are not limited to, oxystearin, lecithin and polyglycerol esters of fatty acids.

  Salad dressings must be shelf stable both during storage and while in use. Typically, dressings are used a portion at a time, and stored under refrigeration between uses. Therefore, oxidative stability is of premium importance. Stability is determined by the oxidative stability index (OSI). In this test, the oil is blanketed with air and kept at a constant temperature between 110° and 130°C. As the oil oxidizes, it develops volatile organic acids, which are captured and measured. The amount of time in which rapid acceleration of oxidation occurs is known as the "induction period."

  Citric acid can also help maintain the shelf life of salad dressings by sequestering heavy metals, which contribute to oxidation of oil. The tartness provided by this acid typically blends well in a low-pH product. Synthetic antioxidants can also be added to dressings. Total antioxidant content may not exceed 0.02% of the fat or oil content of the product.

  For those looking for a natural alternative, mixed tocopherols can provide some protection from rancidity, and have a synergistic effect when combined with citric or ascorbic acids. There is no mandated usage level for tocopherol antioxidants in non-standard products other than that dictated by GMPs.

  In addition, whey phospholipids possess antioxidant properties as well as acting as emulsifiers. Researchers at the Southeast Dairy Foods Research Center at North Carolina State University, Raleigh, have studied the functionality of whey phospholipids, and see possibilities for salad-dressing applications. "This double benefit derived from whey phospholipids offers food manufacturers an alternative to adding synthetic antioxidants to formulations that need emulsification characteristics," says Leon C. Boyd, associate professor, food science.

Body building

  While many salad dressings require shaking before pouring, some consumers prefer a more cohesive dressing blend, which can be achieved by adding an emulsifier to the dressing.

  Emulsifiers reduce the surface tension between the dispersed and the continuous phases in an emulsion. Their molecular structure consists of two sections of opposite polarity, which work to join the molecules of water (polar, hydrophilic), and oil (non-polar, hydrophobic) in a salad-dressing system. Full-fat pourable salad dressings are an example of a water/oil emulsion.

  Lecithin, derived from soybeans, is an effective emulsifier because it interacts with both water and oil. Its polar head aligns with the water in a dressing, while its hydrocarbon tail aligns with the oil phase. The result is a stable and effective emulsifier. Typical usage levels of lecithin in a mixture, according to ADM Lecithin, Decatur, IL, are 1% to 5% of the fat in a water/oil emulsion and 5% to 10% in an oil/water emulsion. The amount of lecithin used in a formula is also affected by factors such as pH, the presence of proteins and gums in the formula, and salt concentrations.

  Flavor components associated with excessive oil in some lecithin compounds can contribute to off-flavor development in formulations. De-oiled lecithin can reduce or prevent flavor problems in delicately flavored salad dressings.

  Other emulsifiers used in salad dressings include monoglycerides, which are made from the reaction of a glycerol with a fat under vacuum at high temperatures, and whey-protein concentrates.

Varying viscosity

  A typical 35/65 oil-and-water blend has the viscosity of water. However, Boyd Coffee Company's Today Foods division, Portland, OR, finds that many of its foodservice customers prefer a thicker salad dressing that doesn't run straight to the bottom of the salad bowl. Consumers have a tendency to use less dressing when they can see it sitting on top of the salad - this results in less waste in a self-serve situation, such as a salad bar.

  Paramount to using thickeners and emulsifiers in salad dressings is the ability of the ingredient to be stable under acidic conditions. Many types of thickeners are used to improve the clingability of a dressing. Florian Ward, Ph.D., vice president of TIC Gums, Belcamp, MD, recommends using a synergistic system to maximize the benefits of gums in a salad-dressing blend. Xanthan gum, guar gum and gum arabic yield a creamy, consistent mouthfeel and good flavor retention. Xanthan gum and gum acacia can be used in salad dressings to reduce gumminess. In addition, says Ward, these ingredients are natural thickeners, which appeals to consumers.

  Another natural thickener, carrageenan helps stabilize emulsions and suspend particulates. It complexes with milk-protein ingredients, so it can improve particle distribution in salad dressings that contain dairy ingredients. In addition, kappa carrageenan exhibits synergies with locust bean gum, and the iota form is synergistic with starch. These are stable at a pH above 3.8.

  "Modified cellulose gum, methylcellulose (MC) and hydroxypropyl methylcellulose (HPMC) can be used in conjunction with stabilizers such as xanthan gum to improve mouthfeel and augment emulsion stability," says Dave Bell, development associate, The Dow Chemical Company, Midland, MI. "Methocel gums enhance richness in dressings due to their fat-like sensory characteristics and lubricity when hydrated. MC and HPMC are useful alternative stabilizers to propylene glycol alginate."

  In pourable dressings, modified cellulose gums improve the cleanness of the break during pouring. "Some hydrocolloids impart a stringy texture," says Bell, "which can try a consumers' patience when pouring the product, not to mention producing a less than optimal mouthfeel. A more immediate cessation of pouring is the result of the pseudoplastic, or shear-thinning, behavior."

  Alginates and whey ingredients also improve emulsification in salad dressings, and can provide improved mouthfeel and viscosity. Likewise, microcrystalline cellulose (MCC) functions as a thickener and viscosity increaser. According to Stauffer, it is often used in formulations that contain tomato products, where it imparts clingability and a smooth texture to the product.

  For cold-processed dressings, instant starches might be another alternative, especially in lower fat applications where they might add a creamy mouthfeel. Adding native starches provides two benefits: a more "natural" label and better flavor release. "Sensory tests show that our functional native starches provide better flavor release," says William King, business development director, National Starch and Chemical Company, Bridgewater, NJ. "These starches don't mask flavor of a food system the way some gums and modified starches do. You notice more of the spices, seasonings and flavors that are in the food system."

  To increase consumption, and therefore sell more product, salad-dressing manufacturers are recommending using dressings in a variety of non-salad applications. Thus, consumers are being urged to use salad dressings as marinades, cooking sauces, or as seasonings for grilled meats and vegetables. This means that the dressings must stand up to heat. Locust bean gum, says Ward, is stable under heat, retaining its viscosity. This makes it a useful ingredient when formulating a multi-purpose dressing.

Mix in the mayo

  Mayonnaise was first introduced into the salad world 250 years ago, and remains popular as a base for many spoonable salad-dressing formulas. Mayonnaise provides binding and flavoring in such items as tuna and potato salads, and it can also maintain texture in some non-salad items such as crab cakes. Aïoli is a garlic-flavored mayonnaise that complements meats and seafoods, as well as vegetables.

  Mayonnaise is 65% oil by weight, and contains whole eggs or egg yolks, which act as an emulsifier and contribute flavor and color; acids such as vinegar, lemon juice or lime juice; and spices. Monosodium glutamate may also be added. If oil in the formula is less than 65%, the product must be labeled as salad dressing.

  Mayonnaise is an emulsion with oil droplets of varying size - small droplets of oil fill in between the larger droplets. This has a major impact on its rheological characteristics. Mayonnaise is a Bingham plastic in rheological terms, says Stauffer, which means that it behaves as a solid under low shear conditions, and as a liquid under higher shear conditions. For instance, a mass of mayonnaise, when cut with a knife, remains stable, but when enough pressure is applied to the knife, as in a spreading motion across a piece of bread, it acts as a liquid and flows easily.

  There is art, as well as science, to mayonnaise manufacturing. In a traditional operation, processors rely on the experience of their machine operators to monitor the progress of the operation. Basically, egg yolk (or sometimes whole eggs) and dry ingredients such as mustard and spices are blended in a mixer with a paddle, and the oil phase is slowly added. The operator judges when the oil can be added a little more rapidly, and when it is time to introduce vinegar and any other ingredients to the mixture. Larger commercial manufacturers mix mayonnaise in a two-phase process, making a premix of the egg and dry ingredients, then slowly pumping in the oil and vinegar ingredients.

  Mayonnaise's reputation for causing foodborne illness may be unjustified, says the ADS. It cites findings from studies dating as far back as the 1940s concluding that mayonnaise and salad dressings actually retard spoilage and the growth of microorganisms. The acidity of mayonnaise inhibits, to some extent, the growth of microorganisms in a salad. The real culprits in salad-associated food illnesses are the primary ingredients in the salads - fish, eggs or potatoes that lower the overall pH value of the salad. ADS stresses the importance of careful handling of all salad ingredients, and of maintaining refrigerated temperatures in order to keep the salads fresh and to reduce the growth potential of Salmonella, Staphylococcus and Listeria monocytogenes.

Especially for spoonables

  Starch-based spoonable dressings were originally formulated as a lower-cost alternative to mayonnaise-based dressings. These salad dressings are now produced in their own right, having found a substantial consumer base. These dressings are also manufactured in a two-phase process. First, the starch is cooked with water and vinegar, then cooled. Eggs, oil and spices are added to the starch in a pre-mix tank, and then the final mixture is milled in a colloid mill, where the final texture and viscosity are obtained.

  Starch-based dressings depend on two different types of starch to provide smoothness, creaminess, cuttability and spoonability. Starches with a high amylopectin content, such as waxy starches, provide a smooth, creamy, more-fluid texture in a salad dressing, says Chris McBride, applications specialist, convenience foods, Cerestar USA, Hammond, IN. This is due to the branched formation of the amylopectin molecule, which forms a soft, salve-like gel when cooked and cooled.

  When a firmer texture is desired, common starch is used in conjunction with high-amylopectin starches. The straight-chain amylose molecule in common starch forms a stiffer gel when cooked. Common starch, with an amylose content of 25%, provides the spoonability or cuttability needed in a thicker product.

  "Think of starches as the branches on a tree," says McBride. "Amylose molecules align themselves into a tight bundle when cooked, like a bundle of nice, straight limbs, which is very hard to cut into. Amylopectin molecules are like the tips of the branches, with lots of little branches coming off. These don't align themselves very well when bunched together, producing a creamy texture. The combination of starches can provide distinctive texture characteristics."

  The severity of salad-dressing processing also has an impact on the starch system. Cross-linked starches can stand up to heat processing and the effects of shear. Most salad dressing are pumped through a colloid mill that disperses the oil in the formula into tiny droplets. Starch helps maintain the emulsion, and aids in separating the oil droplets during the milling process, so they don't coalesce after processing. Cross-linking also improves acid stability of the product. "Most salad dressings have a pH of around 3.2 to 3.5 - very acid," says McBride.

  Functional native starches that resist the shear encountered in steam-injection cookers and colloid mills are also available, allowing processors to use a simple "corn starch" declaration in the ingredient legend.

  Modified cellulose gums can also be used in spoonable dressings to improve processing characteristics. "MCs and HPMCs are water soluble under cold conditions, but will not hydrate under hot conditions," says Bell. "This allows the processor to add the ingredient during the cook phase of the process, without contributing viscosity until the product is cooled. During the hot step, this provides such advantages as easier and faster pumping, since the dressing is thinner at this stage in the process and can also reduce burn-on in the heat exchanger. One cooked-emulsion manufacturer has reduced processing times by a third. This can substantially affect the bottom line."

  Retail manufacturers demand a lot from their salad dressings. "Most retail manufacturers are looking for a one-year shelf life. Substitution provides stability in both store shelf life and a refrigeration situation," McBride asserts. In substitution, a hydroxyl molecule is taken off the starch chain and is replaced by a larger molecule, usually acetyl or phosphorus groups. This substitution improves the water-holding capacity of the starch granule and helps prevent syneresis (watering off) in the finished product.

  MCs and HPMCs are freeze/thaw stable. While normal processing and storage conditions typically involve ambient temperatures, wide temperature fluctuations can occur during distribution. "The added benefit of freeze/thaw stability provided by MCs and HPMCs should not be overlooked," says Bell.

Keeping a low-fat profile

  Even though fat-free foods in general have diminished in sales recently, Ward predicts continued interest in reduced-fat salad dressings. Since fat is the primary ingredient in both pourable and spoonable dressings, considerable demand remains for reduced-fat dressings - full-fat dressings can turn a healthy salad into a caloric nightmare.

  Reduced-calorie products generally contain about half the calories of their full-fat counterparts. Typically, the fat in salad dressing is reduced or removed to lower the caloric content. Fat replacers used in salad dressings include dairy-based ingredients such as whey-protein concentrate and skim-milk based yogurtésse, from Mid-America Dairymen, Inc., San Francisco. Dairy ingredients, while providing emulsification and mouthfeel, also contribute opacity to reduced-fat formulations. Fat globules in standard formulas reflect light, producing a white effect in the product. When the fat is removed, so is the white "ranch-dressing look." Dairy ingredients, specifically whey-protein concentrate and whey-protein isolate, add back the color consumers are accustomed to seeing.

  Gums are typically used in reduced-fat salad dressings as the thickening system, although carbohydrate-based fat replaces such as maltodextrins, corn starches and oat fiber ingredients can also be used. Blending xanthan gum, guar gum and gum acacia in a reduced-fat formula provides mouthfeel and viscosity that closely mimic that of full-fat dressings, says Ward. "You need to retain some oil for flavor," she says, but the amount in a formula can be significantly reduced if a good, clean-flavored thickening system is used.

  Cellulose gels can also replace some of the fats in a reduced-fat salad dressing, producing a creamy mouthfeel and excellent cling properties. Philadelphia-based FMC's Avicel-plus! line of cellulose gums is specifically designed to improve the flavor-release profile in fat-free systems and increase customer acceptance of fat-free dressings. Improved dispersion is as an added benefit to this new technology.

  Some newer salad dressings possess the added appeal of being natural, containing organic ingredients, or having nutraceutical effects. Formulations with tofu, miso and other soybean-based ingredients can provide phytochemicals, phytoestrogens and isoflavones. Salad dressings formulated with omega-3 polyunsaturated fatty acids may help lower cholesterol.

  Another healthful option is to add inulin. It acts as a prebiotic, encouraging the growth of beneficial microorganisms in the gut. Because it's a soluble fiber, it contributes only 1.5 kcal/gram. It also provides viscosity and helps stabilize emulsions, especially when combined with traditional gums, where it not only has a synergistic effect, but changes the rheology to a more "fat-like" character - a benefit in reduced-fat applications.

  The future looks fresh for salad-dressing manufacturers. Produce suppliers continue to provide consumers with increasingly greater varieties of salad greens - baby greens, fresh herb salads and exotic leaf mixtures are taking more and more refrigerated shelf space in the store. Suppliers are offering kosher, organic and pesticide-free salad blends. Salad kits that include dressing packets have opened the salad market to the desktop luncher and the harried homekeeper. Whatever the preferences, manufacturers are riding the waves of salad-dressing success, buoyed by the government's recommendation that consumers eat their five servings a day of fruits and vegetables.

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