Over the Top
January 1998 -- Applications

By: James C. Burg
Technical Editor

  As consumers pass through the supermarket fresh section, those neatly arranged, mechanically misted heads of Boston bibb, velvet spinach leaves and fern-like fans of fennel all communicate a unified message: "nutrition." But as appealing as this edible garden is, one more step is needed to make a salad as pleasant to taste as to view -- a stroll down the dressings and dips aisle.  The appeal of dressings and dips largely depends on the oils chosen for the product. Texture, mouthfeel, cling and overall appearance are vital considerations in choosing and using oils. Oil's other benefits include: offering flavor, contributing to the flavor expression of other ingredients, and providing clarity and opacity -- all important factors for the finished product. Oil's nutritional benefits continue to influence new development in oils, which has garnered frequent headlines. However, studies often offer contradictory or confusing conclusions. (See this month's News section for details on a recent study concerning potential negative health consequences associated with trans fatty acids.)  The growing interest in vegetables and the accompanying increase in available varieties will present opportunities for creative product developers to feed the need for new dips and dressings. Creating and sustaining those trends will involve building more healthful oil attributes, as well as offering trendy and novel products originating from ethnic or regional cuisines.Dressing definitions  Standard, full-fat dressings typically contain a minimum of 35% oil. Pourable dressings may be two-phase, such as simple oil-and-vinegar blends. Emulsifiers are not required for these, therefore the formulations and processing are typically less complicated. Or, dressings may be blended and emulsified to create a homogeneous mixture. Any of the salad oils, blends or highly flavored oil additions, such as sesame or walnut, may be used, depending on the profile sought.  Dressings that carry a claim of "less" must incorporate a fat reduction of at least 25% and an actual reduction of more than 3g of fat per serving. "Reduced" fat dressings must have at least 50% of the fat removed, with a minimum reduction of more than 3g per serving. In order to be labeled "low fat," the dressing must contain 3g or less fat per 100g. A dressing may be labeled as "fat free" if it contains less than 0.5g fat per serving; however the fat cannot be added directly in the form of fat or oil, it must come from added ingredients -- for example, butterfat in the form of sour cream, buttermilk or cheese ingredients.  Products containing lower fat levels require more sophisticated formulations to replace the properties of the removed oil. The lower the oil level, the more difficult it becomes to match the full-fat taste, texture and flavor. It is easier to mimic regular dressing's viscosity, mouthfeel, taste and flavor by formulating reduced-fat, rather than low-fat versions, since higher levels of oil more easily convey these sensations. In replacing the oil with water (thus lowering calories), food gums are used to replace viscosity. Xanthan gum often is employed due to its acid stability down to pH 2.0. However, exact matching of the full-fat product is not always attained because it is difficult to duplicate all of fat's properties, especially its effect on flavor.  In lower-fat dressings, levels of vinegar, lemon juice and other acids will probably need to be reduced, and the other basic tastes will likely have to be modified as well to maintain a balanced system. Flavor systems may also need adjustment to achieve a balanced overall profile in the finished product. Matching the flavor of a full-fat product is more readily achieved with emulsified dressings. The creaminess and smoothness of the emulsified product tends to blend the flavors and tastes and increases flavor release. Two-phase, low-fat dressings can have a harsher profile, and tend to show changes in quality sooner.  Pourable dressings, such as classic French, employ emulsifiers to maintain emulsion stability, preventing separation of the water and oil phases. Emulsifiers used in dressings can include polysorbate 60 at levels from 0.10% to 0.40%. Polysorbate 60 can be used with sorbitan monostearate or mono- and diglycerides to provide the most stable emulsion. Propylene glycol alginate, which is functional in acid systems, has emulsifying, thickening and stabilizing effects, and can supply body in dressings. Modified food starches and gums exhibit thickening, binding and stabilizing properties useful in dressings; the viscosity increase that they provide can slow oil droplet coalescence and separation.Checking the dipstick  The cousin to salad dressings, dips, also requires some navigating of ingredients. "Dips consist of a wide-ranging category of products, containing a number of types of fats and oils at varying levels," says Paul Swenson, director, R&D, Bunge Ingredient Systems, Atlanta, GA. "Dips in the high-fat range include blends of mayonnaise and sour cream. Mayonnaise must contain, by standard of identity, no less than 65% oil." Sour cream requires a minimum level of 18% butterfat. These systems use blends of emulsifiers and stabilizers to provide emulsion stability, and prevent syneresis.  Reducing the fat level in these products creates many of the same issues encountered in salad-dressing fat reduction. In addition, dips containing lower oil levels may contain higher protein levels, making cost an issue. The proteins employed, such as whey, gelatin, and soy, yeast and grain proteins, might replace some of the properties of the fats, such as mouthfeel. And modifying emulsifier and stabilizer levels provides texture control to offset the loss of oil.  "Dips for the retail market containing canola or partially hydrogenated soybean oil may contain 8% to 12% oils," Swenson says. "These products are stabilized at the 1.5% to 3.0% level. Foodservice products may contain palm or coconut oil at the 5% to 20% oil level, stabilized at the 0.5% to 1.5% blend level." These stabilizers contain locust bean gum, guar gum and carrageenan for emulsion stability, texture, refrigerated storage and syneresis control. Additional ingredients may include lecithin or modified food starch. Modified starches have increased resistance to hydrolysis in acid systems, thus avoiding loss of thickening and stabilizing effects. Guar gum and locust bean gum lose thickening effectiveness at pHs below 3.5 to 5.0, depending on the exact product.  Sour cream, containing 18% minimum butterfat, or sour half-and half, with 11.5% butterfat, often provide the fat source in traditional dairy-based dips and in some spoonable dressings as well. They also provide tartness, texture, and flavor. "Sour creams used in dips are prepared both through fermentation and via direct acidification," says Bob Loesel, manager, texture ingredients, Bunge Ingredient Systems. "The direct acid addition method, using acetic, lactic and phosphoric acids, provides greater control over the preparation of the product. More consistent flavor and texture are achieved. Chelated agar is also added to improve texture. The reduction of possibility of culture contamination is also improved."Choosing an oil  Suitability of a given oil depends on the desired characteristics of the finished product. The oil must perform well under conditions of shelf storage, providing the longest shelf life practical for the product. The oil also must perform once the dressing is opened and stored in the refrigerator. Development of color problems or off-flavor development due to oil degradation, as well as emulsion stability, must be determined prior to a new product's release.  Saturated fatty acids in salad oils are relatively stable to oxidative rancidity compared to the mono- and polyunsaturated fatty acids. However, since dietary recommendations suggest no more than 10% of calories be consumed as saturated fats due to negative health effects, the more highly unsaturated fats found in oils are of benefit. The monounsaturated fatty acid, oleic acid, has more stability than the polyunsaturated acids linoleic and linolenic. Oleic acid has been shown to have positive effects on cholesterol levels in humans, though some recent research indicates some negative effects as well. The debate will continue for some time to come. Nevertheless, oleic acid appears to be a "good" fat at this point, and oil producers have been able, through hybridization and transgenic methods, to reduce polyunsaturated fatty acid levels, while increasing oleic acid. The polyunsaturated fatty acids -- linoleic and linolenic acid -- are prone to rancidity over time. However, the two acids are essential fatty acids and required in the diet.  "Salad oil" is chosen for its moderate flavor, light color and lower cost. Candidates include soybean oil, canola oil, olive, sunflower, corn and cottonseed oils. Soybean oil is the largest product in terms of volume in this country, and future developments will likely maintain this status. Soybean oil has relatively low levels of saturated fatty acids (15%). Monounsaturated fatty acids (oleic acid) and polyunsaturated fatty acids (linoleic and linolenic acids) average at levels of 24% and 61%, respectively.  Canola oil has only 6% unsaturated fatty acids, the lowest of the commercially available oils. And with 62% monounsaturated fatty acids and 32% polyunsaturated fatty acids, canola makes a good selection. The lower polyunsaturated levels, as compared to soybean, allow for greater stability, and cost is similar between the two. These oils may be blended to achieve intermediate levels of monounsaturated vs. polyunsaturated fatty acids. Higher oleic canola oils with enhanced stability have been developed.  Corn oil has a similar fatty acid profile to that of soybean oil, with 13% saturated, 28% monounsaturated, and 59% polyunsaturated fatty acids. The seed crop yields only 4% oil, but two patents have recently been granted to DuPont Agricultural Products, Des Moines, IA, for producing enriched levels of specific compounds in grains, including oil. Its Optimum corn is said to have up to twice the normal oil level of current varieties.  Cottonseed oil has a level of saturated fatty acids that is somewhat higher at 26% than that of the other oils. Monounsaturated, at 19%, and polyunsaturated acids, at 55% (54% linoleic), round out the profile. Sunflower oil also offers possibilities, with 12% saturated, 19% monounsaturated, and 69% polyunsaturated acids (68% linoleic). Stability becomes more of an issue at the higher polyunsaturated acids level, but blending is an option. Higher oleic acid sunflower oils (up to 81%) have been introduced.  Olive oil, due to its natural high level of monounsaturated fatty acid, 71% oleic, has gained a lot of positive press lately. The saturates are at 16%, and polyunsaturates are at 11%, with 10% linoleic acid and 1% linolenic. Because of the high level of oleic, olive oil may have a beneficial effect on cholesterol. However, some recent reports have challenged that view.  This classic product is experiencing a growth phase in the United States, due to its high monounsaturated fat level, as well as the rising interest in Mediterranean and European cuisines. "Demand for olive oil, and especially extra virgin olive oil, has continued to expand in the U.S.," explains William Monroe, president and chief executive officer, Bertolli USA, Inc., Secaucus, NJ. "This growth has increased, despite large price increases due to weather-related crop failures. Virgin olive oil represents about 70% of the market in Europe, and is approaching about 60% of sales in the U.S.  "Olive oil is graded annually by an expert taste panel of the European Agricultural Authority into four categories," Monroe notes. "The first two are pressed oils, the extra virgin and virgin, with the extra virgin being the most expensive grade. Extra virgin is the first pressing, contains more flavor and chlorophyll, and is the preferred choice in Europe. Pure olive is lighter in color and flavor, making it a good choice in terms of dressings. Commercial grade finds use in dressings and cooking applications."  Cost is tied to the grade, but olive oil remains the most expensive of the commercially available oils. Olive oil can be blended with canola and other oils to reduce cost of the end product. Of course, any blend ratio can be used to achieve the requirements of the finished product. Use of the pure olive oil, which is lighter in color, also lessens the change in color caused by chlorophyll changes during shelf life. The chlorophyll gradually changes to browner shades, with accompanying flavor changes, especially when exposed to light.Stirring the emulsions  Emulsified salad dressings are prepared by using a homogenizer or colloid mill to create a fine dispersion along with the addition of emulsifier compounds. Emulsifiers reduce the surface tension between the oil and the water phases. Once prepared, these emulsions remain stable or are delayed in separation. In emulsion terminology, the dispersed phase consists of droplets or globules suspended in the continuous phase. An oil-in-water emulsion, of which salad dressings and mayonnaise are examples, contains the disperse phase of oil in the continuous phase of water. Emulsifiers are classed by solubility, with hydrophilic having high water solubility, and lipophilic having high oil solubility.  Depending on the product type, the optimum size micelle (or globule of fat or water in the disperse phase) is 1 micron or below. To achieve micelles in that range typically requires a two-stage homogenizer. The first stage provides a dispersion, while the second stage produces the emulsion by controlling the intensity of the first-stage homogenization. The basic process involves passing a premixed product under high pressure and, at low velocity, through the homogenizing valve specified for the product. The product is passed through a small gap in the valve, increasing velocity and impacting a ring enclosing the vent. This disruption caused by the flow produces the small, uniformly dispersed globules.Shelf-life issues  Oil quality, and therefore, quality of the finished dressing or dip product, depends on the oil's properties. While offering health benefits, highly unsaturated oils unfortunately tend to become rancid over time, with higher temperature levels and exposure to light increasing the rate of change. With a given product, the effects might be large enough to cause product problems within the determined shelf life. For dressings, that can be six months or more.  "With proper refining methods and better control of distribution, shelf life of oils and finished products has improved," states Tom Crosby, director, research and development, Bunge Foods, Bradley, IL. "Lower calorie products are more affected in terms of shelf life, but emulsified products provide better products than oil and vinegar types." Dips are always refrigerated, and are generally slated at one to two months shelf life.  Shelf life of oils in dressings and dips is primarily affected by two factors: autoxidation and processing. Autoxidation, or rancidity, of oils is an effect of oxygen on unsaturated fatty acids. Oxygen reacts somewhat slowly at ambient room temperature to form peroxides. These peroxides will further react to ketones, aldehydes, hydrocarbons, epoxides and alcohols. The development of off-flavors from this process is accelerated by light and the presence of heavy metals such as iron and copper. To prevent the heavy metal catalysis, chelating agents -- citric acid, phosphoric acid, or EDTA salts -- can be employed. Chelating compounds bond a metal atom between two attracting atoms on the chelant, thus preventing or delaying the effects of the metal. For instance, EDTA is used in mayonnaise to prevent rancidity because of its strong affinity for metals like copper.  Excluding oxygen from the product is vital for maintaining the freshness of the oil. Using a nitrogen blanket in storage, processing and packaging increases shelf life. Use of aseptic packaging systems offers another, albeit expensive, option, which allows removal of headspace oxygen from the product.  Antioxidants can be utilized to prevent reactions leading to rancidity. Antioxidants scavenge free radicals, which react with unsaturated bonds in the oils to produce, as an end result, aldehydes and ketones -- the source of the off-flavors and colors. The relatively inexpensive synthetic, TBHQ, can be used at a level of 0.02% maximum of the weight of oil. Citric acid, which acts as a mild antioxidant and chelating agent at levels between 0.003% to 0.010%, acts synergistically to extend the shelf life further. For instance, canola oil tested via the oxygen stability index method at a temperature of 110° C, exhibits an increase from 7.5 hours for the control to 27.5 hours with the added antioxidants before rapid oxidation begins.  Other synthetic compounds used include BHA and BHT. Natural compounds, such as tocopherols and rosemary extract, exhibit antioxidant properties as well. The tocopherols are interesting because they exhibit vitamin E activity. Rosemary extract requires compatibility with the flavor of the dressing product. The costs, both on a purchase and use basis, are generally higher for the natural compounds. Flavors and costs will determine choice of antioxidants.  Methods used to test resistance to oxidation in oils include: standard shelf storage tests, the active oxygen method, the oil stability index method, and oven storage tests. Test results have to be interpreted based on temperature and other conditions, which vary from method to method. Good practice includes sensory testing of the products to determine loss of, or change in, quality. The only disadvantage is the amount of time required for a full-term sensory evaluation, but this testing can be, and should be, run even after results of the shorter term methods have been evaluated. A well-trained taste panel can determine when changes in a product begin to occur, and to what extent the change becomes significant enough to signal the end of shelf life.  Even if food product designers do not schedule oil changes for the immediate development future, oil consumption patterns are still likely to be altered. "Whether the changes in consumption of new emerging oils are dictated by labeling requirements or consumer demand, the economic factor will continue to play a significant part in choices at the point of purchase," Crosby says. "It's largely a matter of showing up with a new flavor in the commodity oils trade."  What will flow through the oil pipelines might not yet be determined, but it's safe to say that new products, especially healthy ones, will play a large role in what consumers have to say about oil futures. The twin trends of taste and health should continue to influence product development for at least the next two decades, and innovative oils will continue to lubricate the wheels of new dressing and dip product rollouts.Back to top