The term "acid test," originally referring to a procedure for determining the authenticity of gold, today means any crucial or severe method for assessing value. Put acidulants under that kind of rigorous measure, and because of their special and varied properties, they would certainly qualify as meeting the acid test and probably even surpassing it.
In fact, without these ingredients, the formulation of foods and beverages would be dramatically altered. For example, fruit-flavored beverages and confections would not have quite the right flavor and would be unpleasantly sweet as well. Dairy foods and processed meats would more readily spoil and develop pathogenic organisms. Baked goods would not leaven properly. And gelatin desserts would lose their tartness and gel strength.
With precise control of acidity so important in a number of applications, the use of acidulants can have a significant influence on the final formulation. As will be emphasized in this article, they are capable of performing a wide range of functions—sometimes in relationship with other ingredients, such as antioxidants and proteins.
For example, their tartness can help enhance or modify flavors, creating new formulation opportunities, especially in dairy and beverage products. They can have an effect on microbial control, helping to improve the performance of other preservatives and acting as synergists to antioxidants used to prevent rancidity or other deleterious reactions. They can also have an inhibiting effect on enzymatic browning by reducing the pH below the range of maximum activity of specific enzymes. In addition to flavor modification and aiding preservation, these multifunctional ingredients may be used as agents for leavening, gelling, or chelating, and may serve as buffers, sequestrants, and processing aids. Furthermore, certain of their salts have functionality value as well, including stabilization properties, texture modification, and nutritional uses.
The food industry can choose from a variety of acidulants, including inorganic and organic types. (See sidebar on page 54 for a description of the more commonly used acidulants.) In deciding which acidulant to add to a formulation, several factors have to be considered. In a beverage formulation, for example, these include sour and non-sour characteristics, the lasting time, and the effect on the flavors and quality of the product.
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Although acidulants are not a new ingredient, a reexamination of them and their subsequent developments is especially timely now for a number of reasons.
When thinking about acidulants, the word "sourness" probably comes to mind first. Perception of sourness is different for each type of food acid and also depends on the acid concentration and pH of the food application. To put it another way, the sourness of food acids is not influenced by any single factor alone, but rather is a result of the interaction between several parameters, with pH one of the most important. Although sour taste perception and its physiology are still not fully understood, new studies are being released that are expanding our understanding of this complex event. This article will look at the findings of these studies and the significant impact they can have on future food formulation and the acidification of foods and beverages.
New alternatives for acidifying foods and beverages are being developed. Some examples include a new combination of natural potassium lactate and vinegar; the growing potential of sodium acid sulfate; a new leavening agent that will be introduced at the 2007 IFT Annual Meeting & Food ExpoSM; and improved acidulant blends that do not require masking agents in the formula. Also, vinegar may be getting a surge of attention as new flavor trends are being developed with it.
New opportunities for acidulants are also emerging. Acidulant blends can provide increased benefits in chewing gum and other confections. With the increasing interest in exotic fruits, new and more authentic flavors can be made possible through the appropriate selection of acidulants or combinations of them. The development of new snack dips, deli salads, and other food products that combine convenience with international tastes may be made possible because of the use of these ingredients. In savory applications where sodium has been reduced, acidulants can help provide flavor enhancement properties. New vinegars, in combination with other ingredients, can put a twist on salad dressings or provide a new flavor dimension to cooking. And, of course, acidulants can play a role in nutraceuticals and better-for you products, as well.
So do acidulants score an "A" in food formulating? Judge for yourself based on the following developments.
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New Vinegar Provides Antimicrobial Properties
A new product made with natural potassium lactate and vinegar is said to be effective against pathogens. Launched in the United States by Purac America, Lincolnshire, Ill. (phone 847-634-6330, www.purac. com), Opti.Form Vinegar offers antimicrobial and food safety properties that are comparable to those of existing products.
The company produces Purasal® Opti.Form, a range of products based on lactate and sodium diacetate. These products provide meat and poultry processors with solutions that inhibit a broad range of pathogens, extend shelf life, increase food safety, and enhance and protect flavor. By replacing sodium diacetate with vinegar, the company now adds a new alternative to its product portfolio.
The blend also contains potassium lactate (Purasal HiPure P Plus) which has a clean flavor profile. It is especially suitable for low-sodium food applications, ensuring a minimal taste impact on the final product. Kosher certificates are available on request.
Previously, the company has added other innovations to its Opti. Form line. For example, in 2005 it developed a sodium lactate/sodium diacetate in a powdered form, Purasal Powder Opti.Form. And right before this article went to press, it announced the addition of Opti.Form Ultra, available in three versions: a sodium lactate/sodium diacetate blend (SD4), a potassium lactate/ sodium diacetate blend (PD4), and a sodium lactate/potassium lactate/ sodium diacetate blend (Lite Ultra). In side-by-side taste testing, these three products were chosen as having the cleanest flavor with the least sour and bitter notes, enabling manufacturers to use them without masking agents or other additives.
Purac has also done recent work on the use of acidulants in the development of new flavors, especially savory varieties, which will be covered later in this article.
GDL’s Gradual Rise
How food manufactures are making use of glucono-delta-lactone (GDL)’s special properties is discussed in a brochure from Jungbunzlauer, Newton Centre, Mass. (phone 800-828-0062, www.jungbunzlauer.com). The brochure, "Glucono-delta-Lactone—New Trends," highlights the increasing opportunities that the acidulant has in such applications as sauces, dressings, and dips; potato, chicken, tuna, and other deli salads; meat, poultry, and seafood products; dairy and soy products; and baked goods.
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GDL is a neutral cyclic ester of gluconic acid, produced with the acid by fermentation of glucose. When added into an aqueous solution, it slowly hydrolyzes to form gluconic acid. Because of its slow hydrolysis which ensures a progressive and continuous decrease of pH to equilibrium, GDL functions as a slow-release acidifier. Furthermore, during its hydrolysis, the initial sweet taste of GDL becomes only slightly acidic, making the final flavor of an aqueous solution of GDL much less tart than the solution of other acidifiers.
Its slow rate of acidification and mild taste characteristics sets GDL apart from other acidulants, enabling it to be used in special applications described in the brochure. For example, GDL has found a gradual place as a slow leavening agent in many new value-added baked products, including pizza doughs, breads, muffins, and a variety of innovative premixes, and it can be used as an alternative to baker’s yeast and phosphates. As a controlled-release acidulant, GDL hydrolyzes progressively to gluconic acid when water is added to the dough mix. The gluconic acid then reacts with sodium bicarbonate to release the carbon dioxide that makes the dough leaven. According to the brochure, particularly interesting is the slowness of GDL’s hydrolysis at room temperature and its acceleration when temperature is increased, giving the baker control over the dough rate of reaction.
The acidulant may prove especially valuable in light versions of salad dressings and mayonnaise products. The partial or total replacement of oil with water can compromise the bacteriological stability of low-fat and fat-free products. Also, the acidic taste of the vinegar can become more prominent, causing an undesirable harsh flavor. Partial replacement of the vinegar with GDL allows pH to be reduced to 3.5 or less while maintaining the desired organoleptic properties of the dressing. It also allows an increased resistance to microbial spoilage and an extension of shelf life. GDL may also find increasing use as a mild acidulant in such dips as nacho cheese, onion, crab, and black bean.
Setting New Flavor Trends with Vinegar
Vinegar, which contains acetic acid as a principal component, is one of the oldest fermented food items. When used as a food ingredient, vinegar functions in lowering the pH; controlling the growth of microorganisms; and enhancing flavors. We’ve already seen in this article how vinegar can be used to create new acidulant blends. And not too surprising, when considering its value, vinegar may be combined with other ingredients to create novel flavor opportunities.
As people have developed an increased interest and understanding of the flavor nuances of wines, they have similarly expanded their horizons with regard to vinegars, according to McCormick® Flavor Forecast 2007, published by McCormick & Co., Inc., Hunt Valley, Md. (phone 410-527-8753, www.mccormick.com). Global cuisines and chefs can be credited with introducing varietal vinegars, such as Cabernet, Champagne, Chardonnay, Pinot Grigio, Port, Riesling, and Sherry.
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Riesling vinegar, in particular, is gaining momentum as a new favorite because its medium-bodied, balanced flavor combines well with many foods. The forecast highlighted the pairing of Riesling vinegar with caramelized garlic as a way of providing a new flavor dimension to cooking. The toasted, sweet, sour, fruity, and somewhat bitter flavor of caramelized garlic is said to be well suited to the fruity and tangy taste of Riesling vinegar. "The two add a deeper, more refined flavor to foods and provide a perfect platform for ushering in new trends in taste," observed the forecast.
Riesling vinegar and caramelized garlic are suitable for marinades, sauces, brines, glazes for seafood and meats, fresh slaws, and vegetables, including roasted bell peppers and green beans. To put a new twist on fresh tomato and Mozzarella salad, replace balsamic with this combination.
Fruit-based vinegars may also find increasing use. A low-acid vinegar made from red wine vinegar and fig and grape juice concentrates was recently introduced by a California farmer-owned marketing cooperative, Valley Fig Growers, Fresno, Calif. (phone 559-237-3893, www.valleyfig.com). The product, Blue Ribbon Fig Balsamic Vinegar, is ready to use from the container, and can be rebottled or used as an ingredient in salad dressings, vinaigrettes, sauces, and marinades. It is described by the cooperative as a tangy robust product that provides an excellent base for sauces and balsamic dressings. Furthermore, on the company’s Website is a recipe, Salmon-Fig Kebabs with Orange-Balsamic Glaze, which demonstrates how orange juice and other ingredients can be paired with balsamic vinegar to create a flavorful glaze.
As can be seen from the above developments, flavored vinegars, whether made with garlic, fig, or other flavors, may be gaining momentum, especially as we are exposed to foods from other regions, and may play a flavorful role in the development of new products. The prospects for vinegar are certainly not sour.
Overcoming Specific Challenges
Food acids do more than just lower the pH of a product, noted Dan Sortwell, Senior Food Scientist at Bartek Ingredients, Stoney Creek, Ontario, Canada (phone 905-662-3292, www.bartek.ca). They provide a wide range of functions, such as imparting subtle but important differences in taste and flavor, assisting preservation, forming soluble calcium complexes, and acting as chelating agents, buffers, and leavening controls.
However, the effectiveness of each of the acids for a particular function can vary and the environment in which it is used can play an important role. At the 2006 Fall IFT Dogwood Section Meeting, Sortwell conducted a workshop that discussed how to narrow the selection of acidulants for various types of foods and beverages. Acidulants, such as acetic, citric, fumaric, lactic, malic, phosphoric, sodium acid sulfate, and tartaric were focused on. Attendees learned about the properties of these products and how to choose the best acidulant or acidulant combination for their particular formulation.
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Sortwell also highlighted a number of innovations from the Bartek portfolio to demonstrate how they can overcome specific challenges in food formulation. For example, a proprietary form of calcium fumarate, Sol-U-Cal, is stable in solution in combination with citric acid, making it especially suitable for the fortification of clear beverages. Fruit juice beverages made with the product are said to have a stronger fruit flavor than beverages fortified with other calcium salts.
For manufacturers of artificially sweetened products, malic acid can prove especially effective. Because its sourness is more delayed and persistent than that of citric acid, it complements the lingering sweetness of sucralose in many beverages, helping to offset any aftertaste. The acidulant also enhances fruit flavors and blends discordant flavor notes, creating a smoother flavor profile.
Fumaric acid lowers the pH of tortilla dough, thereby improving a mold inhibitor’s effectiveness. Shelf life of dry tortilla mixes is extended because fumaric acid does not absorb moisture during storage and distribution. In wheat flour tortillas, fumaric acid accelerates the cleavage of disulfide bonds between gluten protein molecules during dough kneading. The result is more easily machined dough and faster production rates. Added cost savings are realized since leavening acids can be replaced with fumaric acid.
Gaining a Better Understanding of Sour Taste
How humans detect sour may now be better understood as a result of research studies published over the past year. Such findings can lead to a number of innovative ways for formulators to manipulate the perception of sourness in food applications.
In the August 24 issue of the journal Nature, researchers from the University of California at San Diego reported the discovery of cells and the protein that enable humans to detect sour. The UCSD researchers theorized that each of the five basic tastes is mediated by distinct, nonoverlapping classes of taste receptor cells. Using bioinformatics—the study of biological information using computer and statistical analyses—and genetic studies, they identified PKD2L1 as the possible acid sensor. PKD2L1 is a member of a group of proteins called the transient receptor potential (TRP) family, known to be involved in taste signal transduction. The researchers chose to study this protein as a possible receptor because it was not found in taste cells that express receptors for sweet, bitter, and umami, but instead was found in a previously unidentified population of taste cells.
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To test whether PKD2L1-expressing cells are indeed the mediators of sour taste, the UCSD researchers engineered a special strain of genetically altered mice lacking PKD2L1 cells and then tested the mice’s ability to detect the taste of sour. The mice were unable to detect sour, but they were able to continue to detect sweet, bitter, umami, and salt, demonstrating that PKD2L1-expressing cells are the mammalian sour taste sensors.
"Our results show that each of the five basic taste qualities is exquisitely segregated into different taste cells," said lead researcher Charles Zuker. "Taken together, our work has also shown that all taste qualities are found in all areas of the tongue, in contrast with the popular view that different tastes map to different areas of the tongue."
In related work, researchers from Duke University, Durham, N.C., also isolated the identical TRP channel receptors, which they describe as "sour-sensing" receptors. In addition to PKD2L1, the Duke University team isolated another protein, PKD1L3, and found that it, too, was specific to a certain population of taste cells that detect only sour taste. These receptor cells were distinct from the taste cells for bitter, sweet, and umami. In research published in the August 15 issue of the Proceedings of the National Academy of Sciences, the Duke team confirmed that the receptors were localized to the taste pore, the site of interaction with sour substances. These receptors were specific for sour taste because they are activated by various acids and not by other types of taste compounds when expressed in tissue culture cells.
The discovery of sour receptors and their taste cells by these two research teams demonstrates that the detection of sour takes place in much the same way that sweet, bitter, and umami are detected—through separate taste-specific cells and their associated receptors. The finding helps refute a belief of some scientists that the detection of sour and salty tastes, which depend on the detection of ions, works differently than with the other tastes. Because the genetically engineered mice could detect salt, the UCSD researchers concluded that salt-sensing cells must also function independently with their own receptors, which sets the stage for future investigation.
Leavening Acid Improves Baked Goods
A new leavening agent from ICL Performance Products, St. Louis, Mo. (phone 314-983-7500, www.iclperfproductslp.com), delivers controlled release, uniform cell structure, and a neutral flavor profile. The ingredient, marketed under the name Levona™, contains calcium acid pyrophosphate—a leavening acid which can help provide calcium enrichment without adding any sodium to the formulation. It can be used in a variety of health-oriented baked goods, such as snack cakes, pizza crusts, muffins, cakes, and biscuits.
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Chemical leavening is the reaction of sodium bicarbonate or baking soda with an acid source. The acid neutralizes the bicarbonate, releasing carbon dioxide. As the carbon dioxide expands, it provides volume and impacts texture and appearance. The leavening acid controls the rate of release of carbon dioxide.
The new product, in addition to contributing calcium and no sodium to bakery formulations, provides a number of advantages, including delayed reaction, consistent leavening, resilient structure, ideal cell structure, clean flavor profile, and excellent volume. It may also be used in products developed for consumer convenience, such as dry mixes, refrigerated dough, frozen batter and dough products, batter coating systems, and breakfast foods.
The new leavening agent and its properties will be discussed at a New Products and Technologies Session, held on Monday, July 30, during the 2007 IFT Annual Meeting & Food Expo.
An Emerging Acidulant
In 1998, a new acidulant, sodium acid sulfate (also known as sodium bisulfate), was designated GRAS by the Food and Drug Administration. Manufactured under the name pHase by Jones-Hamilton Co., Walbridge, Ohio (phone 419-666-5277, www.jones-hamilton.com), it offers an acid strength similar to phosphoric acid; a clean, smooth, tart flavor profile with no bitter aftertaste; and a sour intensity higher than that of other acidulants.
SAS, marketed initially as an alternative to citric acid, provides a reduction in pH necessary for preservation and stability in acidified foods without imparting a sour taste that can overcome the intended favor of the formula. Because of its properties, it can function as a pH control agent, a leavening agent in cake mixes, and a processing aid. It is suitable for use in such applications as beverages, confections, and leavening systems, as well as for creating new opportunities in product formulation.
Since its introduction, a number of studies have highlighted the benefits that this acidulant can offer the food manufacturer. For example, most recently, SAS was studied as a potential browning inhibitor by researchers from the University of Maine in Orono. The objective of the research was to develop a new dip using SAS to improve the quality of fresh-cut potatoes by reducing enzymatic browning. A total of 4 dip treatments (1 and 3% SAS and citric acid) were compared to a distilled water control. At day 14, 3% SAS samples had significantly higher force values than citric acid and control treatments. Utilizing new dip treatments from this research may provide potato processors with an advantage in the fresh-cut and processed potato market. These results will be discussed in a poster presentation at the 2007 IFT Annual Meeting & Food Expo.
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In 2007, two new studies were released, "Microbiological Challenge Study of Salad Dressing Product Acidified with Sodium Acid Sulfate and Acetic Acid," and "Evaluation of C. sporogenes PA3679 Heat Resistance in Pea Puree pH Adjusted with Sodium Acid Sulfate." Copies of these reports are available from Jones-Hamilton.
In 2006, a study, "Application Development of pHase in Retort Products," was also released. It evaluated the effectiveness of the acidulant in sliced carrots, condensed vegetable soup, and Alfredo cream sauces. (See the July 2006 Ingredients section for a more complete discussion.) By reducing the pH of low-acid products through acidification with pHase, current retort products can be made shelf stable with a milder heat treatment. A shelf life of one year can be reached without adversely affecting the flavor, texture, and appearance of the products.
As noted in the April 2007 Ingredients section, this study also discovered that the addition of SAS in retort applications caused an increase in saltiness. As a result, the salt content could be lowered and a significant reduction in sodium achieved.
Studies have also determined that the acidulant is capable of masking the unpleasant aftertastes that can be associated with artificial sweeteners. Lemon-lime sodas containing the acidulant and four different sweetener systems were compared. The beverage made with SAS reportedly had a softer, cleaner taste; a more syrupy mouthfeel; and an improved aftertaste. It was proposed that since the acid flavor release of SAS is more delayed, this has a masking effect on the lingering notes of the intense sweeteners. Tests were also performed on fruit-flavored waters. Products made with SAS were described as having a more natural, ripe fruit pulp flavor with a bright, fruity aftertaste.
Savorizing with Acidulants
The April 2007 Ingredients section looked at different ways that formulators, when developing savory concepts, overcome functionality challenges. That article is a good lead-in to this month’s topic because acidulants can play a very important role in savory flavors.
For example, lactic acid can be especially effective, according to a Focus newsletter from Purac. Acidified dairy flavors, in particular, are enhanced by lactic acid. In yogurt and cheese flavors, as well as cream flavors, lactic acid is used to intensify the creamy perception. Applications such as cheese sauces, yogurt dressings and cheese toppings on snacks all benefit from lactic acid, which is a suitable replacer for citric acid. In many applications it is even possible to reduce the amount of expensive cheese powder when lactic acid is used in the formulation.
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Lactic acid is often associated with dairy flavors, but it can also be used to enhance or modify other savory flavors such as tomato or meat, noted Purac. Lactic acid can change the profile of the tomato flavor, making it less sharp by increasing the sweetness while decreasing the sourness. Because of their natural presence in meat products and meat extracts, lactic acid and lactates are very suitable for use in meat flavors. Lactic acid also has a positive impact on flavor perception in reaction flavors, in which the flavor components are formed by chemical or microbiological reactions. Lactic acid by itself leaves a mild acidic taste, while sodium lactate contributes more to the saltiness of the application. This makes both additives good flavor enhancers when used in the typical concentrations.
The influence of acid on spices can be significant. Depending on the spice, lactic acid can either enhance or reduce the spice impact. This allows for product development to create new flavor formulations. Spices such as pepper, basil, oregano, cayenne, and curry are especially enhanced by lactic acid over other acidulants.
Chewing on the Value of Acidulants
Chewing gums are becoming increasingly innovative as vehicles for delivering flavors; sensations that range from cool to sour; and vitamins, minerals, and other components. The November 2007 Ingredients Section will provide an update on some of these developments, but for now try to imagine this category, especially fruit-flavored products, without the use of acidulants.
Generally speaking, acidulants can provide sourness and when combined with certain sweeteners can stimulate saliva flow—obviously important properties for this category. But as confectionery products become more complex, choosing the right acidic solution becomes equally essential. Encapsulation can prove to be an effective tool, extending or sustaining acidulants in these applications. For example, Jungbunzlauer offers a line of Citricoat® coated organic acids that can provide prolonged sour taste as well as reduce sticking during manufacture. By encapsulating such acids as citric, malic, fumaric, and GDL, the manufacturer can take advantage of the technological properties and taste profiles of these different acidulants.
Combinations of acidulants are being increasingly used as well. Using blends of acids with distinctive properties can result in a sequential release of acid, creating a product that has a prolonged juiciness and flavor during chewing.
According to Tate and Lyle, Decatur, Ill. (phone 217-423-4411, www.tateandlyle.com), malic acid can be used by itself or blended with citric acid to produce a number of unique and distinct properties. Its tart taste builds gradually and lasts longer than other food acids. It extends the flavor sensation without masking the natural fruit notes and allows the full sweetness of natural and artificial sweeteners to come through. It also has a longer sustained sour taste than citric acid and other acidulants. This property allows malic acid to be formulated with high-intensity sweeteners to modify flavor components such as bitter aftertaste or prolonged sweetness characteristic of some sweeteners. Fumaric acid for chewing gum can provide a clean, longer- lasting acid taste.
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Shelf Life Extender Offers Improved Performance in Dairy
A new addition to the DuraFresh line of ingredients from Kerry Bio-Science, Hoffman Estates, Ill. (phone 847-645-7340) provides improved shelf life extension for dairy products. DuraFresh™ 5015 is designed to maintain freshness in cultured dairy products by inhibiting the growth of Gram-negative spoilage bacteria, yeast, and mold.
The reformulated ingredient, which is based on skim milk, has a higher concentration of organic acids and is more effective than previous versions. Furthermore, because less is needed in the formulation, it offers additional cost advantages. Potential applications include cottage cheese, sour cream, buttermilk, yogurt, and desserts.
According to the company, this range of ingredients is manufactured using a patented fermentation process. Combinations of lactic acid bacteria cultures produce fermentates with specific compositions of organic acids, peptides, and other fermentation-produced compounds. All ingredients in the range are spray-dried into a powdered form and are organic, kosher, and halal certified.
Acidifiers Extend Shelf Life without Adding Sour Flavors
Acidulants with low-flavor profiles are being developed today that allow the creation of shelf-stable acidified foods that do not have sour flavors, according to Gordon R. Huber, The XIM Group LLC, Sabetha, Kan. (phone 785-547-5138, www.ximgroup.com). These acidulants can also be used to control internal and surface contamination in a variety of products, such as ready-to-eat meats, fresh produce, and prepared foods.
XIM, a product development, process engineering, and project management group, has developed technologies that incorporate these acidulants to help control or prevent contamination in pies, ready-to-eat pasta, ready-to-eat rice, meat analogs, cookie dough, waffles, and tortillas. Shelf life at room temperature exceeding six months utilizing standard moisture-barrier packaging has been achieved, noted Huber.
GRAS designated acidified calcium sulfate is a perfect fit for these applications," said Huber. "In addition to controlling bacterial contamination, our technology can also be applied to control surface browning in foods such as apples, potatoes, and other fresh-cut produce.
XIM, founded in 2005, explores key technologies that address long-term problems in the food area. The group, which provides consulting services, product innovations, and technological advancements, has focused on a range of areas, including food safety, shelf stability, and continuous processing. Solutions are customized to meet the specific product needs of their customers.
The use of acidulants and their special properties has played a major role in the services they offer to the food industry. "Customers can successfully reduce costs of product preservation, extend shelf life, enhance product freshness, and improve food safety," said Huber. "All this is done while preserving taste and texture characteristics so important to product perception and quality."
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Looking for Acidic Answers
This month’s article has looked at a number of developments related to acidulants and the role they play in food formulating, especially as a way of providing flavor or flavor enhancement. For a further review of sour taste perception, the chemical and physical properties of organic acids, and other flavor characteristics of acids, see the excellent article, "The Chemistry and Physiology of Sour Taste—A Review," that recently appeared in Journal of Food Science (Vol. 72, No. 2, 2007).
According to that article, understanding sour taste requires information at several levels, including the chemistry of compounds that elicit taste responses, interaction of taste elicitor compounds with taste receptor cells, and the physiological and neurochemical responses that mediate sour taste perception. Significant efforts have been put forth to determine the chemical basis for sour taste. Although it is generally accepted that pH and organic acids are responsible for sour taste, it is not currently possible to accurately predict and modify sour taste intensity in foods.
Several studies have also attempted to identify the receptors and transduction mechanisms for sour taste, but as yet the physiology of sour taste is controversial and not completely understood. The article presents an overview of the literature as it relates to the chemistry and physiology of sour taste perception.
The authors concluded that sour taste perception is a complex event from both chemical and physiological standpoints. Before efficient control of flavor in the formulation of acid and acidified foods can be done, a clear understanding of the chemistry and physiology of sour taste is needed. "It is evident that no simple relationship exists between sour taste intensity and hydrogen ions," according to the article. "Likewise, sour taste intensity of acids cannot be entirely explained by other variables, including titratable acidity, buffer capacity, molar concentrations, physical and chemical structure, and so on. The recent hypothesis that sour taste intensity is directly related to the total molar concentration of all organic acid species that have one more protonated carboxyl group plus the concentration of free hydrogen ions may provide a basis for predicting sour taste in the formulation of foods."
The article maintains that the physiology of sour taste perception remains controversial and significant diversity among species exists with regard to cellular schemes used for detection of stimuli. The variety of mechanisms proposed, even within individual species, highlights the complexity of elucidating sour taste transduction. However, recent evidence suggests that at least one specific sour taste receptor protein has been identified. (See page 52 of this Ingredients section.)
Hopefully, studies such as these—accompanied by some of the developments discussed in this Ingredients section—will have an impact on the formulation of acidified foods and beverages, leading to new innovations in flavor and their applications.
Next month, Da’ Preview! The Ingredients Pre-Show coverage of the 2007 IFT Annual Meeting & Food Expo will present the newest ingredient developments and their applications—Chicago-style.
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Some Commonly Used Acidulants
Many different acidulants are used by the food industry, both inorganic acids (e.g., hydrochloric and phosphoric) and organic acids (e.g., citric, malic, fumaric, and lactic). In the flavor industry, for example, inorganic acids mainly contribute sourness, while organic acids also contribute other flavor aspects, such as flavor intensity, astringency, and bitterness.
This month’s article is looking at some of the emerging opportunities that acidulants, because of their special properties, have in formulating foods and beverages. This sidebar will look briefly at some of the more commonly used ones. As most of the developments discussed in this article focus on these particular acidulants, it is appropriate to provide some technical background on them.
• Citric Acid. The most widely used organic acid in the food industry, citric acid is highly soluble in water, can deliver a burst of tartness suitable for flavor modification or enhancement, and can chelate potentially pro-oxidative metal ions, allowing antioxidants to function more effectively in retarding oxidation and product deterioration. In addition, the salts of citric acid may be used for buffering or emulsification, or as a source of cation for technological or nutritional purposes. Made primarily by fermentation, citric acid may be used in such products as beverages, gelatin desserts, baked goods, jellies and jams, fruits and vegetables, dairy, meats, seafood, and fats and oils.
• Malic Acid. A highly soluble, general-purpose acidulant, malic acid provides a smooth, tart taste that lingers in the mouth without imparting a burst in flavor, and is said to have special taste-blending and flavor-fixative qualities. Although its ionization potential is similar to that of citric acid, malic has a stronger apparent acidity which enables smaller amounts of it to be used in certain applications for the same taste effect. Malic acid is made through chemical synthesis by the hydration of maleic acid. Like citric acid, it can be used in a broad range of food applications, especially nonalcoholic beverages, hard candies, canned tomatoes, and fruit pie fillings.
• Lactic Acid. A natural organic acid normally associated with milk, lactic acid has become increasingly important. Its mild acidic taste reportedly will not mask weaker aromatic flavors. It is especially useful in frozen confections where it imparts a milky tart taste that does not compromise other natural flavors. When added to a variety of food systems, the acid functions in acidification, flavor enhancement, and microbial inhibition. It is also used in the production of the emulsifiers calcium and sodium stearoyl lactylates which function as dough conditioners in baked goods. Fermentation and a synthetic process are the methods used to commercially produce lactic acid.
• Fumaric Acid. The strongest of the food acids, fumaric acid is hygroscopic and low in solubility. Interestingly, these properties make it very useful in certain applications. For example, in noncarbonated fruit juice drinks, its greater acid strength allows lower use levels than citric acid. Because it is strongly resistant to absorption of moisture from the atmosphere, it can be especially useful in dry mix products. And although the solubility rate of fumaric is low, it does increase with smaller particle size. Fumaric acid can improve the flavor stability and gel strength of gelatin desserts; function as an antioxidant in oil- and lard-based products; and act as an acidulant and clarifying agent in wine. It can be made synthetically by the isomerization of maleic acid or by fermentation methods.
• Acetic Acid. Vinegar contains acetic acid as a prin- cipal component. When used as an ingredient, vinegar functions in lowering the pH, controlling the growth microorganisms,and enhancing flavors. It is used as an acidifier and flav- oring agent in mayonnaise. Also, vinegar has applications in a variety of products, including sliced, canned fruits and vege-tables, sausages, and salad dressings.
• Glucono-delta-Lactone. GDL, as it is abbreviated, is a neutral cyclic ester of gluconic acid that hydrolyzes in aqueous solutions to form gluconic acid. Its slow rate of acidification and mild taste characteristics set it apart from other acidulants. See page 48 for further discussion. It is produced commercially by a fermentation process.
• Others. Other major acidulants that are used by the food industry include tartaric acid, a dibasic acid which is very water soluble and contributes a strong tart taste that enhances fruit flavors; adipic acid, which functions as a buffer, neutralizing agent, gelling aid, and sequesterant and is characterized by its low hygroscopicity; and phosphoric acid, an inorganic acid which gives the lowest pH of all food acidulants.