May 2004 Issue--The words an “excellent source of calcium” occupy a space on the front of a box of Sunkist (General Mills, Minneapolis) Fruit and Grain Bars. Those words, a phrase growing in popularity on packaging from dairy to baked goods, are reserved for products containing a level of calcium exceeding 20% of the United States' Daily Value (D.V.) for calcium.

The demand for calcium is based on its connection to reducing the risk of osteoporosis, but new research indicates the impact of calcium is much wider. “Calcium is one of those minerals that is involved in every body function that you can think of: nerve [functions], irritability and contractility of the muscles,” says Linda Douglas, Ph.D., R.D., manager of scientific affairs for an ingredient supplier. In fact, Douglas notes, recent studies have implicated dietary calcium in the reduction of the risk of obesity and coronary heart disease, as well.

With such evidence, informed consumers are seeking products that contribute calcium to their diets and manufacturers are responding by adding calcium to their formulations.

Dual Purpose

Although manufacturers are fortifying their products with calcium more than ever before, some may not realize all the benefits that calcium-containing ingredients can contribute. Instead of having three different names on the ingredient list for consumers to puzzle over, manufacturers are letting their calcium work double and triple time.

“Several food manufacturers make a calcium claim on the packaging and take advantage of the functionality of the added calcium salt at the same time,” reports Gerhard Gerstner, Ph.D., technical service manager for a leading supplier of acidifiers and fortifiers.

Aside from nutrient fortification, the functionality of calcium salts includes acting as buffers, dough conditioners, firming agents and even preservatives. Once formulators add calcium, it does not matter what they originally wanted to use it for, the calcium still contributes to the total amount, notes Ellis Hogetoorn, a market development specialist at a supplier of lactates and gluconates. Such dual purposing is not always ideal, of course. For example, although the antimicrobial calcium propionate does add calcium to a product, it affects the flavor when added at higher concentrations.

“You have to balance different calcium forms, as there is no straightforward way that you can take one source of calcium and just add it across the board,” says Ram Chaudhari, Ph.D., senior executive vice president for R&D at a supplier that manufactures custom nutrient premixes for fortification. “Knowing the [properties] of the specific calcium salt opens the way for savings due to optimized processing, improved product quality and prolonged shelflife,” says Gerstner.

The Insoluble Calciums

Sunkist bars contain tricalcium phosphate (TCP) and calcium carbonate, along with monocalcium phosphate and dicalcium phosphate, which act as leavening agents. The combined calcium ingredients give the bars 20% of the D.V. for calcium.

Insoluble calcium salts are useful in dry baking mixes because of their hygroscopic properties. In dry powders, for example, tricalcium phosphate acts as an anticaking agent, regulating moisture absorption so that the powdered product remains free-flowing and lump-free.

Calcium phosphates often are used as leavening acids and neutralizers in baked products, where they can either speed up the leavening process (as with monocalcium phosphate) or slow it down (as with anhydrous monocalcium phosphate).

Also, “when you add a calcium to any type of wheat product, you are going to get firming,” says Douglas. “Calcium firms up the gluten and reduces stickiness by interacting with the water. You're going to see the same response with any type of dough applications.”

TCP and calcium carbonate are two of the most familiar insoluble calcium sources and often are added to cereals, cookies, nutritional bars, snacks and chips. Although they have lower bioavailability than some other calcium sources, they contain a high percent of the mineral calcium, allowing them to be effective fortifiers. Due to its high calcium content (40%), calcium carbonate may be the most cost effective calcium salt within the inorganic salts. Within the organic salts, tricalcium citrate (one form of calcium citrate) is leading (21%), notes Gerstner.

However, characteristics such as taste, mouthfeel and cost also are attributes to consider.

Taste and mouthfeel characteristics are dependent upon the concentration of calcium addition, granulation size, as well as the interaction with other ingredients. For example, when added with fat at a high pH, calcium carbonate can convey a soapy flavor. In some applications, calcium phosphates have a “bland taste.” Both carbonates and phosphates tend to produce a chalky or gritty mouthfeel.


Calcium labeling on a package does not guarantee the recipient will absorb the calcium in the product. There are many variables that determine calcium bioavailability.

For example, when phosphates, phytic and/or oxalic acid combine with calcium—such as during high temperature processing with phytic acid in cereal-based products or oxalic acid in some vegetables—the mineral becomes chelated and is less reactive. While the calcium content of the finished product will not change, it may be less bioavailable.

Chelating has its advantages as well. A less reactive calcium ingredient means it may have less impact on the color and texture of a food. Thus, chelating can improve a product's organoleptic properties.

Other factors also impact calcium. “Calcium carbonate [absorption] varies a lot,” says Hogetoorn. Its bioavailability is “O.K.” when taken with a meal, but if there is no meal present, bioavailability can drop significantly.

Clearly a Chilled Challenge

Soluble calcium sources are generally soluble enough to stay in the solution at refrigerated temperatures. Due to its “inverse solubility,” tricalcium citrate (TCC) shows low reactivity at higher temperatures, reducing side reactions, cleaning intervals and loss of calcium during processing. TCC was influential in increasing the quality of calcium fortified orange juices, such as Tropicana[r]'s (Bradenton, Fla.) Pure Premium[r] Low Acid.

According to Gerstner, TCC has a moderate solubility profile and a tart, clean taste. “Among the organic salts with high bioavailability…it clearly stands out as the most economical option for calcium addition and is the main choice for cloudy beverages,” opines Gerstner.

Many companies sell micronized grades of TCC differentiated by particle size to obtain better solubility and to keep the fine particles in suspension. “Although it is generally used for liquid products, micronization could also be practical in smoothing the texture of nutrition bars or chewing gum by reducing grittiness or sandiness,” says Chaudhari.

Calcium lactate, with a calcium content of 13%, is priced similarly to TCC but is more soluble, making it a good alternative for clear beverages and water like AquaCal by Meridian Beverage (Atlanta, Ga.). Calcium lactate is a free-flowing powder and can be used as a carrier for lactic acid. Unfortunately, it can exhibit a bitter taste at the higher concentrations often needed to achieve fortification. It is not hydroscopic so, as a powder, it does not absorb water over time.

“For those critical applications, CLG (available with up to 13-14% calcium) is worth the premium price to achieve high fortification levels in clear soft drinks or concentrated pre-blends,” says Gerstner. “CLG is not just the dry blend of calcium lactate and calcium gluconate, but it actually has different physical properties,” explains Hogetoorn. “The solubility of the blend is much higher than either one of the components by themselves, plus the flavor profile is much better.”

Problem-solving Solubles

Despite good price incentives, inorganic salts are used less frequently in beverages. Formulators generally turn to soluble calcium salt forms such as tricalcium citrate, calcium lactate, calcium gluconate and calcium lactate gluconate (CLG).

In liquids, soluble calcium salts can operate as emulsifiers or stabilizers to prevent precipitation in dairy products or protein smoothies. Chaudhari suggests that some calcium ingredients are good buffering agents, and that blending calcium sources [soluble with insoluble] will lessen any adverse effects of insoluble forms. “You have to combine them in certain ratios to get the highest buffering capacity so it will not precipitate during processing,” warns Chaudhari.

Soluble calcium salts generally have a lower proportion of calcium mineral than insoluble salts, thus they must be added in larger amounts to achieve the concentrations required for calcium labeling. As for bioavailability, despite a lower percent of calcium mineral, soluble calcium sources are more reactive and thus, some argue, more easily absorbed in the intestine.

Unfortunately, adding a calcium salt for nutrient fortification sometimes can reduce the functionality of another calcium salt. For example, protein chains can become active when heated and will “grab” the free calcium ions causing coagulation, which creates texture problems. “You have to regulate the pH and add a sequestrant, otherwise, the calcium ions will react with the protein,” explains Hogetoorn. The sequestrants shield the calcium ions from the protein chains. Calcium citrate (of which tricalcium citrate is one form) can be used as a sequestering agent, but sodium- or potassium-citrates are more commonly used since calcium citrate would sequester the soluble calcium. In grain-based cereal products, calcium sulfate has better potential as a sequestrant because of the functionality of the sulfate group, adds Chaudhari.

“Sometimes it is very deceiving that the highly bioavailable forms are highly reactive, therefore, you cannot add all soluble forms in every product because they will react with the other components of the product and will create problems with precipitation and flavor,” says Chaudhari.

For example, calcium lactate will precipitate out of milk-based products when it reacts with protein components. Calcium carbonate also tends to settle in such products because it is insoluble. But, by adding calcium lactate and the insoluble dicalcium phosphate as a buffer, calcium carbonate will not precipitate out or settle at the bottom.

The Calcium Frontier

Soy milk has a reputation of being gritty because it uses insoluble calcium sources. “I think a lot of companies in the next couple of years will want to use more-soluble calcium [in soy milk] sources and come out with something that doesn't taste as gritty,” predicts Hogetoorn.

Beverage manufacturers still are confused as to how to tackle calcium fortification of purple grape juice and iced teas. “We still have issues with cloudiness in those products,” states Hogetoorn. Purple grape juice contains tartaric acid and iced teas contain tannic acid, both creating issues. CLG can be used to fortify beverages with tannic acids whereas other calcium salts lead to sedimentation or discoloration.

There is no common denominator to rely upon when adding calcium. Choosing the right form depends upon the desirable characteristics of solubility, processing conditions, labeling, shelflife, price and sensory attributes.

Going Global

Evolus' (Seinäjoki, Finland) Strawberry Flavored Milk by Valio offers 200mg of calcium per 100g. Calcium lactate and calcium gluconate are included, while tricalcium citrate helps to regulate acidity.

Incorporating calcium into clear carbonated beverages is a challenge in balancing acidity to achieve solubility. With calcium lactate and calcium chloride, Aguas Danone de Argentina (Buenos Aires) was able to meet the challenge to make Ser Calcio y Magnesio diet carbonated soft drink. Also incorporated on the product label is algae calcium, a sea mineral extract.

Magnesium assists in calcium absorption and many manufacturers like to incorporate it. Gayelord Hauser's (Distriborg, Saint Genis Laval, France) Blueberry Biscuits with Calcium and Magnesium also uses micronized seaweed extract. Introduced in January 2004, Kellogg's (Anseong, South Korea) Chex Honey Cereal claims 175mg of calcium.

Prebiotics and Calcium Absorption

Prebiotics, which are proven to increase calcium absorption, have proliferated within the international food community but have just begun to infiltrate the U.S. Short-chain fructo-oligosaccharides have been introduced into several U.S. products, including those in the Horizon[r] Organic Dairy Inc. (Boulder, Colo.) line. Products containing the prebiotic—along with a calcium sea mineral matrix originating from the sea plant Lithothamnion--are in development in several countries overseas, as well as in the U.S. Besides being advantageous for calcium absorption, “The [short-chain fructo-oligosaccharides] limit the offnotes of soy, which are sometimes problematic to formulate,” offers Douglas. Stonyfield Farms' yogurt (Londonderry, N.H.) incorporates inulin, a prebiotic, which also helps in the absorption of calcium.