Calcium Citrate in

December 2001

Calcium Citrate in Fortified-Food Applications

By Gerhard Gerstner, Ph.D.Contributing Editor

Calcium is a key mineral in the human body, necessary for the normal growth and development of the skeleton as well as for teeth, nerve, muscle and enzyme functions. As the body’s calcium absorption capabilities reduce with age, it is vital for older individuals to have a sufficient calcium intake. Calcium requirements vary throughout an individual’s life and for different population groups. However, it is generally evident that a significant proportion of the population in Western countries fails to achieve the recommended calcium intakes. Poor dietary habits are seen to be responsible for this situation, especially when fast-food consumption dominates much of the population’s menu.

Various studies, including “The Mineral Fortification of Foods,” published in 1999 by Leatherhead International Ltd., Surrey, UK, showed that a significant proportion of the population groups failed to achieve the calcium intakes in Western countries. This observation is thought to be one of the leading factors causing osteoporosis, and was noted in a 1991 article from the American Journal of Clinical Nutrition titled “Calcium Metabolism and Calcium Requirements During Skeletal Modeling and Consolidation.” As a consequence, national authorities all over the world recently have reconsidered recommendations in order to take remedial measures against calcium deficiency and, accordingly, to reduce the risk of osteoporosis. In this respect, the United States National Institutes of Health (NIH) has increased the amounts of optimal daily calcium intake and defined specific values for each population group. For example, calcium intake should be 1,000 mg/day for adults (25 to 65 years of age) and as much as 1,500 mg/day for seniors (older than 65 years) or lactating women.

There are several options to avoid calcium deficiency by increasing the daily calcium intake: A balanced diet with calcium-rich foods, such as milk, dairy products and certain vegetables (broccoli, Chinese cabbage, legumes), would be the best solution. However, this would require a profound change in dietary habits of Western society. Another possibility would be consuming food products fortified with calcium. The third option is the intake of calcium-supplement products.

Common calcium sourcesThere are different calcium sources commercially available for use in food and dietary supplements:• inorganic salts such as calcium carbonate and calcium phosphate; and• organic salts such as calcium citrate, calcium lactate, calcium lactate gluconate and calcium gluconate.

Other forms of calcium commonly supplied for fortification and supplementation are calcium gluconate in its anhydrous form, as well as calcium lactate gluconate.

Tricalcium citrate (TCC), commonly referred to as calcium citrate, is a high-quality calcium source for food fortification. Its main characteristics are good solubility at low pH, a neutral taste and flavor profile, high calcium content and excellent bioavailability. Besides the standard powder product, TCC is also supplied as a micronized (ultra-fine) granulation that will dissolve even more quickly in acidic applications.

Application selectionThe selection of the appropriate salt for a specific application is usually based on the consideration of a number of properties associated with the respective product, such as solubility, taste, calcium content and bioavailability. Economic considerations are another important factor to review before making a decision.

Solubility. There are calcium salts with a rather good solubility, including calcium gluconate and calcium lactate, but their drawback is a low calcium content. Calcium salts with high calcium content, on the other hand, are poorly soluble. TCC offers a good combination: It shows a high calcium level and moderate solubility. Solubility is strongly influenced by the pH of the system, since the solubility of calcium salts typically increases with decreasing pH. TCC shows improved solubility at pH values below 4.5, as found in orange juice.

And contrary to other salts, TCC is more soluble at low temperatures, which can be an advantage for cold food processing. To further increase the solubility and ease of dispersion, companies such as Jungbunzlauer have developed several types of particularly fine (micronized) TCC grades.

However, the high solubility of calcium salts, such as calcium lactate or calcium gluconate, can also lead to adverse effects. Due to the fact that with high-soluble salts, more free calcium ions are in solution and available for reaction than with TCC, complications in the form of calcium sediments can develop with time. This is the case if components (e.g. free protein, tartrate or phosphate) that give insoluble salts with calcium are present in the product. Thus, although it is possible to add more calcium lactate than TCC to beverages, higher amounts of calcium in the product might be difficult to achieve without control of pH and addition of chelating agents, such as potassium citrate.

Taste and mouthfeel. Generally, high levels of calcium, particularly insoluble forms such as carbonates and phosphates, tend to produce a chalky mouthfeel and may promote astringency or bitter taste in the finished product. Calcium lactate may impart some bitter notes at high concentrations. Calcium carbonate comes across as soapy or lemony and has the disadvantage of developing CO2 in the stomach. Calcium phosphate has a bland flavor, but imparts a gritty mouthfeel. TCC, calcium lactate gluconate and calcium gluconate are considered to be the most neutral calcium salts.

Since the particle size and solubility are linked with mouthfeel properties, companies have developed micronized grades that provide a neutral taste profile in final applications with excellent dispersion characteristics.

Calcium content. Inorganic salts, such as carbonates and phosphates, contain more calcium than the organic salts, but their application in foods and beverages remains limited due to their poor solubility and their influence on taste in the final application. However, organic calcium salts remain an option, with TCC showing by far the highest calcium content (21%), compared to calcium lactate (13%), calcium lactate gluconate (10% to 13%) and calcium gluconate (9%).Economic considerations. Among the organic salts with better solubility and more neutral taste profiles, TCC clearly stands out as the most economic option for calcium addition, especially when the price per gram of calcium added is calculated for the product to be fortified.

Bioavailability. Any nutrient’s effectiveness depends on its bioavailability, which means how well the human body absorbs and utilizes it. On average, only about 10% to 30% of calcium is absorbed from a mixed diet by healthy adults, according to the National Research Council’s “Recommended Dietary Allowances: 10th edition. A Report of the Subcommittee on the Tenth Edition of the RDA.” Several different factors influence this level, including which type of salt provides the calcium.

Various scientific studies have shown that organic calcium salts outperform inorganic calcium sources, such as calcium carbonate and calcium phosphate, with regard to their relative bioavailability. Accordingly, the United States National Institutes of Health has recommended calcium citrate for supplementation, especially for older individuals where absorbability can be a limiting factor due to reduced gastric-acid production. Recently, researchers at the University of Texas, Austin, conducted a meta-analysis of calcium bioavailability, which evaluated studies on the bioavailability of two of the most common forms of calcium supplements, TCC and calcium carbonate. Over 90% of the studies reviewed showed greater absorption of calcium from TCC than calcium carbonate by an average of 22% to 27%.

Similarly, calcium phosphate also has been shown in scientific studies to display lower bioavailability than TCC. Furthermore, it is not considered to be an appropriate ingredient for calcium fortification due to the undesired characteristics of the phosphate anion. Intake of phosphate is reported to exceed adult RDAs in practically 100% of the population. Therefore, further addition of phosphate to food should be avoided in order to gain a higher calcium-to-phosphorus ratio, which is considered favorable for sufficient calcium absorption.

In comparison with the other common organic salts, TCC showed similar bioavailability in various studies, even though significant solubility differences exist among organic calcium salts in plain water. It is concluded that these differences have no effect on absorbability in acidic environments such as the gastric acid in the human stomach. Studies with healthy male volunteers revealed that, compared to calcium lactogluconate/carbonate and calcium phosphate, oral administration of TCC induced the highest serum calcium and greatest reduction in parathyroid hormone, conditions most favorable for building bone mass or minimizing resorption.

Furthermore, TCC displays specific advantages from the nutritional/ pharmacological point of view. Scientific studies showed that contrary to other calcium salts, TCC does not promote, but rather inhibits, the formation of kidney and urinary duct stones by providing beneficial citrate for renal excretion. Additionally, TCC was reported to exhibit only low effects on the absorption on nutritional minerals whereas alternative calcium sources significantly interfered with iron.

The use of TCC is particularly recommended for acidic applications, such as juices and fruit preparations, but also in various dairy products, such as yogurt and cheese. Due to its outstanding biocompatibility and long history of safe use in critical dietetic products and over-the-counter products, it is also the calcium source of choice for baby food as well as dietary supplements.

Gerhard Gerstner, Ph.D. has been Technical Service Manager for Special Salts at Jungbunzlauer Ladenburg GmbH since 2000. Gerstner focuses on nutritional salts of calcium and potassium that are produced for the pharmaceutical and food industries in a dedicated facility.

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