Using calcium in functional food products

Generally, functional foods are neither dietetic products nor food supplements, but processed foods with distinctive added-value features such as health and well-being. In order to be able to differentiate themselves from the established products, food companies use specific health claims, among which the link between calcium and bone health is one of the most widely used and accepted claims worldwide. According to Leatherhead Food International (2005), the functional foods market in the five major European markets, the United States, Japan and Australia had a combined turnover of US$ 9.9 billion in 2003. Leatherhead uses a strict definition, measuring only products that make genuine functional health claims. By country, this can be broken down as follows: Japan, 45.3%; United States, 26.9 %; France, 7.2%; UK, 7.1 %; Spain, 5.5%; Germany, 4.9%; Italy, 1.9%; Australia, 1.2%. Total sales are expected to increase by 16% per annum over the next 5 years to reach US$ 21 billion by 2008, with Japan accounting for the lion's share. The global market can also be segmented by health benefit. Allowing for sector overlap, a breakdown analysis reveals that gut health products dominate, with sales of about US$ 5.7 billion (38%), ahead of immune function with US$ 4.7 billion (32%), heart health with US$ 2.55 billion (17%) and bone health with US$ 1.95 billion (13%).

11.5.1 General aspects: calcium sources used, applications, market segmentation

Table 11.3 gives an overview of the calcium salts significantly used for functional food products in Europe and the United States, their calcium contents, main application areas and typical fortified product examples (baby food, clinical nutrition and dietetic food applications are not considered in this table).

Nowadays, practically every type of foodstuff does have a fortified line already. Looking at the ingredients list, it is evident that there is not 'the' calcium source but rather a range of different products used commercially:

• inorganic salts such as calcium carbonate, calcium chloride and calcium phosphates;

• organic salts such as calcium lactate, calcium lactate gluconate and (tri-)calcium citrate;

• natural calcium salts such as milk calcium (mainly consisting of calcium phosphate);

With regard to total volumes used in the industry, the inorganic salts calcium phosphate and especially calcium carbonate are clearly dominating due to their high calcium content combined with a low price level. However, in addition to economic considerations, technological aspects such as solubility, stability, ease of processing and taste on the one hand, as well as nutritional aspects such as palatability and bioavailability on the other hand, are vital when choosing the appropriate calcium salt.

11.5.2 Technological aspects

Solubility and dispersibility

As summarised in Table 11.3, insoluble forms of calcium (calcium carbonate, calcium phosphate, milk calcium) are preferred in non-liquid applications such as cereals and energy bars and can even be used at high concentration levels. However, when liquid formulations are to be fortified, solubility, stability and taste of ingredients are much more important. As displayed in Table 11.3, there are organic calcium salts with good solubility like calcium lactate and those with excellent solubility like calcium lactate gluconate, but their drawback is a comparably low calcium content (13%). Calcium chloride (27% calcium) displays good solubility, but its use is limited to applications with low fortification levels due to its bitter and salty taste. On the other hand, other inorganic salts with a high calcium content, for example calcium carbonate and calcium phosphate, are poorly soluble and for that reason can only be used in specific liquid applications. Tricalcium citrate offers a good combination, having a high calcium level (21%) and moderate solubility (0.9 g/l).

Table 11.3 Calcium (Ca) salts significantly used for fortification in functional food products in Europe and the United States and current product examples from retail

(%)

Solubility (g/l water, RT)

Main applications

Product example

Ca content of product (mg/100 g)

Ca carbonate

40

Insoluble

Cereals, dairy and soy

Whole grain flakes with

182

products, energy

vitamins, fibres and

bars

minerals

Ca chloride 2aq

27

970

Sports drinks

Non-carbonated sports

24

drink beverage

Ca gluconate

9

35

Beverages

Juice drink with Ca

42

Ca lactate 5aq

13

66

Beverages

Fruit juice lemonade

24

plus Ca

Ca lactate gluconate

13

400

Beverages, dairy

Carbonated soft drink

62

products

with vitamin C and

Ca phosphate

17-36

Insoluble

Cereals, dairy and soy

Soy milk with Ca

120

products, juices,

energy bars

Milk Ca

9-28

Insoluble

Dairy products,

Milk drink with vitamin

120

energy bars

D and Ca

Tricalcium citrate

21

0.9

Beverages, dairy and

Kids dairy dessert with

130

4 aq

soy products

Ca

RT, room temperature; aq, H2O.

RT, room temperature; aq, H2O.

Solubility is strongly influenced by the pH of the system since the solubility of calcium salts typically increases with decreasing pH (Clydesdale, 1988). According to final calcium-fortified liquid products available in European and US supermarkets (Gerstner 2002a, 2004), slightly soluble to insoluble calcium salts (calcium carbonate, calcium phosphate, milk calcium, tricalcium citrate) can be used in the following liquid product categories.

1 Clear beverages at low dosage levels and, preferably, pH below 4.5 (typically <50 mg total calcium/100 ml).

2 Cloudy beverages at pH values below 4.5, such as orange juice (typically <146 mg total calcium/100 ml).

3 Milk and dairy drinks (typically 130-180 mg total calcium/100 ml).

4 Soy drinks (typically 75-140 mg total calcium/100 ml).

In contrast to the beverages of category 1, where calcium salts are dissolved, calcium salts used for the beverages of categories 2-4 are predominantly dispersed. In order to further increase solubility, dissolving or ease of dispersion, particularly fine (micronised) powders have been developed. In the case of tricalcium citrate, particle sizes are <70 |im at a low and <20 |im at a high fortification level. Why are dispersed systems preferred in categories 2-4? One of the main reasons is the lower price for tricalcium citrate, calcium carbonate and calcium phosphate compared with more soluble (organic) calcium forms. In any case, the feasibility of calcium addition has to be considered as cloudy beverages, milk and soy products represent a complex food matrix from the technological point of view.

Taste

Generally, high levels of calcium, particularly insoluble forms like carbonates and phosphates, tend to produce a chalky mouthfeel, form sediments and may promote astringency or bitter taste in the final product (Flynn and Cashman, 1999). Calcium lactate may impart some bitter notes at high concentrations, comparable with characteristics found for calcium chloride (Tordoff, 1996). Calcium carbonate may come across as soapy or lemony. Calcium phosphate has a bland flavour, but imparts a gritty mouthfeel. Negative effects of calcium on taste can be masked with chelating agents (e.g. tripotassium citrate) and the use of stabilisers (e.g. carrageenan), as well as with the addition of flavourings. Tricalcium citrate and calcium lactate gluconate are considered to be among the most neutral tasting salts in most applications and can be applied at high dosage levels.

With regard to calcium lactate gluconate, Technical University Munich-Weihenstephan has performed detailed studies on taste properties (Gerstner, 2002b). Triangle taste panels with trained students and scientists have detected and evaluated differences between fortified and non-fortified samples at different calcium lactate gluconate concentrations. In apple juice for example, fortification with calcium lactate gluconate could not be detected at up to 150 mg added calcium/100 ml. For cloudy juices (category

2), tricalcium citrate and its derivative calcium citrate malate are the preferred choices due to their good compatibility with fruit-based juices and their low effect on taste.

Ease of processing and stability

It is known that using highly soluble calcium salts at high concentrations may lead to adverse effects in dairy and soy applications, especially during the heating step (Flynn and Cashman, 1999, Reddy et al., 1999). The addition of mineral salts and especially of calcium has a strong impact on the functionality of these products. With higher-solubility salts more free calcium ions are in solution and available for reaction than with lower-solubility salts and so complications in the form of gelation and calcium sediments can develop during processing, heat treatment or shelf life. This is the case if phosphates and proteins naturally contained in milk and soy beverages react with available calcium. Thus, although it might be easier to add highly soluble calcium salts rather than insoluble calcium salts to milk and soy products, higher amounts of calcium might be difficult to achieve without control of pH and addition of stabilisers and chelating agents (Flynn and Cashman, 1999, Reddy et al., 1999). In contrast to the other calcium salts, tricalcium citrate is an interesting physical anomaly as it is less soluble at higher temperatures. Due to this inverse solubility, tricalcium citrate is less reactive during the heating process, thus minimising precipitates, fouling and cleaning intervals (Gerstner, 2004).

Among the soluble calcium forms, calcium lactate gluconate has the highest solubility of all commonly used organic calcium salts, which is the main functional advantage of this product (Table 11.3). Its solubility is syn-ergistically enhanced to approximately 400 g/l water and well beyond that of the relatively highly soluble single components calcium lactate (66 g/l) and calcium gluconate (35 g/l). The reason for this phenomenon of extremely high solubility is believed to be the ability of mixtures of lactate and gluco-nate ions to form metastable complexes with calcium ions in solution, which provides additional stability benefits in food and beverage applications. At the Technical University Munich-Weihenstephan, calcium lactate gluco-nate was tested for important processing parameters such as the dissolution characteristics of highly concentrated solutions (K.-H. Engel, personal communication, 2002). Concentrations of up to 50% could be reached within minutes without negative consequences on colour or odour, and with only a slight influence on pH. In storage stability tests, solutions with concentrations of 5, 10 and 30% calcium lactate gluconate remained stable at room temperature for at least 1 week. These characteristics significantly reduce the time needed for adding calcium during processing. High dissolubility and stability can also be deciding factors as to when calcium lactate gluconate is used in concentrates or instant preparations.

It is also possible to combine insoluble with more soluble salts to control costs while having acceptable solubility/dispersibility in the final product. In this respect, calcium-fortified products contain combinations such as calcium phosphate-calcium lactate, calcium carbonate-tricalcium citrate as well as tricalcium citrate-calcium lactate gluconate (Gerstner 2002a, 2004).

11.5.3 Nutritional aspects

Calcium bioavailability of tricalcium citrate compared with calcium carbonate and calcium phosphate

Any nutrient's effectiveness depends on its bioavailability, which means how well the human body absorbs and utilises it. On average, only about 10-30% of calcium is absorbed from a mixed diet by healthy adults (National Research Council, 1989). Several different factors influence this level, among others, the type of calcium salt used for fortification purposes.

A review on calcium citrate and bone health has been published recently (Edelstein, 2004). 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 US National Institutes of Health recommended calcium citrate for supplementation, especially for older individuals where absorbability can be a limiting factor due to reduced gastric acid production (National Institutes of Health, 1994).

Researchers at the University of Texas conducted a meta-analysis of calcium bioavailability, which evaluated 15 studies on the bioavailability of two of the most common forms of calcium supplements, tricalcium citrate and calcium carbonate (Sakhaee et al., 1999). All but one study showed significantly greater absorption of calcium from tricalcium citrate than from calcium carbonate, ranging from +5 to +97%. Based on the statistical evaluation of all 15 studies, the authors confirmed this superior bioavailability of tricalcium citrate and calculated it to be, on average, +22 to +27% compared with calcium carbonate, regardless of whether the supplement was taken on empty stomach or co-administered with meals.

Absorption of calcium from soy milk fortified with tricalcium phosphate reached only 75% of the efficiency of absorption of calcium from cows' milk (Heaney et al., 2000). Similarly, calcium phosphate has also been described in scientific studies to display lower bioavailability than trical-cium citrate or its derivative calcium citrate malate. In commercially marketed calcium-fortified orange juices, bioavailability was 48% greater for calcium citrate malate than for a tricalcium phosphate-calcium lactate blend (Heaney et al., 2005). In long-term clinical studies with elderly women, tricalcium citrate displayed a significant, almost three times higher absorption than calcium phosphate (Riggs et al., 1998).

Effect of calcium lactate gluconate on bone density

Besides tricalcium citrate, calcium lactate gluconate is among the most intensively researched organic calcium salts with regard to bioavailability.

Its superior effect on fractional absorption rate of calcium, calcium bioavail-ability biomarkers (urinary and serum ionised calcium and PTH) and bone mineral density (BMD) have been reviewed previously (Gerstner, 2003).

The main purpose of the recommended high calcium intake is osteoporosis prevention. Therefore, an increase in BMD or bone stability is a better criterion for the efficacy of a calcium salt than its absorbability. Calcium lactate gluconate, when administered to 19 non-menopausal women with osteoporosis during or after a hormone therapy, significantly reduced bone fracture rate (Almustafa et al., 1992). Moreover, in a study in 50 Chinese women, aged 62-92 years, calcium lactate gluconate increased BMD of the hip more than exercise (Lau et al., 1992). Additional evidence of beneficial effects on bone health of calcium lactate gluconate (via Calcium Sandoz®) was supplied by a meta-analysis of Schaafsma et al. (2001). The authors compared 16 clinical studies in elderly and late postmenopausal women (mean age 58-79 years), who were supplemented for 12-48 months with 500-1250 mg/day calcium as calcium lactate gluconate, calcium carbonate, calcium citrate and other salts. Without exception, intake of Calcium Sandoz® calcium lactate gluconate increased BMD of the lumbar spine between +0.2 to +1.8%, whereas other supplements, even very well absorbable salts such as calcium citrate malate, partly decreased BMD. Thus, supplementation with calcium lactate gluconate is likely to improve bone health more effectively than calcium citrate malate or calcium carbonate.

11.5.4 Calcium-rich functional food products with anti-obesity claims

Although the majority of calcium-fortified functional food products have the purpose of providing calcium in sufficient amounts to contribute to the prevention of osteoporosis, there are some products on the market bearing an anti-obesity claim. Three prominent examples from large dairy companies that have been found in supermarkets in 2005 are shown in Table 11.4.

However, these products contain relatively little calcium (<300 mg/ serving, the Dannon product is without supplemental calcium). Therefore for two of the products three to four servings per day are recommended in order to provide a daily dose of 600-900 mg calcium. Such an amount was sufficient in clinical studies to have significant effects on weight and fat metabolism. For the third product no recommendation of several servings per day is given. Hence, although it contains double the amount of calcium compared with a conventional yoghurt, the postulated anti-obesity effect is based on its low energy content (32 cal/serving), supplemental dietary fibre and green tea extract, as well as the recommendation of physical activity.

Besides the calcium originating from the dairy basis, the Yoplait yoghurt had been fortified with tricalcium phosphate, whereas for the Nestlé dairy

Table 11.4 Examples of products rich in calcium and with anti-obesity claims (purchased in 2005)

Product

Weight loss claim

Nutrition facts

Light 'n Fit® non-fat yogurt Blackberry, Dannon, USA

Thick & Creamy Vanilla, Yoplait, USA

Sveltesse Line-Activ® milk drink strawberry, Nestlé, Switzerland

Slim down with yogurt. Lose more weight as part of a reduced calorie diet. Dairy products, like Light 'n Fit® yogurt, have been shown in studies to help you lose more weight and burn more fat than just cutting calories alone.* *3-4 servings daily (providing at least 600 mg of calcium per day) as part of a high-calcium, reduced-calorie diet Burn more fat Recent research shows that dairy foods, like Yoplait, may help you burn more fat and lose more weight than cutting calories alone.* *3 servings of dairy daily in a reduced-calorie diet. Check out www. YoplaitUSA.com for more ways to develop a healthy and effective weight loss plan. Helps to keep your waistline! A delicious milk drink, which - in combination with a balanced diet and regular physical exercise - helps to keep your waistline. Sveltesse Line-Activ® supports the fat metabolism and thus contributes to a healthy and light diet. Each bottle contains dietary fibres, green tea and double as much calcium as a regular yoghurt drink.

Labelled per serving (170 g):

Calories

90

Fat

0 g

Sodium

95 mg

Potassium

270 mg

Carbohydrates

16 g

Protein

6 g

Calcium

15% DV

(150 mg)

Phosphorus

15%

Vitamin A

6% DV

Vitamin D

20% DV

Riboflavin

15% DV

Vitamin B12

10% DV

Labelled per serving (170 g):

Calories

190

Fat

3.5 g

Cholesterol

15 mg

Sodium

100 mg

Potassium

310 mg

Carbohydrates

32 g

Protein

7 g

Calcium

30% DV

(300 mg)

Phosphorus

15%

Vitamin A

15% DV

Vitamin D

20% DV

Labelled per serving (88 g): Calories 32

Sodium 0.03 g

Carbohydrates 4.8 g Protein 1.8 g

Calcium 26% EU-

DV, US daily value, which is 1000 mg for calcium; EU-RDA, recommended daily allowance in the European Union according to Council Directive 90/496/EEC (1990), which is 800 mg for calcium.

drink milk minerals had been used to increase calcium levels. The question of which calcium salt has the best anti-obesity properties in functional foods and drinks cannot be answered, as long as the contribution of the Zemel mechanism and the formation of calcium soaps to the overall calcium effect remains unclear. The former effect requires the use of highly water-soluble complex calcium salts to increase serum calcium concentration, the latter a high calcium concentration in the intestine.

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