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Rationale for multiple fortification
Micronutrient bioavailability and organoleptic quality of fortified foods
Mineral interactions and bioavailability
Designing micronutrient premixes
Quality control in food fortification
Denis Barclay is affiliated with the Nestle Research Centre in Lausanne, Switzerland.
Mention of the names of firms and commercial products does not imply endorsement by the United Nations University.
Diet-related micronutrient deficiencies rarely occur in isolation; deficiencies of iodine and vitamin A or of iron and vitamin A or zinc are often observed in the same populations. In addition, widespread deficiencies of some micronutrients, for example, zinc and calcium, may often go undiagnosed because of the absence of specific and sensitive status indicators. Multiple micronutrient supplementation can be more effective in improving nutritional status than supplementation with single key micronutrients; therefore, the multiple fortification of appropriate food vectors, including beverages, is of interest from the nutritional standpoint.
Beverages fortified with multiple micronutrients include dairy products, chocolate beverages, fruit juices, and soya-based drinks. As well as the documented or estimated micronutrient deficiencies and the requirements of the target population or consumer group, the conception of such a multiply fortified beverage must take into account a number of other important factors. The choice of the chemical form of the fortification micronutrients should be made with consideration of bioavailability, the effects on the organoleptic characteristics of the particular beverage, and cost. The initial calculation of the composition of the micronutrient premix should include the levels of micronutrients in the raw materials used and the estimated losses of specific micronutrients during processing and storage. Preliminary production and storage trials are then needed to determine the actual losses. The composition of the micronutrient premix may then be finalized. Interactions, both positive and negative, between fortification micronutrients may also need to be considered. For example, the bioavailability of iron may be enhanced by the addition of vitamin C, whereas mineral-vitamin and vitamin-vitamin interactions can accelerate the destruction of some vitamins.
To render quality control procedures simple and cost-effective, only a limited number of fortification micronutrients, which are especially sensitive to losses and which are easy to measure, may be analysed. Simple, inexpensive, and rigorous analytical methods for such measurements are now available.
The food category of beverages encompasses a wide range of products, including fruit juices and drinks, milks and milk drinks, chocolate (malt) beverages, instant flavoured drinks, nectars, meal replacers, supplements for pregnancy and lactation, sports drinks, and others. Micronutrient-fortified foods, including beverages, are becoming increasingly popular in many countries. In a recent survey in the United States, more than half of the respondents reported consuming micronutrient-fortified fruit juices or drinks several times weekly . The contribution to micronutrient intakes from fortified foods in the United States ranged from 6% for vitamin B6 and folk acid up to 24% for iron and vitamin B1 .
Nearly all fortified processed foods contain more than one added micronutrient. Milk products are often fortified with vitamins A and D only, whereas other beverages are often fortified with many minerals and vitamins. Multiple fortification of different types of beverages can be justified for a number of reasons. Virtually all broad-based nutrition surveys show that individual micronutrient deficiencies rarely occur in isolation. Since many major foods are excellent sources of several micronutrients, inappropriate food choices and economic constraints leading to unbalanced diets are unlikely to provide adequate levels of all micronutrients.
The existence and extent of the deficiencies of some micronutrients remain largely unknown, partly because of lack of adequate survey data, but also largely because of the absence of easily measurable, sensitive, and specific indicators of micronutrient status. Although the existence of such status indicators has allowed estimation of the dimension of deficiencies of iron, vitamin A, and iodine, this is not the case for other key micronutrients, such as zinc and calcium. Deficiencies of these two minerals maybe as widespread and as costly in terms of human health and well-being as the better-documented deficiencies of iron, vitamin A, and iodine.
Finally, multiple micronutrient supplementation has been shown to have a greater impact on nutritional status than administration of the supposed key deficient single micronutrient. For example, a 10-week, double-blind study on zinc and growth in six- and seven-year-old Chinese children showed that multiple micronutrient supplementation resulted in greater improvement in linear growth than zinc supplementation alone .
Although there are several good arguments in favour of multiple fortification, a number of factors must be taken into account before deciding on the fortification of a particular food product. Obviously, the food vector, the fortification micronutrients, and their levels must be chosen as a function of the nutritional requirements and deficiencies as well as of the dietary habits of the target population or consumer group. As a general rule, and in order to provide nutritionally appropriate amounts of micronutrients without creating excess or imbalance, one portion of the food should not provide too large a proportion of the requirements of the target consumer.
The stability of vitamins is affected by a number of factors, such as temperature, moisture, oxygen, light, pH, minerals (especially iron and copper), vitamin-vitamin interactions, and other food components . Vitamin stability is affected most by heat, moisture, pH, and light, but given their chemical heterogeneity, vitamin losses in different foods vary considerably during both processing and storage of the final product . The most unstable vitamins are C, A, D, B1, and B12. Because of their multiple oxidation states, the presence of metal ions (iron and copper) accelerates degradation of vitamins, especially vitamins C, A, and B1. Fortification with several vitamins may give rise to vitamin-vitamin interactions that may accelerate the rate of breakdown of some vitamins; the best-known interactions are those among vitamins C, B1, B2, B12, and folic acid . The extent of these interactions is also dependent on the nature of the food product as well as on temperature, moisture level, pH, light, etc. during processing and storage.
Therefore, to maintain the micronutrient levels declared on the product label throughout a products shelf life, the amount of vitamins added during processing needs to be higher than the levels reported on the label. The difference between the declared and formulated vitamin levels, termed overage, will be different for each food application. Vitamin overages are normally calculated as a percentage of the declared level:
Overage = (formulated vitamin level - declared level)/ declared level × 100.
For a milk-based drink powder fortified by dry mixing, the overages range from 10% for vitamin E and niacin up to 25% to 30% for vitamins C, A, and D . For liquid beverages stored in cans, the overages may be as high as 100% for vitamin C and other sensitive vitamins.
The nature of the food or beverage vector will have considerable bearing on the fortification, since organoleptic alterations caused by certain added micronutrients must be dealt with quite often. The bioavailability of added micronutrients, especially minerals and trace elements, must also be taken into consideration. In these two respects, iron is undoubtedly the most difficult micronutrient to add to a food, yet iron deficiency is the most widespread micronutrient deficiency in the world today. The choice of an iron-fortification compound depends primarily on the nature of the food itself, and is nearly always a compromise between maximal bioavailability and minimal organoleptic alteration . Soluble iron compounds such as ferrous sulphate are very well absorbed but can give rise to unacceptable colour and taste changes in some products. For example, many milk products are satisfactorily fortified with ferrous sulphate, whereas its use in other foods containing easily oxidizable unsaturated fatty acids leads to rancidity or to colour changes in polyphenol-containing beverages such as cocoa drinks . In many cases, it is possible to improve the bioavailability of iron from foods by the addition of an appropriate amount of ascorbic acid. A molar ratio of ascorbic acid to iron of 2:1 often significantly enhances iron absorption , but the optimal ratio depends on the nature of the food or beverage, and especially on the levels of other enhancers and inhibitors of iron absorption in the product.
Interactions between minerals can also have implications for mineral bioavailability in multiply fortified products. Iron, zinc, and calcium have been the most studied in this respect . For example, in the absence of phytic acid, the effect of calcium on zinc absorption is low. However, when phytic acid is present, calcium significantly inhibits zinc absorption. Likewise, oral iron supplements significantly inhibit inorganic zinc retention when consumed simultaneously at iron-to-zinc ratios as low as 1:1 [11,12]. To determine the nutritional relevance of this interaction in food, zinc bioavailability studies were carried out in human adults using food-fortification levels of iron and zinc that are typical in infant cereals and formulas . The results showed that normal levels of iron fortification do not diminish zinc absorption. This has also been confirmed in infants .
Another extensively studied interaction is that between calcium and iron. A number of single-meal studies have shown that calcium does have an inhibitory effect on iron absorption. For example, Hallberg et al. showed that 165 mg of calcium given as milk reduced iron absorption by as much as 50% to 60%. Recently however, the acute single-meal approach has been questioned as exaggerating the effects of food inhibitors and enhancers of iron absorption. This has led to whole-diet absorption studies in order to evaluate the longer-term effects of inhibitors and enhancers of iron absorption. These studies showed that the strong effects of enhancers and inhibitors on iron absorption observed in acute studies were generally much lower in whole-diet studies [16-18]. Moreover, in a recent chronic dietary labelling study, in which the effects of inhibitors and enhancers were studied on an even longer-term basis of several weeks, Reddy and Cook  did not observe any significant inhibitory effect of dietary calcium on iron absorption nor any enhancing effect of vitamin C. The only dietary components shown by multiple regression techniques to influence iron absorption were meat (enhancing) and polyphenols (inhibiting). It is very likely, therefore, that in varied, adult Western diets, the effects of individual enhancers and inhibitors of iron absorption are of much less nutritional significance than has been suggested by single-meal studies. This remains to be shown for typical diets in other regions of the world. Even if in the long term there is a low to mild inhibition by calcium of iron absorption from iron-fortified milk beverages or from calcium- and iron-fortified beverages, the iron will still be absorbed to an appreciable extent and will, therefore, be of benefit to those consumers whose dietary iron intake is inadequate. Such beverages can provide nutritionally relevant amounts of iron.
Once the appropriate beverage for fortification has been identified, the next step is to design the micronutrient premix(es), as a function of the:
» micronutrient requirements and status of the target consumer,For fortifying with both minerals and vitamins, two premixes are generally used, one for minerals and another for vitamins, in order to minimize metal-catalysed degradation of vitamins during storage of the premix. Usually, a small quantity of the premixes is obtained from micronutrient suppliers for preliminary, small-scale production trials. Complete micronutrient analyses of these trial products are then carried out to calculate the final specifications of the premixes.
» micronutrient levels in the raw materials to be used,
» estimated processing and storage losses (as above),
» expected homogeneity of mixing.
Fortification of staple or processed foods requires properly designed and resourced quality control systems. Neither government legislation nor industrial specifications for food fortification will be effective without adequate quality control, both at the production site and in central laboratories. Reliable quality control of the addition of micronutrients to foods can only be obtained by the careful use of appropriate and validated analytical techniques in the hands of trained analysts. Validation of analytical methods involves the establishment of performance characteristics such as specificity, sensitivity, working concentration range, limit of detection, limit of quantitation, ruggedness, accuracy, and precision.
In order to ensure that the mineral-trace element premix is added to a processed food at the correct level, iron is often used as a tracer. Several methods can be used for iron determination: X-ray fluorescence spectroscopy, which is rapid (10 minutes) and can be used on production lines; atomic absorption spectroscopy, which is the reference method and is generally used in quality control laboratories (2 hours); inductively coupled plasma emission spectrometry (2 hours); and calorimetric methods (rapid test kit, 20 minutes).
The repeatability of the different methods varies from 5% to 10%, whereas the reproducibility varies from 10% to 20%. The method used depends on the available laboratory resources as well as on the desired precision. Quality control data on the addition of trace elements to milk powder by dry mixing show that iron determination alone allows for control of the addition of the trace element premix.
Similarly, the addition of vitamins to foods in a multivitamin premix may be controlled by determination of vitamin C as the tracer in the food, since it is often the most sensitive to degradation. Methods commonly used include high-performance liquid chromatography, titrimetry using a visual or calorimetric end point, or rapid calorimetry (Merck RQ Flex, Darmstadt, Germany). The latter method maybe used on production lines to ensure the presence of the premix in the product. High-performance liquid chromatography and titrimetry are used in quality control laboratories and have better repeatability than the rapid method. Again, quality control data on the stability of vitamins A, C, and D show that determination of vitamin C only can be used to check the levels of the vitamins in the product during prolonged storage.
The numbers and types of fortified beverages are ever-increasing and include milk and milk drinks, chocolate (malt) beverages, meal replacers, slimming beverages, sports beverages, supplements for pregnancy and lactation, cereal drinks (cereal milks), fruit juices, and others. To have an appropriate impact on consumer health and nutrition, the development of such fortified beverages must be based on the dietary habits and nutritional requirements and status of the target consumer. The chemical form of the fortification micro-nutrients must be chosen to have maximal bioavailability while not producing unacceptable organoleptic changes. At normal fortification levels, mineral interactions generally do not lead to nutritionally significant decreases in mineral bioavailability. Micronutrient losses during processing and storage, especially losses of certain vitamins, must be quantified in order to determine the composition of vitamin and mineral premixes. Finally, effective fortification of foods and beverages can only be achieved if there is an appropriate quality control system.
1. Ternus M. Food fortification: It can be a lifesaver, but are we going too far in creating no-brain super foods? Environ Nutr 1996;4:9-12.
2. Lachance PA. Nutritional responsibilities of food companies in the next century. Food Technol 1989;43:144-50.
3. Yang JJ, Shi YG, Zhu JD, Mi MT, Chen HC, Sandstead H. Growth of Chinese children after treatment with zinc. 7th Asian Congress of Nutrition, Beijing. Beijing: Chinese Nutrition Society, 1995:141.
4. Richardson DP. Food fortification. In: Ottaway PB, ed. The technology of vitamins in food. Glasgow, Scotland: Blackie Academic & Professional, 1993:233-44.
5. Killeit U. The stability of vitamins - a selection of current literature. Grenzach-Whylen, Germany: Hoffman-LaRoche AG, 1988.
6. Ottaway PB. Stability of vitamins in food. In: Ottaway PB, ed. The technology of vitamins in food. Glasgow, Scotland: Blackie Academic & Professional, 1993:90-112.
7. Hurrell RF. Nonelemental sources. In: Clydesdale FM, Weimer Kl, eds. Iron fortification of foods. Orlando, Fla, USA: Academic Press, 1985:39-51.
8. Hurrell RF, Reddy MB, Dassenko SA, Cook JD, Shepherd D. Ferrous fumarate fortification of a chocolate drink powder. Br J Nutr 1991;65:271-83.
9. Kastenmayer P, Davidsson L, Galan P, Cherouvrier F, Hercberg S, Hurrell RF. A double isotope technique for measuring iron absorption in infants. Br J Nutr 1994;71:411-24.
10. Couzy F, Keen C, Gershwin ME, Mareschi JP. Nutritional implications of the interactions between minerals. Prog Food Nutr Sci 1993;17:65-87.
11. Solomons NW, Jacob RA. Studies on the bioavailability of zinc in humans: effects of heme and non-heme iron on the absorption of zinc. Am J Clin Nutr 1981;34: 475-82.
12. Sandstrom B, Davidsson L, Cederblad A, Lonnerdal B. Oral iron, dietary ligands and zinc absorption. J Nutr 1985;115:411-4.
13. Davidsson L, Almgren A, Sandstrom B, Hurrell RF. Zinc absorption in adult humans: the effect of iron fortification. Br J Nutr 1995;74:417-25.
14. Fairweather-Tait SJ, Wharf SG, Fox TE. Zinc absorption in infants fed iron-fortified weaning food. Am J Clin Nutr 1995;62:785-9.
15. Hallberg L, Brune M, Erlandsson M, Sandberg AS, Rossander-Hulthén L. Calcium: effect of different amounts on non-heme- and heme-iron absorption in humans. Am J Clin Nutr 1991;53:112-9.
16. Gleerup A, Rossander-Hulthén L, Gramatkovski E, Hallberg L. Iron absorption from the whole diet: comparison of the effect of two distributions of daily calcium intake. Am J Clin Nutr 1995;61:97-104.
17. Tidehag P, Hallmans G, Wing K, Sjostrom R, Agren G, Lundin E, Zhang JX. A comparison of iron absorption from single meals and daily diets using radio Fe (55Fe, 59Fe). Br J Nutr 1996;75:281-9.
18. Cook JD, Dassenko SA, Lynch SR. Assessment of the role of non-heme-iron availability in iron balance. Am J Clin Nutr 1991,54:717-22.
19. Reddy MB, Cook JD. Effect of calcium intake on nonheme-iron absorption from a complete diet. Am J Clin Nutr 1997;65:1820-5.