Measuring the vitamin A content of South African fortified white maize

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The South African context

In South Africa, refined white maize meal is currently the main staple food due to consumer demand (NFCS, 2000). Ironically, the preferences of today’s African consumers for white as opposed to yellow maize as is consumed by the rest of the world, was initially created by the influence of the British starch market. Since 1911, the British starch market provided a premium for white maize and local legislation was passed in some parts of Eastern and Southern Africa requiring that only white maize be accepted for export.
The influence of mines, plantations, and cattle enterprises on to the local economy expanded the demand for food in the country. Eventually the domestic demand for maize grew as Africans left their farms to work on settler farms, in mines or industrial plants. Food consumption preferences were influenced by the rations that employers used as in-kind payments. Diets adapted as “people got used to what they consumed » (Shopo 1985 cited Smale & Jayne, 2003: 11).

Vitamin A and the isomers

Vitamin A is a generic term used for a group of structurally related chemical compounds known as retinoids. Retinoids refer to both naturally occurring and synthetic compounds with, or without, the biological activity of vitamin A (O’Byrne and Blaner, 2005). Figure 2.1 shows the chemical structures of some retinoids. The term vitamin A is often used as a general term for all compounds that exhibit the biological activity of retinol. In vivo, vitamin A is generally found as the free alcohol form (retinol) or esterified with a fatty acid (retinyl ester). All-trans-retinol is by definition vitamin A. The vitamin is available in pure form by chemical synthesis or as vitamin A palmitate or acetate. It is a pale yellow solid, which dissolves freely in oils and fats, but is insoluble in water (Fox and Cameron, 1995).

The role of Vitamin A in human metabolic processes

Although an essential nutrient needed in only small amounts, vitamin A is necessary for normal functioning of the visual system; growth and development; and maintenance of epithelial cellular integrity, immune function and reproduction. Vitamin deficiency disorders occur when body reserves are depleted to the limit at which physiological functions are impaired. Vitamin A in the diets of most human communities comes from a very wide variety of plant and animal sources (FAO, 2001). In the more industrialised countries over two-thirds of dietary vitamin A is derived from animal sources as preformed vitamin A, whereas in developing countries, communities depend primarily on provitamin A carotenoids from plant sources (Ahmed and Darnton-Hill, 2004).

Strategies for controlling Vitamin A deficiencies

Increasing the efficacious nutrient supply, by using food-based approaches or by using pharmanutrient approaches, can control deficiency of vitamin A, as well as deficiency of other micronutrients. Another strategy for controlling VAD is to reduce the nutrient requirements, by for example, controlling infection (Van Lieshout and West, 2004). Food-based interventions are viewed as those most likely to be sustained, provided the culture and ecology of the vitamin A-containing foods is addressed in programs based in agriculture, food processing, social marketing and public health education (Blum et al., 1997).
When considering food approaches for combating vitamin A deficiency, it is necessary to take into account whether the efficacious nutrient supply can be met. Figure 2.4 illustrates the balance between the supply of nutrients and the requirements thereof. The efficacious nutrient supply depends on: • Amount of foods containing vitamin A or provitamin A carotenoids consumed • Vitamin A or provitamin A carotenoid content of each food consumed, and • Bioefficacy of vitamin A or provitamin A carotenoids in the food consumed (Van Lieshout and West, 2004). By far the most efficient food based approach for increasing the nutritional status of the nation is through fortification of widely consumed and accessible staple foods (Randall, 2001).

Fortification of staple foods with Vitamin A

Food fortification refers to the addition of micronutrients to foods during the production process. If fortified foods are consumed on a regular basis they will maintain body stores of nutrients more efficiently and more effectively than intermittent supplements. Fortification generally aims to supply micronutrients in amounts that approximate to those provided by a good, well-balanced diet. Consequently, fortified staple foods will contain “natural” or near natural levels of micronutrients, which may not necessarily be the case with supplements (WHO, 2006). Fortification of widely distributed and widely consumed foods has the potential for improving the nutritional status of a large proportion of the population. Fortification of food with vitamin A and its distribution are most feasible where the processed food industry is well-developed and supported. That may not be the case in resource-poor areas where vitamin A is lacking in the diet, deficiency is most extreme and various barriers exist for the most vulnerable to access fortified food (Trowbridge et al., 1993).

Moisture

Moisture contents in excess of about 7-8% in a food are known to adversely affect the stability of vitamin A. Beyond the critical moisture content, there is a rapid increase in water activity, which permits various deteriorative reactions to occur (Clarke, 1995). The moisture level of South African unfortified super maize meal, unfortified special maize meal and unfortified sifted maize meal is 12.0%, 11.6% and 11.9% respectively (Wolmarans, Danster and Chetty, 2005). A 6.5% moisture content of maize grits showed hardly any loss, whereas 11.4% moisture resulted in a loss of one-fifth of vitamin A (Cort et al., 1976, Lotfi et al., 1996).

Premix and preblend considerations

This is especially important in small-scale fortification. The concentrated premixes made for large scale fortification can be used in small scale fortification once they are properly diluted to a preblend.

TABLE OF CONTENTS :

• DECLARATION
• ACKNOWLEDGEMENTS
• ABSTRACT
• LIST OF ACRONYMS AND ABBREVIATIONS
• LIST OF TABLES
• LIST OF FIGURES
• LIST OF ADDENDA
• CHAPTER 1: THE STUDY IN PERSPECTIVE
  • 1.1 Background to the study
  • 1.2 The South African context
  • 1.3 Motivation for the study
  • 1.4 Objective of the study
  • 1.5 Presentation and structure of the thesis
  • 1.6 References
• CHAPTER 2: LITERATURE REVIEW
  • 2.1 Introduction
  • 2.2 Vitamin A and the isomers
  • 2.2.1 Sensitivity of vitamin A
  • 2.3 Vitamin A metabolism and deficiency
    • 2.3.1 The role of vitamin A in human metabolic processes
    • 2.3.2 Bioavailability of vitamin A
    • 2.3.3 Dietary requirements and toxicity Definitions of Recommended Dietary Allowances, Recommended Safe Intake and Dietary Reference Intake
  • 2.3.3.2 Toxicity
  • 2.4 Vitamin A deficiency
  • 2.4.1 Strategies for controlling vitamin A deficiency
  • 2.5 Fortification of staple foods with vitamin A
  • 2.5.1 Maize meal as vehicle for micronutrient fortification
  • 2.5.2 Vitamin A as fortificant
  • 2.5.3 Factors that affect nutrient delivery in fortification
  • 2.5.4 Summary
  • 2.6 Sampling
  • 2.7 Measuring the vitamin A content of South African fortified white maize
  • 2.7.1 Size of the test portion
  • 2.7.2 Extraction procedures
  • 2.7.3 Chromatography
  • 2.7.4 Method Validation Studying the relative bioavailability of vitamin A in fortified maize meal
  • 2.8.1 Animal models in nutrition research
• • 2.9 Concluding Remarks
  • 2.10 References
• CHAPTER 3: VITAMIN A CONTENT IN FORTIFIED WHITE MAIZE MEAL AS PURCHASED AND IN PORRIDGE AS CONSUMED IN SOUTH AFRICA
  • 3.1 Abstract
  • 3.2 Introduction
  • 3.3 Materials and Methods
  • 3.3.1 Samples
  • 3.3.2 Preparation of porridge samples
  • 3.3.3 Gravimetric determination of dry matter
  • 3.3.4 Determination of total vitamin A as all-trans retinol
  • 3.3.5 Calculation of the retention of vitamin A in porridge
  • 3.3.6 Statistical Analysis
  • 3.4 Results and Discussion
  • 3.4.1 Method performance
  • 3.4.2 Vitamin A content of maize meal as purchased in supermarkets
  • 3.4.3 Vitamin A concentration of maize porridge
  • 3.5 Conclusion
  • 3.6 Acknowledgement
  • 3.7 References
• CHAPTER 4: EFFECT OF DIFFERENT MAIZE MEAL DIETS ON THE GROWTH AND VITAMIN A STATUS OF CHICKENS
  • 4.1 Introduction
  • 4.2 Materials and Methods
  • 4.2.1 Husbandry and rearing of broilers
  • 4.2.2 Measurements and observations
  • 4.2.3 Vitamin A analysis
  • 4.2.4 Statistical analysis
  • 4.3 Results and Discussion
  • 4.3.1 Feed
  • 4.3.2 Body weight
  • 4.3.3 Feed conversion ratio
  • 4.3.4 Mortality
  • 4.3.5 Livers
  • 4.4 Conclusion
  • 4.5 Acknowledgement
  • 4.6 References
• CHAPTER 5: SIGNIFICANCE OF THE STUDY, CONCLUSIONS AND RECOMMENDATIONS
  • 5.1 Introduction
  • 5.2 Significance of the study Vitamin A content in fortified maize meal as purchased and in porridge as consumed in South Africa Effect of different maize meal diets on the growth and vitamin A status of chickens
  • 5.3 Concluding remarks
  • 5.4 Limitations of the study
  • 5.5 Recommendations
  • 5.6 References

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Vitamin A content and bio-availability of South African maize meal (as purchased and consumed)