Carotenoids of Sweet Potato, Cassava, and Maize and Their Use in Bread and Flour Fortification

Carotenoids of Sweet Potato, Cassava, and Maize and Their Use in Bread and Flour Fortification

CHAPTER 28 Carotenoids of Sweet Potato, Cassava, and Maize and Their Use in Bread and Flour Fortification Delia B. Rodriguez-Amaya1, Marilia Regini ...

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Carotenoids of Sweet Potato, Cassava, and Maize and Their Use in Bread and Flour Fortification Delia B. Rodriguez-Amaya1, Marilia Regini Nutti2, Jose´ Luiz Viana de Carvalho2 1 Department of Food Science, Faculty of Food Engineering, University of Campinas e UNICAMP, Campinas, SP, Brazil 2 Embrapa Food Technology, Rio de Janeiro, RJ, Brazil 301

CHAPTER OUTLINE List of Abbreviations 301 Introduction 301 Carotenoids of Sweet Potato (Ipomoea batatas Lam.) 303

Application in the fortification of flour and bread 307

Carotenoids of Maize (Zea mays L.) 308

Carotenoids in roots and flour 303 Application in the fortification of flour and bread 305

Carotenoids of Cassava (Manihot esculenta Crantz) 306 Carotenoids in roots and flour


Carotenoids in kernels and flour 308 Application in the fortification of flour and bread 308 Technological Issues 309

Summary Points 309 References 310

LIST OF ABBREVIATIONS OFSP Orange-fleshed sweet potato

INTRODUCTION Carotenoids are among the most valuable food constituents in terms of food quality and human health effects. As natural pigments, they confer the pleasing yellow, orange, or red color of many fruits, vegetables, egg yolk, crustaceans, and some fish. Aside from the provitamin A activity of some of these compounds, they have also been credited with other Flour and Breads and their Fortification in Health and Disease Prevention. DOI: 10.1016/B978-0-12-380886-8.10028-5 Copyright Ó 2011 Elsevier Inc. All rights reserved.

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health-promoting effects, including immunoenhancement and reduction of the risk of developing degenerative diseases such as cancer, cardiovascular diseases, cataracts, and macular degeneration (Krinsky and Johnson, 2005). The carotenoids’ action against diseases has been widely attributed to their antioxidant activity, specifically to their ability to quench singlet oxygen and interact with free radicals. However, the following mechanisms are being increasingly reported: retinoid-dependent signaling, modulation of carcinogen metabolism, regulation of cell growth, inhibition of cell proliferation, enhancement of cell differentiation, stimulation of gap junctional communication, modulation of DNA repair mechanisms, induction of detoxifying enzymes, and filtering of blue light (Krinsky and Johnson, 2005). The principal carotenoids found in foods are b-carotene, a-carotene, b-cryptoxanthin, lycopene, lutein, and zeaxanthin (Figure 28.1). These carotenoids are also the most commonly found in human plasma and have been the most studied in terms of health benefits. The highly unsaturated carotenoids are prone to geometric isomerization and oxidation (Rodriguez-Amaya, 1999). Losses during home preparation and industrial processing have been widely reported, and instability of carotenoids is a major concern in maintaining the food color and the beneficial effects on health. These losses are due to physical removal and enzymatic or nonenzymatic oxidation. Oxidative degradation depends on the availability of oxygen; is stimulated by light, heat, metals, enzymes, and peroxides; and is inhibited by antioxidants. It is known to increase with the destruction of the food cellular structure, surface area or porosity, duration and severity of the processing conditions, duration and temperature of storage, and with use of packaging permeable to oxygen and light. Enzymatic oxidation occurs prior to heat treatment, during peeling, slicing, pulping, or juicing. 302

Initial stages of oxidation involve epoxidation and cleavage to apocarotenals (Figure 28.2). Subsequent fragmentations result in compounds with low molecular masses. Now devoid of the color and biological activity attributed to carotenoids, these compounds can give rise to desirable flavor or off-flavor. Isomerization of all-E(trans)-carotenoids, the usual configuration in nature, to the Z(cis)isomers occurs along with oxidation (see Figure 28.2). It is promoted by acids, heat, and light, and it results in loss of provitamin A activity and alteration of bioavailability and metabolism. As with the all-E-isomers, the Z-carotenoids are subject to oxidation. For a long time, the major concern about carotenoids in food processing was minimizing their degradation. In more recent years, processing (i.e., mechanical matrix disruption and/ or heat treatment) has been shown to enhance bioavailability (i.e., the fraction of the carotenoid ingested that becomes available for utilization in normal physiological functions or for storage in the human body) (Rock et al., 1998). It softens or breaks membranes and cell walls and denatures proteins complexed with carotenoids, facilitating the release of these compounds from the food matrix during digestion. Processing conditions should therefore be optimized to increase bioavailability without provoking significant degradation of the carotenoids. In this chapter, the carotenoid compositions of three major staple foods consumed by millions of people in many countries, especially developing countries, are reviewed, along with their possible use in the fortification of flour and bakery products.

CAROTENOIDS OF SWEET POTATO (IPOMOEA BATATAS LAM.) Carotenoids in roots and flour All-E-b-carotene is the major carotenoid of sweet potatoes. The orange-fleshed varieties of sweet potato (OFSP) have this carotenoid almost exclusively and in considerable amounts.

CHAPTER 28 Carotenoids of Sweet Potato, Cassava, and Maize





Lycopene OH



Lutein OH



FIGURE 28.1 Structures of carotenoids demonstrated to be important to human health. Although there are many different carotenoids (approximately 100) in food, b-carotene, a-carotene, b-cryptoxanthin, lycopene, lutein, and zeaxanthin are major food carotenoids. They are also the carotenoids commonly encountered in human plasma and have been the most studied and demonstrated to be important in terms of human health.

Other carotenoids (e.g., lutein and b-carotene epoxides) have comparatively higher levels in the lighter colored sweet potatoes, but b-carotene still predominates (Kimura et al., 2007). The b-carotene concentration of sweet potato varies considerably (Table 28.1), from less than 1 mg/g in white-fleshed roots to more than 130 mg/g in OFSP. Unfortunately, the white-fleshed sweet potatoes are the most commonly consumed in Africa, Asia, and Latin America. Aside from the remarkable varietal differences, the carotenoid content is also influenced by such factors as root age and production site (K’osambu et al., 1998). Structurally, vitamin A (retinol) is essentially half of the molecule of b-carotene. This carotenoid is the most potent provitamin A; it is also the most widely distributed carotenoid

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trans-Carotenoids Acids, light, heat Enzyme, heat, light, metals, pro-oxidants



O2, heat, light, metals, pro-oxidants Epoxycarotenoids Apocarotenoids

Low mass compounds

FIGURE 28.2 Possible scheme for the degradation of carotenoids. During processing and storage of food, carotenoids undergo isomerization from the trans-form to the cis-form, with both forms being oxidized to epoxycarotenoids and apocarotenoids. A series of fragmentations then occur forming small compounds, which no longer have the color and the biological activities of carotenoids. Source: Reproduced with permission from Rodriguez-Amaya, D. B. (1999). Changes in carotenoids during processing and storage of foods. Arch. Latinoam. Nutr. 49, 38Se47S.

in foods. The minimum requirement for a carotenoid to have provitamin A activity is an unsubstituted b-ring with a polyene chain of 11 carbon atoms. Thus, a-carotene and b-cryptoxanthin have approximately 50% of the activity of b-carotene. 304

Sweet potatoes are commonly consumed as boiled roots, but in Africa they are traditionally sun-dried for consumption during the dry season when the fresh roots are not available (Bechoff et al., 2009). The roots are crushed or chipped and then dried for several days. The dried product can be rehydrated or milled into flour to be used as porridge. In urban areas, the sweet potato flour can be used to partially replace wheat flour in a variety of baked products.

TABLE 28.1 b-Carotene Content of Sweet Potato Rootsa Origin of Samples Hawaii




Description of Samples

b-Carotene Content (mg/g Fresh Root)b

4 purple-fleshed varieties 7 yellow/white-fleshed varieties 7 orange-fleshed varieties 6 white cultivars 3 cream cultivars 7 pale orange to orange cultivars 9 white, white/yellow cultivars 7 cream, cream/yellow cultivars 7 light yellow, white/yellow cultivars 6 light to deep orange cultivars 6 yellow- and orange-fleshed cultivars

10e50 10e60 67e131 <1 1e10 10e80 <1 20e110 1e10 21e63 12e109

Reference Huang et al. (1999)

K’osambu et al. (1998)

Hagenimana et al. (1999)

Kidmose et al. (2007)

a The color of sweet potato varies from white to deep orange. The content of b-carotene, the provitamin A carotenoid responsible for the color, varies from <1 to 131 mg/g fresh root. b All-E-b-carotene with traces of Z-b-carotenes.

CHAPTER 28 Carotenoids of Sweet Potato, Cassava, and Maize

Several research groups have reported variable carotenoid losses in the production of sweet potato flour, which are affected by the variety utilized, the size and shape of the pieces submitted to drying, and the drying method and condition. Hagenimana et al. (1999) found that drying sweet potato slices in a forced-air oven at 60 C for 12 h reduced the total carotenoid content by 30%. Storing the dried chips in opaque paper bags at ambient conditions for 11 months resulted in a 10% loss. Van Jaarsveld et al. (2004) achieved better b-carotene retention with oven drying compared to sun drying, with the latter provoking greater degradation than drying in the shade. Drying thicker slices retained more b-carotene. Lower retention in open-air sun drying is apparently due to the destructive effect of direct sunlight and the uncontrolled environmental conditions, including greater and more prolonged exposure to oxygen. Kidmose et al. (2007) observed that shade drying of chips resulted in a significant reduction of all-E-b-carotene (approximately 21%), which was further reduced when flour was produced from the chips. Bechoff et al. (2009) reported that all-E-b-carotene losses in flour made from dried chips varied between 16 and 34% under different drying treatments. Hot air cross-flow drying retained significantly more provitamin A than open-air sun drying, but drying in a greenhouse solar dryer and sun drying did not result in significantly different provitamin A retention. The shape of the sweet potato pieces (chip or crimped slice) influenced retention during sun drying, with the crimped slices retaining more provitamin A. Bengtsson et al. (2008) found that drying slices of OFSP at 57 C in a forced-air oven for 10 h reduced the all-E-b-carotene content by 12%. Contrary to Bechoff et al.’s results, solar and sun drying yielded markedly different losses of 9 and 16%, respectively.

Application in the fortification of flour and bread The nutritional quality of bakery products is low because of the inferior nutritional composition of the wheat grain, accentuated by the use of refined flours as the ingredient (Chavan and Kadam, 1993). Substitution of part of the wheat flour with non-wheat flours has been advocated for nutritional enrichment of these products and to reduce cost, utilizing local raw materials preferentially. Although most research has focused on increasing the protein content, the addition of carotenoid-rich flours is now being suggested. Van Hal (2000) extensively reviewed the quality of sweet potato flour, including literature that is not easily accessible, such as reports, proceedings, and pamphlets. Some of the important findings are as follows: l




Processing sweet potato into flour improves shelf life and makes it easier to incorporate into food products. Because of its distinct properties, the use of sweet potato flour in the preparation of bread is restricted, with most researchers reporting substitution of 10e15% of wheat flour with sweet potato flour on a dry weight basis as most acceptable. For other baked products, especially sweet baked products, higher proportions (10e100%) of sweet potato flour can be used. Acceptability depends on the sensory evaluation of the flour, with color, odor, and a high degree of whiteness being the most important marketing quality factors. When made from OFSP, the flour has a high content of b-carotene and reasonable levels of vitamin C, calcium, phosphorus, iron, and potassium.

Utilization of OFSP as a means of alleviating vitamin A deficiency in developing countries has gained impetus with the launching of the VitaAfrica and HarvestPlus biofortification programs. Biofortification has been defined as the development of micronutrient-dense staple crops using the best traditional breeding practices and modern biotechnology (Nestel et al., 2006). The potential to increase the micronutrient density of staple foods by conventional breeding is best exemplified in sweet potatoes, for which lines with high levels of b-carotene (>200 mg/g) have been identified.


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Studies in South Africa (van Jaarsveld et al., 2005) and Mozambique (Low et al., 2007) demonstrated that the consumption of biofortified OFSP significantly increased the vitamin A status of children. Rangel et al. (2008) reported that English cake formulations in which the wheat flour was mixed with OFSP flour (10 or 20%) produced cakes with smaller volume, a more round shape, darker color, and characteristic sweet potato flavor but that were as acceptable as the standard cakes. Cookies were also prepared with the substitution of 10, 30, and 50% wheat flour with OFSP flour or pumpkin flour (Siciliano et al., 2009). Substitution of 30% of wheat flour with OFSP flour was significantly preferred, obtaining the highest score for intention to purchase. Because an adequate gluten formation is necessary to keep the quality of bread, Rangel et al. (2008) evaluated the use of biofortified sweet potato flour (10, 20, and 30%) in the production of bread (sandwich loaves). It was observed that the bread loaves produced with OFSP flour had smaller final volumes and darker color with characteristic flavor, with the changes in the loaves’ characteristics being accentuated by an increase in the OFSP flour level. The loaves with 10% substitution with OFSP better resembled the standard bread. Despite the differences, all the loaves produced with OFSP flour were considered as acceptable for consumption as the standard loaves. The possibility of producing expanded snacks by extrusion using different proportions of OFSP and polished rice flours (15:85, 30:70, and 45:55) was investigated by Silva et al. (2008), with the objective of increasing the product’s shelf life and offering low-cost processed biofortified products. The snacks with 30% OFSP flour presented high water solubility index and viscosity characteristics, indicating that they could be used in other products (e.g., soups). Although the expansion indexes were low, the snacks presented good sensory characteristics such as excellent flavor.


CAROTENOIDS OF CASSAVA (MANIHOT ESCULENTA CRANTZ) Carotenoids in roots and flour The roots of currently used varieties of cassava are of poor nutritional quality, having very low concentrations of carotenoids, iron, zinc, and protein, and they also contain toxic cyanogens. The major carotenoid is also all-E-b-carotene, but unlike sweet potato, in which the Z-isomers are present in only trace amounts, cassava roots have appreciable levels of Z-b-carotenes (Kimura et al., 2007). The total b-carotene concentration varies from nondetectable in the white-fleshed roots to only approximately 5 mg/g in yellow-fleshed cassava (Table 28.2). Using chips from the three cassava cultivars listed in Table 28.2, the average b-carotene retention was higher in oven drying (72%) than in shadow drying (59%), sun drying (38%), and gari production (34%) (Cha´vez et al., 2007). The level of this carotenoid dropped further TABLE 28.2 b-Carotene Content of Cassava Rootsa Origin of Samples Australia Colombia India


Description of Samples 5 cultivars 3 cultivars 11 faint yellow to yellow exotic lines 10 faint yellow to yellow indigenous lines

b-Carotene Content (mg/g Fresh Root)b


0.2e3.0 3.8e4.9 0.4e3.1

Adewusi and Bradbury (1993) Cha´vez et al. (2007) Moorthy et al. (1990)


The color of cassava root varies from white to yellow. The b-carotene of the yellow cassava varies from about 0.2 to 4.9 mg/g fresh root. All-E-b-carotene with appreciable amounts of Z-b-carotenes.


CHAPTER 28 Carotenoids of Sweet Potato, Cassava, and Maize

during storage in regular plastic bags at ambient temperature, with the retention after 4 weeks of storage being approximately 18% in sun-dried chips and in sun-dried chips stored as flour.

Application in the fortification of flour and bread Cassava tubers have to undergo immediate processing after harvest because they deteriorate within 24 h. A versatile crop, different processing techniques have been developed and are shown in Figure 28.3. The fortification of gari and flour with vitamin A, B vitamins, iron, iodine, zinc, and calcium was recommended by Asonye (2001). Gari is considered the most practical product for fortification because it is cheap, easy to prepare, palatable, and suitable for mechanical processing in an industrial setup. It is a fermented, roasted, granular meal that is regularly consumed by urban and rural populations. Fortification of gari and flour with b-carotene also appears feasible. Rangel et al. (2008) used cassava flour in cake formulations. As for cakes with the OFSP flour, the cakes with cassava flour were acceptable but with smaller volume. Because it does not have strong characteristic flavor and color, a greater substitution (20%) of this flour resulted in cakes similar to the standard cake. Evaluating the possibility of producing nonexpanded products by extrusion (pellets) using biofortified cassava flour, Silva et al. (2008) concluded that, according to the extrusion parameters studied (particle size, water absorption index, water solubility index, and viscosity), the production of pellets using a biofortified raw material is feasible.


FIGURE 28.3 Schematic representation of cassava processing into different food and feed products. Cassava is a very versatile crop. The leaves can be eaten boiled or fried or transformed into meal or pellets for animal feed. The root can be processed into flour, chips, or starch. The peel can also be used as feed. Source: Reproduced from the Organisation for Economic Co-operation and Development (2009).

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TABLE 28.3 Carotenoid Contents (mg/g Dry Kernel) of Maize Grainsa Origin of Samples

Description of Samples





Brazil United States

3 cultivars 44 genotypes

1.5e3.6 NDe28

4.0e5.6 0.01e7.7

1.2e1.7 0.08e2.45

1.2e1.6 0.09e7.6

United States

41 genotypes




Reference Kimura et al. (2007) Kurilich and Juvik (1999) Ibrahim and Juvik (2009)

The table shows the variation in the carotenoid contents of some maize cultivars/genotypes, with lutein and/or zeaxanthin as the major carotenoids. The provitamin A carotenoids b-carotene and b-cryptoxanthin are present at low levels. ND, not detected.

CAROTENOIDS OF MAIZE (ZEA MAYS L.) Carotenoids in kernels and flour Yellow maize naturally contains the xanthophylls lutein and zeaxanthin as major carotenoids, with much lower levels of the provitamin A carotenoids b-carotene and b-cryptoxanthin. The concentrations of the different carotenoids vary markedly among maize genotypes: not detected to 28 mg/g lutein, 0.01e8.1 mg/g zeaxanthin, 0.08e2.45 mg/g b-cryptoxanthin, and 0.09e7.65 mg/g b-carotene (Table 28.3). Lutein and zeaxanthin make up the yellow pigment in the macula of the human retina and are believed to be responsible for the protective effect of carotenoids against macular degeneration and cataract, acting as antioxidants and filters of high-energy blue light (Krinsky and Johnson, 2005). Lutein and especially zeaxanthin are not widely distributed in foods. Maize and maize products are among the few foods with high levels of these important xanthophylls. 308

An average of 36% loss of provitamin A was observed following nixtamalization and subsequent snack preparation by deep-frying (Lozano-Alejo et al., 2007). The traditional nixtamalization in Mexico and Central America is the cooking and steeping of maize kernels in an aqueous suspension of calcium hydroxide. It is a central step in the conversion of maize grain to dough and ultimately to maize flour, snacks, and tortillas.

Application in the fortification of flour and bread Because the focus is micronutrient deficiency, biofortification has been directed to increasing the provitamin A content of maize. Considering the important role of lutein and zeaxanthin in health and their infrequent occurrence in commonly consumed foods, maize and maize products being principal dietary sources, it is imperative that elevation of the provitamin A level be achieved not at the expense of these xanthophylls. This means increasing the levels of all carotenoids, not by blocking the formation of lutein and zeaxanthin so as to accumulate b-carotene and b-cryptoxanthin. Aside from conventional breeding, generation of transgenic maize with enhanced provitamin A content in its kernels has been pursued in recent years. Overexpression of the bacterial genes for phytoene synthase and the enzymes (phytoene desaturase and z-carotene desaturase) that catalyze the four desaturation steps of the carotenoid pathway resulted in an increase in total carotenoids up to 34-fold with preferential accumulation of b-carotene in the maize endosperm (Aluru et al., 2008). The high b-carotene trait was found to be reproducible over at least four generations. Gene expression analyses indicated that upregulation of the endogenous lycopene b-cyclase was responsible for the accumulation of b-carotene. The retention of b-carotene in a high b-carotene (10 mg/g) maize during traditional African household cooking was investigated by Li et al. (2007). The cumulative losses in the final

CHAPTER 28 Carotenoids of Sweet Potato, Cassava, and Maize

cooked products were 24% for fermented porridge (ogi) and 25% for the unfermented porridge. The traditional preparation of ogi involves soaking of dried whole maize kernels, milling, addition of water to form a wet flour or dough, and spontaneous fermentation (24e72 h). The ogi is then cooked with added water to prepare the porridge. Cookies were prepared from blends of soybean (10e90%) and maize flours (Akubor and Onimawo, 2003). The soybean flour had higher protein, fat, crude fiber, and ash contents than the maize flour. The soybean flour/maize flour blends possessed good water and oil absorption capacities, foaming capacity, and foam stability in relation to the maize flour. The emulsion activity of the blends was also dependent on soybean flour, whereas bulk density increased with the level of maize flour. Cookies prepared from the blends of 60% soybean flour and 40% maize flour were judged most acceptable. Above 60% soybean substitution levels, the sensory scores for overall acceptability and all sensory qualities evaluated (color, flavor, taste, and texture) except taste decreased steadily. Silva et al. (2008) studied the production of snacks made with bean and maize flours at different proportions (15:85; 30:70, and 45:55) by extrusion. The products were characterized by particle size, water absorption index, water solubility index, viscosity, expansion index, and density. Snacks with 45% of bean flour presented the lowest water solubility index because of a reduction of the starch content and an increase of proteins; however, they showed high water absorption index and could therefore be recommended to prepare instant products using less water at room temperature. The high expansion index obtained with all formulations resulted in pleasant taste and color. In accordance with the extrusion parameters, the use of biofortified maize flour may be recommended for the production of these snacks.

TECHNOLOGICAL ISSUES A major problem in fortification with carotenoids is their instability. Processing conditions should be optimized to ensure good retention of these compounds. This includes processing immediately after peeling, cutting, or maceration; minimum processing time and temperature; protection from light; and exclusion of oxygen. The heat treatment in blanching may provoke losses of carotenoids, but inactivation of oxidative enzymes will prevent further and greater losses during slow processing (as in drying) and storage.






Fortification with the three staple foods reviewed in this chapter is at different stages of development. For all three crops, nutrition education appears to be needed to promote acceptability, considering the current preference for varieties devoid of color in many countries. For OFSP, varieties with considerable amounts of all-E-b-carotene are available; however, for cassava and maize, enhancing the provitamin A content is still being pursued, especially by biofortification, although adding b-carotene to cassava flour may be an alternative. Carotenoid losses during processing and storage of the flours emphasize the need for using optimized conditions. The use of carotenoid-rich or biofortified flours in a variety of products has been shown to be technologically feasible; carotenoid retention during these processes needs to be demonstrated.

References Adewusi, S. R. A., & Bradbury, J. H. (1993). Carotenoids in cassava: Comparison of open-column and HPLC methods of analysis. Journal of the Science of Food and Agriculture, 62, 375e383. Akubor, P. I., & Onimawo, I. A. (2003). Functional properties and performance of soybean and maize flour blends in cookies. Plant Foods For Human Nutrition, 58, 1e12.


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Aluru, M., Xu, Y., Guo, R., Wang, Z., Li, S., White, W., et al. (2008). Generation of transgenic maize with enhanced provitamin A content. Journal of Experimental Botany, 59, 3551e3562. Asonye, C. C. (2001). Fortification of common Nigerian food-cassava meals. Food and Nutrition Bulletin, 22, 423e426. Bechoff, A., Dufour, D., Dhuique-Mayer, C., Marouze´, C., Reynes, M., & Westby, A. (2009). Effect of hot air, solar and sun drying treatments on provitamin A retention in orange-fleshed sweet potato. Journal of Food Engineering, 92, 164e171. Bengtsson, A., Namutebi, A., Larsson Alminger, M., & Svanberg, U. (2008). Effects of various traditional processing methods on the all-trans-b-carotene content of orange-fleshed sweet potato. Journal of Food Composition and Analysis, 21, 134e143. Chavan, J. K., & Kadam, S. S. (1993). Nutritional enrichment of bakery products by supplementation with nonwheat flours. Critical Reviews in Food Science and Nutrition, 33, 189e226. Cha´vez, A. L., Sa´nchez, T., Rodriguez-Amaya, D. B., Nestel, P., Tohme, J., & Ishitani, M. (2007). Retention of carotenoids in cassava roots submitted to different processing methods. Journal of the Science of Food and Agriculture, 87, 388e393. Hagenimana, V., Carey, E. E., Gichuki, S. T., Oyunga, M. A., & Imungi, J. K. (1999). Carotenoid contents in fresh, dried and processed sweet potato products. Ecology of Food and Nutrition, 37, 455e473. Huang, A. S., Tanudjaja, L., & Lum, D. (1999). Content of alpha-, beta-carotene, and dietary fiber in 18 sweet potato varieties grown in Hawaii. Journal of Food Composition and Analysis, 12, 147e151. Ibrahim, K. E., & Juvik, J. A. (2009). Feasibility for improving phytonutrient content in vegetable crops using conventional breeding strategies: Case study with carotenoids and tocopherols in sweet corn and broccoli. Journal of Agricultural and Food Chemistry, 57, 4636e4644. Kidmose, U., Christensen, L. P., Agili, S. M., & Thilsted, S. H. (2007). Effect of home preparation practices on the content of provitamin A carotenoids in coloured sweet potato varieties (Ipomoea batatas Lam.) from Kenya. Innovative Food Science and Emerging Technologies, 8, 399e406. Kimura, M., Kobori, C. N., Rodriguez-Amaya, D. B., & Nestel, P. (2007). Screening and HPLC methods for carotenoids in sweet potato, cassava and maize for plant breeding trials. Food Chemistry, 100, 1734e1746. K’osambu, L. M., Carey, E. E., Misra, A. K., Wilkes, J., & Hagenimana, V. (1998). Influence of age, farming site, and boiling on pro-vitamin A content in sweet potato (Ipomoea batatas (L.) Lam.) storage roots. Journal of Food Composition and Analysis, 11, 305e321.


Krinsky, N. I., & Johnson, E. J. (2005). Carotenoid actions and their relation to health and disease. Molecular Aspects of Medicine, 26, 459e516. Kurilich, A. C., & Juvik, J. A. (1999). Quantification of carotenoid and tocopherol antioxidants in Zea mays. Journal of Agricultural and Food Chemistry, 47, 1948e1955. Li, S., Tayie, F. A. K., Young, M. F., Rocheford, T., & White, W. S. (2007). Retention of provitamin A carotenoids in high b-carotene maize (Zea mays) during traditional African household processing. Journal of Agricultural and Food Chemistry, 55, 10744e10750. Low, J. W., Arimond, M., Osman, N., Cunguara, B., Zano, F., & Tschirley, D. (2007). A food-based approach introducing orange-fleshed sweet potatoes increased vitamin A intake and serum retinal concentrations in young children in rural Mozambique. Journal of Nutrition Community and International Nutrition, 137, 1320e1327. Lozano-Alejo, N., Carrillo, G. V., Pixley, K., & Palacios-Rojas, N. (2007). Physical properties and carotenoid content of maize kernels and its nixtamalized snacks. Innovative Food Science & Emerging Technologies, 8, 385e389. Moorthy, S. N., Jos, J. S., Nair, R. B., & Sreekumari, M. T. (1990). Variability of b-carotene content in cassava germplasm. Food Chemistry, 36, 233e236. Nestel, P., Bouis, H. E., Meenakshi, J. V., & Pfeiffer, W. (2006). Biofortification of staple food crops. Journal of Nutrition, 136, 1064e1067. Organisation for Economic Co-operation and Development (2009). Consensus Document on Compositional Considerations for New Varieties of Cassava (Manihot esculentaCrantz): Key Food and Feed Nutrients, Antinutrients, Toxicants and Allergens. Accessed December 2009. Rangel, C. N., Watanabe, E., Carvalho, J. L. V., Nutti, M. R., & Silva, E. M. M. (2008). Development of Cake and Bread Formulations Using Cassava (Manihot esculenta L.) and Sweet Potato (Ipomoea batatas L.) Flours: An Application for Biofortified Crops. Shanghai, China: Paper presented at the 14th World Congress of Food Science and Technology. Rock, C. L., Lovalvo, J. L., Emenhiser, C., Ruffin, M. T., Flatt, S. W., & Schwartz, S. J. (1998). Bioavailability of b-carotene is lower in raw than in processed carrots and spinach in women. Journal of Nutrition, 128, 913e916. Rodriguez-Amaya, D. B. (1999). Changes in carotenoids during processing and storage of foods. Archivos Latinoamericanos de Nutricio´n, 49, 38Se47S. Siciliano, I., Silva, E. M. M., Silva, J. B. C., Ramos, S. R. R., Deliza, R., Carvalho, J. L. V., et al. (2009). Prefereˆncia de Biscoitos Elaborados com Farinha de Batata-doce de Polpa Alaranjada e Biscoitos com Farinha de Abo´bora. Rio de Janeiro, Brazil: Paper presented at the I Congresso Brasileiro do Processamento de Frutas e Hortalic¸as.

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Silva, E. M. M., Ascheri, J. L. R., Carvalho, J. L. V., Nutti, M. R., Watanabe, E., & Rangel, C. N. (2008). Production of Expanded and Nonexpanded Snacks Using Biofortified Sweet Potato (Ipomoea batatas L.), Cassava (Manihot esculenta L.) and Maize (Zea mays L.). Shanghai, China: Paper presented at the 14th World Congress of Food Science and Technology. van Hal, M. (2000). Quality of sweet potato flour during processing and storage. Food Reviews International, 16, 1e37. van Jaarsveld, P. J., Marais, D. W., Harmse, E., Laurie, S. M., Nestel, P., & Rodriguez-Amaya, D. B. (2004). BetaCarotene Content of Sun-Dried and Oven-Dried Chips of Orange-Fleshed Sweet Potato. Lima Peru: Paper presented at the XXII IVACG Meeting. van Jaarsveld, P. J., Faber, M., Tanumihardjo, S. A., Nestel, P., Lombard, C. J., & Spinnler Benade´, A. (2005). J. b-Carotene-rich orange-fleshed sweet potato improves the vitamin A status of primary school children assessed with the modified-relative-dose-response. American Journal of Clinical Nutrition, 81, 1080e1087.