Swiss Federal Institute of Technology ETH Zurich, Zurich, Suiza
Introduction: Zinc biofortification through conventional breeding aims to increase the content of zinc in staple food crops such as rice, maize, wheat and pearl millet. Zinc-biofortified staple foods show promise to improve zinc intakes when consumed by zinc-deficient populations. Development In a study in Zambian children, the substitution of biofortified (34 μg zinc/g grain) for control maize (21 μg zinc/g) was adequate to meet their zinc physiologic requirements. Absorption of zinc (mg/day) from the biofortified maize (1.1 ± 0.5) was higher than for the control maize (0.6 ± 0.2) (P = 0.0001) (1). Another study examined the absorption of zinc from biofortified pearl millet in young Indian children (2). The mean (± SD) quantities of zinc absorbed from test and control groups were 0.95 ± 0.47 and 0.67 ± 0.24 mg/d, respectively (P = 0.03). The authors concluded that the zinc absorbed from zinc biofortified pearl is more than adequate to meet the physiological zinc requirements for young children (2). It appears that foliar application of Zn in rice offers a practical and useful approach to improve bioavailable Zn in polished rice (3). Jou et al. (4) described a Caco-2 cell model to assess Zn bioavailability from staple foods to guide selection/breeding, and measured Zn bioavailability from conventional rice varieties and one Zn-biofortified rice in a rat pup model in vivo. Absorbed Zn (μg/g rice) was significantly higher from the biofortified rice in both the in vitro Caco-2 cell model (2.1-fold) and the rat pup model (2.0-fold) (4). Cakmak et al. (5) conducted field experiments of soil and foliar application of Zn to wheat. Soil Zn application was effective in increasing grain Zn concentration in the Zn-deficient but not in the Zn-sufficient fields. In all locations, foliar application of Zn significantly increased Zn concentration in whole grain and in each grain fraction. The increase in Zn concentration was pronounced when Zn was sprayed at the late growth stage (5). Arsenault et al. (6) used dietary assessment combined with simulation models and suggested that dietary zinc inadequacy among children and women in rural Bangladesh could be reduced by zinc biofortification of rice. In a study in Mexican women, Rosado et al (7) measured the increase in quantity of Zn absorbed after consumption of wheat biofortified with Zn, and related this to overall dietary Zn and phytate. The biofortified (41 mg Zn/g) or control (24 mg Zn/g) wheat meals were labeled with Zn stable isotopes and fed over two days. Zn intake from the biofortified wheat meals was 5.7 mg/d (72%) higher at 95% extraction (P < 0.001) and 2.7 mg/d (68%) higher at 80% extraction compared with the corresponding control wheat (P = 0.007). Mean Zn absorption from the biofortified wheat meals was 2.1 and 2.0 mg/d for 95 and 80% extraction, respectively, 0.5 mg/d higher than for the control wheat (P < 0.05). Recent unpublished data from the ETH Zurich indicates that intrinsically and extrinsically labeled zinc is equally bioavailable from wheat. Also, results will soon be available from a large school-based efficacy trial of Zn biofortified wheat in Indian children. Conclusions Several variables will determine the ultimate success or failure of biofortification with Zn of staple crops (8). These include: a) the amount of Zn that can be bred into the staple food; b) the amount that remains after usual processing methods; c) the Zn bioavailability from the biofortified food in the setting of the habitual diet; d) the complementary strategy of reduction of the phytate content; and e) the ability to disseminate Zn biofortified crop varieties and the willingness of farmers to adopt them. Key words zinc, biofortification, deficiency, micronutrient, wheat, rice, millet. References 1. Chomba et al. J Nutr 2015;145(3):514- 9. 2. Kodkany BS et al. J Nutr 2013;143(9):1489-93. 3. Wei Y et al. PLoS One 2012;7(9):e45428. 4. Jou MY et al. J Agric Food Chem 2012;60(14):3650-75. Cakmak I et al. J Agric Food Chem 2010;58(16):9092-102. 6. Arsenault JE et al. J Nutr 2010;140(9):1683-90. 7. Rosado JL et al. J Nutr 2009;139(10):1920-5. 8. Hotz C et al. Food Nutr Bull 2009;30(1 Suppl):S172-8.