As stated in 3.2; species, and genotypes/cultivars can have a unique composition of phytonutrients. Natural variation in many crop species has led to selection of a variety of speciality cultivars, for example in tomato, pepper, and lettuce with different colour, taste and fragrance. These differences are often the result of a difference in secondary metabolites, and phytonutrients. In corn, for example, β-Carotene and β-cryptoxanthin are the most abundant provitamins A while α-carotene is present in much smaller amounts. However, the carotenoid composition has considerable variation in the ratio of total provitamins A to total carotenoid concentrations, as well as in the ratio of b-carotene to b-cryptoxanthin. Natural variation for total provitamin A concentration in corn is considerable (about 0–15 mg/g within HarvestPlus; and 0 to almost 9 mg/g at CIMMYT), thus making corn a breeding target for enhanced provitamin A concentration and improved nutritional value.
Certain organic compounds stimulate the absorption of essential mineral elements by humans. These include ascorbate (vitamin C), b-carotene (pro-vitamin A), protein cysteine and various organic and amino acids. Also, here there is considerable intra-specific variation in both ascorbate and b-carotene concentrations in fruit and vegetables (e.g. Figure 5.12).
Figure 5.12: Absolute levels of all-trans lycopene levels (A) and relative levels of rutin (B) in ripe fruits of 94 different tomato cultivars. From each cultivar, 6 plants were grown in a greenhouse and about 20 ripe fruits were harvested and pooled. Dedicated extraction and HPLC analysis of compounds were performed. For (C) the method was similar but then applied on lettuce. Seeds were obtained from the Centre of Genetic Resources in The Netherlands (CGN) and plants simultaneously grown in the same greenhouse in Wageningen. At harvest, per plant 3 leaves were pooled in liquid nitrogen and analysed for (reduced) vitamin C using HPLC-PDA. (Copied from: De Vos et al. 2011)
As discussed in earlier chapters absorption of Fe, Zn and Ca by the gut is limited by the antinutrients phytate and tannins. Phytate occurs widely in plant tissues but is concentrated in seeds or grain. There is considerable intra-specific variation in phytate concentration in edible portions that is independent of variation in Fe and Zn concentrations. In addition, as reviewed by White and Broadley (2005) several low phytic acid (lpa) mutants have been produced by non-transgenic techniques in rice, maize, wheat, barley and soybean. Hence, breeding for reduced concentrations of these antinutrients appears feasible.
De Vos RCH, Hall RD, Moing A. 2011. Metabolomics of a Model Fruit: Tomato. DOI: 10.1002/9781444339956.ch5
White PJ, Broadley MR. 2005. Biofortifying crops with essential mineral elements. 10. DOI: 10.1016/j.tplants.2005.10.001.