Comparison of Zn accumulation and speciation in kernels of sweetcorn and maize differing in maturity

Abstract

Background and Aims Understanding the speciation of Zn in edible portions of crops helps identify the most effective biofortification strategies to increase the supply of nutrients for improving the health and nutrition of consumers. Methods Kernels of 12 sweetcorn and three maize (Zea mays) varieties were analysed for Zn concentration and content. The speciation of the Zn in the embryos, endosperms and whole kernels at 21, 28 and 56 days after pollination (DAP) was then examined for one maize and one sweetcorn variety using synchrotron-based X-ray absorption spectroscopy (XAS). Key Results Averaged across all sweetcorn and maize varieties at 21 DAP, the embryo contributed 27–29% of the whole kernel Zn whilst the endosperm contributed 71–73 %. While sweetcorn embryos contributed a lower proportion to the total kernel Zn than those of maize, the proportion of total Zn in the embryo increased as kernels aged for both varieties, reaching 33 % for sweetcorn and 49% for maize at 28 DAP. Using XAS, it was predicted that an average of 90 % of the Zn in the embryos was present as Zn-phytate, while in the endosperm the Zn was primarily complexed with an N-containing ligand such as histidine and to a lesser extent with phytate. However, in maize endosperms, it was also observed that the proportion of Zn present as Zn-phytate increased as the kernel matured, thereby also probably decreasing its bioavailability in these mature maize kernels. Conclusions The apparent low bioavailability of Zn supplied in maize at its consumption stage (i.e. mature kernels) probably undermines the effectiveness of biofortification of this crop. Conversely, successful biofortification of Zn in sweetcorn and green maize consumed as immature kernels could potentially provide a good source of bioavailable Zn in human diets.

Variation in zinc concentration of sweetcorn kernels reflects source–sink dynamics influenced by kernel number

“…In this study, the trends in Zn concentration and Zn content of embryo tissue and the rest of the kernel as the kernels mature on a well pollinated cob of sweetcorn were similar to those observed in earlier studies ( Cheah et al , 2020 ). We showed that the ratio of Zn content in the embryo to Zn content in the rest of the kernel was constant irrespective of the established kernel number, suggesting that there was no preferential storage of Zn in either tissue with increasingly constrained Zn supplies.…”

Effect of maize processing methods on the retention of minerals, phytic acid and amino acids when using high kernel-zinc maize

“…Post-harvest management and cooking processes can affect the vitamin, mineral and amino acid composition in the final product as compared to raw kernels ( Taleon et al., 2017 ). Since the majority of zinc is located in the maize embryo and pericarp ( Cheah et al., 2020 ) processes that remove large quantities of these two grain structures could reduce the zinc content in the final food product, even below to 10 ​ppm ( Bevis and Hestrin, 2020 ). Processes where not much embryo or pericarp is removed yields high zinc retention ( Bressani et al., 2004 ).…”

Genetic and agronomic biofortification of zinc in sweetcorn

“…In this study, the trends in Zn concentration and Zn content of both embryo and other kernel constituents as the kernels mature on a well-pollinated cob of sweetcorn were similar to those observed in earlier studies (Cheah et al, 2020). We showed that the ratio of Zn contents in the embryo compared to the rest of the kernel was constant irrespective of established kernel number, suggesting there was no preferential storage of Zn in either tissue with increasingly constrained Zn supply.…”

“…Having established the suitability of sweetcorn as a target crop for Zn biofortification, this chapter explores the interactions between genotype and environment that influence the Zn concentration in sweetcorn kernels. Although there is reported data on Zn concentration in mature maize kernels (Lin et al, 2005, Long et al, 2004, Oikeh et al, 2004, few studies have examined Zn concentration in immature kernels of sweetcorn (Warman and Havard, 1998, Cheah et al, 2019a, Cheah et al, 2019b, Cheah et al, 2020. The aim of this study was to quantify immature kernel Zn concentrations across a range of commercial yellow sweetcorn varieties, and contrast this with concentrations in other Zea mays germplasm, including starchy maize lines.…”