Zinc Bioavailability In Rice Grain And Ergulation Mechanisms

Zinc (Zn) deficiency is a well documented global public health problem, affecting nearly half of the world population, particular in developing countries, where high proportion of cereal crops consumed as a staple food. Rice (Oryza stavia L.), is one of the leading staple crop for half of the world’s population and, hence, is the main source of Znto human. Therefore, it’s important to investigate the mechanisms of rice gain Zn bioavailability in term of human nutritioa The current study was aimed to establish Caco-2cell model to assess the Znbioavailability from rice grain. Using this model we evaluate the effect of genotype, different agricutrual practices (foliar Zn ferilization, application of phosphorus and foliar Zn ferilizaion, application of sulfur and Zn ferilization) and grain processing technology (germination and zinc fortification) on Zn bioavailability. The main results are summarized as below:1. The performance of Caco-2cell cultured in our laboratory was assessed, and using this model we investigate the effect of dietary ligands on Zn uptake by cell line. Caco-2cells50000cells/cm2were seeded in to the polycarbonate microporal mebrane in transwell bichambers. After21days of culture, the transepithelial electrical resistance value was630Q. cm2. The activity of alkaline phosphatase in apical side of Caco-2cell layer was significantly higher than that of basolateral side. These results indicated that Caco-2cells cultured in our laboratory had similar to the intestinal epithelial cells in morphologically, formed well tight junctions and produced polarity, and could be used as an in vitro model to investigate absorption mechanisms of nutrients. Using this Caco-2cell model we investigate the Zn solution (0-50μmol/L) to Zn uptake, the results indicated that Zn uptake increased by increasing Zn level (0-50μmol/L). Generally, the uptake of Zn in Caco-2cell model was increased by Zn supplementation. In the current study, the effects of inhibitors and/or promoter on Zn uptake in Caco-2cell model were also investigated. The results were as follows: Phytic acid was inhibited Zn transport, and finally inhibited Zn uptake in Caco-2cell, especially in phytic acid/Zn molar ratio=1:10, maximal the inhibition of Zn uptake was found. Iron has no effect on Zn uptake in lower iron/zinc molar value, only in iron/zinc molar value=1:10, Zn uptake was decreased. Calcium had no effect on zinc uptake in Caco-2cell modeL Vitamin C also had no effect on Zn uptake in Caco-2cell model. Zinc uptake was enhanced by cysteine, methinonine.2. Zinc bioavailability of polished rice among15rice varieties was evaluated. Significant difference on Zn concentration and Zn bioavailability was found among15tested rice cultivars (T<0.05). Analysis of the relationship between grain biochemical properties and Zn bioavailability indicated that no significant correlation between Zn concentration and Zn bioavailability (P>0.05). Phytic acid was negatively related to Zn bioavailability (P<0.05). A significant positive correlation was found between sulfur and cystein content, and Zn bioavailability (P<0.05). Significant difference on amount of bioavailable Zn among15genotypes was observed. The variation on amount of bioavailable Zn might be attributed from the combined effect of Zn concentration, phytic acid (P<0.05), sulfur and cysteine content in polished rice (P<0.05). According to current study, IR68144and Bing91185contain the highest amount of bioavailable Zn, thus IR68144and Bing91185were observed as promising rice genotypes for ongoing Zn biofortification program.3. Four different Zn forms were applied as a foliar treatment among three rice cultivars under field condition. Foliar Zn fertilization was an effective way to promoting grain Zn concentration and Zn bioavailability among three cultivars, especially, in case of Zn-amino acid and ZnSO4. On average, Zn-amino acid and ZnSO4increased Zn concentration in polished rice. Generally, Zn-amino acid and ZnSO4increased Zn bioavailability more effectively than Zn-EDTA and Zn-Cirate. The effectiveness of foliar applied Zn-amino acid and ZnSO4was higher than Zn-EDTA and Zn-Citrate on improvement of Zn concentration, and reduction of phytic acid, as a results higher accumulation of bioavailable Zn in polished rice. Moreover, foliar Zn application could maintain grain yield, the protein and minerals (Fe and Ca) content in polished rice. Foliar application of Zn in rice offers a practical and useful approach to improve bioavailable Zn in polish rice. According to current study, Zn-amino acid and ZnSO4are recommended as excellent foliar Zn forms to ongoing agronomic biofortification.4. We investigate the interaction effects of phosphorus and foliar Zn fertilization on rice grain Zn content and bioavailability. Grain yield was increased with phosphorus fertilization, but no changed by foliar Zn fertilization. Zn content in rice grain increased with the increase phosphorus fertilizer dose from0to100mg/kg and above this dose150-200mg/kg significantly reduces the grain Zn content. The phosphorus application combined with foliar Zn fertilizer can significantly increase rice Zn concentration (P<0.05). Phosphorus application significantly improved the phytic acid content (P<0.05). Application of foliar Zn fertilizers significantly reduce grain phytic acid content (P<0.05). No phosphorus application and high phosphorus application (more than150mg/kg) contain lower Zn bioavailability and amount of bioavailable Zn than those of other phosphorus treatments (50mg/kg,100mg/kg) especially in the level of200mg/kg, the bioavailability of Zn from polished rice was the lowest. When phosphorus fertilizer combined with foliar Zn fertilizer could improve the and Zn bioavailability and amount of bioavailable Zn of polished rice. Thus, regulation of phosphorus level, and combined with folair Zn fertilization should be considered to improvement the amount of bioavailable Zn.5. A soil pot experiment was conducted to evaluate the effect of sulfur and Zn fertilization on Zn content and bioavailability in rice. The results show that sulfur fertilizer had a positive effect on rice grain yield, while Zn fertilization had no effect on rice grain yield. The Zn concentration in polished rice was significant increased by application of sulfur and Zn fertilization. Sulfur fertilization had no effect on phytic acid content, but increased grain total sulfur, cysteine and methinonine content. Zn fertilization has negative effect on phytic acid, but no effect on contents of total sulfur, cysteine and methionine content. Supply of sulfur fertilization alone had no effect on grain Zn bioavailability, when combined with Zn fertilization, and significantly increased Zn bioavailability. The reason might be attributed from the decrease of phytic acid, improvement of Zn content by sulfur fertilization combined with Zn fertilization, as a result increased the bioavailable Zn. 6. We investigated the effect of germination and Zn fortification treatment on Zn bio availability of brown rice of three widely grown cultivars using Caco-2cell model to find a suitable fortification level for producing germinated brown rice. The results showed that Zn content in brown rice increased significantly (P<0.05) as the external Zn supply increased from25to250mg/L. In contrast, no significant influence (P>0.05) on germination percentage of rice was observed when Zn supply was lower than150mg/L. Zn fortification during germination process has significant impact on the Zn content and finally Zn bioavailability. These results might be attributed from the lower molar ratio of phytic acid to Zn and higher Zn content in Zn fortified germinated brown rice, leading to more bioavailable Zn. Likewise, significant difference (P<0.05) was found among cultivars with respect to the capacity for Zn accumulation and Zn bioavailability, this results might be attributed from the differences in molar ratio of phytic acid to Zn and concentration of Zn among the cultivars evaluated. Based on Zn intake among the world population, we recommend germinated brown rice fortified with100mg/L ZnSO4as a suitable concentration to use in the germination process, which contain high Zn concentration and bioavailable Zn. In the current study, the cultivar Bing91185fortified with Zn through germination process contain high amount as well as bioavailable Zn, which was identified as the most promising cultivar for further evaluation to determine its efficiency as a improved sources of Zn for target populations.