Biofortification Of Legumes With Zinc During Their Germination And In Vitro Bioaccessibility

The deficiency of trace element zinc in human dietary is a current urgent global problem. The World Health Organization （WHO） estimates that well over one-third of the world’s population is facing the risk of malnutrition and disease caused by zinc deficiency. It is a worldwide problem that how to improve the bioavailability of zinc in the human diet. So far, unfortunately, there is no effective solutions. Legumes is next in importance to cereals. The research of biofortification of legumes with zinc to improve the zinc nutritional status is of great significance under such a background.Therefore, this article would study the subject of biofortification of legumes with zinc during germination, focus on nutritional value, growth index, anti-nutritional factors, zinc bioavailability, morphology of zinc and the choice of legumes varieties. The main results were summarized as follows:1. The effects of soaking with exogenous zinc on growth characteristics of mung bean sprouts was studied. The results show that under the conditions of this experiment, the mung bean seeds germination rate has increased slightly when the zinc concentration was in the range of 25-75 mgZn²⁺/L, while the mung bean hypocotyl length, root length and biomass with increasing zinc concentration was significantly higher than in CK group and reached the maximum at the concentration of 75 mgZn²⁺/L. When the zinc concentration was in the range of 75-200 mgZn²⁺/L, root length, hypocotyl length and biological yield decreased with the zinc concentration, the germination rate of mung bean seeds decreased quickly when it soaked in zinc sulfate solution in the range of 75-200 mgZn²⁺/L compared with the CK groups. The results show that when the content of zinc is lower, the mung bean sprouts growth is promoted by increasing zinc content properly.2. The changes of important nutrients during the germination of mung bean were studied. The results show that the metabolism of essential food constituents during mung bean germination was influenced by concentrations of exogenous zinc. Overall, the exogenous zinc concentration in 25-75mgZn²⁺/L range contributes to the accumulation of important food components in mung bean sprouts. The vitamin C content of mung bean sprouts reached to the highest value of 23.76mg/g （FW） when the zinc concentration was 50mgZn²⁺/L, the soluble sugar content reached the maximum value of 7.56mg/g （FW）, in when the concentration of zinc was 75mgZn²⁺/L, the total free amino acid content of 8.96mg/g （FW） when the zinc concentration was 50mgZn²⁺/L, the soluble protein content of 56.82mg/g （F W） when the zinc concentration was 50mgZn²⁺/L, and compared with the control group were increased by 16.87%,73%,15.46%,24.17%. Effected by high concentration of zinc, the content of protein, vitamin C and other important food ingredients were decreased in different degree when the concentration above 50 mgZn²⁺/L. This study shows that the nutritional value of mung bean sprouts was not affected by the zinc biofortification, but was increased. The result of this experiment provide scientific basis for the biofortification of legumes with zinc during germination.3. The effect of zinc on the antioxidant activity of bean sprouts was studied. The results showed that different concentrations of exogenous zinc fortified on total flavonoids in mung bean sprouts has a significant effect on total polyphenol accumulation. The mung bean seeds soaked at low concentrations of zinc solution can improve the total polyphenol in mung bean sprouts. Compared with the control group, the content of total polyphenols in mung beans sprouts increased by 108.66%, to 56.84μg/g at concentration up to 50 mgZn²⁺/L. On the contrary, the content of total polyphenol decreased with the exogenous zinc concentration as concentration over 50mgZn²⁺/L. After fortification with 25mgZn²⁺/L through the germination process, the contents of total flavonoids in mung bean sprouts was increased, while it presented "V" changes when concentration of Zn²⁺ was more than 25mg/L. The antioxidant activity of mung bean sprouts reached a maximum after fortification with 25mgZn²⁺/L. It shows a positive correlation between antioxidant activity and total polyphenol or vitamin C （correlation coefficients were 0.678 and 0.561, respectively, DPPH）.4. The zinc bioavailability was evaluated by in vitro digestion and dialysis model in mung bean sprouts. Increasing the concentration of Zn²⁺ rates （0～200mg/L） during the germination process significantly increased （p<0.05） the zinc concentration in the mung bean sprouts, compared with control group. The content of PA and the molar ratio of PA to Zn significantly decreased （p>0.05） both germination and the zinc fortification process. The amount of bioavailable zinc after in vitro digestion increased with the concentration of Zn²⁺ rates （0～200mg/L）. Bioavailable zinc content in mung bean sprouts increased by 30.76% while it showed no significant difference compared with mung bean seeds. The content of bioavailable zinc content increased by 146.15% when the concentration of exogenous zinc was 25 mgZn²⁺/L.The bioavailable zinc content compared to the control group （2.45mg/100g,0.51mg/100g, respectively） increased by 3.8 times when 75mgZn²⁺/L, and the bioaccessiblity of zinc was significantly higher than CK （25.24%,19.42%, respectively）.5. The different forms of zinc supplement and suitable for zinc fortified varieties were screened. Different varieties of beans have different accumulation ability of zinc, and cow gram have the strongest accumulation capacity in six kinds of beans. Mung bean accumulation capacity of four kinds zinc compounds is different, the zinc accumulation ability from strong to weak, followed by Zn-Gluconate, Zn-Sulfete, Zn-Citrate, Zn-EDTA.