| The objective of current research was to prepare Zn-enriched soybean sprouts by biofortification and to evaluate bioavailability of Zn in the sprouts using an in vitro digestion and dialysis method. Soybean sprouts were cultured in two different ways, namely "Zn+Zn" method (soybean seeds were soaked for8h in zinc sulfate solutions containing different concentration of zinc, i.e.0,10,20,30,40,50,60,80,100μg·mL-1, and then cultivated for5days with the same zinc sulfate solutions as above) and "Zn+W" method (soybean seeds were soaked for8h in zinc sulfate solutions containing different concentration of zinc, i.e.0,10,20,30,40,50,60,80,100μg·mL-1, and then cultivated for5days with ultrapure water). The water absorption rate and germination rate of seeds, and the length, fresh weight, water content, biological yield, zinc accumulation, zinc bioavailability of Zn biofortified soybean sprouts were determinated. Meanwhile, the content of minerals in the edible portion of soybean sprouts and the leakage of mineral elements from imbibing seeds were also determined. The results showed as follows:(1) Exogenous zinc soaking with10-100μg·mL-1Zn solution could improve the water absorption rate of soybean seeds. The maximum water absorption rate (140%) was observed when the Zn concentration of soaking solution was100μg·mL-1For the soybean sprouts cultured with "Zn+Zn" method, low concentrations of Zn (10-20μg·mL-1) in culture solution enhanced soybean sprout growth, causing increase in edible portion length of15.1%, in germination percentage of1.25%-1.28%, in edible portion fresh weight of18.7%and in biological yield of3.96%. Meanwhile, the adverse effects on the growth of soybean sprouts were observed when Zn concentration of culture solution was more than20μg·mL-1For the soybean sprouts cultured with "Zn+W" method, exogenous zinc soaking with Zn solutions in the concentration range of10-100μg·mL-1had no obvious effect on the growth of soybean sprouts, whereas, soybean seed germination was inhibited obviously (P<0.05) when cZn2+in soaking solution is great than or equal to30μg·mL-1. In conclusion, the suitable Zn concentration of culture solution and soaking solution for producing Zn biofortified soybean sprouts should be not more than20μg·mL-1in circumstances where normal seed germination and sprout growth are guaranteed.(2) The content of Zn in Zn biofortified soybean sprouts increased significantly (P<0.05) with increasing Zn concentration of culture solution from10μg·mL-1to100μg·mL-1as compared with the control sample cultured in ultrapure water. For the soybean sprouts cultured with "Zn+Zn" method, Zn content ranged from102μg·g-1to395μg·g-1for edible portion (dry weight) and ranged from1.44mg·g-1to5.80mgg·g-1for inedible portion (dry weight). For the soybean sprouts cultured with "Zn+W" method, Zn content ranged from57.2μg·g-1to194μg·g-1for edible portion (dry weight) and ranged from105μg·g-1to357μg·g-1for inedible portion (dry weight). When the Zn concentration of culture solution was10μg·mL-1, enrichment ability of Zn in soybean sprouts was the greatest. In the case of soybean sprouts biofortified with a fixed concentration of Zn, the Zn content and enrichment coefficient of Zn in edible portion were all inferior to those in inedible portion. The NRV%of Zn in the edible portion of soybean sprouts biofortified with10μg·mL-1of Zn was increased by2.4folds ("Zn+Zn" method) and by1.6folds ("Zn+W" method) than that of control sample, reaching to8.4%("Zn+Zn" method) and4.6%("Zn+Zn" method), if the general daily consumption of these soybean sprouts was100g/day, fresh weight. The results indicated that Zn biofortified soybean sprouts may serve as a convenient dietary source of Zn for Zn-deficient people.(3) Biofortification with Zn using germination method had significant influences (P<0.05) on Zn bioavailability of soybean sprouts. In the case of soybean sprouts biofortified with10-100μg·mL-1of Zn, the bioaccessible Zn content from edible ("Zn+Zn" method:3.86-10.1μg·g-1, dry weight;"Zn+Zn" method:2.03-3.63μg·g-1, dry weight) and inedible ("Zn+Zn" method:59.1-300μg·g-1, dry weight;"Zn+W" method:6.02-11.5μg·g-1, dry weight) portions exceeds greatly over those of CK (P<0.05). In the case of soybean sprouts biofortified with a fixed concentration of Zn, the bioaccessible Zn content and bioaccessibility of Zn from inedible portion of sprouts are higher than those from edible portion. Zn bioavailability from edible portion of soybean sprouts biofortified with10μg·g-1of Zn was increased by8.9%("Zn+Zn" method) and19.6%("Zn+W" method) than that of control sample, reaching to3.79%("Zn+Zn" method) and3.54%("Zn+Zn" method). The results indicated that biofortification in soybean sprouts with Zn may induce changes of Zn chemical forms in soybean sprouts into organism forms that may be easily available for uptake by humans.(4) Zn solution soaking treatment of soybean seeds induced the reduction of mineral elements contents (Fe, Cu, Mn, Ca and Mg) in varying degree, compared with those in raw soybean seeds, which respectively lost6.96%-14.4%,33.6%-57.2%,0.7%-46.6%,97.1%-97.7%and2.54%-4.13%. In the case of soybean seeds soaked in solution with a fixed concentration of Zn, Ca was leaked in the greatest percentage followed in decreasing order by Mn, Cu, Fe and Mg, while the amount of these elements leaked was found as the following order:Ca> Mg> Mn> Fe> Cu. No significant differences (P>0.05) in Ca and Mg content were observed between soybean seeds soaked with Zn solution and soaked in ultrapure water. But the Fe, Mn and Cu contents in the soybean seeds soaked in Zn solution were all higher than those in soybean seeds soaked in ultrapure water. The results indicated that the addition of Zn to soaking solution had no influence on the leakage of Ca and Mg, whereas could reduce the leakage of Fe, Mn and Cu. The edible portion of soybean sprouts biofortified with Zn at a fixed concentration ("Zn+Zn" method) contained Fe, Mn, Cu, Ca and Mg in varying quantities, with decreasing order as follows:Mg> Ca> Fe> Mn> Cu. Zn biofortification significantly enhanced (P<0.05) Ca and Fe contents in the edible portion of soybean sprouts when Zn concentration of culture solution ranged from30to100μg·mL-1where will result in adverse effects on the growth of soybean sprouts, whereas Zn biofortification had almost no significant influence (P>0.05) on the contents of Mg, Cu and Mn in the edible portion of soybean sprouts biofortified with10μg·mL-1or20μg·mL-1of Zn. |
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