Effects Of Zinc Biofortification On Nutrients And Trace Elements In Cowpea During Germination

The cowpea(Vigna unguiculata L.Walp)is important grain legume crop of tropics and subtropics in Africa,Asia,and South America.It plays an important role in nutrition supplementing human and animal diet due to its high protein content,calories and vitamins.Cowpea is a popular kind of bean.Therefore,it is of great significance to study zinc biofortification in cowpea.In this dissertation,the effect of zinc biofortification on the nutritional composition and trace elements in cowpea during germination process was studied.The main findings are as follows:(1)The zinc content of 11 kinds of cowpea(Haixiu No.7,U.S.Non-racked Bean,Small Five-leaf,Big Three,Spring and Autumn Red,Xiaguan No.2,Meidafu No.8,Gan Qiuhong,Wuxai No.11,Haixiu No.1,Haixiu No.2)seed ranged from 24.88 to 63.45 mg/kg,iron content from 70.25 to 113.33 mg/kg,copper content from 5.11 to 10.99 mg/kg,and manganese content from 11.72 to 25.02 mg/kg.The content of trace elements in cowpea was significantly affected by the variety.Seed soaking with a solution of zinc sulfate at a concentration of 100 mg/L,there were significant differences in the growth status and zinc enrichment ability of the eleven cowpea varieties.In the experiment,Haijang No.1,Haijiang No.2 and Haixiu No.7 had good germination growth status and high zinc enrichment ability,and they can be used as germination experimental materials.(2)Haijang No.1,Haijiang No.2 and Haixiu No.7 as raw materials,were used to investigate the change of germination on nutritional composition and trace elements during the process of germination.The results showed that soluble proteins of Haijang No.1 and Haixiu No.7(except for Haijiang No.2)significantly were increased after 1 d of germination,and then were gradually decreased in the three cultivars.With the extension of the germination time,three cultivars of cowpea starch all were decreased,and total soluble sugar were decreased first and then increased.The content of reducing sugar in Haijiang No.2 and Haixiu No.7 were increased first and then decreased and HI reducing sugar content was gradually increased.The content of vitamin C(Vc)in Haijang No.1,Haijiang No.2 and Haixiu No.7 reached a maximum level of 20.98,19.51,25.88 mg/100g FW after 3 d of germination,respectively.Significant difference on trace elements(Zn,Fe,Mn,Cu)among 3 cultivars was observed,and there was no regular change during germination but contents were slight increased after 5 d of germination.After 4 days of germination,the contents of phytic acid(PA)and tannin(TA)in Haijang No.1,Haijiang No.2 and Haixiu No.7 were reduced by 48.68%,27.27%,56.23%(PA)and 90.56%,91.79%,90.03%(TA),respectively,then flattened.This shows that germination can increase the nutritional value of cowpea.(3)Cowpea cultivars(Haijang No.1,Haijiang No.2)as raw materials,were used to investigate the effects of zinc sulphate(S)and zinc gluconate(P)on the nutrients(soluble protein,reducing sugar,Vc)and trace elements(Zn,Fe,Mn,Cu)in the germination process.The results showed that the low concentration of zinc biofortfied germination was beneficial to the growth of cowpea sprouts and the accumulation of nutrients(soluble protein,reducing sugar,Vc).However,high zinc concentration has an inhibitory effect on the growth of cowpea,and the inhibitory effect on nutrients is significantly different due to cowpea varieties.In addition,the nutritional components are affected significantly by varieties.Zinc fortification has a significant effect on the zinc content in the germinated cowpea and increases with increasing zinc concentration.In the range of enhanced concentration of 0-300 mg Zn/L,the Zn content of Haijang No.1 sulphate fortification,Haijang No.1 zinc gluconate fortification,Haijiang No.2 sulphate fortification,and Haijiang No.2 zinc gluconate fortification increased 120.3%～1270.9%,112.3%～1355.4%,118.0%～930.8%,119.6%～1156.4%,respectively.Zinc fortification had little effect on other trace elements(Fe,Cu,Mn)of germinated cowpea,except that Haijang No.1 germinated cowpea iron content was significantly reduced at the zinc concentration(5 to 10 mg/L).Therefore,low-concentration zinc enhanced germination can improve the nutrient composition and zinc content of the germinated cowpea and has little effect on other trace elements.