| Selenium（Se）is an essential micronutrient for humans and animals,however more than 40 countries around the world are Se deficient,and about 72%of regions in China are deficient or low Se.Adequate Se supplementation is an important measure to prevent and cure Se deficiency in human body,improve human immunity,and reduce the incidence of epidemics.Due to the lack of Se ore resources in China,using crops to enrich Se from the soil is an effective way to make full use of Se resources and produce Se-rich products efficiently.Hubei province is rich in Se resource.Enshi prefecture is known as the"Se capital of the world",has rich Se-rich soil and Se mineral ore resources,with obvious alpine climate characteristics,which is suitable for the development of characteristic crops.The land of Jianghan Plain is fertile,with a wide area of Se-rich soil and relatively high Se content(0.2-0.4 mg kg-1).It is mainly planted with food crops and has a high commercialization rate,which is suitable for the production of Se-rich food crops.How to make full use of the soil Se resources in the two Se-rich areas of Hubei Province and the Se ore resources in Enshi to efficiently produce high-quality Se-rich agricultural products has important theoretical and practical significance to realize the agricultural value-added,increase farmers’income and speed up poverty alleviation in Hubei Province.Therefore,in this study,pot experiments were carried out to explore the differences in the availability of Se in the soil of two Se rich regions;field experiments were conducted to study the Se rich characteristics,differences,Se rich ability and Se application technology of different crops in the two regions;and the transformation and utilization of Se in processed foods were studied through the processing of Se rich soybeans.The purpose was to provide technical support and theoretical basis for the efficient cultivation,processing and utilization of Se rich agricultural products in Hubei Province,as well as the formulation of Se-rich agricultural product standards.The main conclusions obtained were as follows:（1）The bioavailability of Se in alkaline calcareous alluvial soil in Jianghan Plain was significantly higher than that in acid yellow-brown soil in EnshiSelenite and selenate were applied to the alkaline calcareous alluvial soil from Jianghan Plain and the acid yellow-brown soil from Enshi by pot experiment.When the amount of Se applied was 2 mg kg-1,the amount of Se absorbed by soybean from calcareous alluvial soil was significantly higher than that from yellow-brown soil.Under selenite and selenite treatment,the Se concentrations in various plant parts in various growth stage（seedling stage,flowering stage and pod setting stage）from the calcareous alluvial soil were 1.3-3.3-fold and 1.9-8.0-fold of the concentrations observed in the plant parts from the yellow-brown soil,respectively;Seed Se concentration in calcareous alluvial soil were 3.8-fold and 3.2-fold the concentration in yellow-brown soil,respectively.Following Se application,Se speciation in soybean seeds was generally consistent between the two soil types.Organic Se accounted for>92%of total Se in the seeds.The major species of organic Se was Se Met,which accounted for>90%of the total Se.Under selenite treatment,the effective Se concentration of soluble Se and exchangeable Se in calcareous alluvial soil was significantly higher than that in yellow-brown soil,while the ineffective Se concentration of Fe/Mn oxide bound Se,Organic matter bound Se and residue Se was significantly lower than that in yellow-brown soil.Under selenate treatment,the proportion of soluble Se（most available fraction）in yellow-brown soil and calcareous alluvial soil was 22%and 34.6%respectively,and the proportion of soluble Se in the calcareous alluvial soil was 12.6%higher than that in yellow-brown soil.In conclusion,under the same Se content,the bioavailability of Se in calcareous alluvial soil is significantly higher than that in yellow-brown soil,which is conducive to the absorption and utilization of Se by crops.（2）On the Se-rich soil,the Se-rich degree of agricultural products is affected by the variety of crops and the distribution of Se in different parts of crops,so the agricultural products planted and harvested on the Se-rich soil are not all Se-rich productsWithout Se fertilizer,the Se concentration of rice and soybean on calcareous alluvial soil was 0.06 mg kg-1 and 0.21mg kg-1,respectively;the Se concentration of pear,kiwifruit and blueberry on yellow-brown soil was very low,and most of them were lower than the detection line;while the Se concentration of edible parts of radish,cabbage and pepper were lower than 0.11 mg kg-1.Applying 0.3 t ha-1 Se ore powder,the Se concentration in brown rice and soybean seed was 576.7μg kg-1 and 884.6μg kg-1,respectively.The Se concentration in soybean seed was 1.5-fold higher than that in brown rice after application of Se ore powder at the same rate.After application of Se ore powder,the Se content in various parts of rice was increased in the order husk<brown rice<straw<root,and the order in soybean was pod<straw<root<seed.After spraying with 75 g ha-1 Se fertilizer,the Se concentration in soybean seeds was2.4-6.1-fold that in rice seeds.Foliar sprayed with 75 g ha-1 selenite,the Se concentration in the edible parts of vegetables was:radish tuber>pepper>cabbage heart;sprayed with the same amount of selenate,the Se concentration in edible parts of vegetables was:radish tuber>cabbage heart>pepper.Under the treatment of spraying Se,the sequence of Se concentration in various parts was:leaf>tuber（radish）,side leaf>cabbage heart>root（cabbage）and leaf>pepper>straw>root（pepper）.In summary,there are significant differences in the absorption and utilization capacity of Se in different crops and different parts,especially edible parts,and the Se availability in different soils is different.Therefore,the agricultural products naturally produced in Enshi and Jianghan Plain may not meet the Se-rich standard.（3）Adding exogenous Se fertilizer is an effective way to ensure the production of high quality Se-rich agricultural products in Se-rich soilIn Jianghan Plain,following application of 0.3 t ha-1Se ore powder,the Se concentration in brown rice and soybean seeds was 0.58 mg kg-1 and 0.88 mg kg-1,respectively,which was 10.0-and 4.2-fold higher than controls.The percentage of protein Se in brown rice and soybean seeds was 47.6%and 67.0%,respectively.There are 91.3%Se Met and 8.7%Se Cys2 in brown rice,96.2%Se Met and 1.0%Se Cys2 in soybean seeds.In Jianghan Plain,Se ore powder from the Se mining area of Enshi can be applied for the production of Se-rich agricultural products in the short-term.The possible environmental impacts of adding considerable amounts of scarcely mobile Se in soil should be taken into consideration during the long-term application of Se ore powder.Spraying 75 g ha-1 selenite or selenate on Jianghan Plain,the Se concentration of brown rice and soybean seed was more than 0.38 mg kg-1 and 1.41 mg kg-1,respectively.The organic rate of Se in brown rice and soybean seed was more than 80%and 90%,and the proportion of protein Se was more than 44%and 58%,respectively.At the same spraying stages,the Se concentration of rice and soybean seeds treated with selenate was 1.8-2.2 and 2.6-3.1-fold that with selenite,respectively.With the same Se source,the Se concentration of rice seeds sprayed at the full heading stage was 3.1-3.6-fold that sprayed at the end of tillering stage,and that of soybean seeds sprayed at the pod setting stage was 2.0-1.7-fold that sprayed at the early flowering stage.The accumulation of Se in rice and soybean grains increased with delay of spraying stage.In summary,appropriately delaying the spraying stage and selecting selenate as the Se source can be more efficient for producing Se-enriched rice and soybean.The highest safe concentration of Se in pear,kiwifruit and blueberry was 40,100and 200 mg L-1,respectively.When the concentration exceeded this range,the fruit trees appeared toxic symptoms.Spraying 40 g ha-1 selenite or selenate in Enshi,the concentration of Se in pear juice,pomace and peel was more than 7.04,18.62 and154.57μg kg-1,respectively.The transformation of inorganic Se to organic Se compounds was>80%and 74%in the peel and pomace,respectively,while in the juice the rate was notably low at<8%.With the delay of spraying stage,the absorption and utilization rate of Se was higher and it was easier to transfer to the fruit.More than 70%Se was accumulated in juice in inorganic speciation under selenate treatment.Therefore,appropriately delaying the spraying stage and selecting selenite as the Se source can be more efficient for producing Se-enriched pears.Spraying 100g ha-1 selenite or selenate in Enshi,the concentration of Se in flesh of kiwifruit reach more than 34.74μg kg-1,and the transformation of inorganic Se to organic Se compounds in the flesh was more than 61%.The Se concentration of kiwifruit flesh treated with selenate was significantly higher than that of selenite,and it was easier to transfer and accumulate Se to the flesh when spraying in young fruit stage.Therefore,it is beneficial for the production of Se-enriched kiwifruit to select selenate as the Se source and appropriately delay the spraying stage.Spraying 200 g ha-1 selenite or selenate in Enshi,the Se concentration of blueberry was over 44.34μg kg-1,and the transformation of inorganic Se to organic Se compounds was over 76%.With the delay of spraying stage,the Se concentration of different parts of blueberry fruit decreased significantly,but there was no significant difference under different Se sources.Therefore,Se-rich blueberry production spraying stage should be appropriately moved forward.Spraying 75 g ha-1 selenite or selenate in Enshi,the Se concentration of edible parts of radish,cabbage and pepper reach more than 0.96,0.58 and 0.86 mg kg-1,respectively,and the transformation of inorganic Se to organic Se compounds is over76%.The Se concentration in edible parts of three vegetables treated with selenate was significantly higher than that of selenite.Therefore,selenate is more economical and efficient for vegetables.（4）Se-enriched soybeans have high organic Se concentration and high processing utilization rate,which is beneficial to the deep processing of Se-enriched foodSoybean has a strong ability of enriching Se,and the organic degree of Se is more than 90%.Therefore,Se-rich soybean has the double functions of plant protein and organic Se source.The efficient utilization of Se in Se-rich soybean is the key in the process of supplementing Se.The Se concentration in soybean sprouts decreased significantly with the prolongation of germination time,but the distribution ratio of Se remained stable above 95%.With the increase of water-soybean ratio,the Se concentration of soya-bean milk decreased significantly,but the distribution ratio of Se in soybean milk increased.The order of Se concentration of each tofu is:gypsum tofu≈bittern tofu>gluconolactone tofu,but the distribution ratio of Se is just opposite.During the preparation of Se-rich soybean products,the recovery rate of total Se is high,which is more than 80%.For three Se-rich soybean products,the recovery efficiency of Se from soybean sprouts was the highest,above 85%,followed by tofu（43-53%）,and soya-bean milk（29-45%）.When the Se concentration of soybean is between 1.5-2.5 mg kg-1,it is suitable to be processed into tofu for consumption;when it is between 2.5-4.5 mg kg-1,it is suitable to be ground into soya-bean milk for drinking;when it is between 4.5-8.0 mg kg-1,it is more reasonable to generate soybean sprouts for consumption.In addition,soybean dregs,a by-product of the production of Se-enriched tofu and Se-enriched soya-bean milk,can be reused.（5）The Se-enriching ability of soybean SPI and 11S is significantly higher than that of SPC and 7S,and the enrichment of Se did not change the structure and functional characteristics of protein,thus affecting the nutritional characteristics of soybeanSPC,SPI,7S and 11S proteins were extracted from Se-rich soybean(11.47 mg kg-1)and analyzed.It was found that Se had no significant effect on the protein purity of SPC,SPI,7S and 11S.The order of purity was 11S>7S>SPI>SPC.The Se concentration of SPI and 11S were 18.50 mg kg-1 and 18.42 mg kg-1,respectively,while those of SPC and 7S were 14.27 mg kg-1 and 13.35 mg kg-1,respectively.The Se concentration of SPI and 11S were significantly higher than those of SPC and 7S.Se in different proteins mainly exists in the organic form of Se Met,accounting for more than 80%,and the highest organic degree of Se in 11S is over 97%.The enrichment of Se reduced the sulfur-containing amino acid methionine in SPI and 11S,but its range was not enough to affect the nutritional value of protein.Selenium had no significant effect on the subunits,functional groups,secondary structures,micro morphology and functional properties of different soybean proteins.In conclusion,SPI and 11S are more efficient sources of Se,and Se has no significant effect on the structure and functional characteristics of different proteins. |
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