大米中硒的有机形态及其生物利用度研究

为了探究典型长寿区大米有机硒的赋存形态与人体硒营养水平的关系,本研究分析了江西典型长寿区大米中有机硒、谷蛋白硒、硒代蛋氨酸(Selenomethionine,Se Met)等的组成特征,并运用胃肠体外模拟法对大米硒的生物可利用度及其与各有机硒组分之间的相关关系进行了研究。结果表明,大米中的硒主要以有机形式(78.67±13.52)%赋存,其中,(53.73±8.27)%的有机硒为谷蛋白硒,且65%以上的谷蛋白硒可酶解消化为Se Met。大米硒的生物可利用度为(55.58±10.53)%。大米谷蛋白中Se Met比例相对较高且易于被人体吸收利用,这可能与当地居民的健康长寿关系密切。不过,Se Met与大米可利用硒的相关系数仅为0.55。因此,未来有必要对大米中不同硒蛋白的代谢产物(如Se Met)进行研究。     

富硒、非富硒大米有机硒的组成及硒的可利用度分析

为探究人体对大米硒营养的利用状况,比较富硒、非富硒大米之间有机硒、碱溶谷蛋白、硒蛋氨酸等的组成差异,并运用体外模拟法对大米硒的可利用度进行研究。结果表明:有机硒是大米中硒的主要形态,富硒大米有机硒的比例[(77.6±11.3)%,n=7]高于非富硒大米[(64.1±7.5)%,n=8],(P0.05)。大米碱溶谷蛋白的胃肠模拟消化液中仅有硒蛋氨酸被检出,硒蛋氨酸占碱溶谷蛋白硒的比例为33.1%~97.6%。虽然人体对富硒大米硒的可利用度[(62.6±7.8)%,n=7]高于非富硒大米[(46.1±10.3)%,n=8](P0.05),但是,富硒大米谷蛋白中硒蛋氨酸的比例[(45.5±9.0)%,n=7]却明显低于非富硒大米[(81.2±12.3)%,n=8](P0.05)。可见,富硒水稻中硒蛋氨酸的转化及对人体健康的作用尚需进一步研究。     

不同加工方式对富硒大米硒损失、形态及体外生物利用度影响

为探究不同加工方式对富硒大米中硒的影响,以重庆市江津区高硒含量大米为实验原料,使用常用加工方式处理,并比较分析处理前后富硒大米硒含量、硒形态及硒生物利用度的差别。结果表明,挤压处理导致硒含量损失43.05%,常压蒸煮、高压蒸煮、微波处理不会对硒含量产生显著影响(P>0.05);4种加工方式均可降低大米中硒代蛋氨酸(selenomethinonine, SeMet)含量;亚硒酸盐经微波、高压蒸煮及挤压处理后完全损失;微波处理使甲基硒代半胱氨酸含量增加;体外模拟胃肠消化实验结果发现,常压蒸煮、高压蒸煮及微波处理后的样品胃肠消化总硒生物利用度分别为74.99%、67.93%、50.38%及40.08%,都显著高于未处理样品(P<0.05);富硒大米中SeMet的生物利用度在加工处理后显著提高(P<0.05),其中常压蒸煮后SeMet的生物利用度最大,达到47.49%。常压和高压蒸煮方式对富硒大米总硒含量及形态影响较小,有利于机体对硒的吸收利用,实验结果为富硒大米加工过程中硒的变化情况提供数据支撑,同时为富硒大米加工后机体对硒的消化吸收效果研究提供了理论参考。     

富硒农产品中硒代氨基酸形态及其在不同蛋白组分中的分布

目的：探究富硒西兰花、富硒大豆、富硒玉米、富硒大麦苗不同溶解性蛋白组分中硒代氨基酸形态及分布情况。方法：利用高效液相色谱—氢化物发生—原子荧光光谱联用技术测定4种富硒禾谷类和十字花科农产品中硒代蛋氨酸(SeMet)、硒代胱氨酸(SeCys2)、甲基硒代半胱氨酸(MeSeCys)和硒代乙硫氨酸(SeEt)含量,并分析各硒代氨基酸在清蛋白、球蛋白、醇溶蛋白和谷蛋白等不同溶解性蛋白组分中的分布特点。结果：4种富硒植物的硒代氨基酸在不同蛋白组分中的含量及分布存在显著差异(P＜0.05)。富硒大豆、富硒玉米、富硒大麦苗的有机硒以SeMet形式存在,在4类蛋白组分中分布较一致且相对含量均高于66%,不存在SeEt;富硒西兰花的有机硒主要以SeCys2和SeMet为主、MeSeCys次之,前二者在清蛋白和谷蛋白组分中的分布较一致且约占有机硒含量的36%,但在球蛋白和醇溶蛋白组分中均以SeMet存在,相对含量最高达60%,其次为SeCys2约占有机硒含量的34%。富硒西兰花中存在极少量的SeEt约占有机硒含量的5%。结论：3种禾谷类农产品(富硒大豆、富硒玉米、富硒大麦苗)的不同溶解性蛋白中均以SeMet为主;而富硒西兰花的不同溶解性蛋白则以SeMet和SeCys2为主,并且其清蛋白和谷蛋白还富含较多的MeSeCys。     

富硒大米中硒形态分析

采用原子荧光光度法分析了天然富硒大米中硒的主要赋存形态、分布及含量.本实验中,硒的检测线性范围为4 μg/L～20μg/L,相关系数是r=0.999 3,总硒测定的相对标准偏差(RSD)为0.966％(n=6),总硒的加标回收率为103.12％.实验表明富硒大米中的总硒含量为206.708 μg/kg,达到60 μg/kg～300 μg/kg的富硒标准,而硒主要以对人体有益的有机硒形态存在,含量为168.875 μg/kg,占总硒的81.70％,而有机硒中最主要的赋存形态是蛋白硒,含量90.170 μg/kg,占53.40％,其次多糖硒占9.28％,RNA硒占1.86％,其它形态的有机硒占35.46％.     

柱前衍生-反相高效液相色谱法研究稻谷中有机硒形态

建立了稻谷中有机硒化合物测定方法,采用温和水解富硒大米蛋白的提取条件,利用柱前衍生―反相高效液相色谱测定水解大米蛋白中有机硒含量。结果表明:采用6 mol/L HCl溶液、50℃水解富硒大米蛋白48 h的条件提取率高。以4–氯–3,5–二硝基三氟甲苯(CNBF)为衍生剂的柱前衍生―反相HPLC检测富硒大米中有机硒化合物主要是硒代甲硫氨酸(SeMet),最低检出限为0.14μmol/L,线性范围为0.40⁴80μmol/L,加标回收率为89.9%480μmol/L,加标回收率为89.9%⁹0.8%,硒代甲硫氨酸含量为4.122μg/g,占有机硒含量65.29%。该方法简便、灵敏、重现性好、干扰少,可为稻谷中有机硒测定提供一种完善检测方法。     

富硒茶叶中硒的赋存形态研究

利用氢化物—原子荧光光度法分析硒在富硒茶叶中的主要赋存形态及分布规律。结果表明,富硒茶叶中的总硒含量为533.5μg/kg,硒主要以对人体有益的有机结合态形式存在,其含量占总硒的比例为83.66%,而有机硒中最主要的赋存形态为蛋白硒,占有机硒含量的76.35%,茶叶中的硒还有少部分与核酸和多糖结合。     

雪莲菌富硒条件优化及体外抗氧化活性分析

利用雪莲菌吸收和转化无机硒为有机硒,旨在通过优化富硒条件制备菌活性和有机硒占比较高的富硒雪莲菌。针对不同优化需求,确定不同优化指标,从而选择最佳的富硒条件。优化后富硒温度为28 ℃、富硒时间为24 h、亚硒酸钠添加时间为雪莲菌接种后3 h;通过摇床培养,进行梯度驯化富硒;以透析后总硒含量占比、生物量、富硒率（selenium enrichment rate,SER）和有机硒占比（organic selenium percentage,OSP）确定梯度富硒底物浓度为3、6、9、12、15 μg/mL。在最优富硒条件下所制备的富硒雪莲菌的总硒含量（total selenium content,TSC）为（2 194.41±58.49）μg/g,有机硒占比为（84.57±1.45）%。通过抗氧化活性测定发现富硒雪莲菌的抗氧化活性极显著高于雪莲菌（P＜0.001）。     

高效液相色谱–电感耦合等离子体质谱联用测定稻米中5种硒形态（网络首发、推荐阅读）

利用高效液相色谱–电感耦合等离子体质谱联用技术建立了富硒大米中5种硒形态的检测方法。采用反向C18 色谱柱，对流动相离子对浓度、洗脱盐浓度、pH值进行了优化，最终确定流动相组成为15 mmol/L乙酸铵溶液，pH5.5和0.2 mmol/L四丁基氢氧化铵（TBAH），硒–甲基硒代半胱氨酸（SeMeCys）、硒代半胱氨酸（SeCys）、硒代蛋氨酸（SeMet）、四价硒Se(VI)和六价硒Se(IV)5种硒形态获得基线分离。大米样品用酶提法提取，通过对酶的种类、酶的用量及酶解时间等对提取效率的研究，确定样品与蛋白酶（protease）XIV酶量比为20∶1为最佳，且最佳酶解时间为20 h。结果表明本方法分离效率高，方法线性良好，灵敏度高，回收率为77.1%~107.3%，硒–甲基硒代半胱氨酸（SeMeCys）、硒代半胱氨酸（SeCys）、硒代蛋氨酸（SeMet）的检出限和定量限分别为0.0015mg/kg和0.005 mg/kg，四价硒Se(VI)和六价硒Se(IV)检出限和定量限分别为0.002 5 mg/kg和0.009 mg/kg。为全面评价富硒大米质量和后续开展富硒大米膳食暴露评估提供技术支撑。     

富硒小麦提取物中硒含量及其抗氧化特性

为研究富硒小麦的富硒水平和硒的赋存形态,选用兰州高硒地区生产的富硒小麦为原料,通过超声、离心、透析的方法将富硒小麦中的有机硒和无机硒分离,用火焰原子吸收光谱法测定小麦硒水平。结果表明,富硒小麦硒的主要赋存形态是有机态,占总硒的84.36%。有机态硒主要为硒蛋白（54.46%）,硒多糖次之,少量为硒核酸和其他有机态硒。在蛋白态硒中,清蛋白和谷蛋白硒含量较高,分别占总硒的19.46%和16.83%。抗氧化性分析结果表明,多糖相对于蛋白和核酸提取物,具有更长的诱导时间、更高的1,1-二苯基-2-三硝基苯肼（1,1-diphenyl-2-picrylhydrazyl,DPPH）自由基清除能力和Fe3+还原力。皮尔逊相关性分析表明,小麦富硒提取物抗氧化能力与其硒含量之间表现为显著的正相关性。     

Selenium uptake and species distribution in selenium-enriched bean (<Emphasis Type="Italic">Phaseolus vulgaris</Emphasis> L.) seeds obtained by two different cultivations

In this work, bean plants were cultivated in two different ways using two modes of selenium supplementation in the form of sodium selenate. Each group consisted of the same four cultivars. Group A plants were grown in soil and twice foliarly sprayed at an interval of 10 days with an aqueous solution of 10 mg Se L⁻¹ at flowering time. Group B plants were hydroponically cultivated after the maternal seeds were soaked in nutrient solution containing the same Se content as used for foliar fertilisation. Bean seeds obtained from group A plants accumulated much more Se (around 2 μg g⁻¹ dry weight) than those seeds obtained from group B plants (around 0.6 μg g⁻¹ dry weight). No differences in Se content within each group were found. After enzyme hydrolysis, 85±7% of soluble selenium was found in group A and 65±2% of soluble Se in group B with respect to the total Se content in seeds. In bean seed supernatants SeMeSeCys, SeMet and two unknown species were found. These four species together represented 79±8 and 53±9% of the Se mass fraction of group A and group B, respectively. No differences in the presence of selenium species were found between the four cultivars and cultivation conditions.     

Speciation of selenium in selenium-enriched seeds,buckwheat (<Emphasis Type="Italic">Fagopyrum esculentum</Emphasis> Moench) and quinoa (<Emphasis Type="Italic">Chenopodium quinoa</Emphasis> Willdenow)

Buckwheat (Fagopyrum esculentum Moench) and quinoa (Chenopodium quinoa Willdenow) are widely used as food ingredients. The nutritional characteristics of these plants, i.e., high contents of proteins and amino acids suggest that selenium (Se) is preserved as selenoamino acid derivatives, in particular, selenomethionine (SeMet) in proteins, similar to selenized yeast. Therefore, buckwheat and quinoa are expected to be a good nutritional source of Se. Selenized buckwheat and quinoa were cultivated on Se-fortified soil using sparingly soluble Se salts, such as barium selenate and barium selenite. Se concentration in the edible parts of these plants was determined, and Se extraction efficiency with enzyme or alkali was evaluated. In addition, the chemical species of Se in the low molecular weight fraction of these plants were determined by HPLC-ICP-MS. Total Se concentrations in the edible parts of selenized buckwheat and quinoa were 170.4 ± 2.9 μg/g and 102.7 ± 2.4 μg/g wet weight, respectively. Thus, these selenized seeds were found to be Se accumulators. The results indicate that Se in selenized buckwheat exists mainly as SeMet, while Se in selenized quinoa exists not only as SeMet but also as selenate (Se(VI)) and non-protein forms.     

Current knowledge in species-related bioavailability of selenium in food

Selenium is an essential trace element that has raised interest because of its antioxidant and anticancer properties. The beneficial or toxic effect of Se is not only dose-dependent, but also relates to the chemical form of the element and its bioavailability. In this review, recently published data is summarised concerning both Se speciation and Se relative bioavailability in various foodstuffs. In addition, Se bioavailability is discussed in relation to the species-dependent metabolism in humans. In this way, the understanding of the potential health impact of Se species in commonly consumed food is aimed to be improved. It is strongly suggested on the basis of a higher retention and a lower toxicity, that organic Se (especially SeMet, the major species in food) is more recommendable than inorganic Se in the frame of a balanced diet. Further research is however desirable concerning the characterisation of unidentified Se species and determination of their health effects.     

Selenium species in buckwheat cultivated with foliar addition of Se(VI) and various levels of UV-B radiation

Common (Fagopyrum esculentum Moench) and tartary (Fagopyrum tataricum Gaertn.) buckwheat was treated by spraying the leaves with a water solution containing 15 mg Se per litre in the form of sodium selenate in the flowering period. The selenium content in all parts of plant was found to be less than 200 ng g⁻¹ in non-treated and in the range 2700–4650 ng g⁻¹ in selenium treated buckwheat. Exposure to UV-B radiation lead to higher Se accumulation in flowers of both Se enriched cultivars. For speciation analysis enzymatic hydrolysis was carried out, separation and detection of selenium species was performed by high performance liquid chromatography–ultraviolet treatment–hydride generation atomic fluorescence spectrometry (HPLC–UV–HG-AFS). In flowers and leaves, on average 11% of the Se content was soluble and in the form of Se(VI), representing between 0.6% (flowers) and 3% (leaves) of the Se content. The remaining soluble non-amino acid organic Se was not detected by HPLC–UV–HG-AFS. In seeds 93% of the selenium content was found in the extracts and the main selenium species was SeMet with 93 ± 5% relative to the selenium content.     

Selenium accumulation in protein fractions during germination of Se-enriched brown rice and molecular weights distribution of Se-containing proteins

This study investigated the accumulation of selenium (Se) in protein fractions of albumin, globulin, prolamin and glutelin extracted from Se-enriched brown rice and the molecular weight distribution of Se-containing proteins. Results showed that the amount of total Se (T-Se) and protein-bound Se (PB-Se) in brown rice was significantly (P < 0.05) increased after germination with 10–60 μmol/l sodium selenite. Except prolamin, the amount of all the other three protein fractions decreased significantly (P < 0.05) with the increase of germination time. Low Se concentrations had promoting effects on degradation of albumin and globulin, while no significant effects were observed on prolamin and glutelin. The accumulation of T-Se and PB-Se were in the order of albumin > glutelin > globulin > prolamin. Sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS–PAGE) analysis showed that Se was distributed in all the proteins of which molecular weights varied from 13.6 to 121.4 kDa; however, 84.34% of Se was observed in the proteins whose molecular weights less than 36.3 kDa.     

Bioavailability Assessment of Copper,Iron, Manganese,Molybdenum, Selenium,and Zinc from Selenium‐Enriched Lettuce

Cu, Fe, Mn, Mo, Selenium (Se), and Zn bioavailability from selenate‐ and selenite‐enriched lettuce plants was studied by in vitro gastrointestinal digestion followed by an assay with Caco‐2 cells. The plants were cultivated in the absence and presence of two concentrations (25 and 40 µmol/L of Se). After 28 days of cultivation, the plants were harvested, dried, and evaluated regarding the total concentration, bioaccessibility, and bioavailability of the analytes. The results showed that biofortification with selenate leads to higher Se absorption by the plant than biofortification with selenite. For the other nutrients, Mo showed high accumulation in the plants of selenate assays, and the presence of any Se species led to a reduction of the plant uptake of Cu and Fe. The accumulation of Zn and Mn was not strongly influenced by the presence of any Se species. The bioaccessibility values were approximately 71%, 10%, 52%, 84%, 71%, and 86% for Cu, Fe, Mn, Mo, Se, and Zn, respectively, and the contribution of the biofortified lettuce to the ingestion of these minerals is very small (except for Se and Mo). Due to the low concentrations of elements from digested plants, it was not possible to estimate the bioavailability for some elements, and for Mo and Zn, the values are below 6.9% and 3.4% of the total concentration, respectively. For Se, the bioavailability was greater for selenite‐enriched than selenate‐enriched plants (22% and 6.0%, respectively), because selenite is biotransformed by the plant to organic forms that are better assimilated by the cells.     

Selenium in cereals: Insight into species of the element from total amount

Selenium (Se) is a trace mineral micronutrient essential for human health. The diet is the main source of Se intake. Se-deficiency is associated with many diseases, and up to 1 billion people suffer from Se-deficiency worldwide. Cereals are considered a good choice for Se intake due to their daily consumption as staple foods. Much attention has been paid to the contents of Se in cereals and other foods. Se-enriched cereals are produced by biofortification. Notably, the gap between the nutritional and toxic levels of Se is fairly narrow. The chemical structures of Se compounds, rather than their total contents, contribute to the bioavailability, bioactivity, and toxicity of Se. Organic Se species show better bioavailability, higher nutritional value, and less toxicity than inorganic species. In this paper, we reviewed the total content of Se in cereals, Se speciation methods, and the biological effects of Se species on human health. Selenomethionine (SeMet) is generally the most prevalent and important Se species in cereal grains. In conclusion, Se species should be considered in addition to the total Se content when evaluating the nutritional and toxic values of foods such as cereals.     

Selenium speciation in enriched vegetables

The ability of several plants to accumulate and transform inorganic forms of selenium into bioactive organic compounds has important implications for human nutrition and health. Se-enriched Allium group vegetables such as garlic, onion and ramps have been mainly the subject of several studies in the recent years. Apart from the total Se uptake, enrichment treatments normally undergo certain metabolic changes that determine the final product as well as its translocation and accumulation in different plant tissues. For this reason, it is important to find which form of selenium should be used for supplementation to obtain a high content of this element in the final plant. Moreover, its distribution in different parts of plants as well as characterisation and quantification of individual species becomes an issue. This review gives a brief, critical overview of the studies carried out to characterise selenium species produced by different enriched vegetables. The use of different extraction and clean-up methodologies will be discussed in conjunction with different selenium enrichment procedures.     

Selenium speciation studies in Se-enriched chives (Allium schoenoprasum) by HPLC-ICP–MS

In this study, three liquid chromatographic techniques were employed to better understand selenium species distribution in Chives (Allium schoenoprasum) separately grown in three different supplementation media Se(IV), Se(VI), and SeMet. The highest selenium accumulation up to 700 μg Se g⁻¹ was observed in the case of the Se(VI)-enriched samples on the basis of total selenium measurements. Size-exclusion chromatography (SEC-HPLC) was performed for investigation of selenium containing proteins in chives. For speciation of selenium containing amino acids, reversed-phase ion-pairing chromatography (RP-IP-HPLC) and for enantiomeric separations, a crown ether column was used. In all three cases online detection with inductively coupled plasma mass spectrometry was performed for selenium specific detection. Two extractions (perchloric acid–ethanol and enzymatic) were carried out on chive samples. Speciation analysis on the chives grown in three different media revealed that selenium distribution among different forms of amino acids in the sample strongly depends on the type of enrichment employed. Enrichment with Se(VI) leads to accumulation of selenium in inorganic forms, while in case of Se(IV) and SeMet-enriched samples, methyl-selenocysteine and selenocystine were found to be present. Not surprisingly, chiral speciation revealed the presence of the l-enantiomeric forms of selenoamino acids in the sample. The major enantiomer found in the perchloric acid–ethanol extracts was l-MeSeCys, while in the enzymatic extracts l-SeMet was also detected.     

不同pH条件下米谷蛋白的理化及结构特性研究

为探索溶解大米蛋白的最适pH值,扩大其应用范围,表征了不同pH(pH 3.0,4.0,7.0)条件下大米蛋白中主要成分——米谷蛋白的理化及结构性质。结果表明,与中性条件下相比,酸性条件下米谷蛋白的溶解度和结构性质发生了明显改变,pH 7.0时米谷蛋白分子结合紧密,形成庞大的分子聚集体,溶解度仅(6.24±1.25)%;而在酸性条件下,米谷蛋白逐渐分散,分子间二硫键断裂,呈现分散疏松的小分子体状态,pH 3.0时其溶解度最高,达到(72.47±2.36)%。