蔬菜营养与硝酸盐的关系

蔬菜硝酸盐累积是无公害蔬菜生产的限制因子之一,与蔬菜营养的关系密切．喜硝性是蔬菜作物的营养特性,NO3^-通过高亲和吸收转运系统和低亲和吸收转运系统被蔬菜吸收,在钼、锰、铁、铜、硫、磷等多种必需营养元素参与下被还原同化．文中简述了必需营养元素在蔬菜硝酸盐吸收和还原同化中的作用,重点论述了氮肥用量、种类及形态配比、施用时期、方法和氮素供应方式、磷素营养、钾索营养、中微量元素营养和平衡营养与蔬菜硝酸盐累积的关系,提出了今后研究工作的主攻方向,为控制蔬菜硝酸盐累积、提高蔬菜品质和生产无污染、安全、优质的无公害蔬菜提供参考．     

重庆市蔬菜硝酸盐、亚硝酸盐含量及其与环境的关系

在重庆市的主要蔬菜中,硝酸盐含量依次为根菜类＞叶菜类＞葱蒜类＞瓜类＞豆类＞茄果类,前３类的硝酸盐含量超标,但各种蔬菜的亚硝酸盐含量一般较低,未超过卫生标准。就同一种蔬菜的不同样品而言,硝酸盐和亚硝酸盐含量的差异很大,说明品种或环境条件可显著影响其含量。重庆市多雾少光,冬春低温,土壤含氮量和钠高子含量较高,有效钾含量较低可能是导致蔬菜大量积累硝酸盐的环境因素。蔬菜不同器官硝酸盐和亚硝酸盐含量各异,根＞茎＞叶柄＞叶片。     

降低蔬菜硝酸盐含量的食前处理方法

以小白菜、萝卜和四季豆为试材,研究了不同食前处理（清水浸泡、盐渍、漂烫）对蔬菜硝酸盐和维生素C（VitC）含量的影响。结果表明,清水浸泡和漂烫处理均可较大程度地降低蔬菜硝酸盐含量;盐渍处理硝酸盐含量下降不明显,其中萝卜经盐渍后硝酸盐含量反而升高;三种处理方式以漂烫0.5 min处理蔬菜VitC含量损失最小。     

六种野菜不同部位硝酸盐、亚硝酸盐及维生素C的含量

报道了6种野菜不同部位的硝酸盐、亚硝酸盐和维生素C的含量。参考蔬菜中硝酸盐含量分级评价标准和无公害蔬菜亚硝酸盐含量限量标准,结合各种野菜及不同部位的维生素C的含量,对这6种野菜评价如下:鼠麴草的叶、龙葵的叶、苋的嫩茎和叶,属于一级野菜,可以安全食用;鼠麴草的嫩茎属二级蔬菜范围,不宜生食,煮熟或盐渍可安全食用;龙葵的嫩茎、树仔菜的嫩茎,属于三级蔬菜,不可生食和盐渍,可熟食。白子菜的嫩茎和狗肝菜的嫩茎,属于四级蔬菜,不宜食用或限量食用;树仔菜的叶、白子菜的叶亚硝酸盐含量高于我国制定的无公害蔬菜亚硝酸盐含量的限量标准,所以不宜食用或限量食用。     

湛江常见野菜安全可食性探讨

对湛江野菜所含的硝酸盐、维生素C、胡萝卜素及氨基酸进行了测定和分析。结果表明,刺苋和野当归富含维生素C和胡萝卜素,硝酸盐含量较低,实为品质上乘野蔬。东风菜和枸杞虽然胡萝卜素含量很高,但前者维生素C和氨基酸含量较低,后者硝酸盐含量已超过三级蔬菜标准。不宜大量食用。其余几种野菜营养成分比传统蔬菜高,属于安全食用性野菜。     

Plant polyphenols: how to translate their in vitro antioxidant actions to in vivo conditions

Epidemiological evidence demonstrates that diets rich in fruit and vegetables promote health, and attenuate, or delay, the onset of various diseases, including cardiovascular disease, diabetes, certain cancers, and several other age-related degenerative disorders. The chemical components and the physiological and molecular mechanisms by which fruit and vegetables reduce the risk for these pathophysiological conditions are matters of intense investigation. Regarding plant components, polyphenols are a group of phytochemicals that are gaining acceptance as responsible for the health benefits offered by fruit and vegetables. Because of their chemical structure, plant polyphenols are able to scavenge free radicals and inactivate other pro-oxidants. The connection of these chemical properties to a physiological antioxidant action has triggered extensive research aimed to relate the consumption of plant polyphenols with human health. Although significant progress has been made, there are still some critical areas that need to be elucidated to arrive at definitive conclusions on the mechanisms linking plant polyphenol consumption, reduction in oxidative damage, and health improvement. Some of these topics will be discussed in this review of alternative molecular mechanisms, based on polyphenol-membranes and polyphenol-proteins interactions that develop in an antioxidant protection but are not directly related to free radical scavenging or metal chelating.     

Gastroprotective and blood pressure lowering effects of dietary nitrate are abolished by an antiseptic mouthwash

Recently, it has been suggested that the supposedly inert nitrite anion is reduced in vivo to form bioactive nitric oxide with physiological and therapeutic implications in the gastrointestinal and cardiovascular systems. Intake of nitrate-rich food such as vegetables results in increased levels of circulating nitrite in a process suggested to involve nitrate-reducing bacteria in the oral cavity. Here we investigated the importance of the oral microflora and dietary nitrate in regulation of gastric mucosal defense and blood pressure. Rats were treated twice daily with a commercial antiseptic mouthwash while they were given nitrate-supplemented drinking water. The mouthwash greatly reduced the number of nitrate-reducing oral bacteria and as a consequence, nitrate-induced increases in gastric NO and circulating nitrite levels were markedly reduced. With the mouthwash the observed nitrate-induced increase in gastric mucus thickness was attenuated and the gastroprotective effect against an ulcerogenic compound was lost. Furthermore, the decrease in systemic blood pressure seen during nitrate supplementation was now absent. These results suggest that oral symbiotic bacteria modulate gastrointestinal and cardiovascular function via bioactivation of salivary nitrate. Excessive use of antiseptic mouthwashes may attenuate the bioactivity of dietary nitrate.     

广东8种野菜中硝酸盐、亚硝酸盐及Vc的含量

测定了广东菊科8种野菜中硝酸盐、亚硝酸盐和维生素C的含量,结果表明：革命菜、一点红、苣荬菜的硝酸盐含量低于轻度污染水平,属于一级野菜;山莴苣、地胆草、加拿大蓬和艾的硝酸盐含量低于785mg/kg,达中度污染水平,属二级蔬菜范围,不宜生食,煮熟或盐渍可安全食用;甜菜籽属于三级蔬菜,不可生食和盐渍,可熟食.这些野菜维生素C的含量均低于50mg/100g（鲜重）,属于中、低维生素C含量的野菜.     

蔬菜作物积累硝酸盐的基因型差异及环境意义

城郊土壤富营养化已成为目前城郊农业生态系统可持续发展不可回避的环境问题之一,氮、磷养分富集是城郊土壤富营养化的重要表现形式,因土壤氮素积累而引起的蔬菜可食部位硝酸盐超标是一个亟待解决的技术难题.本文综述了不同蔬菜种及品种间吸收积累硝酸盐的基因型差异及其差异形成的生理生化机制,指出充分利用我国丰富的蔬菜种质资源,以植物吸收积累硝酸盐的基因型差异为理论基础,筛选弱吸收低积累蔬菜作物品种,是削减、控制蔬菜可食部位硝酸盐含量的关键性技术,有可能缓解城郊区脆弱生态环境条件下集约化生产对硝酸盐农艺阻控措施的依赖.     

The increase in plasma nitrite after a dietary nitrate load is markedly attenuated by an antibacterial mouthwash

Recent studies surprisingly show that dietary inorganic nitrate, abundant in vegetables, can be metabolized in vivo to form nitrite and then bioactive nitric oxide. A reduction in blood pressure was recently noted in healthy volunteers after dietary supplementation with nitrate; an effect consistent with formation of vasodilatory nitric oxide. Oral bacteria have been suggested to play a role in bioactivation of nitrate by first reducing it to the more reactive anion nitrite. In a cross-over designed study in seven healthy volunteers we examined the effects of a commercially available chlorhexidine-containing antibacterial mouthwash on salivary and plasma levels of nitrite measured after an oral intake of sodium nitrate (10 mg/kg dissolved in water). In the control situation the salivary and plasma levels of nitrate and nitrite increased greatly after the nitrate load. Rinsing the mouth with the antibacterial mouthwash prior to the nitrate load had no effect on nitrate accumulation in saliva or plasma but abolished its conversion to nitrite in saliva and markedly attenuated the rise in plasma nitrite. We conclude that the acute increase in plasma nitrite seen after a nitrate load is critically dependent on nitrate reduction in the oral cavity by commensal bacteria. The removal of these bacteria with an antibacterial mouthwash will very likely attenuate the NO-dependent biological effects of dietary nitrate.     

Intragastric nitration by dietary nitrite: implications for modulation of protein and lipid signaling

Inorganic nitrite, derived from the reduction of nitrate in saliva, has recently emerged as a protagonist in nitric oxide (^?NO) biology as it can be univalently reduced to ^?NO, in the healthy human stomach. Important physiological implications have been attributed to nitrite-derived ^?NO in the gastrointestinal tract, namely modulation of host defense, blood flow, mucus formation and motility. At acidic pH, nitrite generates different nitrogen oxides depending on the local microenvironment (redox status, gastric content, pH, inflammatory conditions), including ^?NO, nitrogen dioxide (^?NO₂), dinitrogen trioxide (N₂O₃), and peroxynitrite. Thus, the gastric environment is a significant source of nitrating and nitrosating agents, especially in individuals consuming a nitrate/nitrite-rich diet on a daily basis. Both, the gastric lumen and mucosa contain putative targets for nitration, not only proteins and lipids from ingested aliments but also endogenous proteins secreted by the oxyntic glands. The physiological and functional consequences of nitration of gastric mediators will impact on local processes including food digestion and ulcerogenesis. Additionally, gastric nitration products (such as nitrated lipids) may be absorbed and affect systemic pathways. Thus, dietary ingestion of nitrate will have direct consequences for endogenous protein nitration, as indicated by our preliminary data.     

Dietary nitrite induces occludin nitration in the stomach

The clinical implications of the nitrate–nitrite–nitric oxide pathway have been extensively studied in recent years. However, the physiological impact of bioactive nitrogen oxides produced from dietary nitrate has remained largely elusive. Here, we report a hitherto unrecognized nitrite-dependent nitrating pathway that targets tight junction proteins in the stomach. Inorganic nitrate, nitrite or saliva obtained after the consumption of lettuce were administered by oral gavage to Wistar rats. The enterosalivary circulation of nitrate was allowed to occur for 4?h after which the animals were euthanized and the stomach collected. Nitrated occludin was detected by immunoprecipitation in the gastric epithelium upon inorganic nitrite administration (p??NO production rates from inorganic and salivary nitrite under simulated gastric conditions, suggests that competing reactions at acidic pH determine the production of nitrating agents (^?NO₂) or other, more stable, oxides. Accordingly, it is shown in vitro that salivary nitrite yields higher steady state concentrations of ^?NO (0.37?±?0.01?μM) than sodium nitrite (0.12?±?0.03?μM). Dietary-dependent reactions involving the production of nitrogen oxides should be further investigated as, in the context of occludin nitration, the consumption of green leafy vegetables (with high nitrate content), if able to modulate gut barrier function, may have important implications in the context of leaky gut disorders.     

Effect of glutamic acid foliar applications on lettuce under water stress

The yield and quality of leafy vegetables can be compromised by reduced water availability. Glutamic acid is involved in different biological processes and among them it plays an important role in chlorophyll and proline biosynthesis. The aim of this work was to evaluate the possible efficacy of glutamic acid in counteracting water stress in romaine lettuce. Lettuce plants were grown in pots filled with substrate and subjected to water deprivation. A glutamic acid solution (1.9 mM) was applied as foliar treatment, both in stressed and non-stressed plants. The effect of the treatment was evaluated at different time points during the experiment in order to evaluate changes at a molecular, physiological, biochemical and agronomic level. Yield was reduced by 35% in stressed plants, while no significant changes in quality parameters were observed, except for nitrate content, which increased under water stress. At a molecular level, the expression of genes encoding for ROS scavenging enzymes was monitored but, apparently, glutamic acid did not significantly prevent the water stress response. Slightly positive effects deriving from glutamic acid application were found for nitrate and proline contents, suggesting that a possible mode of action of glutamic acid would involve a role for these molecules. Further studies are required, also on other crop species, for confirming these results. Different concentrations and application modes should be also tested.     

粤西四种野菜营养成分分析

以常规方法对黄鹌菜、鸡屎藤、打碗花、一点红的营养成分进行了测定和分析.结果表明,4种野菜都含有较高的膳食纤维.打碗花、鸡屎滕的抗坏血酸含量及打碗花中的胡萝卜素含量比传统蔬菜白菜、波菜要高.四种野菜所测的矿质元素含量差异较大,其中一点红的含铁量最高.在硝酸盐和亚硝酸盐含量的分析中,黄鹌菜、一点红属一级无公害蔬菜,可放心食用.鸡屎藤、打碗花属二级蔬菜范围,不宜生食,煮熟和盐渍后可放心食用.     

植物叶片和采后果蔬的过氧化氢酶活性

为了认识不同植物种类和采后果蔬过氧化氢酶(CAT)的生理特性,测定了40种植物叶片和30种采后果蔬的CAT活性和过氧化氢(H₂O₂)含量,分别从不同光合碳代谢类型和不同植物器官的角度进行了分析比较。结果表明,C3植物叶片的CAT活性大于C4和CAM植物,C4植物叶片的CAT活性大于CAM植物,叶片的CAT活性反映了不同光合碳代谢类型所具有的生理生态特性。叶菜类的CAT活性最大,其次是花菜类,结球叶菜类和果实类的CAT活性大于鳞茎菜类、地下茎菜类和地下根菜类,采后果蔬的CAT活性一般与植物器官的生理生态特性相关。     

Protection from nonsteroidal anti-inflammatory drug (NSAID)-induced gastric ulcers by dietary nitrate

Nitrate is abundant in our diet with particularly high levels in many vegetables. Ingested nitrate is concentrated in saliva and reduced to nitrite by bacteria in the oral cavity. We recently reported that application of nitrite-containing saliva to the gastric mucosa increases superficial blood flow and mucus generation via acid-catalyzed formation of bioactive nitrogen oxides including nitric oxide. Here we studied if dietary supplementation with nitrate would protect against gastric damage caused by a nonsteroidal anti-inflammatory drug. Rats received sodium nitrate in the drinking water for 1 week in daily doses of 0.1 or 1 mmol kg(-1). Control rats received 1 mmol kg(-1) sodium chloride. Diclofenac (30 mg kg(-1)) was then given orally and the animals were examined 4 h later. In separate experiments we studied the effects of dietary nitrate on intragastric NO levels and mucus formation. Luminal levels of NO gas were greatly increased in nitrate-fed animals. The thickness of the mucus layer increased after nitrate supplementation and gene expression of MUC6 was upregulated in the gastric mucosa. Nitrate pretreatment dose dependently and potently reduced diclofenac-induced gastric lesions. Inflammatory activity was reduced in the rats receiving nitrate as indicated by lower mucosal myeloperoxidase activity and expression of inducible NO synthase. We conclude that dietary nitrate protects against diclofenac-induced gastric ulcers likely via enhanced nitrite-dependent intragastric NO formation and concomitant stimulation of mucus formation. Future studies will reveal if a diet rich in nitrate can offer an additional nutritional approach to preventing and treating peptic ulcer disease.     

Molecular and Regulatory Properties of the Nitrate Reducing Systems of Rhodobacter

Phototrophic bacteria of the genus Rhodobacter possess several forms of nitrate reductase including assimilatory and dissimilatory enzymes. Assimilatory nitrate reductase from Rhodobacter capsulatus E1F1 is cytoplasmic, it uses NADH as the physiological electron donor and reduced viologens as artificial electron donors, and it is coupled to an ammonium-producing nitrite reductase. Nitrate reductase induction requires a high C/N balance and the presence of nitrate, nitrite, or nitroarenes. A periplasmic 47-kDa protein facilitates nitrate uptake, thus increasing nitrate reductase activity. Two types of dissimilatory nitrate reductases have been found in strains from Rhodobacter sphaeroides. One of them is coupled to a complete denitrifying pathway, and the other is a periplasmic protein whose physiological role seems to be the dissipation of excess reducing power, thus improving photoanaerobic growth. Periplasmic nitrate reductase does not use NADH as the physiological electron donor and is a 100-kDa heterodimeric hemoprotein that receives electrons through an electron transport chain spanning the plasma membrane. This nitrate reductase is regulated neither by the intracellular C/N balance nor by O₂ pressure. The enzyme also exhibits chlorate reductase activity, and both reaction products, nitrite and chlorite, are released almost stoichiometrically into the medium; this accounts for the high resistance to chlorate or nitrite exhibited by this bacterium. Nitrate reductases from both strains seem to be coded by genes located on megaplasmids. Received: 17 April 1996 / Accepted: 28 May 1996     

综述: 柚皮素：新一代免疫调节剂

大量研究表明,植物来源的黄酮类化合物具有广泛的生理活性和药理作用,日常摄取适量的黄酮类化合物能够显著降低许多疾病的发生.柚皮素作为一种自然界分布广泛的黄酮类化合物富含于水果、蔬菜、坚果、咖啡、茶和红酒等日常饮食中,与其他黄酮类化合物相比柚皮素易于胃肠道吸收、生物利用度高且安全剂量大.自2004年起我们对柚皮素调节免疫的分子机制进行了深入系统的研究.本文将重点介绍柚皮素作为一种新型免疫调节剂的研究进展.     

四种野菜硝酸盐,亚硝酸盐及维生素C的含量

四种野菜硝酸盐、亚硝酸盐及维生素Ｃ的含量邱贺媛（唐山师范专科学校化学系,唐山０６３０００）Ｔｈｅｃｏｎｔｅｎｔｓｏｆｎｉｔｒａｔｅ,ｎｉｔｒｉｔｅａｎｄｖｉｔａｍｉｎＣｏｆｆｏｕｒｅｄｉｂｌｅｗｉｌｄｖｅｇｅｔａｂｌｅｓＱｉｕＨｅ－Ｙｕａｎ（Ｃｈｅｍ...     

Daily changes in uptake, reduction and storage of nitrate in spinach grown at low light intensity

Under poor light conditions, as normally used during winter production of greenhouse vegetables, the nitrate concentration in the shoot of spinach ( Spinacia oleracea L. cv. Vroeg Reuzenblad) showed a diurnal rhythm. This rhythm was mainly caused by a decrease during the day, followed by an increase during the night in the leaf blade nitrate concentration. Nitrate was mainly located in the vacuoles of the leaf blades. A strong correlation was found between net uptake of nitrate by the roots and the nitrate concentration in the leaf blade vacuoles. The nitrate concentration in the leaf blades increased during the initial hours of the night. This increase was caused by a marked increase in the net uptake rate of nitrate by the roots during the first hours of the dark period. During the second part of the night both net uptake rate of nitrate by the roots and the vacuolar nitrate concentration in the leaf blades remained constant.
We conclude that nitrate is taken up for osmotic purposes when light conditions are poor because of a lack of organic solutes. During the night, nitrate influx into the vacuole is needed for replacement of organic solutes, which are metabolized during the night, and possibly also for leaf elongation growth. During the day, vacuolar nitrate may be exchanged for newly synthesized organic solutes and be metabolized in the cytoplasm. A strong diurnal rhythm in nitrate reductase (NR; EC 1.6.6.1.) activity was absent, due to the poor light conditions, and in vitro NR activity was not correlated with nitrate flux from the roots. In vivo NR activity also lacked a strong diurnal rhythm, but it was calculated that in situ nitrate reduction was much lower during the night, so that the major nitrate assimilation took place during the day.