共查询到19条相似文献,搜索用时 125 毫秒
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硝酸盐二元混合溶剂体系相平衡的研究 总被引:1,自引:1,他引:1
测定了硝酸钾、硝酸铵和硝酸钠在甲醇-水、氨-水二元混合溶剂体系的相平衡数据,查明了甲醇和氨对三种硝酸盐溶解度的影响规律。研究结果表明,随着甲醇浓度的增加,硝酸钾、硝酸铵和硝酸钠的溶解度均随之降低,其中硝酸钾的溶解度变化更为明显;随着氨浓度的上升,硝酸钾和硝酸钠的溶解度随之减少,而硝酸铵的溶解度却显著增加。氨对硝酸钾的选择分离结晶效果较好。 相似文献
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对京郊52种蔬菜产品,以及同一种类不同品种、同一品种产品的不同部位的硝酸盐、亚硝酸盐和VC含量等进行测定。结果表明:供试蔬菜产品器官的硝酸盐含量在不同种类、品种及其不同部位间存在明显差异。以蔬菜鲜质量器官中硝酸盐含量均值计算,根菜类(420.66mg/kg)>叶菜类(281.24mg/kg)>茎菜类(279.54mg/kg)>果菜类(176.54mg/kg)>花菜类(157.93mg/kg);同种蔬菜品种间的硝酸盐含量相差1.13~5.48倍;产品器官不同部位的硝酸盐含量也有较大差异,如结球叶菜硝酸盐含量外叶>中叶>内叶,叶柄>叶片,黄瓜果实顶部、基部>中部,果肉>果心,萝卜根皮>根肉。各供试蔬菜产品器官的亚硝酸盐含量多在1mg/kg以下,个别蔬菜种类如茼蒿可达6.74mg/kg,不同蔬菜种类、品种和部位间亚硝酸盐含量差异不如硝酸盐含量差异明显。果菜类、叶菜类和花菜类蔬菜产品器官的VC含量普遍较高,如辣椒可达146.56mg/100g,但品种间VC含量差异不显著。由此可见,目前京郊蔬菜产品器官中的硝酸盐和亚硝酸盐含量多在安全范围内,但仍建议消费者科学合理进行蔬菜种类搭配以保障人体健康。 相似文献
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10℃K^+,NH4^+/NO3^-—CH3OH,H2O混合溶剂体系相平衡研究 总被引:5,自引:2,他引:3
文章选择CH3OH作为添加剂,测定10℃条件下不同浓度(0%~60%)的CH3OH对K^ ,NH4^ /NO3^-—H2O体系相平衡的影响,结果表明:在无CH3OH加入时,体系中平衡固相有硝酸钾、硝酸铵和硝酸钾铵三种盐;随着CH3OH浓度的增大,硝酸钾结晶区显著增大;当CH3OH浓度大于50%时,体系中的硝酸钾铵混晶区完全消失。 相似文献
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贮存条件对蔬菜及其食品中硝酸盐、亚硝酸盐含量的影响 总被引:9,自引:0,他引:9
蔬菜是一种易于富积硝酸盐的植物性食品,据White等报道,人类摄取的硝酸盐80%以上来自蔬菜。虽然硝酸盐对人体的直接毒害性不大,但它很容易被还原成为亚硝酸盐,导致人畜患高铁血红蛋白症;更为严重的是,亚硝酸盐还可在人和动物体内与摄入的次级胺等含氮物结合,转化形成公认的强致癌物——亚硝胺,从而诱发消化系统癌变。因此,控制硝酸盐及亚硝酸盐的摄入量,对于维护人体健康至关重要。本文以几种常见的高富积硝酸盐蔬菜为试材,就不同的温度、不同质地的炊具和容器等贮存及烹制条件对鲜菜或菜汤中硝酸盐和亚硝酸盐含量状况的影响进行了初步研究… 相似文献
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对采自粤东地区的7种野生蔬菜的可食部分中硝酸盐、亚硝酸盐和Vc的含量进行测定,并参考WHO建议亚硝酸盐和硝酸盐的ADI值,进行卫生评价,结果表明,被测7种野菜的硝酸盐和亚硝酸盐的含量都低于限量标准;同时发现这7种野菜的Vc含量很高,营养丰富。 相似文献
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菠菜体内硝酸还原酶部分酶学性质及贮藏控制 总被引:4,自引:0,他引:4
以采后新鲜菠菜为原料,研究了菠菜体内硝酸还原酶(简称NR)部分酶学性质,及贮藏过程中ClO2处理对菠菜体内硝酸还原酶活性及亚硝酸盐生成量的影响。结果表明,菠菜体内NR最适反应温度为30℃;最适反应pH值为7.5;KNO3诱导对NR有激活作用,在一定浓度范围内,随着KNO3浓度的增加,菠菜体内NR活性增强,酶促反应速度加快;不同菠菜品种间NR活性存在显著性差异;与抽气后相比,抽气前加入DNP可明显抑制菠菜体内NR活性;贮藏过程中采用ClO2处理可以降低菠菜体内NR活性,从而降低亚硝酸盐的积累。 相似文献
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采用MSMPR结晶器研究了不同悬浮密度、氨水浓度和过饱和度下,KNO3在氨-水体系中的结晶动力学特性,并得到KNO3在氨水溶液中的结晶动力学模型.研究结果表明:随着悬浮密度的减少,晶体平均粒径增大,粒径分布变得均匀;氨的浓度增加,结晶成核 速率与生长速率均下降,晶体平均粒径减少,但粒径分布变均匀;随着过饱和度的加大,结晶成核速率与生长速率均增加,但晶体平均粒径减小,且粒径分布变差.研究结果可为硝酸钾生产工艺中结晶器的设计提供基础数据. 相似文献
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The nitrate and nitrite content of leaf vegetables (Swiss chard, sea beet, spinach and cabbage), “inflorescence” vegetables (cauliflower) and fruit vegetables (eggplant and vegetable marrow) grown with organic fertilizers have been determined by a modified cadmium–Griess method. Samples were purchased from organic food stores as well as collected directly from an organic farm in Madrid (Spain). Nitrate levels were much higher in the leaf vegetables (especially Swiss chard species; average over the different samples and species of 2778.6 ± 1474.7 mg kg? 1) than in inflorescence or fruit products (mean values between 50.2 ± 52.6 and 183.9 ± 233.6 mg kg? 1). Following Swiss chard species, spinach (1349.8 ± 1045.5 mg kg? 1) showed the highest nitrate content, and nitrite was found above the limit of detection in some samples only (spinach, 4.6 ± 1.0 mg kg? 1; sea beet, 4.2 ± 0.7 mg kg? 1 and Swiss chard, 1.2 ± 0.4 mg kg? 1). Some vegetables (spinach, cabbage and eggplant) had lower nitrate content in the samples harvested in summer, showing the influence of climatic conditions on the nitrate levels in a plant. The samples taken directly from the organic farm, with the exception of eggplant, had higher or slightly higher average nitrate values than samples purchased in the organic food stores, ranging from 117 to 1077%. 相似文献
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Pietro Santamaria 《Journal of the science of food and agriculture》2006,86(1):10-17
Nitrate content is an important quality characteristic of vegetables. Vegetable nitrate content is of interest to governments and regulators owing to the possible implications for health and to check that controls on the content are effective. Nitrate itself is relatively non‐toxic but its metabolites may produce a number of health effects. Until recently nitrate was perceived as a purely harmful dietary component which causes infantile methaemoglobinaemia, carcinogenesis and possibly even teratogenesis. Recent research studies suggest that nitrate is actually a key part of our bodies' defences against gastroenteritis. In this review are reported: (1) vegetable classification as a function of nitrate accumulation; (2) vegetable contribution to the total dietary exposure of nitrate; (3) European Commission Regulation No. 563/2002 which sets limits for nitrate in lettuce and spinach; (4) the maximum levels set in some countries for beetroot, cabbage, carrot, celery, endive, Lamb's lettuce, potato, radish and rocket; (5) the results of surveys on the nitrate content of vegetables in Italy and other European countries. Copyright © 2005 Society of Chemical Industry 相似文献
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Levels of nitrate and nitrite in 73 different vegetables, a total of 708 individual samples grouped into leafy, legumes, root and tuber, and fruiting vegetables, which are traded mainly in Hong Kong, were measured. Where available, five samples of each vegetable type were purchased from different commercial outlets during the winter of 2008 and summer of 2009. Levels of nitrate and nitrite were determined by ion chromatography and flow injection analysis, respectively. Nitrate and nitrite levels of all samples ranged <4–6300 and <0.8–9.0 mg?kg?1, respectively. Nitrate concentrations for the different groups, in descending order, were leafy?>?root and tuber?>?fruiting and legume vegetables. More than 80% of vegetables had mean nitrate concentrations less than 2000?mg?kg?1, but mean nitrate concentrations of three types of leafy vegetables, namely Chinese spinach, Shanghai cabbage and Chinese white cabbage, were >3500?mg?kg?1. On the other hand, nitrite concentrations were generally low –?<1?mg?kg?1 on average. Nitrate in vegetables (i.e. Chinese flowering cabbage, Chinese spinach and celery) can be reduced significantly (12–31%) after blanching for 1–3?min, but not after soaking. 相似文献
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广东产苋科6种野菜中硝酸盐、亚硝酸盐及VC的含量 总被引:16,自引:2,他引:16
测定了广东产苋科6种野菜中硝酸盐、亚硝酸盐和维生素C的含量。结果表明:青葙、刺苋的硝酸盐较高、亚硝酸盐含量符合我国无公害蔬菜限量标准,维生素C含量又较为丰富,它们为品质较好的野菜;繁穗苋维生素C含量高,硝酸盐含量高,亚硝酸盐含量较低,煮熟可安全食用;空心莲子草、皱果苋和苋菜的维生素C含量较高,亚硝酸盐含量较低,但硝酸盐含量严重超标,须采取一定的措施,限量食用。 相似文献
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Francesco Serio Antonio Elia Angelo Signore Pietro Santamaria 《Journal of the science of food and agriculture》2004,84(11):1428-1432
Potato is classified among the vegetables with low nitrate content but, in diet, it contributes most to the daily intake of nitrate, because of its high per capita consumption. Two trials were carried out in winter–spring and autumn–winter cycles using a trough bench subirrigation system. Potato seedlings were transplanted into pots containing peat, pumice and vermiculite in a 3:1:1 volume ratio. Both trials were carried out to compare three nutrient solutions having the same nitrogen concentration (6.4 mM ), but different ammonium:nitrate (NH4‐N:NO3‐N) percentage ratios (100:0, 50:50 and 0:100). In the winter–spring cycle, tubers were lower in weight and were more numerous than in the autumn–winter cycle. The tuber yield of ammonium‐fed plants was lower than with the mixed form and 100% NO3‐N, but only in the trial carried out in the winter–spring period. Nitrate‐fed plants yielded a number of tubers almost 3‐fold higher than ammonium‐fed plants. The NO3 content of tubers harvested in spring in the presence of 100% NH4‐N in the nutrient solution was a 25% of that in nitrate‐fed plants (44 vs 169 mg kg?1 of fresh mass); in tubers harvested in winter, with worse light conditions, nitrate content increased with increasing NO3‐N in the nutrient solution (26, 109, and 225 mg kg?1 of fresh mass with NH4‐N:NO3‐N 100:0, 50:50 and 0:100, respectively). The substrate electrical conductivity increased with increasing ammonium concentration in the nutrient solution, and was higher in the upper layer of the substrate. Copyright © 2004 Society of Chemical Industry 相似文献
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David J Lyons George E Rayment Peter E Nobbs Leith E McCallum 《Journal of the science of food and agriculture》1994,64(3):279-281
Vegetables were collected near peak harvest from the main production regions in Queensland and were analysed for residues of nitrate and nitrite. A small sample of hydroponic produce was also included in the survey. Nitrite-N from 1 to 4 mg kg-1 was found only in dwarf beans and in lettuces. Levels of nitrate in potatoes, cabbages and beets were higher than those reported in other surveys and exceeded threshold limits set in one other country. The median nitrate-N concentration measured in hydroponic lettuce (465 mg kg-1 nitrate-N) was more than twice the median concentration for field-grown lettuce. Poor correlation between total N and nitrate in vegetables raises doubts about the use of total N alone as an indicator of N status. 相似文献
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厦门市售蔬菜重金属、硝酸盐和亚硝酸盐污染研究及评价 总被引:8,自引:0,他引:8
为了解厦门市蔬菜中有害重金属、硝酸盐和亚硝酸盐的污染情况,于2004年8月至2005年12月从厦门市各超市、农贸市场、蔬菜批发市场和蔬菜产地上采集46个品种532份蔬菜样品,用国标法(GB/T5009.11-17-1996、GB/T5009.33-2003)分别分析蔬菜中的重金属、硝酸盐和亚硝酸盐的含量。结果表明,检测样品中Pb、Cd、As、Hg、硝酸盐和亚硝酸盐的平均值分别为0.0099、0.083、0.056、0.003、1090.3、0.59mg/kg;根据国家标准1-2,仅部分品种如菠菜、甘蓝、花菜、萝卜的铅超标,有潜在污染风险;大部分蔬菜中砷、汞、镉三种重金属的含量都较低,潜在的污染风险不大。硝酸盐污染程度严重的占36.5%;中、重度污染的占20.2%;轻度的占43.3%,硝酸盐含量依次为嫩茎叶菜类>根茎类>花菜类>瓜菜类>鲜豆菜>茄果类>水生蔬菜类,各样品间含量差别较大;而蔬菜中亚硝酸盐含量相对较低。 相似文献