Ascorbic acid,nitrate, and nitrite concentration relationship to the 24 hour light/dark cycle for spinach grown in different conditions

Nitrate, nitrite and ascorbic acid (vitamin C) concentrations were determined for spinach (Spinacia oleracea L.) over a 24 h period to determine if light intensity (including dark periods) at time of harvest impacts concentrations in raw vegetables. Nitrate, nitrate and ascorbic acid concentrations varied significantly over the 24 h period and appeared to be related to changes in light intensity. Light intensity at the time an experimental sample is collected may affect the concentration of some constituents that a researcher is studying. Also, nitrate and nitrite concentrations in raw spinach can be reduced by harvesting at the best time of day. The highest nitrate concentrations in spinach occurred in the dark just prior to an increase in light intensity. Ascorbic acid was near its highest level for the 24 h period when the light intensity initially increased, then decreased to its lowest level around 3–6 h later.     

Nitrate-N determination in leafy vegetables: Study of the effects of cooking and freezing

Nitrate upon reduction to nitrite can cause methaemoglobinaemia or act as precursor in the endogenous formation of carcinogenic nitrosamines. The leafy vegetables are the major vehicle for the entry of nitrate into the human system. The present study was conducted to establish a flow injection analysis (FIA) technique to investigate the nitrate-N contents of four commonly consumed fresh leafy vegetables (Chinese cabbage, celery, lettuce and English cabbage) from market in Fiji. Two extraction techniques (activated carbon and alkaline extraction) were assessed to extract nitrate-N and the activated carbon extraction was preferred over alkaline extraction and applied. The recoveries of spiked nitrate-N in vegetable matrices ranged from 90.40% to 112.80% in activated carbon extraction with an average of 100.62%. The effects of cooking (boiling, baking and frying) and deep-freezing on the nitrate-N contents were also studied. Nitrate contents in selected leafy vegetables were determined by FIA coupled with Greiss protocol involving sulfanilamide and N-(1-naphthyl)ethylenediamine dihydrochloride as color reagents. Nitrate was determined in the linear range from 1.0 to 20.0 mg L⁻¹ with the method detection limit of 0.042 mg L⁻¹ (0.34 mg kg⁻¹). The results of the study show that nitrate contents in fresh leafy vegetables ranged from 1297 to 5658 mg kg⁻¹. Boiling reduces nitrate content by 47–56% whereas frying in Soya bean oil elevates nitrate content by as much as 159–307%. No significant change was observed in nitrate content after baking. The deep-freezing of the selected leafy vegetables shows that nitrate-N content fluctuates slightly from the original nitrate-N values over the seven day period. The FIA throughput was 38 samples h⁻¹.     

Nitrate and nitrite levels in commonly consumed vegetables in Hong Kong

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.     

Nitrate and nitrite quantification from cured meat and vegetables and their estimated dietary intake in Australians

High dietary nitrate and nitrite intake may increase the risk of gastro-intestinal cancers due to the in vivo formation of carcinogenic chemicals known as N-nitroso compounds. Water and leafy vegetables are natural sources of dietary nitrate, whereas cured meats are the major sources of dietary nitrite. This paper describes a simple and fast analytical method for determining nitrate and nitrite contents in vegetables and meat, using reversed-phase HPLC-UV. The linearity R² value was >0.998 for the anions. The limits of quantification for nitrite and nitrate were 5.0 and 2.5 mg/kg, respectively. This method is applicable for both leafy vegetable and meat samples. A range of vegetables was tested, which contained <23 mg/kg nitrite, but as much as 5000 mg/kg of nitrate. In cured and fresh meat samples, nitrate content ranged from 3.7 to 139.5 mg/kg, and nitrite content ranged from 3.7 to 86.7 mg/kg. These were below the regulatory limits set by food standards Australia and New Zealand (FSANZ). Based on the average consumption of these vegetables and cured meat in Australia, the estimated dietary intake for nitrate and nitrite for Australians were 267 and 5.3 mg/adult/day, respectively.     

Survival of Listeria innocua in dry fermented sausages and changes in the typical microbiota and volatile profile as affected by the concentration of nitrate and nitrite

The involvement of nitrate and nitrite in the formation of N-nitrosamines in foods is a matter of great concern. This situation has led to revise the real amount of nitrate and nitrite needed in meat products to exert proper technological and safety activities, and also to extensive research to find alternatives to their use. The present study addresses the possibility of reducing the ingoing amounts of these additives below the legal limits established by the current European regulations. Different concentrations of nitrate and nitrite were tested on Spanish salchichón-type dry fermented sausages concerning their role in the microbiota and volatile profile. Sausages were manufactured with the maximum ingoing amounts established by the EU regulations (150 ppm NaNO₃ and 150 ppm NaNO₂), a 25% reduction and a 50% reduction; control sausages with no nitrate/nitrite addition were also prepared. The mixtures were inoculated with 5 log cfu/g of Listeria innocua as a surrogate for Listeria monocytogenes. L. innocua numbers in the final product were approximately 1.5 log cfu/g lower in the batch with the maximum nitrate/nitrite concentration when compared to 25 and 50% reduced batches, and about 2 log cfu/g in comparison to the control sausages. The final numbers of catalase-positive cocci were 1 log cfu/g higher in the 50% nitrate/nitrite reduced batch and 2 log cfu/g higher in the control sausages, compared to products manufactured with the maximum nitrate/nitrite concentration. This increase was related to a higher amount of volatile compounds derived from carbohydrate fermentation and amino acid degradation. Sausages with no addition of nitrate/nitrite showed higher amount of volatiles from lipid oxidation. Enterobacteriaceae counts reached detectable values (1-2 log cfu/g) in both nitrate/nitrite reduced sausages and in the control batch, while these organisms were not detected in the batch with the maximum ingoing amount. Nitrate and nitrite exerted a significant effect on the typical microbiota of dry fermented sausages and effectively contributed to control Listeria. These considerations should be taken into account in view of a future restriction in the use of these curing additives.     

Effects of high hydrostatic pressure and varying concentrations of sodium nitrite from traditional and vegetable-based sources on the growth of Listeria monocytogenes on ready-to-eat (RTE) sliced ham

The objective of this study was to determine the effect the source of added nitrite and high hydrostatic pressure (HHP) had on the growth of Listeria monocytogenes on ready-to-eat (RTE) sliced ham. Use of 600 MPa HHP for 3 min resulted in an immediate 3.9–4.3 log CFU/g reduction in L. monocytogenes numbers, while use of 400 MPa HHP (3 min) provided less than 1 log CFU/g reduction. With the 600 MPa HHP treatment, sliced ham with a conventional concentration of sodium nitrite (200 ppm) was not different in L. monocytogenes growth from use with 50 or 100 ppm of sodium nitrite in pre-converted celery powder. Instrumental color values as well as residual nitrite and residual nitrate concentrations for cured (sodium nitrite and nitrite from celery powder) and uncured ham formulations are discussed.     

Mild Fe-deficiency improves biomass production and quality of hydroponic-cultivated spinach plants (Spinacia oleracea L.)

It is of great practical importance to improve yield and quality of vegetables in soilless cultures. This study investigated the effects of iron-nutrition management on yield and quality of hydroponic-cultivated spinach (Spinacia oleracea L.). The results showed that mild Fe-deficient treatment (1 μM FeEDTA) yielded a greater biomass of edible parts than Fe-omitted treatment (0 μM FeEDTA) or Fe-sufficient treatments (10 and 50 μM FeEDTA). Conversely, mild Fe-deficient treatment had the lowest nitrate concentration in the edible parts out of all the Fe treatments. Interestingly, all the concentrations of soluble sugar, soluble protein and ascorbate in mild Fe-deficient treatments were higher than Fe-sufficient treatments. In addition, both phenolic concentration and DPPH scavenging activity in mild Fe-deficient treatments were comparable with those in Fe-sufficient treatments, but were higher than those in Fe-omitted treatments. Therefore, we concluded that using a mild Fe-deficient nutrition solution to cultivate spinach not only would increase yield, but also would improve quality.     

Nitrate and Nitrite Methods of Analysis and Levels in Raw Carrots, Processed Carrots and in Selected Vegetables and Grain Products

Methods for quantitative estimation of nitrate and nitrite were compared. Levels of these ions were measured in vegetables and grain products and effects of processing on nitrate and nitrite levels in carrots were measured. These data allow more accurate estimation of ingestion levels and suggest means to reduce exposure to these ions. High performance liquid chromatography (HPLC) had better precision and recoveries than either a classical Cd-Griess method nitrate or a Griess method for nitrite. Nitrate concentration by HPLC varied greatly within and between vegetables, ranging from 1 μmol/100g in mushrooms to 5000 μmol/100g in celery and averaging 9.7 ± 4.4 μmol/100g in grains. Nitrate levels in vegetables sold as “organic” were not different (p<0.05) from conventional vegetables. No nitrite was detected in either vegetables or grains. Nitrate was unevenly distributed in carrots with the core having the most. Storage of carrots at -18°C for 10 wk did not alter nitrate levels and no nitrite developed. Fifty-seven percent of nitrate was leached into cooking liquid when frozen carrots were boiled. Thirty-two percent of nitrate was lost during canning and 47% of the remainder was in the liquid. No nitrite developed during 10 wk of canned storage.     

黄鹌菜中硝酸盐、亚硝酸盐及VC的含量

本文测定分析了不同生长发育阶段黄鹌菜中硝酸盐、亚硝酸盐和VC的含量,以及漂烫对其影响。结果表明:在各个不同发育阶段,黄鹌菜的硝酸盐和亚硝酸盐含量变化不大,除了花期属于二级野菜外,其余各期均为一级野菜;随着漂烫时间的加长,其硝酸盐、亚硝酸盐和VC的含量逐渐降低。     

蔬菜中亚硝酸盐和硝酸盐检测技术研究进展

硝酸盐和亚硝酸盐广泛存在于人们的生活中,人体外源性硝酸盐的摄入大多来自蔬菜。硝酸盐对人体没有直接危害,但它可以在人体内的酶和微生物的作用下转化为有毒的亚硝酸盐,使血液的输氧能力下降,导致高铁血红高蛋白症。蔬菜在人们的日常膳食中占据重要的地位,检测蔬菜中的硝酸盐含量具有重要的现实意义。本研究对蔬菜中硝酸盐和亚硝酸盐的检测技术进展进行了概述和比较,以期为蔬菜中硝酸盐和亚硝酸盐的检测及快速检测技术的发展提供基础参考。     

晋南野菜和蔬菜硝酸盐、亚硝酸盐和维生素C含量分析

目的对山西南部的10种野菜和4种常食用蔬菜的硝酸盐、亚硝酸盐和维生素C含量进行测定。方法硝酸盐含量测定采用镉柱法;亚硝酸盐含量测定采用盐酸萘基乙二胺法;维生素C含量测定采用2,6-二氯酚靛酚滴定法。结果苜蓿、黄瓜和西红柿的硝酸盐含量低于轻度污染水平,亚硝酸盐含量低于亚硝酸盐含量的限量标准,维生素C的含量较低,属于一级蔬菜,可以安全生食;马齿苋、荠菜、蒲公英的硝酸盐含量低于中度污染水平,亚硝酸盐含量低于或相当于亚硝酸盐含量的限量标准,维生素C的含量高或较高,属于二级蔬菜,不宜生食,可盐渍和熟食;苣荬菜、车前草、苦菜、胡萝卜的硝酸盐含量过高,低于重度污染水平,不宜生食和盐渍,可以熟食;藜菜、菠菜、白蒿、地肤的硝酸盐含量高于1234mg/kg,属于高度污染水平,亚硝酸盐含量超过或相当于亚硝酸盐含量限量标准,维生素C的含量高或极高,不宜食用或限量食用。结论大多数供试野菜的各个指标含量均高于栽培蔬菜。     

Evolution of nitrate and nitrite during the processing of dry-cured ham with partial replacement of NaCl by other chloride salts

Nitrate and nitrite are commonly added to dry-cured ham to provide protection against pathogen microorganisms, especially Clostridium botulinum. Both nitrate and nitrite were monitored with ion chromatography in dry-cured hams salted with different NaCl formulations (NaCl partially replaced by KCl and/or CaCl(2), and MgCl(2)). Nitrate, that is more stable than nitrite, diffuses into the ham and acts as a reservoir for nitrite generation. A correct nitrate and nitrite penetration was detected from the surface to the inner zones of the hams throughout its processing, independently of the salt formulation. Nitrate and nitrite achieved similar concentrations, around 37 and 2.2 ppm, respectively in the inner zones of the ham for the three assayed salt formulations at the end of the process, which are in compliance with European regulations.     

Monitoring nitrite and nitrate residues in frankfurters during processing and storage

Frankfurter-type sausages were prepared in a pilot plant with different concentrations of NaNO(2) (75, 125 or 250 ppm) combined or not with 200 ppm KNO(3). A meat system, free of curing agents, was also used as control. Nitrite and nitrate levels were tested in various processing steps and over 120 days storage at 3 °C of the vacuum-packaged frankfurters. Little influence of the originally added nitrite level on the amount of nitrate formed was observed. Important losses of nitrite and nitrate were due to cooking. Thereafter about 50% of the nitrite added initially remained in this form in all samples (39, 59 and 146 ppm, respectively) and between 10 and 15% as nitrate. When only nitrate was initially added, formation of nitrite after cooking was observed (maximum level 43 ppm NaNO(2)). Formulations prepared with both nitrate and nitrite showed no significant differences (p < 0.01) respect to their nitrite or nitrate counterparts. A good correlation among nitrite and nitrate levels and storage time was showed by multiple linear regression analysis. It is concluded that the use of nitrate in combination with nitrite in cooked meat products seems to have little technological significance and adds to the total body burden of nitrite.     

蔬菜中硝酸盐和亚硝酸盐检测方法的研究进展

硝酸盐和亚硝酸盐主要通过蔬菜食用进入人体,亚硝酸盐是一种有毒物质,人食用后会在体内产生致癌性 的亚硝胺。光谱法、色谱法、快速检测法是目前检测蔬菜中硝酸盐和亚硝酸盐的主要方法。本文在对上述方法进行 介绍并比较的基础上,对蔬菜中硝酸盐和亚硝酸盐检测方法的研究进展进行了概述与展望。     

Persistency of methane mitigation by dietary nitrate supplementation in dairy cows

Feeding nitrate to dairy cows may lower ruminal methane production by competing for reducing equivalents with methanogenesis. Twenty lactating Holstein-Friesian dairy cows (33.2 ± 6.0 kg of milk/d; 104 ± 58 d in milk at the start of the experiment) were fed a total mixed ration (corn silage-based; forage to concentrate ratio 66:34), containing either a dietary urea or a dietary nitrate source [21 g of nitrate/kg of dry matter (DM)] during 4 successive 24-d periods, to assess the methane-mitigating potential of dietary nitrate and its persistency. The study was conducted as paired comparisons in a randomized design with repeated measurements. Cows were blocked by parity, lactation stage, and milk production at the start of the experiment. A 4-wk adaptation period allowed the rumen microbes to adapt to dietary urea and nitrate. Diets were isoenergetic and isonitrogenous. Methane production, energy balance, and diet digestibility were measured in open-circuit indirect calorimetry chambers. Cows were limit-fed during measurements. Nitrate persistently decreased methane production by 16%, whether expressed in grams per day, grams per kilogram of dry matter intake (DMI), or as percentage of gross energy intake, which was sustained for the full experimental period (mean 368 vs. 310 ± 12.5 g/d; 19.4 vs. 16.2 ± 0.47 g/kg of DMI; 5.9 vs.4.9 ± 0.15% of gross energy intake for urea vs. nitrate, respectively). This decrease was smaller than the stoichiometrical methane mitigation potential of nitrate (full potential = 28% methane reduction). The decreased energy loss from methane resulted in an improved conversion of dietary energy intake into metabolizable energy (57.3 vs. 58.6 ± 0.70%, urea vs. nitrate, respectively). Despite this, milk energy output or energy retention was not affected by dietary nitrate. Nitrate did not affect milk yield or apparent digestibility of crude fat, neutral detergent fiber, and starch. Milk protein content (3.21 vs. 3.05 ± 0.058%, urea vs. nitrate respectively) but not protein yield was lower for dietary nitrate. Hydrogen production between morning and afternoon milking was measured during the last experimental period. Cows fed nitrate emitted more hydrogen. Cows fed nitrate displayed higher blood methemoglobin levels (0.5 vs. 4.0 ± 1.07% of hemoglobin, urea vs. nitrate respectively) and lower hemoglobin levels (7.1 vs. 6.3 ± 0.11 mmol/L, urea vs. nitrate respectively). Dietary nitrate persistently decreased methane production from lactating dairy cows fed restricted amounts of feed, but the reduction in energy losses did not improve milk production or energy balance.     

Retention of ethyl butyrate by gellan gels in the presence of potassium ions

The air/biopolymer partition coefficient (K) and percentage of retention (R%) of ethyl butyrate (400 ppm) added to gellan gels were determined, using static headspace gas chromatography. Potassium chloride (40–120 mM) was used to induce gellan gelation. When 5 g of sample were left to equilibrate at 37 °C for 2 and 24 h, the coefficient values initially decreased with salt concentration to a certain value after which they raised again. The lower coefficient values, for the 24 h period, were observed at higher salt concentration than for the 2 h. Moreover, for both time periods, the lower coefficient values were found for the gellan gels with the greater strength and rigidity and were accompanied by positive percentages of retention. When 15 g of sample were used, after equilibration at 37 °C for 24 h, no significant changes in aroma release were observed. Moreover, negative percentages of retention values were calculated for all salt concentrations.     

Hypolipemic activity of polyphenol-rich extracts from Ocimum basilicum in Triton WR-1339-induced hyperlipidemic mice

The hypocholesterolemic and hypotriglyceridemic activities of the aqueous and organic extracts of Ocimum basilicum were studied using Triton WR-1339-induced hyperlipemic mice as an experimental model. Hyperlipidemia was developed by intraperitoneal injection of Triton (200 mg/kg body weight “BW”). The animals were divided into eight groups of eight mice each: normolipidemic control group (NCG), hyperlipidemic control group (HCG), hyperlipidemic plus DMSO control (HDCG), crude aqueous basil extract-treated group (CETG), dichloromethane extract-treated group (DETG), ethyl acetate extract-treated group (EETG), methanol extract-treated group (METG), and aqueous fraction-treated group (AFTG). After 7 h and 24 h of treatment, the intragastric administration of all extracts caused a significant decrease of plasma total cholesterol. Triglyceride levels were also significantly lowered but not in DETG. Similar results were observed for LDL-cholesterol concentrations. Although no significant change of HDL-cholesterol was noticed after 7 h of treatments, a significant increase of this cholesterol fraction was observed in EETG and AFTG after 24 h. Furthermore, crude aqueous basil extract and all polar solvent (methanol, ethyl acetate, water)-soluble fractions showed a significant ameliorative action on elevated atherogenic index (AI) and LDL/HDL-C ratios, while these atherogenic markers were not statistically suppressed by the dichloromethane-soluble extract. This finding indicates that O. basilicum may contain polar products able to lower plasma lipid concentrations and might be beneficial in treatment of hyperlipidemia and atherosclerosis.     

Nitrite promotes protein carbonylation and Strecker aldehyde formation in experimental fermented sausages: Are both events connected?

The role played by curing agents (nitrite, ascorbate) on protein oxidation and Strecker aldehyde formation is studied. To fulfill this objective, increasing concentrations of nitrite (0, 75 and 150 ppm) and ascorbate (0, 250 and 500 ppm) were added to sausages subjected to a 54 day drying process. The concurrence of intense proteolysis, protein carbonylation and formation of Strecker aldehydes during processing of sausages suggests that α-aminoadipic semialdehyde (AAS) and γ-glutamic semialdehyde (GGS) may be implicated in the formation of Strecker aldehydes. The fact that nitrite (150 ppm, ingoing amount) significantly promoted the formation of protein carbonyls at early stages of processing and the subsequent formation of Strecker aldehydes provides strength to this hypothesis. Ascorbate (125 and 250 ppm) controlled the overall extent of protein carbonylation in sausages without declining the formation of Strecker aldehydes. These results may contribute to understanding the chemistry fundamentals of the positive influence of nitrite on the flavor and overall acceptability of cured muscle foods.     

Nitrate in leafy vegetables,culinary herbs,and cucumber grown under cover in Estonia: content and intake

The content of nitrate in leafy vegetables, culinary herbs, and cucumber was determined during the years 2006–2008. All samples of Estonian origin, except white cabbage, were grown under cover. Seasonal differences in nitrate concentrations were observed in lettuce and spinach. Nitrate concentrations in lettuce were 22% and those in spinach were 24% higher in winter crops compared with samples collected in summer. The mean nitrate level was 3023 mg kg^–1 for fresh lettuce and 2337 mg kg^–1 for spinach. On average, 11.6% of fresh lettuce and spinach samples nitrate concentration exceeded the maximum level specified in European Commission Regulation No. 1881/2006. The mean levels were 999 mg kg^–1 for imported iceberg lettuce and 1287 mg kg^–1 for frozen spinach, which are below the maximum European Commission limits. Parsley, dill, basil, thyme, and rucola contained high concentrations of nitrate from mean levels of 2134 mg kg^–1 for parsley up to 8150 mg kg^–1 for rucola. Mean nitrate concentrations ranged from 382 to 1115 mg kg^–1 for white cabbage and Chinese cabbage, respectively. The per capita mean daily intake of nitrates related to the consumption of leafy vegetables, culinary herbs, and cucumber for the whole Estonian population was 31.3 mg day^–1, which comprised 14.2% of the acceptable daily intake (ADI).     

冷藏对蔬菜中亚硝酸盐及硝酸盐含量的影响

目的 探索冰箱冷藏(4℃)条件下蔬菜中硝酸盐和亚硝酸盐含量随时间的变化,对冷藏食品的安全性进行评价.方法 分别采用重氮偶合分光光度法和麝香草酚分光光度法对生菜、菠菜、油麦菜及苦苣4种常用蔬菜在冷藏条件下其亚硝酸盐及硝酸盐的含量变化进行测定.结果 1～4d内,生菜、苦苣中的亚硝酸盐含量随着时间的延长逐渐增加;菠菜、油麦菜中亚硝酸盐含量分别在第2天和第3天达到最大,之后逐渐降低,而菠菜中亚硝酸盐含量在第4天又出现上升趋势.4种蔬菜中亚硝酸盐含量4d中最大值仅为0.419 4 mg/kg(生菜),均＜4 mg/kg的限量值.苦苣和油麦菜中硝酸盐含量在1～4d内逐渐上升.菠菜中硝酸盐含量第2天达到418.48 mg/kg,之后又降低至20.83 mg/kg.生菜中硝酸盐含量在第3天达到最大值317.26 mg/kg,之后逐渐下降,但均在安全范围内(432 mg/kg).结论 在4℃下冷藏4d后,4种常见蔬菜均可安全食用.可见,冷藏能有效减缓亚硝酸盐和硝酸盐含量的升高.