A survey of nitrate and nitrite concentrations in conventional and organic-labeled raw vegetables at retail

Impact of nitrogen fertilizer type and application rate on growth, nitrate accumulation, and postharvest quality of spinach

Background

A balanced supply of nitrogen is essential for spinach, supporting both optimal growth and appropriate nitrate (NO3 -) levels for improved storage quality. Thus, choosing the correct nitrogen fertilizer type and application rate is key for successful spinach cultivation. This study investigated the effects of different nitrogen (N) fertilizer type and application rates on the growth, nitrate content, and storage quality of spinach plants.

Methods

Four fertilizer types were applied at five N doses (25, 50, 200, and 400 mg N kg-1) to plants grown in plastic pots at a greenhouse. The fertilizer types used in the experiment were ammonium sulphate (AS), slow-release ammonium sulphate (SRAS), calcium nitrate (CN), and yeast residue (YR). Spinach parameters like Soil Plant Analysis Development (SPAD) values (chlorophyll content), plant height, and fresh weight were measured. Nitrate content in leaves was analyzed after storage periods simulating post-harvest handling (0, 5, and 10 days).

Results

The application of nitrogen fertilizer significantly influenced spinach growth parameters and nitrate content. The YRx400 treatment yielded the largest leaves (10.3 ± 0.5 cm long, 5.3 ± 0.2 cm wide). SPAD values increased with higher N doses for AS, SRAS, and CN fertilizers, with AS×400 (58.1 ± 0.8) and SRAS×400 (62.0 ± 5.8) reaching the highest values. YR treatments showed a moderate SPAD increase. Fresh weight response depended on fertilizer type, N dose, and storage period. While fresh weight increased in all fertilizers till 200 mg kg-1 dose, a decrease was observed at the highest dose for AS and CN. SRAS exhibited a more gradual increase in fresh weight with increasing nitrogen dose, without the negative impact seen at the highest dose in AS and CN. Nitrate content in spinach leaves varied by fertilizer type, dose, and storage day. CNx400 resulted in the highest NO3 - content (4,395 mg kg-1) at harvest (Day 0), exceeding the European Union's safety limit. This level decreased over 10 days of storage but remained above the limit for CN on Days 0 and 5. SRAS and YR fertilizers generally had lower NO3 - concentrations throughout the experiment. Storage at +4 °C significantly affected NO3 - content. While levels remained relatively stable during the first 5 days, a substantial decrease was observed by Day 10 for all fertilizers and doses, providing insights into the spinach's nitrate content over a 10-day storage period.

Conclusion

For rapid early growth and potentially higher yields, AS may be suitable at moderate doses (200 mg kg-1). SRAS offers a more balanced approach, promoting sustained growth while potentially reducing NO3 - accumulation compared to AS. Yeast residue, with its slow nitrogen release and consistently low NO3 - levels, could be a viable option for organic spinach production.

Microorganisms in Organic Food-Issues to Be Addressed

The review aimed to analyse the latest data on microorganisms present in organic food, both beneficial and unwanted. In conclusion, organic food's microbial quality is generally similar to that of conventionally produced food. However, some studies suggest that organic food may contain fewer pathogens, such as antibiotic-resistant strains, due to the absence of antibiotic use in organic farming practices. However, there is little discussion and data regarding the importance of some methods used in organic farming and the risk of food pathogens presence. Concerning data gaps, it is necessary to plan and perform detailed studies of the microbiological safety of organic food, including foodborne viruses and parasites and factors related to this method of cultivation and specific processing requirements. Such knowledge is essential for more effective management of the safety of this food. The use of beneficial bacteria in organic food production has not yet been widely addressed in the scientific literature. This is particularly desirable due to the properties of the separately researched probiotics and the organic food matrix. The microbiological quality of organic food and its potential impact on human health is worth further research to confirm its safety and to assess the beneficial properties resulting from the addition of probiotics.

Nitrate Quantification in Fresh Vegetables in Shanghai: Its Dietary Risks and Preventive Measures

To investigate nitrate and nitrite content in fresh vegetables, 264 samples were randomly collected in the farmers' markets in Shanghai, Southeast China. The results indicate that 25.0% of the fresh vegetables were critically or more contaminated by nitrate [>1440 mg/kg FW (Fresh weight)]. Generally, leafy vegetables were more highly enriched in nitrate than root-tuber and fruit vegetables. About 22.6% of the leafy vegetables had a nitrate content exceeding the limit for edible permission (>3000 mg/kg FW). Nitrite content in the fresh vegetables was all within the safe level (<1 mg/kg FW). It was estimated that the daily nitrate intake through eating vegetables in Shanghai exceeded the WHO/FAO allowable limit. The field experiment indicated that the hyper-accumulation of nitrate and nitrite in the vegetables was mainly attributed to the excessive application of chemical fertilizers. The maxima of nitrate and nitrite in the vegetables were attained one week after applying chemical fertilizer, and thus they cannot be picked for dietary use. Applying organic manure can effectively lower the risk of nitrate and nitrite contamination in vegetables. The old leaves and leaf petioles were more easily enriched in nitrate due to their weaker metabolic activity. Vegetables with high nitrate content had a high risk of nitrite toxicity during storage due to the biological conversion of nitrate into nitrite, which is easily triggered by suitable temperature and mechanical damage processing. Therefore, fresh vegetables should be stored by rapid cooling and in undamaged forms to prevent nitrite accumulation.

The first harmonised total diet study in Portugal: Nitrate occurrence and exposure assessment

A harmonised TDS methodology was used to assess the Portuguese population's nitrate baseline dietary exposure and the risk of exceeding the Acceptable Daily Intake (ADI). Nitrate occurrence in 164 TDS samples pooled based on 20 FoodEx2 groups, representative of 18 to 75 years old population diet, was determined using UV-HPLC. The 'vegetables' group had the highest mean nitrate concentration (353 mg/kg), followed by 'starchy roots' (62 mg/kg), 'composite dishes' (53 mg/kg) and 'fruits' (46 mg/kg). Lettuce contained the most nitrates (1729 mg/kg). The estimated mean nitrate exposure of 1.17 mg/kg bw/day, with 3.18% of individuals exceeding the ADI, was assessed on a semi-probabilistic approach using the MCRA software. Lettuce (28%) contributed most to nitrate exposure followed by vegetable soup (13%). Processed meat contribution to exposure was 0.86% and 2.44% (overall population and consumers only). At population level the nitrate estimated exposure (mean and 95th percentile) revealed no reason for concern.

Nitrate, nitrite and nitrosamines in the global food supply

Inorganic nitrate provided by either nitrate salts or food supplements may improve cardiometabolic health. However, current methods to assess dietary nitrate, nitrite and nitrosamine consumption are inadequate. The purpose of this study was to develop a reference database to estimate the levels of nitrate, nitrite and nitrosamines in the global food supply. A systematic literature search was undertaken; of the 5,747 articles screened, 448 met the inclusion criteria. The final database included data for 1,980 food and beverages from 65 different countries. There were 5,105 unique records for nitrate, 2,707 for nitrite, and 954 for nitrosamine. For ease of use, data were sorted into 12 categories; regarding nitrate and nitrite concentrations in food and beverages, 'vegetables and herbs' were most reported in the literature (n = 3,268 and n = 1,200, respectively). For nitrosamines, 'protein foods of animal origin' were most reported (n = 398 records). This database will allow researchers and practitioners to confidently estimate dietary intake of nitrate, nitrite and nitrosamines. When paired with health data, our database can be used to investigate associations between nitrate intake and health outcomes, and/or exercise performance and could support the development of key dietary nitrate intake guidelines.

The oral microbiome, nitric oxide and exercise performance

The human microbiome comprises ∼10¹³-10¹⁴ microbial cells which form a symbiotic relationship with the host and play a critical role in the regulation of human metabolism. In the oral cavity, several species of bacteria are capable of reducing nitrate to nitrite; a key precursor of the signaling molecule nitric oxide. Nitric oxide has myriad physiological functions, which include the maintenance of cardiovascular homeostasis and the regulation of acute and chronic responses to exercise. This article provides a brief narrative review of the research that has explored how diversity and plasticity of the oral microbiome influences nitric oxide bioavailability and related physiological outcomes. There is unequivocal evidence that dysbiosis (e.g. through disease) or disruption (e.g. by use of antiseptic mouthwash or antibiotics) of the oral microbiota will suppress nitric oxide production via the nitrate-nitrite-nitric oxide pathway and negatively impact blood pressure. Conversely, there is preliminary evidence to suggest that proliferation of nitrate-reducing bacteria via the diet or targeted probiotics can augment nitric oxide production and improve markers of oral health. Despite this, it is yet to be established whether purposefully altering the oral microbiome can have a meaningful impact on exercise performance. Future research should determine whether alterations to the composition and metabolic activity of bacteria in the mouth influence the acute responses to exercise and the physiological adaptations to exercise training.

Nutrient and Nitrate Composition of Greenhouse-Grown Leafy Greens: A Trial Comparison Between Conventional and Organic Fertility Treatments

Arugula (Eruca sativa), mizuna (Brassica rapa var. nipponsinca), red giant mustard (Brassica juncea), and spinach (Spinaciaoleracea “Tyee”) are fresh produce crops high in nutritive value that provide shortfall and high interest nutrients addressed in the U.S. Dietary Guidelines. The primary objective of this project was to evaluate fertility treatments unique to these crops that optimize their nutritional capacity. Measurements discussed include: vitamin C, dietary fiber, calcium, iron, potassium, sodium, and nitrate. Plants were grown at the University of Minnesota St. Paul Campus (St. Paul, MN) in a greenhouse from November to April under an 18 h photoperiod and a 24/13°C day/night temperature. Plants were grown using five different fertility treatments, including four organic treatments and one conventional control. The plant treatment combinations were replicated three times and the entire experiment was duplicated. Fertility treatments had a high impact on vitamin C (with over a 3-fold difference in treatments in the first experiment), nitrate (over 10-fold difference among fertility treatments in some species) and potassium concentrations (over 5-fold difference among fertility treatments in some species) in analyzed plant tissue. No consistent differences were found for fiber, calcium, iron and sodium concentrations in tissue analyzed. This is the first study to analyze the impact that different organic treatments can have on multiple nutrients and compounds addressed by the U.S. Dietary Guidelines for high-impact, highly-consumed produce crops.

Nitrogen Accumulation in Oyster (Crassostrea gigas) Slurry Exposed to Virucidal Cold Atmospheric Plasma Treatment

Viral contamination of edible bivalves is a major food safety issue. We studied the virucidal effect of a cold atmospheric plasma (CAP) source on two virologically different surrogate viruses [a double-stranded DNA virus (Equid alphaherpesvirus 1, EHV-1), and a single-stranded RNA virus (Bovine coronavirus, BCoV)] suspended in Dulbecco’s Modified Eagle’s Medium (DMEM). A 15 min exposure effectuated a statistically significant immediate reduction in intact BCoV viruses by 2.8 (ozone-dominated plasma, “low power”) or 2.3 log cycles (nitrate-dominated, “high power”) of the initial viral load. The immediate effect of CAP on EHV-1 was less pronounced, with “low power” CAP yielding a 1.4 and “high power” a 1.0 log reduction. We observed a decline in glucose contents in DMEM, which was most probably caused by a Maillard reaction with the amino acids in DMEM. With respect to the application of the virucidal CAP treatment in oyster production, we investigated whether salt water could be sanitized. CAP treatment entailed a significant decline in pH, below the limits acceptable for holding oysters. In oyster slurry (a surrogate for live oysters), CAP exposure resulted in an increase in total nitrogen, and, to a lower extent, in nitrate and nitrite; this was most probably caused by absorption of nitrate from the plasma gas cloud. We could not observe a change in colour, indicative for binding of NO_x to haemocyanin, although this would be a reasonable assumption. Further studies are necessary to explore in which form this additional nitrogen is deposited in oyster flesh.

African nightshades (Solanum nigrum complex): The potential contribution to human nutrition and livelihoods in sub-Saharan Africa

Achieving zero hunger in sub-Saharan Africa (SSA) without minimizing postharvest losses of agricultural products is impossible. Therefore, a holistic approach is vital to end hunger, simultaneously improving food security, diversity, and livelihoods. This review focuses on the African nightshades (ANS) Solanum spp. contribution to improving food and nutrition security in SSA. Different parts of ANS are utilized as food and medicine; however, pests and diseases hinder ANS utilization. African nightshade is rich in micronutrients such as β-carotene, vitamins C and E, minerals (iron, calcium, and zinc), and dietary fiber. The leaves contain a high amount of nutrients than the berries. Proper utilization of ANS can contribute to ending hidden hunger, mainly in children and pregnant women. Literature shows that ANS contains antinutritional factors such as oxalate, phytate, nitrate, and alkaloids; however, their quantities are low to cause potential health effects. Several improved varieties with high yields, rich in nutrients, and low alkaloids have been developed in SSA. Various processing and preservation techniques such as cooking, drying, and fermentation are feasible techniques for value addition on ANS in SSA; moreover, most societies are yet to adopt them effectively. Furthermore, promoting value addition and commercialization of ANS is of importance and can create more jobs. Therefore, this review provides an overview of ANS production and challenges that hinder their utilization, possible solutions, and future research suggestions. This review concludes that ANS is an essential nutritious leafy vegetable for improving nutrition and livelihoods in SSA.

Dietary nitrate and population health: a narrative review of the translational potential of existing laboratory studies

BACKGROUND

Dietary inorganic nitrate (NO3-) is a polyatomic ion, which is present in large quantities in green leafy vegetables and beetroot, and has attracted considerable attention in recent years as a potential health-promoting dietary compound. Numerous small, well-controlled laboratory studies have reported beneficial health effects of inorganic NO3- consumption on blood pressure, endothelial function, cerebrovascular blood flow, cognitive function, and exercise performance. Translating the findings from small laboratory studies into 'real-world' applications requires careful consideration.

MAIN BODY

This article provides a brief overview of the existing empirical evidence basis for the purported health-promoting effects of dietary NO3- consumption. Key areas for future research are then proposed to evaluate whether promising findings observed in small animal and human laboratory studies can effectively translate into clinically relevant improvements in population health. These proposals include: 1) conducting large-scale, longer duration trials with hard clinical endpoints (e.g. cardiovascular disease incidence); 2) exploring the feasibility and acceptability of different strategies to facilitate a prolonged increase in dietary NO3- intake; 3) exploitation of existing cohort studies to explore associations between NO3- intake and health outcomes, a research approach allowing larger samples sizes and longer duration follow up than is feasible in randomised controlled trials; 4) identifying factors which might account for individual differences in the response to inorganic NO3- (e.g. sex, genetics, habitual diet) and could assist with targeted/personalised nutritional interventions; 5) exploring the influence of oral health and medication on the therapeutic potential of NO3- supplementation; and 6) examining potential risk of adverse events with long term high- NO3- diets.

CONCLUSION

The salutary effects of dietary NO3- are well established in small, well-controlled laboratory studies. Much less is known about the feasibility and efficacy of long-term dietary NO3- enrichment for promoting health, and the factors which might explain the variable responsiveness to dietary NO3- supplementation between individuals. Future research focussing on the translation of laboratory data will provide valuable insight into the potential applications of dietary NO3- supplementation to improve population health.

Consumer Preference, Quality, and Safety of Organic and Conventional Fresh Fruits, Vegetables, and Cereals

Growing and purchasing demand for organic fresh produce is increasing rapidly. Consumers are aware of health, environmental safety, pesticide harmfulness, nutrients, bioactive compounds, and safe food. Many research works are available on organic and conventional fresh produce. As organic fresh produce growing and purchasing demand is increasing, it has become necessary to review the recent trends in quality, safety, and consumer preferences of organic and conventional fresh food products. A few reports have been compiled on organic and conventional fresh produce. Researchers have started working on organic and conventional fresh produce with the help of modern technology to improve nutritional and functional quality, safety, and consumer preferences. Nutritional and functional quality, safety, and consumer preferences depend on cultivation techniques, treatment, crop cultivar, and appearance of products. Therefore, it is necessary to compile the literature on organic and conventional fresh produce based on quality, safety, and consumer preferences.

Organic plant products are of more improved chemical composition than conventional ones

Considering the negative effects of conventional agricultural production, organic food production is a sustainable approach to production, which preserves the environment and protects human health. Organic products are products of high quality, without residues of pesticides and other harmful chemicals. Through the review of literature data, the authors of this paper presented a comparative study on the chemical compositions of organically vs. conventionally grown plants and their products. Dry matter, nitrates, sugars, vitamins, macro-and microelements, as well as, secondary metabolites have been singled out. The analysis of collected data revealed that organic products contained more dry matter, significantly fewer nitrates, fewer proteins and a higher proportion of amino acids, more sugars, vitamin C, numerous macro-and microelements (particularly Fe, Mg and P), more polyphenols and they had higher total antioxidant capacity than conventional products. Although many authors have been dealing for many years with the comparison of the nutritional composition of organic and conventional food products, a clear consensus whether organic products have an improved chemical composition compared to conventional products has not been reached yet, i.e. the conclusions are ambivalent. Therefore, further long-term studies are necessary to clarify the existing doubts.

Organic plant products are of more improved chemical composition than conventional ones

Considering the negative effects of conventional agricultural production, organic food production is a sustainable approach to production, which preserves the environment and protects human health. Organic products are products of high quality, without residues of pesticides and other harmful chemicals. Through the review of literature data, the authors of this paper presented a comparative study on the chemical compositions of organically vs. conventionally grown plants and their products. Dry matter, nitrates, sugars, vitamins, macro-and microelements, as well as, secondary metabolites have been singled out. The analysis of collected data revealed that organic products contained more dry matter, significantly fewer nitrates, fewer proteins and a higher proportion of amino acids, more sugars, vitamin C, numerous macro-and microelements (particularly Fe, Mg and P), more polyphenols and they had higher total antioxidant capacity than conventional products. Although many authors have been dealing for many years with the comparison of the nutritional composition of organic and conventional food products, a clear consensus whether organic products have an improved chemical composition compared to conventional products has not been reached yet, i.e. the conclusions are ambivalent. Therefore, further long-term studies are necessary to clarify the existing doubts.

Investigating the Effects of Chinese Cabbage Powder as an Alternative Nitrate Source on Cured Color Development of Ground Pork Sausages

This study investigated the effects of Chinese cabbage powder as a natural replacement for sodium nitrite on the qualities of alternatively cured pork products. Chinese cabbages grown in Korea were collected and used for preparing hot air dried powder. Different levels of Chinese cabbage powder were added to pork products and evaluated by comparing these products to those with sodium nitrite or a commercially available celery juice powder. The experimental groups included control (100 ppm sodium nitrite added), treatment 1 (0.15% Chinese cabbage powder added), treatment 2 (0.25% Chinese cabbage powder added), treatment 3 (0.35% Chinese cabbage powder added), and treatment 4 (0.4% celery juice powder added). The cooking yields and pH values of treatments 1 to 3 were significantly lower (p<0.05) than the control. However, all of the alternatively cured products were redder (higher CIE a* values; p<0.05) than the control and this result was supported from higher nitrosyl hemochrome, total pigment, and curing efficiency. Furthermore, the inclusion of vegetable powders to these products resulted in considerably less residual nitrite content. However, Chinese cabbage powder (0.25% and 0.35%) was effective in producing alternatively cured meat products with a higher curing efficiency comparable to those of the traditionally cured control or the products with celery juice powder. Therefore, Chinese cabbage powder exhibited the efficacy for use as a natural replacer for alternatively cured meat products.

Evaluation of nitrate contents in regulated and non-regulated leafy vegetables of high consumption in the Canary Islands, Spain: Risk assessment

The nitrate content of the most consumed green leafy vegetables in the European Region of the Canary Islands was determined. The sampling included chard and watercress, which are not regulated but highly consumed in this region. The levels of nitrates in organic vegetables were significantly higher than those of conventional cultivation. However, no seasonal differences were observed, and overall nitrate levels were lower than those reported in other studies. Median nitrate levels in the analyzed vegetables were: lettuce (3 varieties) = 573.7 mg/kg; ready-to-eat salad mixes = 595.0 mg/kg; spinach = 1044.2 mg/kg; arugula = 3144.2 mg/kg; watercress = 450.5 mg/kg; and chard = 1788.4 mg/kg. In general, the nitrate levels of watercress and chard were significantly higher than those of regulated vegetables with similar culinary uses. The average per capita daily intake of nitrates through regulated vegetables was 17.5-32.5% of acceptable daily intake (ADI). On the contrary, the consumption of unregulated vegetables in this archipelago represents a similar, or even higher, percentage of ADI (23.6-44.3%). We, therefore, consider that the establishment of maximum limits of nitrate by the EU regulatory authorities would be appropriate for chard and watercress and similar to those set for spinach.

Chemometric strategies for nondestructive and rapid assessment of nitrate content in harvested spinach using Vis-NIR spectroscopy

The overuse of nitrogenous fertilizers leads to an increase in the nitrate content of green leafy vegetables. Consumption of food with excess nitrate is not advisable because it results in human ailment. In this study, spinach leaves were harvested from plants grown under nine varying (0 to 400 kg/ha) nitrogenous fertilizer doses. A total of 261 samples were used to predict the nitrate content in spinach leaves using Vis-NIR (350 to 2,500 nm). The nitrate content was measured destructively using the ion-selective conductive method. Partial least square (PLS) regression models were developed using whole spectra and featured wavelengths. Spectral data were pre-processed using different spectral pre-processing techniques such as Savitzky-Golay (SG) derivative, standard normal variate (SNV), multiplicative scatter correction (MSC), baseline correction, and detrending. The predictive accuracy of the PLS model had improved after pre-processing of spectral data with MSC (RPD_CV = 1.767; SE_CV = 545.745; bias_CV = -3.107; slope_CV = 0.698) and SNV (RPD_CV = 1.768; SE_CV = 545.337; bias_CV = -3.201; slope_CV = 0.698) technique, but this was not significant (P < 0.05) as compared with raw spectral data (RPD_CV = 1.679; SE_CV = 572.669; bias_CV = -7.046; slope_CV = 0.687). The effective wavelengths for measurement nitrate content in spinach leaves were identified as 558, 706, 780, 1,000, and 1,420 nm. The performance of PLS model developed with effective wavelengths also had good prediction accuracy (RPD_CV = 1.482; SE_CV = 648.672; bias_CV = -3.805; slope_CV = 0.565) but significantly lower than the performance of model developed with full spectral data. The overall results of this study suggest that Vis-NIR spectroscopy can be an important tool and has great potential for the rapid and nondestructive assessment of nitrate content in harvested spinach, with a view to ascertain the suitability of the harvest for food uses. PRACTICAL APPLICATION: Better production and brighter color of leafy vegetable drive the farming community to overuse nitrogenous fertilizer. This has resulted in higher nitrate content in vegetables. It has been widely reported that consumption of these vegetables has carcinogenic effects on human beings. The prediction of nitrate content in leafy vegetables by traditional methods is time-consuming (30 min, including sample preparation time), destructive, and tedious; moreover, it cannot be used for inline applications. This study reports spectroscopy-based rapid (<5 s) assessment technique for nitrate measurement. A multivariable PLS model was developed using wavelengths representing nitrate content. This model can be adopted by food industries for inline applications.

Hazards of nitrogen fertilizers and ways to reduce nitrate accumulation in crop plants

In modern agriculture, farm produce accumulates a lot of nitrates that can reach toxic levels owing to the unfair use of nitrogen fertilizers, cultural methods, farming policies in multiple areas of the world, thereby increasing concerns about the availability of hygienic food supply and environmental hazards. Over the past few decades, global interest in achieving greater output through intensive fertilization has been a growing trend. The fertilizer based on urea or ammonium mainly yields ammonium, which is then transformed to nitrate through the oxidation process that is biologically mediated. Nitrate tends to accumulate differently in distinct crop plants and distinct components of agricultural commodities based on species, crop variety, genetic history, environmental circumstances, harvest phase, post-harvest storage conditions, agronomic variables, nature, and fertilizer application rate. The current article highlights various factors that could directly or indirectly contribute to the accumulation of nitrates in different parts of crop plants and discusses strategies to minimize the accumulation of nitrates in farm produce, thus ensuring healthy food supply and protecting the environment from the accumulation of nitrates.

Nitrates/Nitrites in Food-Risk for Nitrosative Stress and Benefits

In the context of impact on human health, nitrite/nitrate and related nitrogen species such as nitric oxide (NO) are a matter of increasing scientific controversy. An increase in the content of reactive nitrogen species may result in nitrosative stress-a deleterious process, which can be an important mediator of damage to cell structures, including lipids, membranes, proteins and DNA. Nitrates and nitrites are widespread in the environment and occur naturally in foods of plant origin as a part of the nitrogen cycle. Additionally, these compounds are used as additives to improve food quality and protect against microbial contamination and chemical changes. Some vegetables such as raw spinach, beets, celery and lettuce are considered to contain high concentrations of nitrates. Due to the high consumption of vegetables, they have been identified as the primary source of nitrates in the human diet. Processed meats are another source of nitrites in our diet because the meat industry uses nitrates/nitrites as additives in the meat curing process. Although the vast majority of consumed nitrates and nitrites come from natural vegetables and fruits rather than food additives, there is currently a great deal of consumer pressure for the production of meat products free of or with reduced quantities of these compounds. This is because, for years, the cancer risks of nitrates/nitrites have been considered, since they potentially convert into the nitrosamines that have carcinogenic effects. This has resulted in the development and rapid expansion of meat products processed with plant-derived nitrates as nitrite alternatives in meat products. On the other hand, recently, these two ions have been discussed as essential nutrients which allow nitric oxide production and thus help cardiovascular health. Thus, this manuscript reviews the main sources of dietary exposure to nitrates and nitrites, metabolism of nitrites/nitrates, and health concerns related to dietary nitrites/nitrates, with particular emphasis on the effect on nitrosative stress, the role of nitrites/nitrates in meat products and alternatives to these additives used in meat products.

Incorporating Exogenous and Endogenous Exposures into Dietary Risk Assessment of Nitrates and Nitrites in Vegetables: A Probabilistic Integrated Toxicokinetic Modeling Approach

This study aimed to estimate the dietary risk of nitrates and nitrites in vegetables based on internal dose in a probabilistic manner by integrating exogenous exposure based on measured concentrations in vegetables with endogenous exposure using a toxicokinetic (TK) model. We optimized and validated a previous TK model and incorporated Monte Carlo simulations to account for variability across different age populations for predicting internal dose. High levels of nitrates were detected in leafy vegetables (from 545 ± 274 to 1641 ± 873 mg/kg). Nitrite contents of vegetables were generally low (from 1.26 ± 1.40 to 8.20 ± 14.1 mg/kg). The dietary risk was found to be different based on internal versus external dose, suggesting that it is critical to include endogenous nitrite formation into risk assessment. Nitrate and nitrite exposure from vegetables is unlikely to result in appreciable risks for most populations but may be a potential risk for preschoolers.

Determination of the [15N]-Nitrate/[14N]-Nitrate Ratio in Plant Feeding Studies by GC⁻MS

Feeding experiments with stable isotopes are helpful tools for investigation of metabolic fluxes and biochemical pathways. For assessing nitrogen metabolism, the heavier nitrogen isotope, [¹⁵N], has been frequently used. In plants, it is usually applied in form of [¹⁵N]-nitrate, which is assimilated mainly in leaves. Thus, methods for quantification of the [¹⁵N]-nitrate/[¹⁴N]-nitrate ratio in leaves are useful for the planning and evaluation of feeding and pulse–chase experiments. Here we describe a simple and sensitive method for determining the [¹⁵N]-nitrate to [¹⁴N]-nitrate ratio in leaves. Leaf discs (8 mm diameter, approximately 10 mg fresh weight) were sufficient for analysis, allowing a single leaf to be sampled multiple times. Nitrate was extracted with hot water and derivatized with mesitylene in the presence of sulfuric acid to nitromesitylene. The derivatization product was analyzed by gas chromatography–mass spectrometry with electron ionization. Separation of the derivatized samples required only 6 min. The method shows excellent repeatability with intraday and interday standard deviations of less than 0.9 mol%. Using the method, we show that [¹⁵N]-nitrate declines in leaves of hydroponically grown Crassocephalum crepidioides, an African orphan crop, with a biological half-life of 4.5 days after transfer to medium containing [¹⁴N]-nitrate as the sole nitrogen source.

The occurrence of nitrate and nitrite in Mediterranean fresh salad vegetables and its modulation by preharvest practices and postharvest conditions

Winter and summer nitrate/nitrite concentrations in 11 salad vegetables were surveyed using a validated HPLC-DAD method. Nitrate was highest in rocket, both in winter (x̅ = 3974 mg kg^-1 fw) and summer (x̅ = 3819 mg kg^-1 fw). High nitrate accumulators included spinach, purslane, chards, dill, coriander and parsley. Wide intra-species variability and levels in excess of permitted maxima highlighted the importance of monitoring vegetable production methods to protect consumer health. Occurrence of detectible nitrite (14-352 mg kg^-1 fw) was most frequent in winter head cabbage. Three additional experiments examined the seasonal effects of nitrogen (N) fertilization rate, application method, formulation and postharvest storage on nitrate and nitrite levels in lettuce, rocket and spinach. Violation of current nitrate limits is likely when total N exceeds 200 kg ha^-1, particularly in rocket and spinach. Postharvest nitrate reduction requires exogenous microbial nitrate reductase activity, which is unlikely to be achieved without visible loss of quality.

Isolation of nitrite-degrading strains from Douchi and their application to degrade high nitrite in Jiangshui

BACKGROUND

Excessive nitrite in food is potentially harmful to human health because of carcinogenic effects caused by its nitroso-derivatives. Douchi, which widely distributed throughout the country, is a traditional solid fermented soybean food with low nitrite content.

RESULTS

In this study, bacteria which can degrade nitrite were isolated from Douchi and identified from their 16S rDNA sequences. Acinetobacter guillouiae, Acinetobacter bereziniae, Bacillus subtilis, Bacillus tequilensis, Bacillus amyloliquefaciens, Bacillus licheniformis, Bacillus aryabhattai and Bacillus methylotrophicus were selected. It was shown that all strains were able to degrade nitrite to some extent, including Bacillus subtilis NDS1, which was able to degrade 99.41% of nitrite. The enzyme activities of these strains were determined at 24 and 48 h and were shown to correspond with their nitrite degradation rates. The strains were used to inoculate Jiangshui, a kind of traditional fermented vegetable from northwest China that often has a high nitrite content. Of the strains tested, Bacillus subtilis NDS1, Bacillus tequilensis NDS3, Acinetobacter bereziniae NDS4, Bacillus subtilis NDS6, and Bacillus subtilis NDS12 were able to degrade nitrite in Jiangshui more rapidly, with Acinetobacter bereziniae NDS4 degrading almost all nitrite in 48 h compared with 180 h of control.

CONCLUSION

These results indicate that the selected strains have potential to be used as nitrite-degrading agents in food. © 2018 Society of Chemical Industry.

Determination of dietary nitrite in patients with esophageal pre-cancerous lesion and normal people: a duplicate diet study

The goal of this study was to find the relationship between dietary nitrite and risk of esophageal cancer, and determine the amount of nitrite intake to establish the oral highest daily intake to prevent the occurrence of esophageal cancer. Duplicate portions of three-consecutive-day diets were collected from 100 patients with esophageal precancerous lesions and 100 controls. The average nitrite daily intakes for esophageal precancerous lesions and normal people were 15.72 mg/d and 11.11 mg/d. The median nitrite daily intakes for cases and controls were 8.76 mg/d and 5.33 mg/d. Positive association was observed between the risk of esophageal precancerous lesions and dietary nitrite intake (p = 0.035). An increased risk of esophageal precancerous lesions was observed for cases or controls in the highest intake quartile of nitrite (highest vs. lowest quartile odds ratio (OR) = 2.256, 95% confidence interval (CI): 1.012-5.026). These results suggest that dietary nitrite intake may influence the risk of esophageal cancer; populations with high incidence of esophageal cancer should take control of nitrite intake as one of the measures to prevent esophageal cancer.

Relationship of dietary nitrate intake from vegetables with cardiovascular disease mortality: a prospective study in a cohort of older Australians

PURPOSE

Short-term trials indicate inorganic nitrate and nitrate-rich vegetables may have vascular health benefits. However, few observational studies have explored the relationship between nitrate intake and long-term cardiovascular disease (CVD) outcomes. The primary aim of this study was to investigate the association of nitrate intake from vegetables with CVD mortality in a sample of older Australians.

METHODS

A subgroup of participants without diabetes or major CVD at baseline (1992-1994) were included from the Blue Mountains Eye Study, a population-based cohort study of men and women aged ≥ 49 years. Diets were evaluated using a validated food frequency questionnaire at baseline, 5 years and 10 years of follow-up. Vegetable nitrate intake was estimated using a comprehensive vegetable nitrate database. Cox proportional hazard regression was used to explore the association between vegetable nitrate intake and CVD mortality.

RESULTS

During 14 years of follow-up, 188/2229 (8.4%) participants died from CVD. In multivariable-adjusted analysis, participants in quartile 2 [69.5-99.6 mg/day; HR 0.53 (95% CI 0.35, 0.82)], quartile 3 [99.7-137.8 mg/day; HR 0.51 (95% CI 0.32, 0.80)], and quartile 4 [> 137.8 mg/day; HR 0.63 (95% CI 0.41, 0.95)] of vegetable nitrate intake had lower hazards for CVD mortality compared to participants in quartile 1 (< 69.5 mg/day).

CONCLUSIONS

In older Australian men and women, vegetable nitrate intake was inversely associated with CVD mortality, independent of lifestyle and cardiovascular risk factors. These findings confirm a recent report that intake of vegetable nitrate lowers the risk of CVD mortality in older women and extend these findings to older men.

NITRATE IN LEAFY GREEN VEGETABLES AND ESTIMATED INTAKE

BACKGROUND

Vegetarian diets are rich in vegetables. Green leafy vegetables are foods that contain considerable amounts of nitrate, which can have both positive and negative effects on the human body. Their potential carcinogenicity and toxicity have been proven, particularly after the reduction of nitrate to nitrite itself or just serving as a reactant with amines and/or amides in the formation of N-nitroso compounds -N-nitrosamines and other nitrogen compounds which may have high levels of nitrate. The aim of this study was to determine whether there is a significant difference, considering the location and seasonal sampling period, in the level of nitrate in certain types of green vegetables, all in order to be able to assess their intake, and possible impact on human health, especially knowing that exposure to nitrate can be potentially higher for vegetarian population group.

MATERIALS AND METHODS

For this purpose, the sampling of 200 different leafy green vegetables was conducted, all of which could be found in free sale in the Republic of Croatia. The sampling was conducted during two seasonal periods - the spring and autumn period. In the springtime, lettuce (sem), spinach (pinacho), kale (kale), chard (mangel) and cabbage (brassica) were sampled, and in autumn lettuce, spinach, kale, chard and arugula. Samples were analyzed using high performance liquid chromatography (HPLC) with UV detection.

RESULTS

The results from the spring sampling phase were in the range of 603 mg/kg for cabbage - 972 mg/kg for chard, and for autumn phase of 1.024 mg/kg for chard to 4.354 mg/kg for the arugula. The results showed that there were significant differences (p <0.05) for most of the samples analyzed, considering the sampling locations and time period.

CONCLUSION

The results indicate that the analyzed vegetables contain significant amounts of nitrate in their composition, which represents relatively significant, but still acceptable intake into the human body.