Contribution of different vegetable types to exogenous nitrate and nitrite exposure

The association of dietary nitrates/nitrites intake and the gut microbial metabolite trimethylamine N-oxide and kynurenine in adults: a population-based study

Background

Dietary nitrate and nitrite may affect the gut microbiota and its metabolites, such as trimethylamine N-oxide (TMAO) and kynurenine (KYN). However, this association and the exact mechanism are still unclear. Therefore, this study aimed to assess the association between dietary consumption of nitrite and nitrate on TMAO and KYN levels in adults.

Methods

This cross-sectional study was employed on a subsample baseline phase of the Tehran University of Medical Sciences (TUMS) Employee's Cohort Study (TEC). A total of 250 adults aged 18 years or older were included in the current analysis. Data on the dietary intakes were collected using a validated dish-based food frequency questionnaire (FFQ), and dietary intakes of nitrite and nitrate were estimated using the FFQ with 144 items. Serum profiles and TMAO and KYN were measured using a standard protocol.

Results

The findings of this study demonstrate a significant association between the intake of animal sources of nitrate and nitrite and the likelihood of having elevated levels of TMAO and KYN. Specifically, after adjustment, individuals with the highest intake adherence to nitrates from animal sources exhibited increased odds of having the highest level of TMAO (≥51.02 pg/ml) (OR = 1.51, 95% CI = 0.59-3.88, P = 0.03) and KYN (≥417.41 pg/ml) (OR = 1.75, 95% CI = 0.73-4.17, P = 0.02). Additionally, subjects with the highest animal intake from nitrite sources have 1.73 and 1.45 times higher odds of having the highest levels of TMAO and KYN. These results emphasize the potential implications of animal-derived nitrate and nitrite consumption on the levels of TMAO and KYN.

Conclusion

The present evidence indicates that a high level of nitrate and nitrite intake from animal sources can increase the odds of high levels of TMAO and KYN. Further studies suggest that we should better evaluate and understand this association.

Highly sensitive capacitance-based nitrite sensing using polydopamine/AuNPs-modified screen-printed carbon electrode

Regulatory bodies play a crucial role in establishing limits for food additives to ensure food quality and safety of food products, as excessive usage poses risks to consumers. In the context of processed animal-based foodstuffs, nitrite is commonly utilized as a means to slow down bacterial degradation. In this study, we have successfully leveraged the redox activity of an electrochemically deposited polydopamine (pDA) film onto gold nanoparticle (AuNP)-modified screen-printed electrodes (SPCE) to develop a sensitive and versatile methodology for the detection of nitrite using redox capacitance spectroscopy. By exploiting the interaction of the AuNPs/pDA electroactive interface with the target nitrite ions, we observed distinct changes in the redox distribution, subsequently leading to modifications in the associated redox capacitance. This alteration enables the successful detection of nitrite, exhibiting a linear response within the concentration range of 10 to 500 μM, with a limit of detection of 1.98 μM (S/N = 3). Furthermore, we applied the developed sensor to analyze nitrite levels in processed meats, yielding good recoveries. These results demonstrate the potential of our approach as a promising method for routine detection of ions.

A worldwide systematic review, meta-analysis and meta-regression of nitrate and nitrite in vegetables and fruits

This study aimed to conduct on the concentration of nitrate/nitrite (mg kg^-1) in vegetables and fruits with a special emphasize on the effect of climate condition. The highest concentration (mean and 95%CI) of nitrate/nitrite was determined in Rocket (4825.15; 3044.14-6606.16), Mizuna (3500; 2702.48-4297.52), and Bok choy (3407.40; 2841.39-3973.42) in vegetable group and in wolfberry (2395.83; 1611.89-3179.77), Jack fruit (237.8; 202.88-272.71) and Cantaloupe (220.32; -224.53 to 665.19) in fruits group. Brazil (2816.77), Estonia (2133.76), Republic of China, Taiwan (2118.28) were the nations with the highest average concentration of nitrate/nitrite in all samples taken from these nations across the globe. Furthermore, Chinese fruits contain the highest concentrations of nitrates/nitrites of other countries (500.57; 416.74-584.41). Nitrate is present in greater quantities in fruits (44.02; 42.12-45.93) and vegetables (438.31; 422.51-454.11) than nitrite; however, the quantity of nitrite has a relatively similar content in both. Our findings revealed that increase in humidity (> 60%), annual rainfall (> 1500 mm), average temperature (> 10 °C) and application of fertilizers lead to significant increase in accumulation of nitrate/nitrite composition of vegetables and fruits (p < 0.05). According to the results of rating countries using the Food Security Index (GFSI), countries with high scores-like Poland and Portugal, which have GFSI scores of 75.5 and 78.7 and average contamination levels of 8.26 and 11.08, respectively-have a trend of average nitrate/nitrite levels of fruit and vegetable products that is significantly decreasing (p = 0.00). Although GFSI levels and other environmental variables can influence nitrate/nitrite levels, fertilizer usage (kg ha^-1) is one of the most significant controllable and impactful factors in contaminants residue, which should be manage. The result of our study, will serve as a basis to estimate the dietary exposure to nitrates and nitrites from fruits and vegetables among populations around the world based on climatology and monitor the related health outcomes.

Characterization of different contaminants and current knowledge for defining chemical mixtures in human milk: A review

Hundreds of xenobiotics, with very diverse origins, have been detected in human milk, including contaminants of emerging concern, personal care products and other current-use substances reflecting lifestyle. The routes of exposure to these chemicals include dermal absorption, ingestion and inhalation. Specific families of chemicals are dominant among human milk monitoring studies (e.g., organochlorine pesticides, bisphenol A, dioxins), even though other understudied families may be equally toxicologically relevant (e.g., food-processing chemicals, current-use plasticizers and flame retardants, mycotoxins). Importantly, the lack of reliable human milk monitoring data for some individual chemicals and, especially, for complex mixtures, is a major factor hindering risk assessment. Non-targeted screening can be used as an effective tool to identify unknown contaminants of concern in human milk. This approach, in combination with novel methods to conduct risk assessments on the chemical mixtures detected in human milk, will assist in elucidating exposures that may have adverse effects on the development of breastfeeding infants.

Nitrate in groundwater and agricultural products: intake and risk assessment in northeastern Iran

The suitability of groundwater and agricultural products for human consumption requires determining levels and assessing the health risks associated with potential pollutants. Here, particularly pollution with nitrate still remains a challenge, especially for those urban areas suffering from insufficient sewage collection systems, resulting in contaminating soil, endangering food safety, and deteriorating drinking water quality. In the present study, nitrate concentrations in the commonly consumed fruit and vegetable species were determined, and the results, together with the groundwater nitrate levels, were used to assess the associated health risks for Mashhad city residents. For this assessment, 261 water samples and 16 produce types were used to compute the daily intake of nitrate. Nitrate in groundwater was analyzed using a spectrophotometer, and produce species were examined using High-Performance Liquid Chromatography. Ward's hierarchical cluster analysis was applied for categorizing produce samples with regard to their nitrate content. Additionally, to account for the sanitation hazards associated with groundwater quality for drinking purposes, total coliform and turbidity were also assessed using the membrane filter (MF) technique and a nephelometer, respectively. Nitrate concentrations exceeded the prescribed permissible limits in 42% of the groundwater wells. The outcomes also exhibit significantly higher nitrate accumulation levels in root-tuber vegetables and leafy vegetables compared to fruit vegetables and fruits. Using cluster analysis, the accumulation of nitrate in vegetables and fruits was categorized into four clusters, specifying that radish contributes to 65.8% of the total content of nitrate in all samples. The Estimated Daily Intake (EDI) of nitrate and Health Risk Index (HRI) associated with consumption of groundwater exceeded the prescribed limit for the children's target group in Mashhad's south and central parts. Likewise, EDI and HRI values for produce consumption, in most samples, were found to be in the tolerable range, except for radish, lettuce, and cabbage, potentially posing risks for both children and adult consumers. The total coliforms in groundwater were found to violate the prescribed limit at 78.93% of the sampling locations and were generally much higher over the city's central and southern areas. A relatively strong correlation (R² = 0.6307) between total coliform and nitrate concentrations suggests the release of anthropogenic pollution (i.e., sewage and manure) in the central and southern Mashhad.

Inhibition of nitrite in prepared dish of Brassica chinensis L. during storage via non-extractable phenols in hawthorn pomace: A comparison of different extraction methods

The objective of this study was to investigate whether non-extractable phenols (NEP) prepared by acid, enzymatic and alkaline hydrolysis in hawthorn pomace could reduce the nitrite content in prepared vegetable dishes (PVDs), analyzed through ultraviolet spectrophotometry and high performance liquid chromatography. The results showed that on the seventh day of storage, compared with the control group, the nitrite content of the samples added with acid, enzymatic and alkaline hydrolyzed NEP decreased by 40%, 28% and 19%, respectively, depending on different contents and chemical compositions of the recovered NEP. The nitrite reduction caused by NEP was mainly attributed to the growth inhibition of microorganisms producing nitrite (e.g., Escherichia coli and Pseudomonas aeruginosa) and the direct scavenging effect on nitrite, rather than affecting the activities of nitrate reductases and nitrite reductases in plant tissues. Use of hawthorn pomace is potentially a promising option to reduce nitrite in PVDs.

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.

Garlic essential oil microcapsules prepared using gallic acid grafted chitosan: Effect on nitrite control of prepared vegetable dishes during storage

In order to lower the nitrite content in prepared vegetable dishes (PVDs) within a week, microcapsules loaded with garlic essential oils (GEO) were prepared using modified chitosan (CS) with different mass ratios of gallic acid (GA) to CS, and their physicochemical properties were determined. The effects of GEO alone and of microcapsules made using native CS and GA-CS (GA-grafted CS) with the highest conjugation degree on the nitrite content in PVD_S were measured quantitatively. Also, the reasons for the differences were identified. The results showed that the microcapsules prepared using GA-CS (at a mass ratio of 0.5:1) presented the best physicochemical properties, including antioxidant activity, encapsulation efficiency, sustained release, etc. GA-CS microcapsules enhanced growth inhibition of bacteria producing nitrites, thus showing its excellent ability to inhibit nitrites, compared to GEO alone and microcapsules made using native CS. GA-CS encapsulation is a new option to lower the nitrite content in PVDs.

A novel propylene glycol alginate gel based colorimetric tube for rapid detection of nitrite in pickled vegetables

The detection of nitrite is of great significance because it is closely related to food safety. In this work, a rapid colorimetric method was developed for nitrite detection based on the reaction of propylene glycol alginate (PGA) gel interface. In the reaction of nitrite and 4-Aminoacetophenone, diazo compound formed, which could be further transformed to purplish red compound by reacting with N-(1-Naphthyl)ethylenediamine (NED). Nitrite exhibited a linear relationship with the grayscale of the gel interface in the range of 0.3-9 μg mL^-1 with a detection limit of 0.3 μg mL^-1. The method was applied to detect nitrite in four types of pickled vegetables with recovery of 80.9-119.02% and relative standard deviation of 0.11-6.73%. Notably, the detection process can be accomplished within 5 min. The proposed colorimetric method exhibited advantages of simplicity, quickness and sensitivity, showing potential application prospects for the real-time and on-site detection of nitrite in pickled vegetables.

Short-Term Impact of Two Kinds of Vegetables to Exogenous Total Nitrate and Nitrite Intake: Is Antibacterial Mouthwash Influential?

Background:

Nitrate is a compound with adverse effects on human health that can exist also in vegetables. This study aimed to determine the intake of total nitrate/nitrite from lettuce and carrot as high and low nitrate content, respectively. Moreover, the effect of chlorhexidine mouthwash on the elimination of the nitrite level in saliva and urine was surveyed.

Methods:

This study was designed as a crossover based on the randomized selection method. Thirty-nine participants were divided into two groups; the lettuce and carrot juice consumers (control group). The case group was consumed these two vegetables, while they used antibacterial mouthwash. The background of nitrate/nitrite of the participants was determined before exposure. The intake of total nitrate and nitrite via lettuce and carrot juice consumption was investigated. The Griess colorimetric reaction was used for nitrate and nitrite determination in samples.

Results:

Total nitrate concentrations in case and control groups were detected 0.79 and 0.78 mM in saliva and 1.78 and 1.38 mM in urine after lettuce consumption, respectively. However, it was determined 1.55 and 2.43 mM in saliva and 2.92 and 3.04 mM in urine after carrot ingestion. Salivary nitrite concentration 0.53 mM was decreased to 0.45 mM after antibacterial mouthwash application (P-value <0.05).

Conclusions:

This study indicated that the intake of total nitrate/nitrite via leafy vegetables was higher than rooty ones. The chlorhexidine mouthwash is an appropriate recommendation to reduce the nitrite concentration in the human body for preventing the probable side effects of nitrate metabolites such as N-nitrosamines forming.

Potential health risks of toxic heavy metals and nitrate via commonly consumed bivalve and vegetable species in Ho Chi Minh City, Vietnam

This study aimed to evaluate the health risks of cadmium (Cd), lead (Pb), inorganic arsenic (As), and nitrate exposure through the consumption of bivalves and vegetables collected from local markets in Ho Chi Minh City. The present study analyzed four favorite bivalve species (Meretrix lyrate; Perna viridis; Anadara subcrenata; Anadara granosa) for concentrations of Cd, Pb, and inorganic As and 9 vegetable species (Brassica juncea; Brassica integrifolia; Brassica rapa chinensis; Nasturtium officinale; Lactuca sativa; Ipomoea aquatica; Amaranthus gangeticus; Ipomoea batatas; Spinacia oleracea) for concentrations of Pb and nitrate. The target hazard quotient (THQ) and target cancer risk (TR) were calculated to estimate non-carcinogenic and carcinogenic health risks, respectively. For bivalves, Cd and inorganic As were present at relatively lower concentrations, whereas a relatively higher accumulation of Pb was recorded. The THQ for Cd, Pb, or inorganic As was below the threshold of 1, suggesting no potential health risks. In the case of vegetables, Pb was present at relatively low concentrations, while nitrate accumulation was at relatively high concentrations. The THQ for nitrate was higher than the threshold of 1, suggesting a potential health risk. The combined effects are estimated according to the hazard index (HI), which shows the health risks associated with the consumption of these bivalves and vegetable species. Therefore, continuous and excess consumption for a lifetime of more than 70 years has a probability of target cancer risk.

Effect of Different Ratios of Blue and Red LED Light on Brassicaceae Microgreens under a Controlled Environment

The consumption of microgreens has increased due to their having higher levels of bioactive compounds and mineral nutrients than mature plants. The lighting conditions during the cultivation of microgreens, if optimally selected, can have a positive effect by further increasing their nutritional value. Thus, our study aimed to determine the changes in mineral nutrients contents of Brassicaceae microgreens depending on different blue–red (B:R) light ratios in light-emitting diode (LED) lighting and to evaluate their growth and nutritional value according to different indexes. Experiments were performed in controlled environment growth chambers at IH LRCAF, 2020. Microgreens of mustard (Brassica juncea ‘Red Lace’) and kale (Brassica napus ‘Red Russian’) were grown hydroponically under different B:R light ratios: 0%B:100%R, 10%B:90%R, 25%B:75%R, 50%B:50%R, 75%B:25%R, and 100%B:0%R. A 220 μmol m⁻² s⁻¹ total photon flux density (TPFD), 18 h photoperiod, 21/17 ± 2 °C temperature and 60% ± 5% relative humidity in the growth chamber were maintained during cultivation. We observed that an increasing percentage of blue light in the LED illumination spectrum during growth was associated with reduced elongation in the microgreens of both species and had a positive effect on the accumulation of mostly macro- and micronutrients. However, different B:R light ratios indicate a species-dependent response to changes in growth parameters such as leaf area, fresh and dry mass, and optical leaf indexes such as for chlorophyll, flavonol, anthocyanin, and carotenoid reflectance.

Study of nitrate levels in fruits and vegetables to assess the potential health risks in Bangladesh

Nitrate is a chemical compound naturally present in fruits and vegetables. This study aims at assessing the nitrate levels and health risks arising from high consumption of fruits and vegetables in Bangladesh. Sixteen species of fruits and vegetables were examined for nitrates using High-Performance Liquid Chromatography with Photo Diode Array (PDA) detector. Ward's hierarchical cluster analysis was carried out to identify the cluster of tested fruits and vegetables for the nitrate contents. A point estimate of the daily intake was applied to find the health risks that arise due to elevated levels of nitrate in fruits and vegetables. The results show that root and tuber vegetables accumulate significantly higher levels of nitrate in comparison to fruits and fruit vegetables (P < 0.05). In cluster analysis, the nitrate accumulation of fruits and vegetables show four clear clusters contributing to 29.54%, 7.17%, 4.42%, and 58.57% of the total nitrate content in the entire sample. The risk assessment of the Estimated Daily Intake (EDI) and Health Risk Index (HRI) of almost all the tested samples was in the acceptable range, except for radish, thereby indicating the acceptance of risk due to nitrate intake in Bangladesh. As nitrate may have had risk factor for health, during cultivation and storing the product should be properly monitored.

Strategies to Improve Meat Products' Quality

Meat products represent an important component of the human diet, their consumption registering a global increase over the last few years. These foodstuffs constitute a good source of energy and some nutrients, such as essential amino acids, high biological value proteins, minerals like iron, zinc, selenium, manganese and B-complex vitamins, especially vitamin B12. On the other hand, nutritionists have associated high consumption of processed meat with an increased risk of several diseases. Researchers and processed meat producers are involved in finding methods to eliminate nutritional deficiencies and potentially toxic compounds, to obtain healthier products and at the same time with no affecting the sensorial quality and safety of the meat products. The present review aims to summarize the newest trends regarding the most important methods that can be applied to obtain high-quality products. Nutritional enrichment with natural bioactive plant compounds (antioxidants, dietary fibers) or probiotics, reduction of harmful components (salt, nitrate/nitrite, N-nitrosamines) and the use of alternative technologies (high-pressure processing, cold plasma, ultrasounds) are the most used current strategies to accomplish this aim.

Reduction of Nitrite in Meat Products through the Application of Various Plant-Based Ingredients

Nitrite is the most commonly applied curing agent in the meat industry, and is known to affect human health. Nitrites impart a better flavor, taste and aroma; preserve the red-pinkish color of the meat; and prevent the risk of bacterial contamination of the cured meat, especially from Clostridium botulinum. Unfortunately, recent research has demonstrated some negative effects of this technique. Certain N-nitroso compounds have been shown to stimulate gastric cancer; therefore, most of the research groups are studying the effects of nitrates and nitrites. In this review, we discuss the various food sources of nitrites and nitrates and their current legal requirements for use in meat products. We also discuss the possible changes that might come up in the regulations, the concerns associated with nitrates and nitrites in meat products, and the use of plant-based nitrite and nitrate substitutes. All these topics will be considered with respect to ensuring a high level of microbiological protection, oxidative stability and acceptable sensory quality (color, taste and smell) in meat products.

Stand-Alone and Combinatorial Effects of Plant-based Biostimulants on the Production and Leaf Quality of Perennial Wall Rocket

Modern agriculture is facing many difficulties due to a rapidly changing climate, and environmental damage from agricultural production. The commitment of scientists and farmers to increase environmentally sustainable agricultural practices is one way to help mitigate environmental impacts. Among these practices, the use of biostimulants could be beneficial for increasing fertilizer efficiency and reducing excessive use in agriculture, and as plant growth regulators capable of increasing both production volume and quality of crops. In our study, rocket plants were grown in a greenhouse and treated with two biostimulants (protein hydrolysates or tropical plant extract), either individually or combined, to assess the effect on yield, dry biomass, mineral content, qualitative parameters as well as on economic profitability of foliar biostimulant applications. Total yield and dry biomass of the plants treated with the three biostimulant combinations on average increased by 48.1% and 37.2% respectively compared to untreated plants, without significant differences between treatments. Biostimulant application increased the content of chlorophyll, K, Mg and Ca, compared to the untreated plants. Furthermore, a biostimulant synergistic effect was detected concerning the content of total ascorbic acid. Our results confirmed that the biostimulants are eco-friendly products, able to boost plant growth and product quality and thus increase growers’ profitability.

Nitrate and Nitrites in Foods: Worldwide Regional Distribution in View of Their Risks and Benefits

Nitrate and nitrite ions are used as food additives to inhibit the growth of microorganisms in cured and processed meats. Vegetables contain significant quantities of nitrate and nitrite. Actually, the vast majority of consumed nitrate and nitrite comes from natural vegetables and fruits rather than food additives. For years, the cancer risks of these two ions have been discussed, since they potentially convert into the carcinogenic nitrosamines. However, recently, these two ions have been considered essential nutrients which promote nitric oxide production and consequently help cardiovascular health. It seems that the role of these two ions in our diet is important now from a different point of view. In this review, the nitrate and nitrite contents of food products from different countries are displayed globally in order to reinterpret the risks/benefits of our consumption quotations. This review article is based on Science Citation Index (SCI) articles reported between 2008 and 2018.

Biochar reduces nitrate level in red beet

Impacts of red beet consumption both on human and animal health are subject of intense research. In particular, products that are not heat-processed contain plethora of bioactive compounds that hold promise against numerous degenerative and aging-associated diseases. However, high level of nitrates (typically more than 2 g NO₃^- kg^-1) whose health effects are perceived with reasoned objections counterbalance these benefits. Following the above, from a certain level, the increased consumption of red beet has contrary impacts, creating a limiting factor not only from the economic point of view but also in terms of beneficial compounds intake. Reduction of NO₃^- levels (- 35%) has been achieved by soil amendment via increased doses of biochar. The data obtained indicates that the mechanism can be explained as follows. The soil improvement reduces soil density, increases soil temperature, improves water retention, and other prerequisites for increased activity of soil microorganisms. Accelerated metabolism of soil biota turned more nitrogen from fertilizers into organic forms. Hence, less mineral nitrogen is left for red beet intake.

Effects of spinach nitrate on insulin resistance, endothelial dysfunction markers and inflammation in mice with high-fat and high-fructose consumption

Background

Insulin resistance, which is associated with an increased risk of cardiovascular morbidity and mortality, has become a leading nutrition problem. Inorganic nitrate enriched in spinach has been demonstrated to reverse the pathological features of insulin resistance and endothelial dysfunction. However, the effects of a direct intake of nitrate-enriched spinach on insulin resistance and endothelial dysfunction have not been studied.

Objective

To investigate the effects of spinach nitrate on insulin resistance, lipid metabolism, endothelial function, and inflammation in mice fed with a high-fat and high-fructose diet.

Design

A diet intervention of spinach with or without nitrate was performed in mice. A high-fat and high-fructose diet was used to cause insulin resistance, endothelial dysfunction, and inflammation in mice. The impacts of spinach nitrate on lipid profile, insulin resistance, markers of endothelial function, and inflammation were determined in mice.

Results

Spinach nitrate improved the vascular endothelial function of the mice with high-fat and high-fructose consumption, as evidenced by the elevated plasma nitrite level, increased serum nitric oxide (NO) level and decreased serum ET-1 level after spinach nitrate intervention. Spinach nitrate also reduced serum triglycerides, total cholesterol, and low-density lipoprotein-cholesterol levels and elevated serum high-density lipoprotein-cholesterol levels in the mice fed with a high-fat and high-fructose diet. Mice receiving spinach with 60 mg/kg of nitrate (1.02±0.34) showed a significantly low homeostasis model assessment-insulin resistance index as compared with the model mice (2.05±0.58), which is indicating that spinach nitrate could effectively improve the insulin resistance. In addition, spinach nitrate remarkably decreased the elevated serum C-reactive protein, tumor necrosis factor α, and interleukin-6 levels induced by a high-fat and high-fructose diet.

Conclusions

The intake of spinach nitrate can augment NO status, improve lipid homeostasis, relieve inflammation, and enhance endothelial function, suggesting that spinach is promising dietary supplements for insulin resistance prevention.

Effect of electrolyzed oxidizing water treatment on the reduction of nitrite levels in fresh spinach during storage

Leafy vegetables are the major source of nitrite intake in the human diet, and technological processing to control nitrite levels in harvested vegetables is necessary. In the current work, the effect of electrolyzed oxidizing water (EOW) on the nitrite and nitrate levels in fresh spinach during storage was studied. EOW treatment, including slightly acidic electrolyzed water and acidic electrolyzed water, was found to effectively reduce nitrite levels in fresh spinach during storage; levels in the late period were 30 to 40% lower than that of the control. However, the nitrate levels in fresh spinach during storage were not influenced by EOW treatment. The reduction of nitrite levels in EOW-treated fresh spinach during storage can be attributed to the inactivation of nitrate reductase directly and to the reduction of bacterial populations. Our results suggest that treatment with slightly acidic electrolyzed water may be a better choice to control nitrite levels in fresh vegetables during storage. This study provided a useful method to reduce nitrite levels in fresh spinach.

Effects of agriculture production systems on nitrate and nitrite accumulation on baby-leaf salads

Nitrate and nitrite are widespread contaminants of vegetables, fruits, and waters. The levels of these compounds are increased as a result of using organic wastes from chemical industries, domestic wastes, effluents, nitrogenous fertilizers, and herbicides in agriculture. Therefore, determining the nitrate and nitrite levels in biological, food, and environmental samples is important to protect human health and the environment. In this context, we set this study, in which we report the effect of production system (conventional and organic) on the accumulation of nitrates and nitrites in fresh baby-leaf samples. The average levels of the nitrate () and nitrite () contents in six different baby-leaf salads of a single species (green lettuce, red lettuce, watercress, rucola, chard, and corn salad) produced in organic and conventional agriculture system were evaluated. Spectrophotometric analytical method recently published was validated and used. Nitrates and nitrites were detected in all samples. The nitrates levels from organic production varied between 1.45 and 6.40 mg/kg fresh weight (FW), whereas those from conventional production ranged from 10.5 to 45.19 mg/kg FW. The nitrites content was lower than nitrates and ranged from 0.32 to 1.89 mg/kg FW in organic production system and between 0.14 and 1.41 mg/kg FW in conventional production system. Our results showed that the nitrate content was dependent on the agricultural production system, while for nitrites, this dependency was less pronounced.

Nitrite biosensing via selective enzymes--a long but promising route

The last decades have witnessed a steady increase of the social and political awareness for the need of monitoring and controlling environmental and industrial processes. In the case of nitrite ion, due to its potential toxicity for human health, the European Union has recently implemented a number of rules to restrict its level in drinking waters and food products. Although several analytical protocols have been proposed for nitrite quantification, none of them enable a reliable and quick analysis of complex samples. An alternative approach relies on the construction of biosensing devices using stable enzymes, with both high activity and specificity for nitrite. In this paper we review the current state-of-the-art in the field of electrochemical and optical biosensors using nitrite reducing enzymes as biorecognition elements and discuss the opportunities and challenges in this emerging market.