Nitrate Content In Lettuce Research Articles

Utilizing co-composted biochar as a growing medium for buttercrunch lettuce

In this study, we explored the utilization of co-composted biochar (COMBI), the end product of co-composted poultry carcasses and biochar, as a growth medium for buttercrunch lettuce in a controlled environment. Despite the potential benefits that COMBI could provide, its use is currently limited, as reported in previous studies. The study's objective was to compare the performance of COMBI with various types of biochar with a comparison to a control group that used soil only. The results indicated that the application of COMBI treatment led to an increased water-holding capacity of the soil, ranging from 29% to 34%, which could help to mitigate drought stress and retain water-soluble nutrients under certain circumstances. However, there were no significant differences in stem diameter, dry shoot weight, or dry root weight of lettuce between the COMBI and control groups. While the use of COMBI did not result in increased crop yield, the study found that the application of wood-based biochar (WBC) and distiller's grain biochar (DGBC) in COMBI reduced the nitrate content in lettuce by 20.3–29.7% compared to the control group. Additionally, the application of COMBI treatment significantly lowered the Cu content of lettuce leaves. These findings suggested that the use of co-composted biochar as a growing media can have some benefits, particularly in terms of water-holding capacity and reduced nitrate and Cu content in lettuce leaves. However, the study highlights the need for continued research and development of this approach to ensure that it meets safety and quality standards and is a viable and sustainable option for crop production.

Nanoparticulate Fertilizers Increase Nutrient Absorption Efficiency and Agro-Physiological Properties of Lettuce Plant

The extensive use of chemical fertilizers is responsible for numerous environmental problems including low food quality, soil degradation, and toxicity to beneficial living organisms in the soil. Nano-fertilizers (NFs) application may be a promising solution for combat these challenges. The current study focused on the efficiency of applying small amounts of NFs incorporated with conventional nitrogen, phosphorus, and potassium (NPK) fertilizers to reduce the quantities of conventional fertilizers (CFs) in lettuce cultivated in sandy soil. This study evaluated the effect of these incorporations on plant growth, yield, phytochemical accumulation, leaf nutrient, and leaf nitrate. A pot experiment was conducted during the winter seasons of 2020/2021 and 2021/2022 using the following treatments: CF100: 100% CFs, CF75NF25: 75% CFs + 25% NFs, CF50NF50: 50% CFs + 50% NFs, CF25NF75: 25% CFs + 75% NFs, and NF100: 100% NFs (=10% of CFs). Our findings displayed that the CF75NF25 and CF50NF50 treatments recorded the highest plant growth parameter values (plant length, root length, number of leaves, and fresh and dry biomass). The maximum of chlorophyll fluorescence measurements (photosystem II efficiency) were obtained in plants fertilized with CF75NF25, followed by CF50NF50 and CF100. The improvement ratios of photosynthetic pigments (Chlorophyll (Chl) a, b, and total) for CF75NF25 were 23.77, 50, and 23.72% in the first season and 10.10, 51.0, and 24.90% in the second season for Chl a, b, and total, respectively, as compared with the CF100 treatment. A similar tendency was observed for the CF50NF50 treatment. Generally, CF75NF25 significantly raised the content of total phenolic compounds (TPC), total flavonoid content (TFC), and antioxidant activity (AOA) in lettuce plants by 36.09, 47.82, and 40.16% in the first season and by 30.39, 37.53, and 32.43% in the second season, respectively, compared with CF100. In addition, the levels of leaf nutrient content and uptake of N, P, and K were significantly higher in plants fertilized with CF75NF25 compared to the other treatments, whereas CF25NF75 had the lowest values among the different treatments across both seasons for most of the tested traits. The nitrate content in lettuce leaves (NO3−) for both seasons was lower than the acceptable level for human consumption. These results indicate that incorporating a low concentration of NFs into CFs could be a promising strategy to reduce the amount of CFs to 75% or 50% of lettuce NPK requirements without significant adverse effects on the growth and productivity of lettuce plants cultivated in sandy soil.

Optimization of light intensity and nitrogen concentration in solutions regulating yield, vitamin C, and nitrate content of lettuce

ABSTRACT Light intensity and nitrogen concentration in nutrient solutions are two main factors affecting the growth and nutritional quality of lettuce(Lactuca sativa L.). This study investigated the method of regulating vegetable cultivation through the interactive control of the light environment and solution ratio. A quadratic regression orthogonal model was developed to understand the role of light intensity (43 to 237 µmol m−2s−1) and nitrogen concentration (4.3 to 23.7 mmol L−1) in lettuce growth. Dry weight, vitamin C, and nitrate contents were measured and modelled to understand the coupling effect of light intensity and nitrogen concentration on lettuce. The optimised conditions for lettuce growth were 237 µmol m−2 s−1 of light intensity and 9.2 mmol L−1 of nitrogen concentration, and these conditions were predicted to produce lettuce with an average dry biomass of 3.9 g plant−1, 149.9 µg g−1 of Vitamin C, and 212.1 µg g−1 of nitrate content based on their respective weighting factors (0.50, 0.25, and 0.25). The lettuce yield and quality were verified using the modelled optimised growth conditions and the lettuce grown was indeed more nutritional compared to the commercially available lettuce. The findings are important for mass production of lettuce in plant factories and greenhouses.

Quantification of nitrate content with FT-NIR technique in lettuce (Lactuca sativa L.) variety types: a statistical approach

According to the Commission Regulation (EC) No. 1258/2011, the maximum allowed nitrate content of lettuce is defined within a broad range (2000–5000 mg NO3/kg), depending on harvest season and technology. This study focuses on the identification of the differences in nitrate accumulation between lettuce types and varieties, depending on production technology and on the investigation of the application of non-destructive FT-NIR spectroscopy for nitrate quantification, towards widely used UV–Vis spectroscopy.In the present study, combinations of seasons and technologies (spring × greenhouse, autumn × open field) were employed for the production of types (batavia, butterhead, lollo and oak leaf; both red and green colored); a total of 266 lettuce heads were analyzed. It was found that with standardized technology and conditions, autumn harvested green oak leaf lettuce types accumulated significantly less nitrate, than red oak or lollo leaf types. With spring harvested lettuces, batavia types generally accumulated generally more nitrates than butterhead types. Based on the linear discriminant analysis (LDA) of FT-NIR measurements the four distinct variety types diverge; the lollo type explicitly diverges from batavia and butterhead types. The LDA further revealed, that within lollo and oak leaf variety types, red and green leaved varieties diverge as well. A model was successfully built for the FT-NIR quantification of the nitrate content of lettuce samples (R2 = 0.95; RMSEE = 74.4 mg/kg fresh weight; Q2 = 0.90; RMSECV = 99.4 mg/kg fresh weight). The developed model is capable of the execution of a fast and non-invasive measurement; the method is suitable for the routine measurement of nitrate content in lettuce.

NITRATE ACCUMULATION IN LETTUCE AND ROCKET IN RESPONSE TO NITROGEN FERTILIZATION IN INTERCROPPING

ABSTRACT In the cultivation of leafy vegetables, it is common to apply high amounts of nitrogen fertilizer. The imbalance between the absorption and the use of nitrogen (N) by the plant increases the nitrate content and decreases the quality of the vegetables because nitrate has a strong association with compounds harmful to human health. On the other hand, there is a lack of information on how N dose in intercropping, in order to improve yield, affects the quality (nitrate content) of vegetables. Thus, the objective of this study was to evaluate the nitrate content of intercropped lettuce and rocket, with nitrate content acting as a function of the nitrogen dose applied to these crops. The experiment was carried out at UNESP, Jaboticabal, SP, from September to December 2006. The experimental design was a complete randomized block design with four replications. The treatments were arranged in a 4 × 4 + 2 factorial scheme, with four varying concentrations of N each for lettuce and rocket (0, 65, 130 and 195 kg ha-1 of N), plus two treatments corresponding to lettuce and rocket monocrops. Nitrate content in lettuce under intercropping is 42% less compared to that in the monocrop. Increasing nitrogen concentrations increased nitrate levels for lettuce and rocket under intercropping; however, these levels are below those found for their respective monocrops.

Effect of sulfate anions on nitrates accumulation and total Kjeldahl nitrogen content in lettuce plants cultivated in peat-perlite mixture

Intensive agriculture is characterized by increased use of synthetic nitrogen fertilizers. If the supplied nitrogen fertilizers are excessive, many vegetables, particularly leafy vegetables, accumulate high levels of nitrates. Increased vegetable nitrate content is related to possible implications for health, as nitrate metabolites can cause carcinogenesis, infantile methaemoglobinaemia and possibly even teratogenesis. The aim of the present study was to investigate the effect of sulfate ions on nitrate accumulation and total Kjeldahl nitrogen (TKN) content in lettuce (Lactuca sativa var. crispa ‘Lollo Bionda’), as an attempt to suggest possible ways to reduce nitrate levels. Plants were grown in peat-perlite mixture and fertilized by nutrient solutions under glasshouse conditions. Three levels of nitrogen concentrations (100, 200 and 400 mg L(‑1) N) have been applied in combination with three levels of sulfate anions (15, 150 and 300 mg L(‑1) S as SO(4)2-). At harvest stage, the fresh weight of leaves, nitrate accumulation, total sulfur concentration and TKN tissue content were determined. As expected, foliar biomass, nitrate accumulation and TKN content were enhanced when nitrogen concentration was increased. However, the increased levels of sulfates (150 and 300 mg L(‑1) S) had no effect on plant weight whereas a decline of nitrate accumulation was observed when sulfate fertilization increased. Moreover, a concentration of 150 mg L(‑1) S caused TKN increase while the reverse was the case for the concentration of 300 mg L(‑1) S. The results of the present study indicate that the enhanced concentrations of sulfates resulted in decreased nitrate accumulation in lettuce leaves. This may be due to interference in the uptake of nitrates by sulfates ions and may be proposed as a possible way to decrease nitrate content in lettuce, resulting in consumer safety.

Use of raw and composted poultry litter in lettuce produced under field conditions: microbiological quality and safety assessment

Lettuce (Lactuca sativa L.) constitutes one the most important vegetable crops worldwide. Poultry litter is being applied as an economically suitable alternative to nitrogen fertilizers in lettuce cultivation. However, little is known about the effects of this practice over this fresh product safety that is usually consumed as a salad. The aim of this work was to determine the microbiological quality and the nitrate content in lettuce produced, under field conditions, using either raw or composted poultry litter, coming from the same original batch. Two experiments were conducted in the experimental field of Facultad de Ciencias Agrarias (UNL, Santa Fe, Argentina) to assess the effects of recently extracted poultry litter that consisted of broiler chicken manure plus rice husk, or composted for 12 mo. The application amounts were: 20 T ha-1 (T1); 40 T ha-1 (T2); and no application of manure (T). Increasing the applied quantities had also increased the health risk associated with lettuce consumption, due to higher nitrate levels and microbial contamination. However, these risks were reduced by composting the material. Even when lettuce contamination with faecal bacteria was mainly due to the use of poultry litter, the number and incidence of pathogens were reduced when properly composted manure was applied instead of raw one. Increasing the dose of poultry litter applied also increases the health risk in lettuce. Though, when the material is properly composted, its fertilizing capacity is maintained, giving proper yields with lower nitrate levels and microbial contamination by enterobacteria.

Regulating nitrate excess in lettuce-planted greenhouse soil with available carbon addition through irrigation.

Nitrate excess is common in greenhouse soils, imposing environmental risks and degrading vegetable quality. In this study, the effectiveness of adding sucrose as available carbon through irrigation to cut nitrate excess in lettuce-planted soil was investigated under impacts of soil texture and irrigation type. In the pot experiment using two loam soils of same origin with different clay to sand ratios (50.2% and 39.8%) and nitrate excess (116.1 and 417.7mg/kgN), three-time sucrose addition through flood irrigation was more effective in lowering net formation of nitrate-based inorganic N and increasing lettuce yield in the soil with the higher clay to sand ratio, and sucrose addition at 150-450mg/kg reduced nitrate accumulation and leaching, and nitrate content of lettuce at harvest by 62.5-89.6%, 19.3-36.1%, and 11.4-76.0%, respectively. In the micro-plot field experiment with two-time sucrose addition at 0.6-1.2g/L through furrow irrigation (42mm) into two other soils of same origin with different clay to sand ratios (56.9%, 48.4%), nitrate accumulation at 0-30-cm depth at the prone-leaching furrow location at harvest decreased by 30.9-36.0% under the higher clay to sand ratio but increased by about 35% under the lower clay to sand ratio. The nitrate content and yield of ridge-planted lettuce was less affected in either soil. Hence, carbon addition rate, irrigation type, and clay to sand ratio all affected the effect of available carbon addition on nitrate accumulation in vegetable-planted soil, and their joint impacts need better quantification for cutting nitrate excess in soil and improving vegetable quality and even yield.

The nitrification inhibitor 3,4-dimethylpyrazole phosphate decreases leaf nitrate content in lettuce while maintaining yield and N2O emissions in the Savanna of Bogotá

The nitrification inhibitor 3,4-dimethylpyrazole phosphate decreases leaf nitrate content in lettuce while maintaining yield and N2O emissions in the Savanna of Bogotá

Interaction effects of light intensity and nitrogen concentration on growth, photosynthetic characteristics and quality of lettuce (Lactuca sativa L. Var. youmaicai)

Light intensity and nitrogen concentration of nutrient solution are considered crucial for the contents of vitamin C and nitrate in cultivated leaf vegetables. We here investigated the effects of various combinations of light intensity (60, 140 and 220μmolm−2s−1) and nitrogen concentration (7, 15 and 23mmolL−1) of the solution on the growth, photosynthetic characteristics, vitamin C and nitrate content of lettuce. Our results demonstrate that the lettuce had the largest dry biomass at the high illumination of 220μmolm−2s−1 and low nitrogen of 7mmolL−1. The higher light and low nitrogen also contributed to the accumulation of vitamin C and decrease of nitrate in lettuce leaves. The effect of nitrogen supply on chlorophyll concentrations was more efficient under low light than high illumination. Our results reveal that there was an obvious interaction between light intensity and nitrogen available for the photosynthesis, yield and quality of lettuce. This study provides valuable insights into the combinational regulation of light intensity and nitrogen supply for improving growth and nutritional quality of vegetables grown in greenhouse and plant factory.

Accumulation and Primary Metabolism of Nitrate in Lettuce (Lactuca Sativa L. Var. Youmaicai) Grown Under Three Different Light Sources

ABSTRACTLight-emitting diodes (LEDs) hold great potential as electric light source for leafy vegetable production in controlled environment. However, most of LED lights in vegetable cultivation were only combined with red and blue LEDs, and the spectral composition was oversample. Previous studies reported that light spectral composition could influence nutritional quality of vegetables, e.g., nitrate content. In order to better understand the influence of spectral composition on nitrate accumulation of leafy vegetables grown in closed-type system. The nitrate content, nitrate primary metabolism of 35-day-old lettuce (Lactuca sativa L. Var. youmaicai) in vivo and its biomass were investigated. The results showed that cool white fluorescent light (T5) and high-pressure sodium light (HPS) with wide spectrum significantly reduced nitrate content in lettuce than red and blue combination LED light (RB-LED) treatment. Our findings demonstrated that a proper optimizing procedure of light spectrum with supplemental other wavebands in RB-LEDs is necessary for reducing nitrate accumulation of lettuce.

Effect of Water Recirculation Duration and Shading on Lettuce ( Lactuca sativa ) Growth and Leaf Nitrate Content in a Commercial Aquaponic System

Two experiments were conducted to evaluate the effects of three water recirculating duration (daytime (07.00h to18.00h); nighttime (18.00h to 07.00h); and 24 hours control) and shading (30%, 60% and no shading control), respectively, on growth and sap's nitrate content of lettuce in a commercial aquaponic system integrated with red tilapia culture. First experiment showed that water recirculating time did not affect the lettuce growth, thus offering the possibility to increase aquaponics profitability by reducing the operational cost. The second experiment revealed that shading affected nitrate content in the sap of the leaf midribs, but it remained in range specified by EU regulations in all treatments. The highest lettuce growth was observed at the rate of 30% shading whereas 60% shading gave the lowest growth (P<0.05). (Resume d'auteur)

Effect of flood fertigation on yield of greenhouse lettuce grown in different substrates

The hydroponic system is very often used for greenhouse vegetable production. The flood irrigation on a bench or on the flood floors is applied in the production of ornamental plants and vegetable transplants. This system is environmentally friendly, since fertigation is used in a closed system using the recirculation of nutrient solution. The aim of this study, conducted in 2010-2012, was to determine the effect of flood fertigation with different concentrations of nutrient solution (EC: 1.0; 2.0; 3.0; 4.0 mS cm-1) on the yield and quality of the butterhead lettuce cultivar Natalia grown in different substrates (coconut coir, peat and rockwool). The experiment was conducted in the spring and autumn cycle. The highest marketable yield at each concentration of the nutrient solution was achieved in the cultivation in rockwool, both within the spring and autumn. The highest nitrate content in lettuce in terms of both cultivation cycles was found in the lettuce grown in the nutrient solution concentration of EC 4 mS cm-1, and the lowest one was achieved in the nutrient solution concentration of EC 1.0 mS cm -1. Significantly less of nitrates was in lettuce grown in spring than in autumn. Higher levels of EC significantly increased the content of P and K in lettuce leaves during in both growing cycles, while the content of Ca and Mg was not significantly different. The applied substrates had a significant impact on the content of K, P, Ca and Mg in leaves of lettuce. The best concentration of the nutrient solution used for flood fertigation of greenhouse lettuce was EC 3.0 mS cm-1 for the spring cultivation and EC 4.0 mS cm-1 for the fall crop.

Effects of nitrogen fertilizers on the growth and nitrate content of lettuce (Lactuca sativa L.).

Nitrogen is an essential element for plant growth and development; however, due to environmental pollution, high nitrate concentrations accumulate in the edible parts of these leafy vegetables, particularly if excessive nitrogen fertilizer has been applied. Consuming these crops can harm human health; thus, developing a suitable strategy for the agricultural application of nitrogen fertilizer is important. Organic, inorganic, and liquid fertilizers were utilized in this study to investigate their effect on nitrate concentrations and lettuce growth. The results of this pot experiment show that the total nitrogen concentration in soil and the nitrate concentration in lettuce increased as the amount of nitrogen fertilizer increased. If the recommended amount of inorganic fertilizer (200 kg·N·ha−1) is used as a standard of comparison, lettuce augmented with organic fertilizers (200 kg·N·ha−1) have significantly longer and wider leaves, higher shoot, and lower concentrations of nitrate.

Effects of Nano-Devices on Growth, Quality and Activities of Enzymes in Nitrogen Metabolism of Hydroponic Lettuce

To improve yield and quality of lettuce in hydroponic, the growth, quality and activities of enzymes in nitrogen metabolism of lettuce in hydroponics were studied with nanodevices. The results showed that the nitrate reductase activities (NRA) in plants with nanodevices were significantly higher than the control at 16rd day after transplanting (DAT). On the 25th DAT, the shoot fresh weight of lettuce treated with 5.6cm2/L nanodevices was 17.8% higher than the control, while there was no difference in dry weights of shoot among different treatments. The NRA of lettuce increased gradually with the amount of nanodevices increasing from 0 cm2/L to 5.6 cm2/L, then decreased with nanodevices amount increasing. There was no obvious difference in the activities of glutamate dehydrogenase (GDH) and glutamate synthase (GOGAT) among different treatments,while glutamine synthase (GS) activity was enhanced with the increasing of nanodevices amount. On the 34th DAT, the shoot fresh weight of lettuce treated by 5.6cm2/L nanodevices was 11.2% higher than the control. The activities of NR and GS treated by 11.2cm2/L increased 39.7%, 97.7%, respectively compared with CK, while the activities of GDH and GOGAT treated by 5.6cm2/L increased 89.0%, 77.3%, respectively. In treatment with 5.6 cm2/L nanodevices in nutrient solution, the contents of soluble protein, flavonoid, soluble phenolic and ascorbic acid (VC) in lettuce increased 92.8%, 19.8%, 36.7% and 61.5%, respectively.The nitrate content in lettuce significantly increased with the using of nanodevices, but did not exceed the national standard. In conclusion, the yield and quality of hydroponic lettuce were improved by nanodevices, and the activities of enzymes in nitrogen metabolism were enhanced, especially at 25th and 34th DAT and best dosage of nanodevices is 5.6 cm2/L.

Effect of Variety and Production Methods on Nitrate Content in Lettuce

Certain trials, the effect of variety and different production methods on the content of damaging substances i.e. nitrate in lettuce leaf were carried out on the experimental field of the Faculty of Agriculture in East Sarajevo during the period of three years. The trial was set in a randomized block-system with three replications and the plot size of 2.4 m2 (0.3x8m). Three lettuce varieties (Archimeds RZ, Santoro RZ, Kibou RZ) were analyzed in the trial. Each row of variety was tested in the following variants of covering: planting on soil that was not covered, mulching with PE-black folium before planting; agro-textile - covering of plants with agro textile (17gr) after planting; combination of mulching + agro textile. The three-year researches have shown that the production method and variety significantly affect the nitrate content. An average nitrate content was 2196.33 mg/kg on the control variant, and 2526.24 mg/kg on agro textile. Leafy lettuce of oak leaf type „Kibou“ had lower nitrate content (2176.85 mg/kg) compared to „Archimed“ (2843.05 mg/kg) and „Santoro“ (2221.37 mg/kg).

The effect of biodegradable nonwovens in butterhead lettuce cultivation for early harvest

Abstract Field experiments using ‘melt-blown’ biodegradable nonwovens were carried out on the ‘Melodion’ butterhead lettuce (Lactuca sativa var. capitata L.) cultivar for early harvest. All biodegradable nonwovens were manufactured in the Institute of Biopolymers and Chemical Fibres and POLMATEX CENARO in Łódź, Poland. Lettuce seeds were sown into boxes in a greenhouse at the beginning of March, and transplants were planted into the field at the beginning of April. Biodegradable nonwovens - aromatic polyester IBWCH 75 g m-2, polybutylene succinate Bionolle 100 g m-2 and standard polypropylene PP Agro 20 g m-2 - were stretched over the lettuce in the field. The covers were kept on until 4-5 days before harvest. Plots without covers were defined as the control. Ascorbic acid, soluble sugar, dry matter, nitrates, chlorophyll a, chlorophyll b and carotenoid contents were recorded in the leaves. All biodegradable nonwovens showed a positive effect on yielding in comparison to the control in 2009. In the second year of the experiment, there were no significant differences between covers with regard to the yield. Dry matter and soluble sugar content in both years of the experiment was diversified. Nonwovens used as covers in 2009 significantly increased the content of nitrates in comparison to the control. In the second year, the highest level of nitrates was demonstrated in the control object. It is worth underlining that the maximum allowed limit of nitrate content in lettuce (4000 mg kg f.w.) was not exceed. The kind of cover had no significant effect on the level of chlorophyll a in 2009 or chlorophyll b and carotenoids in 2009 and 2010 in the lettuce

Nitrate Evolution in Soil, Leaching Water, and Lettuce Plant Crops using Different Fertilization Strategies

The aim of this study was to investigate the effects of different fertilizing strategies applied during three successive cycles on lettuce growth and the nitrate evolution in the soil, leaching water, and the lettuce plant itself. Four fertilization treatments were compared: integrated production fertilization (IP), organic fertilization (ORG), slow-release N fertilizers (SRF), and plant-associative bacteria (PAB). The nitrate content of the pore water and leachate decreased toward harvesting time in each crop cycle. The accumulation of residual nitrates in the soil decreased in each successive cycle in all treatments. The greatest lettuce head weight was achieved by ORG and SRF in the first cycle and by IP in the third cycle; IP and SRF produced the greatest nitrate content in lettuce leaves, especially in the second and third cycles. The nitrate content of leaves fell in the last cycle, as nitrate levels in soil and in leaching fell in all treatments.

Nitrate content in dandelion (Taraxacum officinale) and lettuce (Lactuca sativa) from organic and conventional origin: intake assessment

To estimate the actual intake of nitrate by consumption of different lettuce varieties, 52 samples of lettuce of different origins and dandelion from 15 different areas of northeast Slovenia were analysed. For determination of actual nitrate content, a continuous flow method was used. The lowest nitrate content was detected in dandelion, with a mean value of 195 mg kg−1 (ranging 47–487 mg kg−1). Nitrate content in lettuce of different origins ranged 85–3237 mg kg−1, with a mean value of 1196 mg kg−1. The mean nitrate content in organically cultivated lettuce was 890 mg kg−1, which was considerably lower than the nitrate level in conventionally cultivated lettuce (1298 mg kg−1). Consumption of 100 g of dandelion would result in a maximal nitrate intake corresponding to 22% of the acceptable daily intake (ADI), with values up to seven times higher for lettuce.

Vegetable-borne nitrate and nitrite and the risk of methaemoglobinaemia

High levels of nitrate in vegetables are frequently reported. The potential hazard of vegetable-borne nitrate is from its conversion to methaemoglobin-producing nitrite before and/or after ingestion. Methaemoglobin cannot bind oxygen and produces a leftward shift in oxygen-dissociation curve, causing hypoxaemia. Infants under 3 months old are particularly susceptible to methaemoglobinaemia. Older infants and children are also at risk. Adults are not thought to be at risk of vegetable-borne nitrate or nitrite induced methaemoglobinaemia. This view should now change if the high nitrate levels in some vegetables and the effects of storage and food processing on its conversion to nitrite are taken into consideration. In fresh, undamaged vegetables, the nitrite concentrations are usually very low. Under adverse post-harvest storage conditions, nitrite concentrations in vegetables increase as a result of bacterial contamination and endogenous nitrate reductase action. Nitrite accumulation in vegetables is inhibited under frozen storage because endogenous nitrate reductase is inactivated. Pureeing releases endogenous nitrate reductase, increasing nitrite concentrations in vegetables. Oral reduction of nitrate is the most important source of nitrite. In order to maximise the health benefits from eating vegetables, measures should be taken to reduce the nitrate and nitrite exposures while maintaining the recommended vegetable intake. Excessive use of nitrogen fertilizers should be avoided so as to reduce nitrate build up in soil or vegetables. Vegetables must be stored and processed properly to prevent bacteria contamination. Removal of stem and midrib results in a decrease of nitrate content in lettuce and spinach. Peeling of potatoes and beetroot decreases the nitrate content. Nitrate levels in some vegetables can decrease after cooking in water or blanching. Home prepared infant food containing vegetables should be avoided until the infant is 3 months or older.