Dietary exposures to nitrate have been estimated for two different groups of UK consumers. The daily dietary exposure of the general population was estimated from the UK 1997 Total Diet study to be 52 mg/day. Vegetables contributed approximately 70% to this total dietary exposure. Dietary exposure estimates for adult consumers of vegetables commonly eaten in the UK were 93 mg/day and 140 mg/day for mean and 97.5th percentile consumers, respectively. Dietary exposures to nitrate of UK consumers are similar to those in other European countries and are less than the Acceptable Daily Intake (ADI) for nitrate set by the European Commission's Scientific Committee for Food.

Dietary exposures to nitrate in the UK

Concentrations of nitrate and nitrite have been determined in a range of foods and the dietary intake estimated from the MAFF Total Diet Study. The estimated dietary intake of nitrate ion for the UK population was 54 mg/day and the estimated dietary intake of nitrite ion was in the range 2.4-4.2 mg/day in 1985. The main source of nitrate in the diet is from the consumption of vegetables.

Nitrate and nitrite in foods and the diet

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

Ion chromatographic determination of nitrate and nitrite in meat products.

Net mineralization of N from a range of shoot and root materials was determined over a period of 6 months following incorporation into a sandy-loam soil under controlled environment conditions. Biochemical “quality” components of the materials showed better correlation with net N mineralization than did gross measures of the respiration and N content of the soil microbial community during decomposition. The quality components controlling net N mineralization changed during decomposition, with water-soluble phenolic content significantly correlated with net N mineralization at early stages, and water-soluble N, followed by cellulose at later stages. C-to-N and total N were correlated with net N mineralization towards the end of the incubation only. Cumulative microbial respiration during the early stages of decomposition was correlated with net N mineralization measured after 2 months, at which time maximum net N mineralization was recorded for most residues. However, there was no relationship between microbial-N and net N mineralization. Biochemical quality factors controlling the C and N content of the residue remaining at the end of the incubation as light fraction organic matter (LFOM) were also investigated. Both C and N content of LFOM derived from the residues were correlated with residue cellulose content, and the chemical characteristics of LFOM were highly correlated with those of the original plant material. Incorporation of low cellulose, high water-soluble N-containing shoot residues resulted in more N becoming mineralized than had been added in the residues, demonstrating that net mineralization of native soil organic matter had occurred. Large amounts of N were lost from the mineral-N pool during the incubation, which could not be accounted for by microbial immobilization.

Fate of nitrogen from crop residues as affected by biochemical quality and the microbial biomass.

A method is described for the determination of nitrate-nitrogen in vegetables in which an automated anion-exchange high-performance liquid chromatographic technique has been adapted to accommodate the interferences caused by organic matter present in the samples. The described method has been found to be accurate, rapid and precise.

Deborah J. Seymour

Papers

Method for measuring nitrate-nitrogen in vegetables using anion-exchange high-performance liquid chromatography.