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

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