Relation of Ascorbic Acid to Nitrate Content of Turnip Greens and to Methemoglobin Formation

Turnip greens that received shading and excessive fertilization had higher nitrate contents and 39 per cent less ascorbic acid than those grown with less fertilizer and without shade. Since ascorbic acid decreases in plants as nitrate content increases, the effect of the nitrate content of turnip greens was studied in relation to ascorbic acid loss during cooking. The greatest losses of ascorbic acid did not occur in turnip greens containing the largest concentration of nitrate, nor did loss of ascorbic acid correlate with the amount of nitrate present. Therefore, the presence of nitrate in turnip greens is not a significant factor in loss of ascorbic acid during cooking. Although ascorbic acid has been used as an antidote for methemoglobinemia, the addition of small amounts (equal to or greater than those found normally) to human blood had no protective effect against methemoglobin formation. Guinea pigs, which had been kept for twenty days on a diet low in ascorbic acid, were no more susceptible to nitrite toxicity than those which had been fed supplements of ascorbic acid. Accidental or climatic shading of highly fertilized turnip greens introduces no health hazard even though the greens have low ascorbic acid and high nitrate content. The retention of ascorbic acid during cooking was not affected. The unknown protective agent in vegetables, that has confined the nitrate toxicity reported in the literature to babies drinking formulas prepared with water containing large amounts of nitrates, is apparently not ascorbic acid.