Studies on Nitrate and Nitrite in Horticultural Products

Part VI. Changes of concentration in pumpkin and squash during growth and storage

Abstract

Kogiku pumpkin (Japanese type) and Chikanari-ebisu squash (Western type) contained 200 and 280 ppm of nitrate in pulp at harvesting stage, respectively. The concentration of nitrate hardly varied in Chikanari-ebisu fruit and varied in Kogiku fruit with some of variation attributable to parts when harvested.
During the growing period, nitrate concentration in Kogiku fruit reached a maximum at harvesting stage. In earlier and later stages of maturity than harvesting stage, nitrate concentrations were lower. The concentration of nitrate did not change in unripe fruits during the storage, but rapidly decreased in ripe fruits during the short period of storage, for example, nitrate concentration of Chikanari-ebisu decreased to one tenth of the initial one.
The ratio of nitrate-N to total N in Chikanari-ebisu fruits decreased during storage, whereasthe ratio of protein-N and amino acid-N to total N increased. Similar tendency was also observedon placenta tissue of the fruit. From above observation, conversion of nitrate-N to protein oramino acid may be considered.