Effects of freezing and storing of frozen products on the content of nitrates, nitrites, and oxalates in dill (Anethum graveolens L.)

The aim of the work was to compare the contents of nitrates, nitrites, and oxalates in the leafy part of dill and in whole plants (leaves with petioles and stems) of dill harvested at the 25 cm stage of growth. Changes in the levels of these compounds in the technological processes of freezing and refrigerated storage were also determined. The investigation concerned two kinds of the raw material (leafy parts and whole plants), different treatments before freezing (blanching or non-blanching of the raw material), differentiated temperature of storing frozen products (−20 and −30 °C), and a storage time of 12 months. Analyses of the frozen products were conducted every three months. In relation to whole plants (leaves, petioles, and stems) the leaves alone of fresh dill were characterized by a much lower content of nitrates (54%), a higher content (though below 1 mg/1000 g) of nitrites, and also a higher one of oxalates (26%). The blanching induced a considerable reduction of the contents of nitrates, nitrites, and oxalates. This concerned whole plants to a greater degree than leaves, oxalates being an exception. Freezing did not affect the levels of the analysed compounds in frozen products with the exception of non-blanched whole plants in which the level of nitrites significantly rose in relation to the raw material. Irrespective of the applied temperatures during refrigerated storage, the level of analysed compounds was slightly changed in relation to that recorded in the material directly after freezing.