Study on the influence of food processing on nitrate levels in vegetables
Nitrate is a naturally occurring compound that is part of the nitrogen cycle, as well as an approved food additive. Vegetables are the major source of nitrate in our nutrition, but nitrate content depends on type of vegetable as well as on environmental and agricultural factors. Apart from external factors, nitrate content of the vegetable can be influenced by kitchen processing techniques (PTs) used for preparing vegetables for food. In the present work we studied effects of common kitchen PTs on nitrate content in lettuce, spinach, potato, green bean, carrot, red beet, white cabbage, Chinese cabbage and courgette. Changes in the nitrate content between raw and processed samples were statistically evaluated where possible with respect to winter or summer time of harvest, agricultural cultivation and vegetable variety. In general, some kitchen PTs i.e boiling and washing decreased nitrate content irrespectively of the vegetable type. Blanching and purée decreased nitrate content during processing of all tested vegetables. In contrast, some techniques increased nitrate content i.e. deep frying, sauté and grilling. Time of harvest and agricultural cultivation system influenced nitrate content in raw vegetables, but were generally found less important for the changes during processing. Further research is needed for determination of vegetable varieties with the highest nitrate reduction during processing.