Comparison Of Contents Of Nitrate, Nitrite And Vitamin C In Different Storage Conditions Of Deep - Frozen And Common Cooked Vegetables

Objective:This project aimed to compare the changes of nitrite, nitrate, and vitamin C contents in vegetables before and after cooking over time under different storage methods by simulating family dining habits, cooking methods and storage methods, which finally provides scientific basis for the reasonable storage of vegetables. Additionally, this project also aimed to evaluate the changes of nitrite, nitrate, and vitamin C contents of a new Deep-frozen-pot vegetable under different storage ways, then compared with that in ordinary cooking method, so as to provide basic data for market development and promotion of Deep-frozen-pot dishes.Method:We determined the contents of nitrate, nitrite and vitamin C in vegetables separately by ion chromatography and HPLC, and explored changes of nitrate, nitrite and vitamin C contents in different kinds of vegetables (Chinese cabbage, celery, potato, cucumber, tomato and cowpea) under different cooking methods (Deep-frozen-pot and ordinaryl cooking), different packaging ways (sealed and exposured storage) and different storage temperature (4℃ and 25℃). Similarly, we determinated changes of nitrate, nitrite and vitamin C contents in the vegetables cooked by deep frozen pot under different storage temperature, and then, compared it with that in an ordinary way.Results:1. The order from high to low of 6 kinds of fresh vegetables nitrate content is:leaf vegetables> stem vegetables> legume vegetables> root vegetables> melons vegetables> fruit vegetables. The order from high to low of nitrite content is:leaf vegetables> stem vegetables> root vegetables> fruit vegetables> legume vegetables. The order from high to low of vitamin C content is:leaf vegetables> root vegetables> legume vegetables> fruit vegetables> stem vegetables> melons vegetables.2. The changes of nitrate contents in Chinese cabbage, celery, potato, cucumber, tomato and cowpea presented an increasing trend firstly, then decreasing, at last increasing again with the extension of storage time. The slowest changing trend of nitrate content and the lowest content were found under sealed storage at 4℃, suggesting that sealed storage at 4℃ may be a more conducive style of storage vegetables. The trend of nitrite content changes with the time in 6 kinds of vegetables showed increasing at first, decreasing followed, and appearance of the peak after 3 d or 4 d, which were higher than the limit standard of 4.0 mg/kg (GB 2762-2005). The vitamin C contents of 6 kinds of vegetables before cooking showed a decreasing trend with the time, and the most gently trend and the highest content of vitamin C appeared when stored at 4℃ sealed storage.3. The change trend of nitrate contents in ordinary cooking Chinese cabbages and potatoes under different storage conditions with time appeared increasing trend firstly, then decreasing, and another increasing at last; the changing trend with storage time of nitrite contents showed decreasing first and then increasing; the vitamin C contents appeared downward trend. The nitrate and nitrite contents in ordinary cooking Chinese cabbages and potatoes storage at 4℃ were lower than that under storage at 25℃ in the same packingway and the same time. Under the same temperature and the same time, the nitrate, nitrite and vitamin C contents of ordinary cooking Chinese cabbages and potatoes in a sealed storage were lower than exposure to store contents.4. The contents of nitrate in finished products of Chinese cabbages and potatoes cooked in Deep-frozen-pot under the condition of 25℃ and 4℃ sealed storage showed an increasing trend firstly and then decreasing, while the peak point appeared at time of 24 h, and the nitrate content was lower when stored at 4℃ than at 25℃. Whereas nitrite contents were firstly decreased and then increased, under both storage at -18℃ and -60℃ for 72 h, and the contents never excess the standard content of 4.0 mg/kg.5. With comparison between Chinese cabbages and potatoes cooked in ordinary way and Deep-frozen-pot cooking, we found that the contents of nitrate and nitrite in vegetables cooked in Deep-frozen-pots was lower than that cooked in ordinary way with the same spices and raw materials, whereas the vitamin C content being higher. Vegetables cooked in Deep-frozen-pots presented a tender increasing of the nitrate and nitrite content and a relative slowly decreasing of vitamin C, whether the deep frozen temperature was -60℃ or -18℃.Conclusion:1. The contents of nitrate, nitrite and vitamin C in leaf vegetables were higher than those in the other 5 kinds of vegetables.2. Vegetables storage time should not be more than 3 d. Vegetables storage under sealed conditions at 4℃ can be effective to reduce the nitrite content, and delay the increasing trend of nitrate, as well as the decreasing of vitamin C content.3. Ordinary cooking vegetables should be stored under sealed conditions at 4℃ bestly, and the storage time should not exceed 60 h.4. The semi-finished products of vegetables cooked in Deep-frozen-pot stored in -18℃ cold chain should be more appropriate, and the finished products of vegetables should be better to be stored under 4℃ in sealed storage.5. Deep-frozen-pot cooking can prevent the loss of vitamin in vegetables, and nitrate and nitrite contents were lower than ordinary cooking vegetables. Deep-frozen-pot dishes showed a delayed increasing of both nitrate and nitrite contents, and a postponed decreasing in the content of vitamin C, whether stored in -18℃ or -60℃. It was proved to be a safer cooking method, retaining more nutritious with enormous potential.