Study On The Effects Of Storage And Cooking On Nitrate Safety Risks In Water Spinach And Cabbage

In recent years,the excessive accumulation of nitrates in leafy vegetables in our country has become more and more serious,and high levels of nitrates will cause potential safety risks to human health.But the antioxidants rich in vegetables also have the effect of inhibiting the harm of nitrite,so the potential safety risk of nitrates should depend on the balance between the nitrate content and antioxidant capacity of vegetables.However,storage and cooking processes can lead to changes in the balance between the two,which can affect the potential safety risk of nitrates in leafy vegetables.Therefore,this paper mainly takes water spinach and cabbage as the research objects,and studies the dynamic changes of nitrate content and antioxidant capacity of two vegetables during fresh-keeping storage,cooking processing and post-meal storage.The balanced relationship between oxidative capacity and the potential safety risk of nitrate in two vegetables were evaluated to provide a theoretical reference for people’s dietary health.The main research results of this paper are as follows:(1)The effects of storage temperature and sealing conditions on the potential safety risk of vegetable nitrate were studied,and a vegetable antioxidant model was constructed to verify the feasibility of A/N value for nitrate safety risk assessment.The results showed that low-temperature storage significantly inhibited the increase of nitrite content in water spinach,but also significantly decreased the total antioxidant capacity by 38.6 ～ 70.3%(P < 0.05)in the early storage period,and had no significant effect on the potential safety risk of water spinach nitrate.,which is due to the chilling damage of the water spinach due to the too low storage temperature.The micro-aerobic environment formed by closed storage will lead to Pseudomonas and Comamonas to become the dominant flora,and the relative abundances increase by up to 21.9% and 25.1%,respectively,thus promoting the changes in the nitrate and nitrite content of vegetables..The vegetable antioxidant model indicated that the A/N value could be used to evaluate the potential safety risk of nitrate in vegetables.Based on the evaluation results of the A/N values of the four storage methods of open normal temperature,closed normal temperature,open low temperature and closed low temperature,the potential safety risk of nitrate was lower when water spinach was stored openly at room temperature,while the potential safety risk of nitrate was lower when cabbage was closed at room temperature.(2)The effects and mechanisms of four common home cooking methods and cooking time on the potential safety risks of vegetable nitrate were studied.The results showed that the effect of cooking(stir-frying,steaming,microwaving and boiling)on the potential safety risk of vegetable nitrates depended on the cooking method and cooking time.Stir-frying and boiling in the early stage of cooking(within2 min)have a good control effect on the potential safety risks of nitrates in cabbage and water spinach respectively;microwaving are relatively low risk within the allowable range of edibility(within 4 min).cooking method,while steaming is more advantageous for longer cooking times(after 4 min).Cooking greatly increased the cell membrane permeability of vegetables by 38.7% to 84.2%,and the water mobility was enhanced,resulting in varying degrees of changes in various components in vegetables,thus affecting the balance of nitrate and antioxidant capacity.(3)The actual occurrence of nitrate safety risks in vegetables during postprandial storage was studied.The results showed that the nitrate content of vegetables showed a decreasing trend during the postprandial storage process,and the nitrite content first increased and then decreased.The cooking method will affect the storage performance of vegetables.Boiled vegetables produce nitrite peaks at 24 h,while stir-fried vegetables produce nitrite peaks at 36 h.The antioxidant content and total antioxidant capacity of vegetables showed a decreasing trend during postprandial storage.According to the results of the principal component analysis during the post-meal storage process,the potential nitrates safety risk of boiled water spinach is lower than stir-fried water spinach,while the safety risk of stir-fried cabbage is lower than boiled cabbage.The storage time of both vegetables after stir-frying should not exceed 24 h,and should not exceed 12 h after boiling.