Effect of Cooking Process on the Potential Safety Risks of Nitrate in Water Spinach and Cabbage

In this study, the effects of four cooking methods (stir-frying, steaming, microwaving and boiling) on the nitrate and nitrite contents and antioxidant capacity of water spinach and cabbage were investigated, and the potential safety risk of nitrate was evaluated by the antioxidant/in vivo nitrite ratio (A/N). The results showed that stir-frying increased the content of nitrate (28.03%‒49.57%) and ferric reducing power (108.88%‒218.35%) of leafy vegetables, while boiling was the opposite. Microwaving and steaming decreased the content of nitrate (31.25%‒46.61%) and increased ferric reducing power (76.35%‒112.99%). Based on the edibility and A/N ratio, the potential safety risk of nitrate in water spinach and cabbage cooked for less than two minutes could be controlled using boiling and stir-frying, respectively. Microwaving is a relatively safe way to cook both kinds of leafy vegetables, but should not exceed four minutes, while steaming is more suitable for longer cooking (> 4 min).