Effect of cooking methods on the health-promoting compounds, antioxidant activity and nitrate of tatsoi (Brassica rapa L. ssp. narinosa)

To study the change of the health-promoting compounds, antioxidant activity and nitrate of tatsoi (Brassica rapa L. ssp. narinosa) caused by different cooking methods. Four cooking methods, that is, boiling, microwave, steaming and stir-frying were used to treat tatsoi, a leafy Brassica vegetable. All the four cooking methods reduced total soluble sugar, vitamin C and total glucosinolates (GSLs) content. Steaming retained greatest vitamin C and total GSLs content, followed by stir-frying and microwave. Boiling reduced the antioxidant activity and total phenolic content (TPC). Steaming enhanced the TPC and antioxidant activity. Microwave resulted in great loss of antioxidant activity but not significant change of TPC. No significant change of TPC and antioxidant activity were observed in stir-fried tatsoi. Boiling led to significant reduction of nitrate, while stir-frying resulted in significant increase in nitrate, microwave and steaming did not cause nitrate change to significant degree. Practical applications There is no consensus regarding the best way to consume thermal-processed leafy vegetables and the literature pertaining to the preparation of leafy vegetables is still inconsistent. Information on the effects of cooking methods on nutritional properties and antioxidant activity of tatsoi are still limited. The present study will provide cumulative information for the selection of industrial or household cooking methods for the desired quality and products of tatsoi as well as Brassica leafy vegetables.