Abstract: Chinese yam, carrot and lotus root were stored, cooked or preserved by different methods to explore the effects of different processing methods on nitrite contents in root and stem vegetables. The results showed that nitrite contents were increased at the early stage and decreased at the late stage in three vegetables kept in room or cooled temperature for 7 days, but nitrite contents in vegetables stored at room temperature were higher than those at cold temperature. The nitrite contents in vegetables at both temperatures were below 4 mg/kg. In contrast, cooking methods revealed a remarkable effect on nitrite content. Boiling, stir-frying and baking could result in the loss of nitrite content by 70% to 83%, 66% to 80% and 33% to 55%, respectively. The highest and lowest loss rates of nitrite content were observed in carrot and lotus root. During storage at room and cold temperatures, nitrite content in cooked vegetables revealed an increase with the extension of storage time. However, the nitrite content was still less than 4 mg/kg at the end of 48th h of storage at room or cold temperatures. In contrast, the nitrite content (reaching up to 1.03 mg/kg) in cooked vegetables stored at cold temperature was much lower than that (reaching up to 1.98 mg/kg) at room temperature. According to the limit standard of nitrite content in vegetable foods, the safety period was 48 h storage both at cold and room temperatures (20 ℃). Moreover, boiling and stir-frying for cooked vegetables were superior to baking.

Key words: root and stem vegetables, nitrate content, processing style