Abstract:

In the present study, we evaluated the nitrite scavenging effect of the mechanically prepared juice from Chinese onion eaten as a condiment vegetable in China. Single factor experiments were initially carried out to investigate the effects of preheating temperature and amount of the juice and reaction pH and time on its scavenging ratio against nitrite and based on these investigations, orthogonal array design was then used to search for the optimum values of the above reaction conditions maximizing its scavenging ratio against nitrite. The results showed that preheating at high temperature was necessary for scavenging nitrite by the juice. The scavenging ratio of the juice against nitrite was over 50% at natural pH. pH had exceedingly significant effect on this index. The reaction of 11.0 mL of the juice for 10 min at pH 2.0 gave a nitrite scavenging ratio of 82.7%. Furthermore, precooked mustard leaves (as a simulation for cooking) was soaked in the juice or deionized water (as control) and stored at 7 ℃ and the accumulation of nitrite in mustard leaves was observed during storage. After 13 days of storage, a slow accumulation of nitrite was observed for mustard leaves soaked in deionized water or the juice. Mustard leaves soaked in the juice always presented a lower nitrite content than those soaked in deionized water did throughout the entire storage period. Thus, precooking, low temperature and soaking in the juice all had the ability to suppress the formation of nitrite. Meanwhile, the fresh leaves of mustard were cleaned and packaged in polyethylene bags and stored at 40 ℃ (as a simulation for high-temperature storage and transportation environment) and the nitrite content change of mustard leaves was examined during storage. It was found that the nitrite content in mustard leaves slightly increase in the first days of storage at 40 ℃, followed by a steep increase and reached 356.4 mg/kg on the sixth day and that 2.0 mL of the juice gave nitrite scavenging ratios of 21.1% on the first day and 5.9% on the sixth day.

Key words: Chinese onion, mustard, nitrite, scavenging ratio