Variations of nitrate,nitrite concentrations of lettuce and the relationships with growth of microorganism during storage

The variations of nitrate and nitrite concentrations in fresh lettuce and stir-fried lettuce were investigated in this paper.The relationships between the nitrate,nitrite concentration variations and the growth of microorganism were also discussed.The nitrate and nitrite concentration of lettuce were measured one day at refrigerated(4℃)and ambient temperatures(25℃)for 7 days.It showed that the concentrations of nitrate and nitrite did not change significantly at ambient temperature and refrigerated.However,nitrate and nitrite concentrations in the stir-fried lettuce by refrigerated storage showed no changes over 7 days.But 6 hours after the stir-fried lettuce was stored at ambient temperature,the concentration of nitrite was more than 4mg/kg(GB).The main reason was bacterial growth,which causing nitrite concentration increased.