Effect of lactic acid microorganisms on the content of nitrates in tomato in the process of pickling

Abstract

We established the content of nitrates in vegetables and studied special features in the course of microbiological and denitrification processes during pickling of tomatoes with a different content of nitrates. It was found that 15 % on average of the samples of vegetable produce, grown in open ground, contained the amount of nitrates that exceeded MPC (maximum permissible concentration). For vegetables grown in greenhouses, the number of samples with the nitrate content above the norm reached 25−30 %. It was discovered that in the process of pickling tomatoes with the amount of nitrates at 137±10 mg/kg (within MPC), there occurs an intensive growth of lactic acid microorganisms. As a result of the reproduction of lactic acid microflora, there happens a denitrification process with the amount of nitrates in pickled tomatoes reduced to 17±2 mg/kg. When pickling tomatoes with a nitrate content twice as large than MPC at 619±32 mg/kg, microbiological and denitrification processes slow down at the beginning. Then they are recovered with the amount of nitrates reduced to 134±5 mg/kg. When pickling tomatoes with the nitrate content five times larger than MPC (1,576±114 mg/kg), the pickling does not occur because of the inhibiting influence of nitrates on the growth of microflora. Thus, the data obtained indicate that the tomatoes that contain nitrates within 600−700 mg/kg can be used for the preparation of pickled products. Vegetable produce containing nitrates in the amount above 1,500 mg/kg must not be used in pickling due to the inhibiting influence of nitrates on lactic acid microflora