Pickle is a kind of lactic acid fermented vegetable product with unique flavor, which has the advantages of diverse raw materials, simple production, low cost, convenient eating, good sensory quality and suitable taste. However, there are also some food safety problems in the fermentation process of kimchi, among which nitrite is the most noteworthy. Nitrite poisoning usually shows three types: after nitrite enters human body, nitrite oxidizes normal hemoglobin in human blood into methemoglobin, which reduces the oxygen carrying capacity of blood, thus leading to methemoglobinemia; Nitrite synthesizes nitrosamines in the body and induces cancer; Causes glomerular hypertrophy of small glands in the kidney. However, controlling nitrite in a safe range will not cause harm to human body.
Through the study of kimchi, the causes of nitrite formation and its growth and decline law in kimchi were revealed. Nitrate and nitrite are chemicals widely existing in the natural environment, and there are more nitrate and nitrite in picked vegetables. The nitrite content of vegetables is low in the early stage of curing and storage, but due to nitrate reductase of miscellaneous bacteria (Enterobacteriaceae bacteria and fungi, etc.). In the early stage of fermentation, a large number of nitrates in vegetables were converted into nitrite, which made the nitrite content increase sharply. With the decrease of oxygen in the fermentation system, the growth of lactic acid bacteria leads to the decrease of pH value, the proliferation of miscellaneous bacteria is limited or even dead, and lactic acid bacteria gradually evolve into dominant flora. Due to lactic acid produced by lactic acid bacteria metabolism and its own enzyme system, a considerable part of nitrite is degraded, which also weakens the ability to reduce nitrate. At the end of fermentation, the nitrite content dropped to the lowest point or even disappeared. Therefore, from the whole lactic acid fermentation process of kimchi, the change of nitrite content in the fermentation process will inevitably have a nitrite peak.
When making and eating kimchi, we should not only pay attention to nitrite, but also pay attention to whether the additives used exceed the standard. Preservatives, saccharin and sulfite often exceed the standard in production. Compared with nitrite, these additives are less toxic, but after all, they exceed the national standards and should be unqualified products. In addition, biogenic amines also exist in kimchi. The main biogenic amines in pickles are tyramine, histamine, putrescine, cadaverine, phenylethylamine, tryptamine, spermine and spermidine. Biogenic amines are produced by microorganisms involved in kimchi fermentation, such as Enterobacteriaceae, Pseudomonas, mold and lactic acid bacteria. The accumulation of biogenic amines in fermented vegetables can be reduced by inoculating lactic acid bacteria and increasing the amount of salt.