Blocking the path to amine production in food
Foods produced by fermentation with lactic acid bacteria are prone to spoilage with unwanted amines. These are the products of the decarboxylation of the corresponding amino acid. In the case of tryramine which is the cause of a headache and increased blood pressure, tyrosine is the precursor molecule. Tyrosine is one of the amino acid building blocks in casein, a milk protein. For project partners at the University of Groningen in the Netherlands, the key to blocking the production of tyramine was the biochemical pathway for its production. The focus was put on a transporter molecule that is not only responsible for the uptake of the precursor tyrosine but then the excretion of the tyramine in the cell. The line of attack then was to use a compound that would compete with this tyramine exchanger, known as TyrP. A total of 19 compounds structurally related to tyrosine that would potentially compete with the TyrP transporter activity were studied. The set of molecular analogues varied at different key sites in the amino molecule. Studies showed that there are two important sites for interaction of the transporter and amino acid molecule. These are the amino group, characteristic of all amino acids, and a phenyl ring with a hydroxyl (OH) group. When the molecular competitor involved modification at either of these sites, there was an encouraging ten-fold reduction in exchange activity. A good candidate molecule should be able to bind strongly to the transporter and inhibit translocation. The team found that the most successful candidate was L-phenylalanine. This reduced the translocation activity of TyrP to less than 10% normal and counterflow activity was inhibited by more than 95%. Moreover, L-phenylalanine is a very common naturally occurring amino acid in foods, particularly milk. Addition of extra L-phenylalanine to milk during the fermentation process would appear to be an answer to the accumulation of tyramine. Translation of the research into practice on the production line stands to increase the competitiveness of the European dairy industry. It also means safer healthier food for the consumer.
