Servizio Comunitario di Informazione in materia di Ricerca e Sviluppo - CORDIS

PCR method for detection of tyramine producer lactic acid bacteria in cheese

Lactic Acid Bacteria (LAB) are essential in the Dairy Industry as starters; nevertheless, the metabolic activity of some strains can produce toxic substances known as Biogenic Amines (BA). Ingestion of foods with high levels of BA cause serious upheavals, that could even jeopardize the life of the consumer, specially in those people with deficiencies in the intestinal amino-oxidases, the detoxification enzymes.

The most frequent and concentrated BA in cheeses is tyramine. Tyramine is formed via decarboxylation of its corresponding amino acid, tyrosine, through the action of enzymes produced by microorganisms present in the food. The result summarised here is a fast, sensitive and easy method to detect, at any point of the food chain, tyramine-producing LAB. The production of this BA is more related to strain than to species and the producer bacteria can be either contaminants of fermented foods or constitute part of starter cultures.

Therefore, it is very important to determine which strains produce this undesirable compound, to avoid that they could be used in the starter cultures. Although several qualitative and quantitative methods have been developed to determine BA production, demands of consumers for better and healthier foods have resulted in an increased interest in the development of rapid and sensitive methods for detecting BA-producing microorganisms in food. The present method allows fast and sensitive identification of tyramine-producing strains by PCR, by use of specific tdcA primers.

The tdcA gene encodes the tyrosine descarboxylase, which catalyses the synthesis of tyramine. The comparison of the tdcA sequence from Enterococcus durans IPLA655 with those included in the databases, led to the design of specific primers for amplification of an internal fragment of the tdcA gene from different genera, allowing the identification of any tyramine-producing LAB. Since, it is unnecessary to purify the DNA of the strains to be tested (an isolated colony can be used as a template) these new method is fast and easy. Moreover, the proposed PCR technique offers the possibility of detecting potential tyramine-producing strains in milk, at any point of milk fermentation, and in final products such as cheese.

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