Forschungs- & Entwicklungsinformationsdienst der Gemeinschaft - CORDIS

Quantitative real-time pcr method for detection of histamine producer lactic acid bacteria in cheese

Biogenic Amines (BA) are toxic substances that appear in foods and beverages as a result of amino acid decarboxylation. The enzyme histidine decarboxylase (HdcA) catalyses the decarboxylation of histidine to histamine, the BA most frequently involved in food poisoning. A real-time quantitative polymerase chain reaction (real-time qPCR) assay for the direct detection and quantification of histamine-producing strains in milk and cheese has been developed.

A set of primers was designed, based on the histidine decarboxylase gene sequence of different Gram-positive bacteria. The results showed that the proposed procedure is a specific and highly sensitive technique for detecting potential histamine-producing strains in culture media, milk and curd. The method has been also optimised to quantify the presence of histamine-producing microorganisms in cheeses and during the cheese-making process.

Chromatographic methods (HPLC) verified the capacity of real-time qPCR to correctly quantify histamine accumulation. Moreover, the entire process only takes about two hours, and 96 samples can be processed simultaneously. This could be very beneficial for the dairy industry, since microbiological methods require more than 24 h to be completed. In addition, the procedure allows the identification of potential histamine-producing LAB, which would be useful, when screening for starter strains is been performed. Another important advantage of this method is that it can be used at any point in the manufacturing process, even when histamine is still undetectable by other methods.

In conclusion, the proposed method offers a rapid and simple way of characterizing the LABs in different types of dairy substrate. It could be employed to prevent the selection of histamine-producing strains as starter cultures. It is much faster than any microbiological procedure for the detection and quantification of HDC+ strains in milk, curd and cheese, and even allows an estimation of the histamine content of these substrates. Since HDC+ LAB of different origins were detected in this study, the proposed method might be of use with other types of fermented foods and drinks.

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