qPCR for quantitative detection of tyramine-producing bacteria in dairy products

Biogenic amines (BAs) are organic nitrogenous compounds that occur naturally in small concentrations in most living organisms, in which they have different biological functions. However, they can accumulate in foods due to the decarboxylating activity of certain bacteria. The consumption of food containing large amounts of some BAs can have toxicological consequences. Tyramine is one of the most active and common BAs found in cheeses. This article reports the design of an real-time quantitative PCR (qPCR) qPCR method for the detection and quantification of the microorganisms responsible for tyramine production in cheeses. A good linear relationship was obtained between the quantity of tyramine-producer DNA used in PCR reactions and the Ct (threshold cycle) value. The method was validated using 57 cheese samples in which the tyramine concentration was analysed by HPLC. Tyramine-producing bacteria were detected in different numbers in all samples, although tyramine itself was only detected in 56.1% of the samples. The results suggest that, independent of technological conditions such as pasteurisation or the ripening period, the presence of tyramine-producing bacteria over a threshold limit Of 10(4) cfu g(-1) - easily detected by the proposed qPCR method - leads to the accumulation of tyramine beyond recommendable limits. (C) 2009 Elsevier Ltd. All rights reserved.