Tyramine formation by Pediococcus spp. during beer fermentation

The role of Pediococcus spp. in the production of tyramine was studied. Strains of these microorganisms were isolated from industrial beer fermentations where high tyramine formation occurred. It has been verified that Pediococcus spp. are able to form tyramine during beer fermentation, and the quantity of tyramine produced depends on the degree of contamination. Thus, CFU of Pediococcus spp. ranging from 4 X 10(3) to 1 X 10(4) CFU/ml led to low tyramine formation (<5 mg/liter). Tyramine production between 5 and 15 mg/liter was related to Pediococcus spp. counts from 1 X 10(4) to 5 X 10(4) CFU/ml, while counts of these microorganisms above 5 X 10(4) CFU/ml led to tyramine levels ranging from 15 to 20 mg/liter. Prolonged storage in culture media of the isolated strains of Pediococcus spp. as well as isolation of these microorganisms from beer and transfer to media caused them to lose their ability to produce tyramine. Determination of tyramine levels in beer was found to be a reliable indicator of the degree of contamination by Pediococcus spp. during beer fermentation.