Formation of tyramine by Lactobacillus curvatus LTH 972.

The effect of food-related environmental factors on the formation of tyramine by Lactobacillus curvatus LTH 972 was investigated in liquid culture supplemented with tyrosine. The highest concentrations of tyramine (up to 201 mg/l) were formed at 30 degrees C, pH 5.2 and at a water activity (aw) of 0.97. At lower temperatures and at higher pH- and aw values the reaction slowed down but was still clearly detectable. Glucose, nitrate and nitrite had no effect at concentrations applied in sausage fermentations. The strain was able to form tyramine from tyrosine-containing di- and tripeptides in phosphate buffer. Therefore, in proteinaceous substrates an increased formation of tyramine cannot be excluded when ongoing proteolysis creates precursors, as is the case in the presence of proteolytic micro-organisms.