Effect of enhanced proteolysis on formation of biogenic amines by lactobacilli during Gouda cheese ripening.

The effect of enhanced proteolysis on amine formation by amino acid decarboxylase positive Lactobacillus sp. during Gouda cheese ripening was examined. A commercial proteolytic enzyme preparation was added to pasteurized milk prior to cheese preparation. The effect of this manipulation on the formation of putrescine, histamine and tyramine was investigated in the presence and absence of amino acid decarboxylase-positive strains during a 12-week ripening period. Four batches were supplemented with a proteolytic enzyme. Batch I contained the proteolytic enzyme only, whereas batches II-IV were additionally supplemented with Lactobacillus delbrueckii LTH 1260 (batch II), Lactobacillus buchneri LTH 1388 (batch III) or Lactobacillus brevis LTH 2560 (batch IV). In batch I putrescine was detected with 4 mg/kg, in batch II, 42 mg/kg putrescine, 238 mg/kg histamine and 636 mg/kg tyramine were found. Batch III contained 13 mg/kg putrescine and 418 mg/kg histamine, whereas in batch IV, 26 mg/kg putrescine and 776 mg/kg tyramine were present. Batch V was supplemented with all three lactobacilli but did not contain the proteolytic enzyme. In this experiment, 4 mg/kg putrescine, 179 mg/kg histamine and 337 mg/kg tyramine were detected. A control cheese batch (VI) without addition of amine forming lactobacilli or a proteolytic enzyme was produced and only 4 mg/kg putrescine were detected. An increase in amine concentration during cheese ripening under conditions of enhanced proteolysis in the presence of starter and spoilage lactobacilli was evident from the experiments.

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.