The Impact of Carvacrol on Ammonia and Biogenic Amine Production by Common Foodborne Pathogens.

The impact of carvacrol at different levels (0.1%, 0.5%, and 1%) on ammonia (AMN) and biogenic amines (BAs) production by 8 common foodborne pathogens (FBPs) (Staphylococcus aureus, Escherichia coli, Klebsiella pneumoniae, Enterococcus faecalis, Pseudomonas aeruginosa, Listeria monocytogenes, Aeromonas hydrophila, and Salmonella Paratyphi A) was studied using a rapid high-performance liquid chromatography method. Significant differences among bacteria (P < 0.05) in AMN and BA production were observed using a tyrosine decarboxylase broth. Tyramine, dopamine, agmatine, spermine, and putrescine were the main amines produced by the bacteria. Tyramine production by P. aeruginosa was the highest (967 mg/L), whereas K. pneumoniae was the poorest tyramine producer (6.42 mg/L). AMN and BA production varied significantly depending on carvacrol levels and the specific bacterial strains. Tyramine production for all bacterial strains was significantly suppressed by addition of carvacrol at levels of 0.5% and 1%, but not 0.1%. Consequently, the effect of carvacrol on BA and AMN formation by FBP was dependent on bacterial strain as well as carvacrol level.

Reduction of tyramine by addition of Schizandra chinensis baillon in Cheonggukjang.

This study was performed to examine the microorganisms responsible for the high tyramine content of Cheonggukjang, a traditional Korean fermented soy food, and to establish a technology for controlling the growth of these microorganisms. The tyramine content in 13 collected Cheonggukjang samples averaged 604.9 mg/kg. Since the tyramine content measured from most samples was sufficient to cause harm to the human body, it is necessary to control its production in food. Enterococci were confirmed to be the bacterial species producing most of the tyramine through the microbial examination and were present in high numbers from not detected (<10(1)) to 7.0 × 10(10) colony-forming units (CFU)/g. To control the growth of enterococci, various plant extracts with antimicrobial activity, common salts, and variable temperature conditions were tested. It was found that 4 samples among the 159 plant extracts had a strong antimicrobial activity in Cheonggukjang, especially against Enterococcus faecium, showing viable cell counts of <10(1)-10(3) CFU/g after 24 h of ripening, which were significantly lower values compared to the control (10(9)-10(11) CFU/g). The Cheonggukjang with the addition of the four plant extracts showed ∼83%-95% lower concentrations of tyramine compared to the control. Cheonggukjang prepared with the Schizandra chinensis Baillon extract had the lowest tyramine content without sacrificing the sensory quality. Not only was the bacterial species of E. faecium reduced more remarkably, by up to 10(3) CFU/g compared to the 10(9)-10(11) CFU/g shown in the control, but it also decreased the tyramine content by up to 91%.

Expression of Lactobacillus brevis IOEB 9809 tyrosine decarboxylase and agmatine deiminase genes in wine correlates with substrate availability.

AIMS: Lactobacillus brevis IOEB 9809 is able to produce both tyramine and putrescine via tyrosine decarboxylase and agmatine deiminase enzymes, respectively, when cultured on synthetic media. The aims of this study were to assess the expression of L. brevis IOEB 9809 tdc and aguA1 genes, during wine fermentation and to evaluate the effect of substrate availability and pH on tdc and aguA1 expression, as well as on biogenic amine production and L. brevis viability. METHODS AND RESULTS: The relative expression of L. brevis IOEB 9809 tdc and aguA1 genes was analysed in wine by quantitative real-time RT-PCR (qRT-PCR) during a period of incubation of 30 days. Cell viability, pH values, putrescine and tyramine concentration were monitored throughout the experiments. CONCLUSIONS: The wine trials indicated that L. brevis IOEB 9809 is able to produce both tyramine and putrescine during wine fermentation. Increased cell viability was also observed in wine supplemented with tyrosine or agmatine. qRT-PCR analysis suggests a strong influence of substrate availability on the expression of genes coding for tyrosine decarboxylase and agmatine deiminase in L. brevis IOEB 9809. Less evident is the relationship between putrescine and tyramine production and tolerance to wine pH. SIGNIFICANCE AND IMPACT OF STUDY: To our knowledge, this study represents the first assessment of relative expression of L. brevis IOEB 9809 genes involved in biogenic amine production in wine. Furthermore, an effect of biogenic amine production on viability of L. brevis during wine fermentation was established.

A multifactorial design for studying factors influencing growth and tyramine production of the lactic acid bacteria Lactobacillus brevis CECT 4669 and Enterococcus faecium BIFI-58.

A central composite face design was used to study growth and tyramine production of two strains of lactic acid bacteria, Lactobacillus brevis CECT 4669 and Enterococcus faecium BIFI-58. The effects of five physicochemical factors (incubation temperature and time, environmental pH, added tyrosine concentration, and pyridoxal-5-phosphate (PLP) supplementation) on cell growth and tyramine production were analyzed under aerobic and anaerobic conditions. The parameters of the quadratic model for each response variable were estimated by multiple linear regression (MLR), and statistical analysis of the results led to the elucidation of mathematical models capable of predicting the behavior of the responses as a function of the main variables involved in the process. Incubation time was found to be the most important variable influencing growth in L. brevis, while pH showed the highest contribution in E. faecium. The production of tyramine was dependent on the added tyrosine concentration and incubation time. The proposed MLR model predicted the optimum conditions that gave maximum responses for L. brevis and E. faecium growth and tyramine production. In both strains, this model predicted that the anaerobic condition at acidic pH (4.4) in the presence of a high tyrosine concentration favors tyramine production.

Induction of hydroxycinnamoyl-tyramine conjugates in pepper by Xanthomonas campestris, a plant defense response activated by hrp gene-dependent and hrp gene-independent mechanisms.

Inoculation of pepper leaves, Capsicum annuum cv. Early Calwonder ECW 10R, with strains of Xanthomonas campestris led to an accumulation of the phenolic conjugates feruloyltyramine (FT) and p-coumaroyltyramine (CT) 24 h postinoculation in nonhost- and gene-for-gene-determined incompatible interactions with X. campestris pv. campestris and X. campestris pv. vesicatoria, respectively. In contrast, neither compound was detected in compatible interactions with X. campestris pv. vesicatoria. The accumulation of FT and CT was preceded by an increase in the extractable activity of tyrosine decarboxylase as well as increases in the transcription of genes encoding phenylalanine ammonia-lyase and tyramine hydroxycinnamoyl transferase. No such changes were detected in compatible interactions. Very rapid accumulation of FT and CT occurred (4 h postinoculation) in pepper in response to a X. campestris pv. campestris mutant carrying a deletion of the hrp gene cluster. In contrast, hrp mutants of X. campestris pv. vesicatoria failed to elicit the production of FT and CT. These observations suggest the existence of hrp gene-dependent and -independent activation mechanisms of a defense response involving hydroxycinnamoyltyramines.

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.