Eva Lorencová

Monitoring of biogenic amines in cheeses manufactured at small-scale farms and in fermented dairy products in the Czech Republic

The aim of the study was the monitoring of six biogenic amines (histamine, tyramine, phenylethylamine, tryptamine, putrescine, and cadaverine) and two polyamines (spermidine and spermine) in 112 samples of dairy products purchased in the Czech Republic, namely in 55 cheeses made in small-scale farms and in 57 fermented dairy products. The products were tested at the end of their shelf-life period. Neither tryptamine nor phenylethylamine was detected in the monitored samples; histamine was found only in four cheese samples containing up to 25mg/kg. The contents of spermine and spermidine were low and did not exceed the values of 35 mg/kg. Significant amounts of tyramine, putrescine, and cadaverine occurred especially in cheeses produced from ewes milk or in long-term ripened cheeses. In about 10% of the tested cheeses, the total concentration of all the monitored biogenic amines and polyamines exceeded the level of 200mg/kg, which can be considered toxicologically significant. In fermented dairy products, the tested biogenic amines occurred in relatively low amounts (generally up to 30 mg/kg) that are regarded safe for the consumers health.

Decarboxylation activity of enterococci isolated from rabbit meat and staphylococci isolated from trout intestines

The aim of the study was to explore production of seven biogenic amines (phenylethylamine, histamine, cadaverine, tyramine, putrescine, spermine and/or spermidine) by selected staphylococci and enterococci. Thirty three enterococcal strains isolated from rabbit meat (Oryctolagus cuniculus f. domesticus) and 21 staphylococcal strains isolated from intestinal content of trout (Salmo trutta morpha fario) were tested. Production of biogenic amines was evaluated after cultivation of the tested microorganisms in the de Man, Rogosa and Sharpe Broth (enterococci) or in the Brain Heart Infusion Broth (staphylococci). Both the above cultivation media were enriched with selected amino acids (histidine, tyrosine, arginine, ornithine and lysine; 2g/L each) serving as precursors of biogenic amines. After cultivation, levels of the monitored biogenic amines in broths were analysed by a high performance liquid chromatography equipped with a UV/VIS DAD detector. Among 21 staphylococci, 18 strains produced tyramine or cadaverine, 13 strains formed putrescine or phenylethylamine and only one strain generated histamine. Two staphylococcal strains produced cadaverine levels above 1000 mg/L. Among 33 enterococcal strains, 27 formed cadaverine, 18 strains produced tyramine, 10 strains generated phenylethylamine, and 2 strains gave putrescine. Most of the tyramine producing enterococci generated more than 1000 mg/L of this biogenic amine. Production of spermine or spermidine by the studied strains was not proved.

Antibacterial effect of phosphates and polyphosphates with different chain length

The aim of this study was to monitor the antibacterial effect of seven phosphate salts on selected strains of Gram-negative and Gram-positive bacteria, which could be considered responsible for food-borne diseases (Bacillus cereus, Bacillus subtilis, Enterococcus faecalis, Micrococcus luteus, Staphylococcus aureus, Citrobacter freundii, Escherichia coli, Proteus mirabilis, Salmonella enterica ser. Enteritidis and Pseudomonas aeruginosa). For these purposes, phosphates differing in chain length were used. The tested concentrations were in the range of 0.1–2.0% (wt v−1) applied at the model conditions. In the majority of cases the visible inhibitory effect on the growth of observed microorganisms could be seen. Due to the chemical structure of salts and their dissociation both the pH values of cultivation broth and similarly the growth characteristics of bacterial strains were affected. The inhibition of above mentioned bacteria was apparently supported by this dissociation. Phosphates obviously made the development of most Gram-positive bacteria impossible. Especially Micrococcus luteus was extremely sensitive to the presence of these substances. On the other hand, Gram-negative bacteria seemed to be resistant to the phosphate incidence. The exemption clause from the tested salts was represented by a high alkaline trisodium phosphate. It should be pointed out that generally the most significant antibacterial effects were shown by polyphosphates HEXA68 and HEXA70, trisodium phosphate undecahydrate, tetrasodium pyrophosphate and finally trisodium phosphate. By comparing the inhibitory effects of various phosphate salts can be concluded that the antibacterial activity was not determined only by the condensation degree but there was also proved the dependence on pH values.

The influence of fat and monoacylglycerols on growth of spore-forming bacteria in processed cheese

Highly undesirable microbial contaminants of processed cheese are endospore-forming bacteria of the genera Bacillus and Clostridium. Survival of Bacillus subtilis, B. cereus, Clostridium butyricum and C. sporogenes was examined in model processed cheese samples supplemented with monoacylglycerols. In processed cheese samples, monoacylglycerols of undecanoic, undecenoic, lauric and adamantane-1-carboxylic acid at concentration of 0.15% w/w prevented the growth and multiplication of both Bacillus species throughout the storage period. The two species of Clostridium were less affected by monoacylglycerols in processed cheese samples and only partial inhibition was observed. The effect of milk fat content on microbial survival in processed cheese was also evaluated. The growth of Bacillus sp. was affected by the fat level of processed cheese while population levels of Clostridium sp. did not differ in processed cheese samples with 30, 40 and 50% fat in dry matter.

FACTORS AFFECTED DECARBOXYLATION ACTIVITY OF ENTEROCOCCUS FAECIUM ISOLATED FROM RABBIT

Normal 0 21 false false false SK JA X-NONE Biogenic amines (BA) are basic nitrogenous compounds formed mainly by decarboxylation of amino acids. There are generated in course of microbial, vegetable and animal metabolisms. The aim of the study was to monitor factors affected production of biogenic amines by Enterococcus faecium, which is found in rabbit meat. Biogenic amines were analyzed by means of UPLC (ultrahigh performance liquid chromatography) equipped with a UV/VIS DAD detector. Decarboxylation activity of E. faecium was mainly influenced by the cultivation temperature and the amount of NaCl in this study. E. faecium produced most of the monitored biogenic amines levels: tyramine ˂2500 mg.l -1 ; putrescine ˂30 mg.l -1 ; spermidine ˂10 mg.l -1 and cadaverine ˂5 mg.l -1 . doi:10.5219/182

EFFECT OF SODIUM PHOSPHATES ON SELECTED FOOD GRADE BACTERIA

The aim of this study was to examine the inhibitory effect in vitro of selected sodium phosphates (under the corporate names Hexa 68, Hexa 70, Trikrystal, FST, Pyro 52, KPS, Didi) on selected gram-positive and gram-negative bacteria. Seven different concentrations of each phosphate were used. Sensitivity of the bacterial strains to phosphates was observed in broth supplemented with salts. In vitro was showed a negative effect of various phosphates on growth of selected gram-positive bacteria. Orthophosphates and diphosphates (pyrophosphates) did not have significant inhibitory effect on tested bacteria at neutral pH. With the exception of phosphate Trikrystal has not been found in vitro significant inhibitory effects on gram-negative bacteria. doi:10.5219/141