Minced Pork Meat Spoilage our samples are known, results indicated that bacterial diversity needs to be addressed on the level of food companies, batches variation and food storage conditions. Present data illustrate that the combined approach provides complementary results on microbial dynamics in minced pork meat samples, considering batches and packaging variations.

The ability of the yeast Saccharomyces cerevisiae to bioconvert stereo-selectively octyl-4-chloroacetoacetate (OCA) into the corresponding chiral alcohol, precursor of L-carnitin, an important physiological agent, was investigated. In a monophasic system with free cells, more than 90% of OCA (0.018 M) bioconversion have been reached after 6 h (enantiomeric excess for the R form, eeR:97%). Immobilized cells in alginate beads were less efficient in conversion of OCA than free cells. In a two-phase system with free cells, the level of reduction of OCA (0.018 M) reached 85% after 48 h. With a medium containing a higher OCA concentration (0.270 M), 41% of this product were bioconverted after the same period. On the other hand, immobilized cells did not show any significant bioconversion of OCA in two-phase reactors. The limiting factor of these reactors in the regeneration of the cofactors involved in the OCA reduction.

Pseudomonas fluorescens (strain BTP9) was found to have at least two NAD(P)-dependent vanillin dehydrogenases: one is induced by vanillin, and the other is constitutive. The constitutive enzyme was purified by ammonium sulfate fractionation, gel-filtration, and Q-Sepharose chromatography. The subunit Mr value was 55,000, determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis. The native Mr value estimated by gel-filtration chromatography gave a value of 210,000. The enzyme made use of NAD+ less effectively than NADP+. Benzaldehyde, 4-hydroxybenzaldehyde, hexanal, and acetaldehyde were not oxidized at detectable rates in the presence of NAD+ or NADP+. The ultraviolet absorption spectrum indicated that there is no cofactor or prosthetic group bound. The vanillin oxidation reaction was essentially irreversible. The pH optimum was 9.5 and the pI of the enzyme was 4.9. Enzyme activity was not affected when assayed in the presence of salts, except FeCl2. The enzyme was inhibited by the thiol-blocking reagents 4-chloromercuribenzoate and N-ethylmaleimide. NAD+ and NADP+ protected the enzyme against such a type of inhibition along with vanillin to a lesser extent. The enzyme exhibited esterase activity with 4-nitrophenyl acetate as substrate and was activated by low concentrations of NAD+ or NADP+. We compared the properties of the enzyme with those of some well-characterized microbial benzaldehyde dehydrogenases.

The inability of psychrophilic microorganisms to grow at moderate temperatures (>20°C) presently represents an unresolved thermodynamic paradox. Here we report for the psychrophilic yeast Rhodotorula aurantiaca A19, isolated from Antarctic ice, that the inability to grow at temperatures close to 20°C is associated with profound alterations in cell morphology and integrity. High performance liquid chromatography analysis of the intracellular acyl-CoA esters revealed an abnormal accumulation of myristoyl-CoA (C14-CoA) in cells cultivated close to the nonpermissive temperature. Its concentration (500 M) was found to be 28-fold higher than in cells cultivated at 0°C. If one considers its ability to disrupt membrane bilayers and to inhibit many cellular enzymes and functions, intracellular myristoylCoA accumulation in the psychrophile R. aurantiaca represents one of the principal causes of growth arrest at moderate temperatures. Intracellular acyl-CoA concentrations are believed to be regulated by thioesterase activity. Thus in an attempt to explore the mechanism by which temperature disrupts myristoyl-CoA metabolism, we isolated and characterized a long chain acylCoA thioesterase. The monomeric 80-kDa thioesterase from the psychrophilic yeast shows a very strong specificity for myristoyl-CoA. The affinity for substrate and the catalytic efficiency of the thioesterase are optimal below 5°C (temperatures habitually experienced by the strain) and dramatically decrease with increasing temperature. The loss of affinity for substrate is related to the intracellular increase of myristoyl-CoA concentration. Our observations reveal one of the probable mechanisms by which temperature fixes the limit of growth for this psychrophilic yeast.

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