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Biomedical subjects

L Leistner

Publications and source records attributed to L Leistner.

17 recordsLinked to original sources

Basic aspects of food preservation by hurdle technology.

Hurdle technology is used in industrialized as well as in developing countries for the gentle but effective preservation of foods. Previously hurdle technology, i.e., a combination of preservation methods, was used empirically without much knowledge of the governing principles. Since about 20 years the intelligent application of hurdle technology became more prevalent, because the principles of major preservative factors for foods (e.g., temperature, pH, a(w), Eh, competitive flora), and their interactions, became better known. Recently, the influence of food preservation methods on the physiology and behaviour of microorganisms in foods, i.e. their homeostasis, metabolic exhaustion, stress reactions, are taken into account, and the novel concept of multitarget food preservation emerged. In the present contribution a brief introduction is given on the potential hurdles for foods, the hurdle effect, and the hurdle technology. However, emphasis is placed on the homeostasis, metabolic exhaustion, and stress reactions of microorganisms related to hurdle technology, and the prospects of the future goal of a multitarget preservation of foods.

Bacteria↗

Mutagenicity and effects of ochratoxin A on the frequency of sister chromatid exchange after metabolic activation.

Primary cultures of hepatocytes derived from untreated rats were incubated in the presence of ochratoxin A for 24 h. Five different strains of histidine auxotroph Salmonella typhimurium were exposed to conditioned cell culture medium before being tested for mutagenicity. A clear hepatocyte-mediated mutagenic response was observed in TA1535, TA1538 and TA100. In addition, sister chromatid exchange frequency was increased in human peripheral lymphocytes that had been incubated in the presence of conditioned medium derived from ochratoxin A-exposed hepatocytes.

Animals↗

Two Penicillium camembertii mutants affected in the production of cyclopiazonic acid.

Penicillium camembertii was mutated and screened for cyclopiazonic acid-negative mutants. With a simple and rapid mini-extraction method for detection of cyclopiazonic acid production, we were able to isolate two strains which were affected in the production of this metabolite. One strain had completely lost the ability to synthesize detectable amounts of this secondary metabolite, whereas the other mutant produced 50 to 100 times less cyclopiazonic acid than the wild type. Also, the former strain had a changed morphology compared with the wild type. This morphological alteration appears to be coupled to the inability to produce cyclopiazonic acid because morphological revertants were able to synthesize cyclopiazonic acid to a level comparable to the wild type. The second mutant accumulated a new metabolite which was detectable by two-dimensional thin-layer chromatography. This new metabolite, however, appears not to be a direct precursor of cyclopiazonic acid.

Genes, Fungal↗

Production of penitrem A by Penicillium crustosum isolated from foodstuffs.

Sixty one isolates of Penicillium crustosum originating from various foodstuffs were screened for penitrem A production by thin-layer chromatography. The highest producers of penitrem A (4 isolates) were grown in various liquid media. Skimmed milk (2%)/potato extract (2%)/sucrose (2%) (SPS) medium supported the highest toxin production and P. crustosum Sp 1552 was selected as the best producer of penitrem A. Optimal conditions for the production of penitrem A were to grow the isolate Sp 1552 (stationary) in 100 ml of SPS medium (with 4% sucrose) in 500-ml flasks for 3 weeks at 25 degrees C with initial pH 5.7. The isolation and purification of penitrem A is described. Approximately 246 mg of pure penitrem A was obtained from 200 flasks each containing 100 ml of SPS medium.

Culture Media↗

[South African biltong--another close look].

Twenty beef biltong samples from various commercial sources were investigated chemically and microbiologically. The biltong contained 5-10% NaCl, little sugar and nitrite but 10-860 ppm nitrate. The addition of nitrate apparently did not ensure stability, since spoiled biltong often contained much residual nitrate. Biltong was stable at the barrier combination of aw less than or equal to 0.77 and pH less than or equal to 5.5 because such samples did not spontaneously become mouldy. A high degree of contamination with moulds and yeasts was found indicating a real health hazard to which consumers might be exposed. Better control measures must be imposed to ensure a better product to the consumer.

Animals↗

Minimal water activity for enterotoxin A production and growth of Staphylococcus aureus.

The minimal water activity (alphaw) for growth was correlated with enterotoxin A formation by two strains of Staphylococcus aureus in a salt mixture broth. Within 7 days at 30 degrees C both strains grew and formed enterotoxin A minimally between alphaw 0.864 and 0.867, but at 25 degrees C, the minimal alphaw for both activities was increased to between 0.870 and 0.887 after a 2-week incubation.

Culture Media↗

Effect of storage and processing on tetracycline residues in meat and bones.

A semiquantitative microbiological screening test for antibiotics, a sensitive and quantitative microbiological assay, and a fluorometric method specific for tetracyclines are described. Using these procedures, tetracycline residues in animals derived from feed can be detected in tissues like organs, muscles, and bones. Meat contaminated with chlortetracycline (CTC) and oxytetracycline (OTC) and stored at +8 degrees C and -22 degrees C showed very little decrease in antibiotic concentration; however, heating above 65 degrees C reduced the tetracycline content in meat. Temperatures above 130 degrees C were necessary to destroy CTC in bones, CTC in bones was insoluble above pH 4. Manufacturing products with contaminated meat reduced the tetracycline content only if heating was involved.

Animal Feed↗

Potential production and detoxification of penicillic acid in mold-fermented sausage (salami).

About 10% of 346 Penicillium cultures isolated from mold-fermented sausage synthesized the toxic metabolite penicillic acid on liquid media. Five of these producing cultures inoculated onto sausage failed to produce this toxin in up to 70 days of ripening. Several amino acids normally occurring in meat (cysteine, glutathione, arginine, histidine, and lysine) were found capable of readily reacting with penicillic acid. The adducts formed by the reaction between cysteine or glutathione with penicillic acid were identified and found to be non-toxic to mice, quails, and in the rabbit skin test but exhibited toxicity to the chick embryo. Hypotheses accounting for this residual toxicity are advanced.

Alkylation↗