Ahmed Lebrihi

Ochratoxin A removal in synthetic and natural grape juices by selected oenological Saccharomyces strains

Aims:  To assess, for the first time the efficiency in removing ochratoxin A (OTA) from laboratory medium [yeast peptone glucose (YPG)], synthetic grape juice medium (SGM) and natural grape juice by viable and dead (heat and acid‐treated) oenological Saccharomyces strains (five S. cerevisiae and one S. bayanus) compared with a commercial yeast walls additive.

Review of mycotoxin reduction in food and feed: from prevention in the field to detoxification by adsorption or transformation

Mycotoxins are secondary metabolites present worldwide in agricultural commodities and produced by filamentous fungi that cause a toxic response (mycotoxicosis) when ingested by animals. Prevention of mycotoxicoses includes pre- and post-harvest strategies. The best way to reduce the mycotoxin content in food and feed is the prevention of mycotoxin formation in the field, but this is often not sufficient, so other methods are needed. To decontaminate and/or detoxify mycotoxin-contaminated food and feed, the most prevalent approach in the feed industry is the inclusion of sorbent materials in the feed thus obtaining more or less selective removal of toxins by adsorption during passage through the gastrointestinal tract. Another reliable approach is to add enzymes or microorganisms capable of detoxifying some mycotoxins. Through a comprehensive review of published reports on the strategies for mycotoxin removal, this present work aims to update our understanding of mycotoxin removal. It provides an insight into the detoxification of mycotoxin present in food and feed. In the future, more emphasis needs to be placed on adsorption of mycotoxins in the gastrointestinal tract. Concerning the enzymatic transformation of mycotoxins, further efforts are required in understanding detoxification reactions, the toxicity of transformation products and in the characterization of enzymes responsible for transformations.

Eucalyptus oleosa essential oils: chemical composition and antimicrobial and antioxidant activities of the oils from different plant parts (stems, leaves, flowers and fruits).

Essential oils obtained by hydrodistillation from the different parts (stems, adult leaves, immature flowers and fruits) of Eucalyptus oleosa were screened for their antioxidant and antimicrobial properties and their chemical composition. According to GC-FID and GC-MS, the principal compound of the stem, immature flowers and the fruit oils was 1,8-cineole, representing 31.5%, 47.0% and 29.1%, respectively. Spathulenol (16.1%) and γ-eudesmol (15.0%) were the two principal compounds of adult leaves oil. In the DPPH (1,1-diphenyl-2-picrylhydrazyl) assay, the oils of the four parts showed moderate antioxidant activity. In the ABTS (2,2’-azinobis-3-ethylbenzothiazoline-6-sulphonate) assay, the most active part was the adult leaves, with a IC50 value 13.0 ± 0.6 mg/L, followed by stems (IC50 = 43.5 ± 1.4 mg/L). The essential oils showed a better antibacterial activity against Gram-positive and Gram-negative bacteria, and a significant antifungal activity also was observed against yeast-like fungi. A strong correlations between oxygenated monoterpenes and antimicrobial activity (especially 1,8-cineole) were noted (R2 = 0.99, 0.97 and 0.79 for B. subtilis, P. aeruginosa and C. albicans, respectively).

Isolation of Bacillus spp. from Thai fermented soybean (Thua‐nao): screening for aflatoxin B1 and ochratoxin A detoxification

Aims:  To study the interaction between Bacillus spp. and contaminating Aspergillus flavus isolated strains from Thai fermented soybean in order to limit aflatoxin production. To study the detoxification of aflatoxin B1 (AFB1) and ochratoxin A (OTA) by Bacillus spp. in order to find an efficient strain to remove these toxins.

Phosphate repression of cephamycin and clavulanic acid production by Streptomyces clavuligerus

SummaryProduction of cephamycin and clavulanic acid by Streptomyces clavuligerus is controlled by the phosphate concentration. Phosphate represses the biosynthesis of “cephamycin synthetase”, expandase and “clavulanic acid synthetase”. In the presence of 2 mM phosphate, the specific activities of expandase, “cephamycin synthetase” and “clavulanic acid synthetase” were higher than in the presence of 75 mM phosphate. The specific activity of cephamycin synthetase is maximal with an initial phosphate concentration of 10 mM, whereas the specific activity of expandase is maximal with 1 mM phosphate. A correlation between cephamycin synthetase specific activity and expandase specific activity was established at phosphate concentrations higher than 10 mM. This shows that the expandase is an important enzyme in the mechanism by which the phosphate concentration affects the biosynthesis of cephamycin.

Fungal contamination and Aflatoxin B1 and Ochratoxin A in Lebanese wine-grapes and musts

Five hundred and ten strains of filamentous fungi were isolated from Lebanese grapes during 2005 at veraison and harvesting periods. Four hundred eighty-seven isolates belonged to the Aspergillus spp. (95.5%) and 23 belonged to the Penicillium spp. (4.5%). Black aspergilli constituted 56.9% (52.2% Aspergillus niger aggregates, 2.9% Aspergillus japonicus and 1.8% Aspergillus carbonarius) while the isolation rate of Aspergillus flavus the none habitual member of grape mycobiota was 43.1% of the total Aspergillus spp. isolated. All isolates were tested for the ability to produce the Ochratoxin A (OTA) and the Aflatoxin B1 (AFB1). A. carbonarius showed that it is the only species able to produce the OTA with a production ability of 100% and a maximum concentration reaching 8.38microg/g CYA. As for the aflatoxigenic ability, 43.4% of A. flavus isolates produced this mycotoxin with a maximum production reaching 22.6microg/g CYA while none of the other isolates showed a production capacity of this mycotoxin. Forty-seven samples of must produced from the collected grapes were also analyzed. None of these samples was contaminated by OTA at a detectable limit while 40% of these same samples were found to contain AFB1 with concentrations ranging from 0.01 to 0.46microgl(-1).

Aspergillus section Flavi and aflatoxins in Algerian wheat and derived products.

Wheat and its derivatives are a very important staple food for North African populations. The aim of this study was to analyze populations of Aspergillus section Flavi from local wheat based on aflatoxins (AFs), cyclopiazonic acid (CPA) and sclerotia production, and also to evaluate AFs-contaminated wheat collected from two different climatic regions in Algeria. A total of 108 samples of wheat were collected during the following phases: pre-harvest, storage in silos and after processing. The results revealed that among the Aspergillus species isolated, those belonging to section Flavi were predominant. Of the 150 strains of Aspergillus section Flavi isolated, 144 were identified as Aspergillus flavus and 6 as Aspergillus tamarii. We showed that 72% and 10% of the A. flavus strains produced AFs and CPA, respectively. Among the 150 strains tested, 60 produced amounts of AFB1 ranging from 12.1 to 234.6 microg/g of CYA medium. Also, we showed that most strains produced large sclerotia. AFB1was detected by HPLC in 56.6% of the wheat samples and derived products (flour, semolina and bran) with contamination levels ranging from 0.13 to 37.42 microg/kg.

Regulation of spiramycin synthesis in Streptomyces ambofaciens: effects of glucose and inorganic phosphate

The production of the 16-membered macrolide antibiotic, spiramycin, in Streptomyces ambofaciens is inhibited by glucose, 2-deoxyglucose and inorganic phosphate. The role of intracellular ATP content and phosphorylated metabolites as common regulating signals of both glucose and phosphate inhibitory effects is discussed. Two enzymatic targets of the effect of phosphate on spiramycin biosynthesis were studied. Valine dehydrogenase, the first enzyme of valine catabolism (supplier of aglycone spiramycin precursors), and alkaline phosphatase, which cleaves phosphorylated intermediates, were repressed in the presence of excess phosphate.

Effect of ammonium ions on spiramycin biosynthesis in Streptomyces ambofaciens

SummaryThe effect of ammonium on growth and spiramycin biosynthesis in Streptomyces ambofaciens cultured on a chemically defined medium was studied. Spiramycin biosynthesis was better in the presence of valine and isoleucine than in the presence of ammonium. This production was reduced in the presence of excess ammonium (100 mm). The addition of catabolic intermediates of valine and isoleucine reserved the negative effect of ammonium. Valine dehydrogenase (VDH), the enzyme responsible for valine, leucine and isoleucine catabolism, was repressed when excess ammonium was present in the medium. This repression was approximately 25% when the ammonium concentration was increased from 50 to 100 mm. In addition to the repression of VDH biosynthesis, ammonium inhibited the activity of this enzyme. This inhibition was 45 and 65% in the presence of 50 and 100 mm ammonium, respectively.

Carbon catabolite regulation of cephamycin C and expandase biosynthesis in Streptomyces clavuligerus

SummaryStreptomyces clavuligerus produces cephamycin C while growing on chemically defined basal medium. Cephamycin C production takes place during the exponential growth phase and is accompanied by vigorous activity of the “cephamycin C synthetase” system and of expandase. An excessive amount of glycerol decreases cephamycin C production. Its negative effect appears to be greatest when it is added in the first phase of fermentation either alone or in the presence of starch. Starch excess also reduces cephamycin C production, but its effect is slight compared with glycerol. Glycerol hinders cephamycin C production by the repression of the cephamycin C synthetase system and particularly expandase biosynthesis. Starch and glycerol inhibit neither cephamycin C synthetase nor expandase activities. However, the phosphorylated intermediates of the glycolytic pathway, glucose 6-phosphate and fructose 1,6-phosphate, strongly inhibit expandase activity.