C.I. Wei

Occurrence of Listeria monocytogenes, Salmonella spp., Escherichia coli and E. coli O157:H7 in vegetable salads

Abstract The occurrence of Listeria monocytogenes, Salmonella spp., Escherichia coli and E. coli O157:H7 in 63 vegetable salads served at 31 food service facilities (four supermarkets, 14 fast food chain restaurants, and 13 family restaurants) was examined. Homogenized salad samples were incubated in half-strength TSB for 6 h, then in specific selective enrichment media for each bacterial species. After cultures were streaked onto sets of selective agar plates, bacterial colonies with characteristic features were confirmed biochemically and immunologically. Escherichia coli was detected in eight salad samples and L. monocytogenes in one sample. The contaminated salads were purchased from one supermarket, two fast food chain restaurants and two family restaurants tested. Vegetable salads served in the other 26 food service facilities contained none of the four pathogens. Therefore, the production and maintenance of safe, quality vegetable salads in supermarkets, family restaurants and fast food chain restaurants is achievable.

Mutagenicity studies of kojic acid

Kojic acid, a fungal metabolite produced by some species of Aspergillus and Penicillium, was found to induce sister chromatid exchanges and chromosomal aberrations in Chinese hamster ovary cells in the presence or absence of the rat liver S9 mix. Furthermore, this compound was demonstrated to induce mutations in Salmonella typhimurium strains TA98 and TA100 using both plate-incorporation and preincubation methods.

An assessment of the genotoxicity of vanadium

The activities of vanadium oxide (V2O3), vanadyl sulfate (VOSO4) and ammonium metavanadate (NH4VO3) in inducing sister chromatid exchange (SCE) and chromosomal aberrations (CAb) were assayed in Chinese hamster ovary cells. The toxic concentrations (TC50) for these compounds were found to be 25, 23 and 16 micrograms elemental vanadium/ml, respectively. At does 1/50-1/4 TC50, vanadium compounds were able to induce significant increases (P less than 0.01) in the SCE frequency with or without the addition of rat hepatic S9 mix. These compounds also induced CAb in the cells at doses closely equivalent to the TC50.

Production of Kojic acid by Aspergillus candidus in three culture media

Aspergillus candidus ATCC 44054 grown without agitation produced more kojic acid in the modified Czapek-Dox liquid medium than cultures shaken at 100 rpm. Of the three culture media tested, yeast extract-sucrose medium permitted more kojic acid production by the fungus than modified Czapek-Dox liquid medium or Tadera medium. Maximal kojic acid (57-59 mg/ml) was produced in the yeast extract-sucrose medium on days 9-12. No aflatoxin by the fungus was detected.

Mutagenicity of the C-nitroso analog of fenitrothion

The chemicals fenitrothion, nitroso fenitrothion, amino fenitrothion and 3-methyl-4-nitrophenol were tested for mutagenicity to Salmonella typhimurium strains TA98 and TA100, both in the presence and absence of rat liver S-9 mix. The strong mutagenicity of nitroso fenitrothion to both strains either in the presence or absence of S-9 mix contrasted with the observation that fenitrothion displayed no mutagenicity in these tester strains. The results suggest that the normal nitroreductases present in TA98 and TA100 cannot metabolize fenitrothion to a mutagenic metabolite. This inability of the tester strains to effect partial nitroreduction results in the failure of this screening system to predict the potential genotoxicity of this pesticide.

Mutagenicity of some monoaromatic hydroxamic acids

The mutagenicity of some monoaromatic hydroxamic acids was tested in the presence and absence of rat liver S-9 with Salmonella typhimurium tester strains TA98 and TA100. Of the five N-(chlorophenyl)-substituted hydroxamic acids and seven N-arylformohydroxamic acids tested, 2 of the first and 4 of the latter series were mutagenic to both strains upon metabolic activation. None of the four N-acetyl-type hydroxamic acids was mutagenic to either strain, even upon activation. Because some of the N-acetyl-derived hydroxamic acids were inactive, whereas the same aromatic nucleus possessing a formyl group displayed significant activity, a consideration of the nature of the aryl group in hydroxamic acid mutagenicity is important.

Comparison of crabmeat protein patterns by isoelectric focusing

Abstract Isoelectric focusing (IEF) of the water and urea extracts of raw or cooked blue crabmeat showed no difference in protein banding patterns with respect to sex, body part (body lump and claw), time of year (January, April, June, August and October) or locations (Florida, Maryland, Louisiana and South Carolina) of harvesting, though differences in intensities of some bands occurred. However, the cooked Taiwanese crabmeat was found to differ in IEF profiles from the US blue crab and the two frozen crabmeat blocks from China. IEF and two-dimensional gel electrophoresis (2-DGE) were not effective for differentiating pasteurized or canned crabmeat from different countries of origin. Heat treatment during pasteurization and canning drastically affected protein composition and thus the profiles.

Genotoxicity studies of the reaction of chlorine or chlorine dioxide with l-tryptophan

Non-volatile reaction products generated from the reactions of 70 mM aqueous chlorine or chlorine dioxide with 10 mM L-tryptophan were shown to be direct-acting mutagens to Salmonella typhimurium TA100 and TA98. Several of the fluorescent bands obtained after thin-layer chromatographic fractionation of the XAD-2/8 resin concentrates of the reaction mixtures were shown to be more mutagenic than the reaction mixtures using the Ames Salmonella/microsome assay. In addition, these fractions were shown to be capable of increasing significantly the frequency of sister chromatid exchange in Chinese hamster ovary cells in the absence of rat liver S9 mix. GC/MS analysis of the products in a highly mutagenic fraction of the aqueous chlorine reaction products identified 1,1,3-trichloropropanone, 1,1,3,3-tetrachloropropanone and dichloroquinoline.

Inhibitory Effect of Beta-Ionone on Growth and Aflatoxin Production by Aspergillus parasiticus on Peanuts1

The volatile ketone (β-ionone showed a dose-related inhibition of fungal growth and aflatoxin production on peanuts after they were soaked in distilled water for 25 or 50 min, inoculated with spores, and incubated at 28°C for up to 2 weeks. For example, aflatoxin B1 (AFB1) production after 1 week of incubation was reduced to less than 11.0 and 6.7% of the control when 2.5 or 5 ml of (β-ionone/100 g of peanuts, respectively, was added to water-soaked (25 min) peanuts. For AFG1, production was reduced to 4.7 (2.5 ml) or 3.3% (5.0 ml) under the same treatment conditions. Unlike controls or those treated with less than 0.1 ml of β-ionone, peanuts treated with more than 0.25 ml of β-ionone had only sparse mycelial growth and supported only limited sporulation. The mycelia, after being transferred to fresh Mycological or Fluorescent Agar plates, still had the ability to form normal colonies and produce aflatoxins. This temporary limitation of fungal growth was also noticed for those Aspergillus cultures on Mycological Agar that had been treated with (β-ionone either by direct contact or volatile bioassay procedures. The fungus was still able to grow of Fluorescent Agar even after the infected peanuts were treated with sodium hypochlorite for 15 or 30 min, indicating that mycelial penetration into peanut tissues occurs. This may confer protection from the action of various antifungal compounds. This observtion is further supported by microscopic detection of mycelial fragments in peanut tissues.