Aims:  To study and compare the efficacy of organic acids and chlorine dipping in inactivation of Escherichia coli and Listeria monocytogenes on fresh‐cut iceberg lettuce. Methods and Results:  Fresh‐cut iceberg lettuce leaves were inoculated with E. coli or L. monocytogenes. After inoculation, samples were stored at 4°C for 24 h and dipped in organic acid or chlorine solutions for 2 and 5 min. E. coli and L. monocytogenes were enumerated on selective media. Treatment of fresh‐cut iceberg lettuce with chlorine solution caused 1·0 and 2·0 log10 CFU g−1 reductions in the number of L. monocytogenes and E. coli, respectively. Maximum reduction for E. coli (about 2·0 log10 CFU g−1) was obtained for samples dipped in lactic or citric acids while maximum reduction for L. monocytogenes (about 1·5 log10 CFU g−1) was attained for samples dipped in lactic acid. Conclusions:  Dipping of iceberg lettuce in 0·5% citric acid or 0·5% lactic acid solution for 2 min could be as effective as chlorine for reducing microbial populations on fresh‐cut iceberg lettuce. Significance and Impact of the Study:  Dipping in solutions containing organic acids is shown to be effective to reduce E. coli and L. monocytogenes on fresh‐cut iceberg lettuce.

No abstract

Lactic and citric acid and ozonated water dippings could be alternative treatments to chlorine dipping to prolong the shelf life of fresh-cut iceberg lettuce. Copyright © 2007 Society of Chemical Industry.

This study evaluated the efficiency of ozone for the degradation of aflatoxins in pistachio kernels and ground pistachios. Pistachios were contaminated with known concentrations of aflatoxin (AF) B 1 , B 2 , G 1 and G 2 . Pistachio samples were exposed to gaseous ozone in a chamber at 5.0, 7.0 and 9.0 mg L −1 ozone concentrations for 140 and 420 min at 20 • C and 70% RH. Aflatoxin degradation was determined by high performance liquid chromatography (HPLC). The efficiency of ozone for aflatoxin degradation in pistachios increased with increasing exposure time and ozone concentration. The results indicated that AFB 1 and total aflatoxins could be reduced by 23 and 24%, respectively, when pistachio kernels were ozonated at 9.0 mg L −1 ozone concentration for 420 min. Only a 5% reduction in AFB 1 and total aflatoxin levels could be achieved for ground pistachios under the same conditions. No significant changes occurred in pH, color, moisture content and free fatty acid values of pistachio kernels and ground pistachios. Fatty acid compositions of pistachios did not change significantly after the ozonation treatments. No significant changes were found between sweetness, rancidity, flavor, appearance and overall palatability of ozonated and non-ozonated pistachio kernels. Significant changes were observed in the organoleptic properties of ground pistachios, except rancidity, after 5.0 mg L −1 ozone treatment for 140 min. Ozonation was found to be more effective for degrading aflatoxins in pistachio kernels than ground pistachios.

This work investigated the improvement of ethanol production by engineered ethanologenic Escherichia coli to express the hemoglobin from the bacterium Vitreoscilla (VHb). Ethanologenic E. coli strain FBR5 and FBR5 transformed with the VHb gene in two constructs (strains TS3 and TS4) were grown in cheese whey (CW) medium at small and large scales, at both high and low aeration, or with whey powder (WP) or sugar beet molasses hydrolysate (SBMH) media at large scale and low aeration. Culture pH, cell growth, VHb levels, and ethanol production were evaluated after 48 h. VHb expression in TS3 and TS4 enhanced their ethanol production in CW (21-419%), in WP (17-362%), or in SBMH (48-118%) media. This work extends the findings that "VHb technology" may be useful for improving the production of ethanol from waste and byproducts of various sources.

No abstract

The bacterial haemoglobin from Vitreoscilla, VHb, displays several unusual properties that are unique among the globin family. When the gene encoding VHb, vgb, is expressed from its natural promoter in either Vitreoscilla or Escherichia coli, the level of VHb increases more than 50-fold under hypoxic conditions and decreases significantly during oxidative stress, suggesting similar functioning of the vgb promoter in both organisms. In the present study we show that expression of VHb in E. coli induced the antioxidant genes katG (catalase-peroxidase G) and sodA (superoxide dismutase A) and conferred significant protection from oxidative stress. In contrast, when vgb was expressed in an oxyR mutant of E. coli, VHb levels increased and the strain showed high sensitivity to oxidative stress without induction of antioxidant genes; this indicates the involvement of the oxidative stress regulator OxyR in mediating the protective effect of VHb under oxidative stress. A putative OxyR-binding site was identified within the vgb promoter and a gel-shift assay confirmed its interaction with oxidized OxyR, an interaction which was disrupted by the reduced form of the transcriptional activator Fnr (fumurate and nitrate reductase). This suggested that the redox state of OxyR and Fnr modulates their interaction with the vgb promoter. VHb associated with reduced OxyR in two-hybrid screen experiments and in vitro, converting it into an oxidized state in the presence of NADH, a condition where VHb is known to generate H2O2. These observations unveil a novel mechanism by which VHb may transmit signals to OxyR to autoregulate its own biosynthesis, simultaneously activating oxidative stress functions. The activation of OxyR via VHb, reported in the present paper for the first time, suggests the involvement of VHb in transcriptional control of many other genes as well.

Flaked red peppers inoculated with Escherichia coli, Bacillus cereus and B. cereus spores were exposed to gaseous ozone at 20°C and 70% relative humidity (RH). Ozone concentrations of 0.1, 0.5 and 1.0 ppm up to 360 min were used to reduce E. coli and B. cereus, whereas 1.0, 5.0, 7.0 and 9.0 ppm ozone concentrations for 360 min were used to treat B. cereus spores. When flaked red peppers were treated with 1.0 ppm ozone concentration for 360 min, B. cereus and E. coli counts were decreased by 1.5 and 2.0 log numbers, respectively. Bacillus cereus spores were reduced by 1.5 log numbers at ozone concentrations of 7.0 ppm or above for 360 min. There were slight changes in flavour, appearance and overall palatability of flaked red peppers treated with ozone between 5.0 and 9.0 ppm. Ozone concentration (1.0 ppm) for 360 min can be used to decrease E. coli and B. cereus, whereas ozone concentrations ‡5.0 ppm can be used to reduce B. cereus spores.