A sensitive method for qualitative screening of bile salt hydrolase-active lactobacilli based on thin-layer chromatography

A sensitive protocol based on thin-layer chromatography (TLC) was developed to screen qualitatively bile salt hydrolase (BSH)-active lactobacilli. The sodium salts of glycocholic acid and taurocholic acid were used as substrates, and bacterial BSH activity was confirmed by detecting cholic acid as a product of the bile conjugates using a TLC assay with direct visual observation. Forty-five lactobacilli isolated from human fecal samples were tested for BSH activity by the TLC assay, a conventional plate assay, and a quantitative colorimetric assay. With the TLC and quantitative colorimetric assays, the same 24 BSH-positive strains were detected. No false-positive or false-negative results were detected by the TLC assay. However, only 20 BSH-positive strains were detected with the conventional plate assay. Compared with the conventional plate assay, the TLC assay is more sensitive for the detection of BSH activity of lactobacilli and, thus, more suitable for screening of BSH-active lactobacilli of human origin.     

Tetrodotoxin in gastropods (snails) implicated in food poisoning in Northern Taiwan

The toxin in the gastropods (snails) Zeuxis sufflatus and Niotha clathrata implicated in a food poisoning incident in northern Taiwan in April 2001 was studied. The symptoms exhibited by four victims were general paresthesia, paralysis of the phalanges and the extremities, paralysis, coma, vomiting, and aphasia. The remaining gastropods were assayed for toxicity in the form of tetrodotoxin (TTX). The ranges of specimen toxicity were 345 to 1,640 mouse units (MU) for Z sufflatus and 190 to 643 MU for N. clathrata. The toxicities of the digestive gland and for other parts of the gastropod were 1,120 +/- 477 MU and 497 +/- 238 MU, respectively, for Z sufflatus and 683 +/- 113 MU and 289 +/- 169 MU, respectively, for N. clathrata. The toxin from the methanolic extract of the gastropods was partially purified by ultrafiltration and Bio-Gel P-2 column chromatography. Cellulose acetate membrane electrophoresis, thin-layer chromatography, high-performance liquid chromatography, and gas chromatography-mass spectrometry analyses demonstrated that the toxin consisted of TTX. It was concluded that the causative agent of the food poisoning in question was TTX.     

Inhibitory effect of Melastoma candidum D. Don acetone extract on foodborne pathogenic bacteria survival in food products

Melastoma candidum D. Don, a Taiwanese folk medicinal plant, has high levels of antibacterial and bactericidal activity. Our aim was to determine whether and to what extent an acetone extract of this plant inhibits the growth of foodborne pathogenic bacteria. M. candidum acetone extract had marked inhibitory effect on test bacteria introduced into sliced pork, which was then stored at 4 degrees C. At the end of storage (day 12), the bacterial concentrations dropped by 1.59 to 2.91 log CFU/g compared with the control. In steamed rice stored at 30 degrees C, a 0.2% extract decreased initial (before storage) concentrations of Bacillus cereus from 2.01 log CFU/g to an undetectable level, which remained for at least 24 h. After 72 to 168 h of storage, test bacterial concentrations were reduced by 2.59 to 5.66 log CFU/g. In fresh noodles stored at 30 degrees C, both initial and final bacterial concentrations were decreased. At the end of storage (72 to 168 h), test bacteria concentrations were reduced by 1.85 to 2.88 log CFU/g. Overall, M. candidum acetone extract had an inhibitory effect on foodborne pathogenic bacteria in different food model systems.     

Size-tunable hydrothermal synthesis of SnS2 nanocrystals with high performance in visible light-driven photocatalytic reduction of aqueous Cr(VI)

SnS(2) nanocrystals with adjustable sizes were synthesized via a hydrothermal method from the aqueous solution of common and inexpensive SnCl(4)·5H(2)O, thioacetamide and citric acid, simply by varying the reaction temperature and reaction time. The structures, Brunauer-Emmett-Teller (BET) specific surface areas and optical properties of the resultant SnS(2) nanocrystals were characterized by X-ray diffraction, transmission electron microscopy, N(2) adsorption/desorption isotherms, and UV-vis diffuse reflectance spectra. Besides, their photocatalytic properties were tested for the reduction of aqueous Cr(VI) under visible light (λ > 420 nm) irradiation. It was found that the photocatalytic activities of SnS(2) nanocrystals in aqueous suspension depended on their synthesis conditions. The product synthesized under suitable hydrothermal conditions (for example, at 150 °C for 12 h) not only showed high visible light-driven photocatalytic activity in the reduction of aqueous Cr(VI), but also showed good photocatalytic stability. Our photocatalytic results suggested that SnS(2) nanocrystals are a promising photocatalyst in the efficient utilization of solar energy for the treatment of Cr(VI)-containing wastewater.     

Efficacy of slightly acidic electrolyzed water in killing or reducing Escherichia coli O157:H7 on iceberg lettuce and tomatoes under simulated food service operation conditions

Abstract: The objective of this study was to evaluate the efficacy of slightly acidic electrolyzed (SAEO) water in killing or removing Escherichia coli O157:H7 on iceberg lettuce and tomatoes by washing and chilling treatment simulating protocols used in food service kitchens. Whole lettuce leaves and tomatoes were spot‐inoculated with 100 μL of a mixture of 5 strains of E. coli O157:H7. Washing lettuce with SAEO water for 15 s reduced the pathogen by 1.4 to 1.6 log CFU/leaf, but the treatments did not completely inactivate the pathogen in the wash solution. Increasing the washing time to 30 s increased the reductions to 1.7 to 2.3 log CFU/leaf. Sequential washing in SAEO water for 15 s and then chilling in SAEO water for 15 min also increased the reductions to 2.0 to 2.4 log CFU/leaf, and no cell survived in chilling solution after treatment. Washing tomatoes with SAEO water for 8 s reduced E. coli O157:H7 by 5.4 to 6.3 log CFU/tomato. The reductions were increased to 6.6 to 7.6 log CFU/tomato by increasing the washing time to 15 s. Results suggested that application of SAEO water to wash and chill lettuce and tomatoes in food service kitchens could minimize cross‐contamination and reduce the risk of E. coli O157:H7 present on the produce. Practical Application: SAEO water is equally or slightly better than acidic electrolyzed (AEO) water for inactivation of bacteria on lettuce and tomato surfaces. In addition, SAEO water may have the advantages over AEO water on its stability, no chlorine smell, and low corrosiveness. Therefore, SAEO water may have potential for produce wash to enhance food safety.     

Validation of high pressure processing for inactivating Vibrio parahaemolyticus in Pacific oysters (Crassostrea gigas)

This study identified and validated high hydrostatic pressure processing (HPP) for achieving greater than 3.52-log reductions of Vibrio parahaemolyticus in the Pacific oysters (Crassostrea gigas) and determined shelf life of processed oysters stored at 5 °C or in ice. Raw Pacific oysters were inoculated with a clinical strain of V. parahaemolyticus 10293 (O1:K56) to levels of 10^4-5 cells per gram and processed at 293 MPa (43 K PSI) for 90, 120, 150, 180 and 210 s. Populations of V. parahaemolyticus in oysters after processes were analyzed with the 5-tube most probable number (MPN) method. Negative results obtained by the MPN method were confirmed with a multiplex PCR detecting genes encoding thermolabile hemolysin (tl), thermostable direct hemolysin (tdh) and TDH-related hemolysin (trh). A HPP of 293 MPa for 120 s at groundwater temperature (8 ± 1 °C) was identified capable of achieving greater than 3.52-log reductions of V. parahaemolyticus in Pacific oysters. Oysters processed at 293 MPa for 120 s had a shelf life of 6-8 days when stored at 5 °C or 16-18 days when stored in ice. This HPP can be adopted by the shellfish industry as a post harvest process to eliminate V. parahaemolyticus in raw oysters.     

Efficacy of electrolyzed oxidizing water in inactivating Salmonella on alfalfa seeds and sprouts

Studies have demonstrated that electrolyzed oxidizing (EO) water is effective in reducing foodborne pathogens on fresh produce. This study was undertaken to determine the efficacy of EO water and two different forms of chlorinated water (chlorine water from Cl2 and Ca(OCl)2 as sources of chlorine) in inactivating Salmonella on alfalfa seeds and sprouts. Tengram sets of alfalfa seeds inoculated with a five-strain cocktail of Salmonella (6.3 x 10(4) CFU/g) were subjected to 90 ml of deionized water (control), EO water (84 mg/liter of active chlorine), chlorine water (84 mg/liter of active chlorine), and Ca(OCl)2 solutions at 90 and 20,000 mg/liter of active chlorine for 10 min at 24 +/- 2 degrees C. The application of EO water, chlorinated water, and 90 mg/liter of Ca(OCl)2 to alfalfa seeds for 10 min reduced initial populations of Salmonella by at least 1.5 log10 CFU/g. For seed sprouting, alfalfa seeds were soaked in the different treatment solutions described above for 3 h. Ca(OCl)2 (20,000 mg/liter of active chlorine) was the most effective treatment in reducing the populations of Salmonella and non-Salmonella microflora (4.6 and 7.0 log10 CFU/g, respectively). However, the use of high concentrations of chlorine generates worker safety concerns. Also, the Ca(OCl)2 treatment significantly reduced seed germination rates (70% versus 90 to 96%). For alfalfa sprouts, higher bacterial populations were recovered from treated sprouts containing seed coats than from sprouts with seed coats removed. The effectiveness of EO water improved when soaking treatments were applied to sprouts in conjunction with sonication and seed coat removal. The combined treatment achieved 2.3- and 1.5-log10 CFU/g greater reductions than EO water alone in populations of Salmonella and non-Salmonella microflora, respectively. This combination treatment resulted in a 3.3-log10 CFU/g greater reduction in Salmonella populations than the control (deionized water) treatment.     

Simultaneous determination of mono- and dicarboxylic acids, omega-Oxo-carboxylic acids, midchain ketocarboxylic acids, and aldehydes in atmospheric aerosol samples

This paper describes a method for the simultaneous determination of monocarboxylic acids (C6-C34), dicarboxylic acids (C2-C24), omega-oxo-carboxylic acids (C2-C9), ketocarboxylic acids (pyruvic and pinonic acid), and select aldehydes (glyoxal, methylglyoxal, and nonanal) in atmospheric particles. Quantification of these compounds gives information on important chemical characteristics of aerosols for source apportioning of aerosol organics and for studying atmospheric processes leading to secondary organic aerosol formation. These target analytes were determined as their butyl ester or butyl acetal derivatives using gas-chromatography mass spectrometry. The method is modified from a method described by Kawamura. Kawamura's original method involved a water extraction step, which practically restricted the method to the determination of only those compounds that are water-soluble. Our method eliminates the water extraction step and combines extraction and derivatization of the target compounds in one step. A mixture of hexane/butanol/BF3 simultaneously derivatizes the polar function groups (i.e., -COOH, -C=O) and extracts the target analytes from the aerosol filter substrates. A prominent advantage of our method is improved recoveries for the more volatile analytes in the target compound classes as a result of eliminating the water evaporation step. Recoveries better than 66% were obtained for the target analytes, including the relatively volatile ones. This improvement for the light species has allowed detection of a new midchain ketocarboxylic acid, 4-oxopentanoic acid, which would have escaped detection by the Kawamura method because of its high susceptibility to evaporative loss. Examples are presented to demonstrate the use of this method in analysis of ambient aerosol samples.     

Use of tuf gene-based primers for the PCR detection of probiotic Bifidobacterium species and enumeration of bifidobacteria in fermented milk by cultural and quantitative real-time PCR methods

Due to the increasing use of bifidobacteria in probiotic products, it is essential to establish a rapid method for the qualitative and quantitative assay of the bifidobacteria in commercial products. In this study, partial sequences of the tuf gene for 18 Bifidobacterium strains belonging to 14 species were determined. Alignment of these sequences showed that the similarities among these Bifidobacterium species were 82.24% to 99.72%. Based on these tuf gene sequences, 6 primer sets were designed for the polymerase chain reaction (PCR) assay of B. animalis subsp. animalis, B. animalis subsp. lactis, B. bifidum, B. breve, B. longum subsp. infantis, B. longum subsp. longum, and the genus of Bifidobacterium, respectively. These Bifidobacterium species are common probiotic species present in dairy and probiotic products. When each target Bifidobacterium spp. was assayed with the designed primers, PCR product with expected size was generated. In addition, for each target species, more than 70 bacterial strains other than the target species, including strains of other Bifidobacterium species, strains of Lactobacillus spp., Enterococcus spp., and other bacterial species, all generated negative results. PCR assay with primers specific to B. animalis subsp. lactis and B. longum subsp. longum confirmed the presence of these Bifidobacterium species in commercial yogurt products. In addition, for each product, enumeration of the bifidobacteria cells by culture method with BIM-25 agar and the quantitative real-time PCR showed similar cell counts. Such results indicated that within 15-d storage (4 °C) after manufacture, all the bifidobacteria cells originally present in yogurt products were viable and culturable during the storage.