Tea extract render probiotic Lactobacillus helveticus more resistant to oxygen exposure through lipid modification mechanism

Exposure to oxygen can cause a decrease in growth rates or a complete inhibition of growth of oxygen-sensitive probiotic bacteria. A recent study in our laboratory demonstrated that the growth of an oxygen-sensitive strain, Lactobacillus helveticus, was stimulated, under aerobic conditions, when the culture medium was enriched with green tea extracts (GTE). However, information on the mechanism by which GTE influenced the growth, in the presence of oxygen, of that strain is limited. In the present work, the effects of GTE concentrations (0 to 2000 μg/mL) and exposure to oxygen on maximal populations of L. helveticus R0052 cells and bacterial lipids were evaluated using viable counts, infrared spectroscopy and gas chromatography analyses. Supplementation of the culture medium with 0 to 500 μg/mL GTE did not have an effect on the populations reached under microaerophilic conditions and on bacterial lipid structure and composition. However, at 2000 μg/mL GTE, high population levels were reached under microaerophilic conditions concomitant with an increase in lipid order and with important changes in fatty acid composition of the bacterial lipids. Interactions between GTE components and bacterial lipids were shown by spectroscopic results. Moreover, bacterial cells have adapted to the presence of 2000 μg/mL GTE in the growth medium by changing their lipid composition. To the best of our knowledge, this work is the first to establish a relationship between the effects of GTE at 2000 μg/mL on bacterial cell's lipids and a stimulation of growth under microaerophilic conditions of an oxygen-sensitive strain.     

Probiotic biological strategies to decontaminate aflatoxin M1 in a traditional Iranian fermented milk drink (Doogh)

Aflatoxin M₁ is an important mycotoxin mostly found in milk and dairy products. The main objective of this work was to study the effects of probiotic strains, a probiotic inoculated population, the physiology of probiotic bacteria and final fermentation pH at four consecutive stages on the reduction of 0.500 ppb of free aflatoxin M₁ (AFM₁) in Doogh (a traditional Iranian fermented milk drink). Samples’ biochemical, microbial and AFM₁ binding characteristics were monitored during fermentation and storage (5 °C for 28 days). An immunoaffinity column was used to extract AFM₁ and a high-performance liquid chromatograph with a fluorescence detector was used to measure it. Results showed that Lactobacillus acidophilus was probiotic strain that most reduced free AFM₁. Inoculation of L. acidophilus at 9 log cfu/mL, despite the higher cost, revealed significantly higher free AFM₁ binding capacity than 7 log cfu/mL. Heat-killed (dead) L. acidophilus bacteria reduced less free AFM₁ at the end of storage than viable. Samples with a final fermentation pH of 4.5 bound more free AFM₁ during fermentation and storage than those with a pH of 4.2. It is concluded that inoculation of 7 log cfu/mL L. acidophilus viable cells in Doogh with a final fermentation pH of 4.5 supplied a safety- and health-promoting and cost-effective drink.     

Growth of Escherichia coli,Salmonella enterica and Listeria spp., and their inactivation using ultraviolet energy and electrolyzed water,on ‘Rocha’ fresh-cut pears

The present study aimed at evaluating the growth of Escherichia coli, Salmonella enterica, and Listeria spp. and studying the efficacy of Ultraviolet-C (UV-C) irradiation, acidic electrolyzed (AEW) and neutral electrolyzed (NEW) waters in the reduction of these bacteria on ‘Rocha’ pear. Fresh-cut pieces were inoculated and incubated at 4–20 °C for 8 days. Inoculated pears were treated with UV-C (2.5–10 kJ/m²), AEW, NEW and sodium hypochlorite (SH) and microbiological and quality parameters were evaluated. The three bacteria, inoculated at 6.1–6.2 log cfu/g, grew on the pear at high growth rates at 12 and 20 °C reaching populations of 8.1–8.6 log cfu/g, in 24 h. At 8 °C the microorganisms increased their populations by at least 1 log cfu/g in three days. At 4 °C adaptation phases of less than 24 h for Listeria spp. were measured before exponential growth occurred and the enterobacteria did not grow despite having survived for 8 days. AEW and NEW caused microbial reductions similar to SH, of approximately 1 log cfu/g, while the best UV-C dose (7.5 kJ/m²) of at least 2.4 log cfu/g. Fresh-cut pears were a good substrate for foodborne bacteria emphasizing the importance of preventing contaminations and cross contaminations. The UV-C was more effective than the chemical decontaminations, as it provided superior microbial reductions without greatly affecting the quality of pears.     

Esterase activity inspired selection and characterization of zearalenone degrading bacteria Bacillus pumilus ES-21

Zearalenone (ZEN), mainly produced by Fusarium species, is an estrogenic mycotoxin which causes reproductive disorders in livestock. In this study, we described a simple and rapid method for screening of ZEN-degrading bacteria by esterase activity assay. Soil bacteria strains were first tested for their esterase activities, then active strains were further evaluated for their ZEN-degrading potentials. A bacterial strain named Bacillus pumilus ES-21 was detected to be able to eliminate ZEN in the culture medium. ZEN degradation conditions were optimized through response surface methodology and the result showed that the degradation rate of ZEN by Bacillus pumilus ES-21 was up to 95.7% at the ZEN concentration of 17.9 μg/ml within 24 h. One of the degradation product was proposed to be 1-(3,5-dihydroxyphenyl)-6′-hydroxy-l′-undecen-l0′-one according to LC-TOF-MS/MS analysis. This study provided a strategy for the isolation of ZEN degrading microbes and a promising degrading strain.     

Experimental approaches for the estimation of uncertainty in analysis of trace inorganic contaminants in foodstuffs by ICP-MS

Total Diet Studies to estimate dietary exposure to food contaminants need to evaluate laboratory measurements data variance. In this process it is critical that data from analytical methods are reliable to correctly scrutinize and compare values over time and between countries. In Europe it is widely recognized that the evaluation of measurement uncertainty is an important parameter when assessing the sources of analytical data variability. Two approaches are considered to estimate uncertainty in analytical measurement. Arsenic, Lead, Chromium and Cadmium, content in several food matrix determined by Inductively Coupled Mass Spectrometry (ICP-MS) microwave digestion assisted, are used as examples. The aim of the present research work is to compare both approaches accepted by Eurolab and GUM: Mathematical modeling to assess uncertainty components based on a classical model (bottom up) and an empirical method (top down), based on either experimental data obtained from a single laboratory validation data or inter-laboratory data from Proficiency Testing schemes. Relative expanded uncertainty calculated by both approaches agree when U (%) <20%. These values are concordant with RSD_R reported in collaborative studies of EN 15763 (2009), which were assumed as target uncertainty. The top down approach described is simple and easy to use when compared with the mathematical modeling approach providing considerable benefits to those who assess data produced by several laboratories.     

Validation of a Method for Quantitation of Soybean Lectin in Commercial Varieties

Soybean agglutinin (SBA) protein, also known as soybean lectin, is regarded as an anti‐nutrient due to its negative effect on the ability of monogastric animals to gain weight following consumption of raw soybean seed. Historically, SBA has been measured using a time‐consuming and cumbersome hemagglutination procedure. The objective of our research was to obtain a validated methodology that is precise and accurate in the measurement of SBA while allowing minimally equipped laboratories to effectively conduct the analysis, thus our focus was on evaluating an existing commercially available ELISA, an enzyme‐linked‐lectin‐assay (ELLA), and a hybrid ELISA/ELLA. A new ELLA technique that can detect and quantify lectins was chosen and modified specifically for the quantitation of SBA in soybean seed. The proposed ELLA methodology is similar to a standard sandwich ELISA, and uses polyacrylamide‐linked N‐acetylgalactosamine (Gal–NAc–PAA) for a capture phase and the biotinylated version (Gal–NAc–PAA–Biotin) for detection. Based upon the validation data, the ELLA method can precisely and accurately determine soybean lectin levels in soybean seed. The validated ELLA method was used to quantify SBA in nine commercial soybean varieties introduced between 1972 and 2008 and demonstrated that the natural variability of SBA is subject to the effects of genotype and environment.