Sunday 30 August 2015

Higher peroxidase activity, leaf nutrient contents and carbon isotope composition changes in Arabidopsis thaliana are related to rutin stress

Journal of Plant Physiology
DOI: 10.1016/j.jplph.2014.05.009

Rutin, a plant secondary metabolite that is used in cosmetics and food additive and has known medicinal properties, protects plants from UV-B radiation and diseases. Rutin has been suggested to have potential in weed management, but its mode of action at physiological level is unknown. Here, we report the biochemical, physiological and oxidative response of Arabidopsis thaliana to rutin at micromolar concentrations. It was found that fresh weight; leaf mineral contents (nitrogen, sodium, potassium, copper and aluminum) were decreased following 1 week exposure to rutin. Arabidopsis roots generate significant amounts of reactive oxygen species after rutin treatment, consequently increasing membrane lipid peroxidation, decreasing leaf Ca2+, Mg2+, Zn2+, Fe2+ contents and losing root viability. Carbon isotope composition in A. thaliana leaves was less negative after rutin application than the control. Carbon isotope discrimination values were decreased following rutin treatment, with the highest reduction compared to the control at 750μM rutin. Rutin also inhibited the ratio of CO2 from leaf to air (ci/ca) at all concentrations. Total protein contents in A. thaliana leaves were decreased following rutin treatment. It was concluded carbon isotope discrimination coincided with protein degradation, increase lipid peroxidation and a decrease in ci/ca values may be the primary action site of rutin. The present results suggest that rutin possesses allelopathic potential and could be used as a candidate to develop environment friendly natural herbicide.

Thursday 20 August 2015

Modeling the batch bacteriocin production system by lactic acid bacteria by using modified three-dimensional Lotka-Volterra equations

Biochemical Engineering Journal
DOI: 10.1016/j.bej.2014.04.010

Different batch cultures of Lactococcus lactis CECT 539, a nisin-producing strain, were carried out in culture media prepared with whey and mussel processing wastes. From these cultures, a reasonable system of differential equations, similar to the three-dimensional Lotka-Volterra two predators-one prey model, was set up to describe, for the first time, the relationship between the absolute rates of growth, pH drop and nisin production.Thus, the nisin production system was described as a three-species (pH, biomass and nisin) ecosystem. In this case, both nisin and biomass production were considered as two pH-dependent species that compete for the nitrogen source. Excellent agreement (R2 values ≥0.9885) resulted between model predictions and the experimental data, and significant values for all the model parameters were obtained. The developed model was demonstrated (R2 values ≥0.9874) for five batch cultivations of the strains L. lactis CECT 539 in MRS broth and Lactobacillus sakei LB 706 (sakacin A producer), Pediococcus acidilactici LB42-923 (pediocin AcH producer), L. lactis ATCC 11454 (nisin producer) and Leuconostoc carnosum Lm1 (leuconocin Lcm1 producer) in TGE broth. These results suggest that the batch bacteriocin production system in these culture media can be successfully described by using the Lotka-Volterra approach.

Saturday 15 August 2015

Assessment of potential probiotic properties and multiple bacteriocin encoding-genes of the technological performing strain Enterococcus faecium MMRA

Food Control
DOI: 10.1016/j.foodcont.2013.09.044

In the present study, Enterococcus faecium MMRA, a safety and technological performing strain, previously isolated from a well-known fermented dairy product of Tunisia, was evaluated for certain properties relevant to probiotic including acid and bile tolerance, gastrointestinal juice resistance and adhesive properties. Acidic pH (2.0-5.0) and bile salt concentrations of 0.3% were used as stress conditions. The adhesive properties were assessed by determination of bacterial hydrophobicity. The strain MMRA showed interesting features such as high tolerance to gastrointestinal tract transit, an extremely high survival rates under stress caused by acidic pHs or bile salts, and a high adhesive potential linked to the elevated percentage of hydrophobicity. Furthermore, the genome of this strain was examined for the occurrence of known enterocin (enterococcal bacteriocins) genes by means of specific PCR assays and this study revealed the genes coding for enterocins A, B, P and X. Although the joint production of these bacteriocins has not been verified, producers of multiple enterocins could have a great technological potential as protective and/or probiotic cultures in the food industry. The results suggested that E.faecium MMRA should be considered as a potential probiotic which meets the criteria to enhance healthy attributes of fermented dairy product besides both of hygienic and sensory aspects.