Fate of Listeria monocytogenes during freezing,thawing and home storage of frankfurters

Little information is available regarding the fate of Listeria monocytogenes during freezing, thawing and home storage of frankfurters even though recent surveys show that consumers regularly store unopened packages in home freezers. This study examined the effects of antimicrobials, refrigerated storage, freezing, thawing method, and post-thawing storage (7 °C) on L. monocytogenes on frankfurters. Inoculated (2.1 log CFU/cm²) frankfurters formulated without (control) or with antimicrobials (1.5% potassium lactate plus 0.1% sodium diacetate) were vacuum-packaged, stored at 4 °C for 6 or 30 d and then frozen (−15 °C) for 10, 30, or 50 d. Packages were thawed under refrigeration (7 °C, 24 h), on a countertop (23 ± 2 °C, 8 h), or in a microwave oven (2450 MHz, 1100 watts, 220 s followed by 120 s holding), and then stored aerobically (7 °C) for 14 d. Bacterial populations were enumerated on PALCAM agar and tryptic soy agar plus 0.6% yeast extract. Antimicrobials completely inhibited (p < 0.05) growth of L. monocytogenes at 4 °C for 30 d under vacuum-packaged conditions, and during post-thawing aerobic storage at 7 °C for 14 d. Different intervals between inoculation and freezing (6 or 30 d) resulted in different pathogen levels on control frankfurters (2.1 or 3.9 log CFU/cm², respectively), while freezing reduced counts by <1.0 log CFU/cm². Thawing treatments had little effect on L. monocytogenes populations (<0.5 log CFU/cm²), and post-thawing fate of L. monocytogenes was not influenced by freezing or by thawing method. Pathogen counts on control samples increased by 1.5 log CFU/cm² at d-7 of aerobic storage, and reached 5.6 log CFU/cm² at d-14. As indicated by these results, consumers should freeze frankfurters immediately after purchase, and discard frankfurters formulated without antimicrobials within 3 d of thawing and/or opening.     

Oxidation of fluoroquinolone antibiotics and structurally related amines by chlorine dioxide: Reaction kinetics, product and pathway evaluation

Fluoroquinolones (FQs) are a group of widely prescribed antibiotics and have been frequently detected in the aquatic environment. The reaction kinetics and transformation of seven FQs (ciprofloxacin (CIP), enrofloxacin (ENR), norfloxacin (NOR), ofloxacin (OFL), lomefloxacin (LOM), pipemidic acid (PIP) and flumequine (FLU)) and three structurally related amines (1-phenylpiperazine (PP), N-phenylmorpholine (PM) and 4-phenylpiperidine (PD)) toward chlorine dioxide (ClO₂) were investigated to elucidate the behavior of FQs during ClO₂ disinfection processes. The reaction kinetics are highly pH-dependent, can be well described by a second-order kinetic model incorporating speciation of FQs, and follow the trend of OFL > ENR > CIP ∼ NOR ∼ LOM > > PIP in reactivity. Comparison among FQs and related amines and product characterization indicate that FQs’ piperazine ring is the primary reactive center toward ClO₂. ClO₂ likely attacks FQ’s piperazinyl N4 atom followed by concerted fragmentation involving piperazinyl N1 atom, leading to dealkylation, hydroxylation and intramolecular ring closure at the piperazine moiety. While FQs with tertiary N4 react faster with ClO₂ than FQs with secondary N4, the overall reactivity of the piperazine moiety also depends strongly on the quinolone ring through electronic effects. The reaction rate constants obtained in clean water matrix can be used to model the decay of CIP by ClO₂ in surface water samples, but overestimate the decay in wastewater samples. Overall, transformation of FQs, particularly for those with tertiary N4 amines, could be expected under typical ClO₂ disinfection conditions. However, the transformation may not eliminate antibacterial activity because of little destruction at the quinolone ring.     

Possibilities and impossibilities of magnetic nanoparticle use in the control of infectious biofilms

Targeting of chemotherapeutics towards a tumor site by magnetic nanocarriers is considered promising in tumor-control. Magnetic nanoparticles are also considered for use in infection-control as a new means to prevent antimicrobial resistance from becoming the number one cause of death by the year 2050. To this end, magnetic nanoparticles can either be loaded with an antimicrobial for use as a delivery vehicle or modified to acquire intrinsic antimicrobial properties. Magnetic nanoparticles can also be used for the local generation of heat to kill infectious microorganisms. Although appealing for tumor-and infectioncontrol, injection in the blood circulation may yield reticuloendothelial uptake and physical obstruction in organs that yield reduced targeting efficiency. This can be prevented with suitable surface modification. However, precise techniques to direct magnetic nanoparticles towards a target site are lacking. The problem of precise targeting is aggravated in infection-control due to the micrometer-size of infectious biofilms, as opposed to targeting of nanoparticles towards centimeter-sized tumors. This review aims to identify possibilities and impossibilities of magnetic targeting of nanoparticles for infection-control. We first review targeting techniques and the spatial resolution they can achieve as well as surface-chemical modifications of magnetic nanoparticles to enhance their targeting efficiency and antimicrobial efficacy.It is concluded that targeting problems encountered in tumor-control using magnetic nanoparticles, are neglected in most studies on their potential application in infection-control. Currently biofilm targeting by smart, self-adaptive and pH-responsive, antimicrobial nanocarriers for instance, seems easier to achieve than magnetic targeting. This leads to the conclusion that magnetic targeting of nanoparticles for the control of micrometer-sized infectious biofilms may be less promising than initially expected.However, using propulsion rather than precise targeting of magnetic nanoparticles in a magnetic field to traverse through infectious-biofilms can create artificial channels for enhanced antibiotic transport.This is identified as a more feasible, innovative application of magnetic nanoparticles in infection-control than precise targeting and distribution of magnetic nanoparticles over the depth of a biofilm.     

Nanoemulsion as advanced edible coatings to preserve the quality of fresh-cut fruits and vegetables: a review

The increasing consumer's demand regarding the healthy diet has promoted the research towards novel approaches for preserving minimally processed fruits and vegetables without the necessity of using preservatives. Emulsion-based edible coatings technology is considered a valuable alternative to improve fresh-cut fruit and vegetable quality. This review discusses some recent advances for the preservation of the quality and safety of fresh-cut fruits and vegetables with respect to the use of nanoemulsion-based edible coatings as carrier of functional compounds such as antimicrobial agents, antioxidants and texture enhancers. It focuses especially on the use of natural functional compounds in food preservation as an alternative to synthetic additives. Moreover, the preparation and characterisation of nanoemulsion are also reviewed.     

Development and evaluation of self-polishing urethane coatings with tethered quaternary ammonium biocides

The synthesis and characterization of hydrolysable, antimicrobial cross-linked polyurethanes are described. Cross-linking of isocyanate-terminated urethane oligomers with glycol-modified silanes was used as a novel method for imparting enhanced mechanical integrity and hydrolytic potential to polyurethane coating systems. By combining these cross-linkers with a variety of biocidal quaternary ammonium salts and polyisocyanates, a library of hydrolysable polyurethanes were developed with controllable mechanical, thermal, hydrolytic, and antimicrobial properties. Up to a 3-log reduction of viable microbes was observed and correlated with the surface content of side chain quaternary ammonium salt moieties. Diminished antibacterial characteristics of completely amorphous systems are attributed to the segregation of low surface energy constituents at the material:air interface and relegation of biocidal species to within the bulk material.     

Catalytic behavior of the Fe/Fe system in the electro-Fenton degradation of the antimicrobial chlorophene

The catalytic behavior of the Fe³⁺/Fe²⁺ system in the electro-Fenton degradation of the antimicrobial drug chlorophene has been studied considering four undivided electrolytic cells, where a Pt or boron-doped diamond (BDD) anode and a carbon felt or O₂-diffusion cathode have been used. Chlorophene electrolyses have been carried out at pH 3.0 under current control, with 0.05 M Na₂SO₄ as supporting electrolyte and Fe³⁺ as catalyst. In these processes the drug is oxidized with hydroxyl radical (OH) formed both at the anode from water oxidation and in the medium from electrochemically generated Fenton's reagent (Fe²⁺ + H₂O₂, both of them generated at the cathode). The catalytic behavior of the Fe³⁺/Fe²⁺ system mainly depends on the cathode tested. In the cells with an O₂-diffusion cathode, H₂O₂ is largely accumulated and the Fe³⁺ content remains practically unchanged. Under these conditions, the chlorophene decay is enhanced by increasing the initial Fe³⁺ concentration, because this leads to a higher quantity of Fe²⁺ regenerated at the cathode and, subsequently, to a greater OH production from Fenton's reaction. In contrast, when the carbon felt cathode is used, H₂O₂ is electrogenerated in small extent, whereas Fe²⁺ is largely accumulated because the regeneration of this ion from Fe³⁺ reduction at the cathode is much faster than its oxidation to Fe³⁺ at the anode. In this case, an Fe³⁺ concentration as low as 0.2 mM is required to obtain the maximum OH generation rate, yielding the quickest chlorophene removal. Chlorophene is poorly mineralized in the Pt/O₂ diffusion cell because the final Fe³⁺–oxalate complexes are difficult to oxidize with OH. These complexes are completely destroyed using a BDD anode at high current thanks to the great amount of OH generated on its surface. Total mineralization is also achieved in the Pt/carbon felt and BDD/carbon felt cells with 0.2 mM Fe³⁺, because oxalic acid and its Fe²⁺ complexes are directly oxidized with OH in the medium. Comparing the four cells, the highest oxidizing power regarding total mineralization is attained for the BDD/carbon felt cell at high current due to the simultaneous destruction of oxalic acid at the BDD surface and in the bulk solution.     

Multiresidue determination of fluoroquinolone antimicrobials in baby foods by liquid chromatography

According to the current EU legislation, the presence of antimicrobial residues in baby foods is forbidden. Nevertheless, there is a lack of analytical methods to determine veterinary antimicrobials in baby foods and support the zero tolerance policy for this type of foods. This paper describes a simple method based on molecularly imprinted solid phase extraction (MISPE) and liquid chromatography with fluorescence detection (LC-FLD) for the determination of residues of fluoroquinolones (FQs) in baby foods. The method involves sample extraction with a solution of o-phosphoric acid (50 mM, pH 3.0)/ACN (20:80, v/v) and further clean-up by loading the extracts onto MIP cartridges. Optimum MISPE conditions led to recoveries of the target FQs in the range of 92–106%, with RSDs <8%. Method validation has been performed according to Commission Decision 2002/657/EC, in terms of linearity, accuracy, precision, selectivity, decision limit (CC_α) and detection capability (CC_β). The proposed method has been successfully applied to the analysis of baby foods of different compositions bought in local supermarkets and pharmacies. The results did not show the presence of residual amounts of FQs in the analysed samples above the method’s decision limits (CC_α between 5 and 151 μg kg⁻¹).     

Identification of antimicrobial resistant bacteria in rivers: Insights into the cultivation bias

In the present study, the antimicrobial resistant (AR) bacteria were quantified and identified in different river samples using in parallel a culture-based approach and a culture-independent one. The objective was to evaluate the importance of the cultivation bias when studying antimicrobial resistance among environmental bacteria. Three different river samples covering a gradient of anthropic influence were tested and three different antimicrobial compounds were used as selective agents: amoxicillin, tetracycline and sulfamethoxazole. From a quantitative point of view, our results highlight the importance of the culture media used, as for the same sample and the same selective agent significant differences were observed in the counts of culturable AR bacteria depending on the culture media used. The identification of AR bacteria through culture or culture-independent methods put on evidence AR bacterial communities that differ dramatically: γ-proteobacteria and more specifically Aeromonadaceae dominated among the isolates while β-proteobacteria (Comamonadaceae), dominated among the sequences obtained without culture. Altogether these results highlight the necessity to develop a methodological consensus preferably without culture, to approach this important topic in the coming years.     

Application of edible coating with essential oil in food preservation

Abstract

Compared with other types of packaging, edible coatings are becoming more and more popular because of their more environmentally friendly properties and active ingredients carrying ability.

The edible coating can reduce the influence of essential oils (EOs) on the flavor of the product and also can prolong the action time of EOs through the slow-release effect, which effectively promote the application of EOs in food. Understanding the different combinations of edible coatings and EOs as well as their antimicrobial effects on different microorganisms will be more powerful and targeted to promote the application of EOs in real food systems.

The review focus on the contribution of the combination of EOs and edible coatings (EO-edible coatings) to prolong the shelf life of food products, (1) specifically addressing the main materials used in the preparation of EO-edible coatings and the application of EO-edible coatings in the product, (2) systematically summarizing the main production method of EO-edible coatings, (3) discussing the antiseptic activity of EO-edible coatings on different microorganisms in food.     

Fish spoilage bacterial growth and their biogenic amine accumulation: Inhibitory effects of olive by-products

The antimicrobial effects of olive by-products (olive leaf extract, olive cake, and black water) on foodborne pathogens and fish spoilage bacteria isolated from anchovy, mackerel, and sardine were investigated. Total polyphenol contents in olive by-products were determined by the Folin–Ciocalteu procedure and their chemical composition was also evaluated by gas chromatography-mass spectrometry. The minimum inhibitory concentrations of olive by-product were performed using the broth microdilution method. Their impact on bacterial growth and biogenic amine production were also monitored in anchovy infusion decarboxylase broth. The total phenol content of olive cake and black water were 14.9 and 20.9 mg gallic acid/g extract, respectively. The major compounds were ethyl oleate (52.3%) and squalene (22.8%) in olive cake and palmitic acid (12.2%), phenanthrene (11.9%), and linoleic acid (11.4%) in olive leaf, while black water consisted of 51.1% squalene and 17.5% oleic acid ethyl ester. The minimum inhibitory concentration of olive leaf ranged from 0.78 to 25 mg/mL. Bacterial strains were more sensitive to olive leaf than other olive by-products. Bacterial load in anchovy infusion decarboxylase broth did not always correlate well with biogenic amine production. The effect of olive leaf, olive cake, and black water on biogenic amine accumulation varied depending on specific bacterial strains and biogenic amine. Olive cake and olive leaf generally had a stronger effect on reducing histamine accumulation by bacteria. Therefore, the results showed the potential effect of olive by-products in preventing or reducing the accumulation of histamine, which may beneficially affect human health.