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There are two chemotypes of Litsea cubeba (Lour.) Pers. (fam. Lauraceae) essential oils (EOs), either dominated by citral and limonene or by citronellal. L. cubeba EOs exhibits broad antimicrobial activity against bacteria and fungi with minimal inhibitory concentrations (MICs) from 0.5 to 2500 µg/mL. This antimicrobial activity is attributed to the monoterpene citral, exhibiting a broad antimicrobial spectrum against bacteria and fungi (MICs 50–1000 µg/mL). Pseudomonas aeruginosa were found most resistant, with MIC values above 1000 µg/mL. Citral's mode of action is not fully investigated. At biocidal concentrations, it affects membrane structure and cell respiration, leading to rapid energy depletion and cell death. Involvement of intracellular reactive oxygen species has not been verified. Limonene exhibits insignificant antimicrobial activity. MICs of d-limonene range from 1 to 20 mg/mL. Citral and L. cubeba EOs were also subjects of food application studies. Promising results have been reported for fresh produce or fruit-juice. [ABSTRACT FROM AUTHOR]

Aims The application of broad-spectrum intense light pulses is an innovative nonthermal technology for the decontamination of packaging materials, liquids or foodstuffs. The objective of this study was the fundamental investigation of the cellular impact of a pulsed light treatment on Listeria innocua and Escherichia coli. Methods and Results Flow cytometry in combination with different fluorescent stains, conventional plate count technique and a viability assay were applied to investigate the effects of a pulsed light treatment on the physiological properties of L. innocua and E. coli. The results showed that loss of cultivability occurred at considerably lower fluences than the shutdown of cellular functions such as the depolarization of cell membranes, the loss of metabolic, esterase and pump activities or the occurrence of membrane damage. Therefore, a considerable proportion of cells appeared to have entered the viable but nonculturable ( VBNC) state after the pulsed light treatment. A high percentage of L. innocua was able to maintain certain cellular vitality functions after storage overnight, whereas a further decrease in vitality was observed in case of E. coli. The loss of culturability was on the other hand directly accompanied by the formation of reactive oxygen species ( ROS) and DNA damages, which were assessed by the ROS-sensitive probe DCFH- DA and RAPD- PCR, respectively. Conclusions A significant discrepancy between conventional plate counts and different viability staining parameters was observed, which shows that a pulsed light treatment does not cause an immediate shutdown of vitality functions even when the number of colony-forming units already decreased for more than 6 log10 sample−1. Oxidative stress with concomitant damage to the DNA molecule showed to be directly responsible for the loss of cultivability due to pulsed light rather than a direct rupture of cell membranes or inactivation of intracellular enzymes. Significance and Impact of the Study The presented results suggest an UV light-induced photochemical rather than a photothermal or photophysical inactivation of bacterial cells by pulsed light under the applied experimental conditions. Flow cytometry in combination with different viability stains proved to be a suitable technique to gain deeper insight into the cellular response of bacteria to inactivation processes like a pulsed light treatment. [ABSTRACT FROM AUTHOR]

To investigate the effect of a cascaded dielectric barrier discharge (CDBD) treatment on the biological structure of a selected bacterium and on the properties of different polymer films. Inactivation kinetics were measured using air as the process gas and using Bacillus atrophaeus spores and vegetative cells, which had been homogeneously distributed on a surface. The changes to the outer coats and the DNA of the endospores and cells after plasma treatment were determined using biomolecular and chemical methods. The experiments showed that damage to the DNA molecules and changes in the cell walls can be observed as a consequence of the CDBD treatment. Furthermore, the influence of the plasma treatment on the properties of various polymer films was investigated using a variety of test methods. Except the sealing strength where a slight decrease was observed (max. 20%), no negative changes of the material properties have occurred. CDBD treatment can affect the DNA of spores and cells, depending on the treatment time. At the same time, practically relevant inactivation rates on packaging materials were observed, without any significant changes to the material properties. Knowledge about CDBD mechanisms was acquired from a biological point of view, and the suitability of the method for treating polymer films was demonstrated. [ABSTRACT FROM AUTHOR]

Aims: Development and evaluation of an antimicrobially active titanium dioxide coating. Methods and results: For this purpose, titanium dioxide coatings were applied to glass slides by using a sol-gel method and then exposed to a light source. The antimicrobial efficiency was determined by a count reduction test for selected test strains ( Aspergillus niger, Bacillus atrophaeus, Kocuria rhizophila), which were homogenously sprayed onto surface. The bacterial count of K. rhizophila was reduced by up to 3·3 log10 on titanium dioxide samples within 4 h of UV-A light exposure. Experiments with spore formers did not lead to any significant log reduction. A further aspect of this work was to evaluate the effect of selected parameters (relative humidity, inoculation density, radiation intensity) on the antimicrobial efficiency to gain knowledge for further optimization procedures. At a high relative humidity (85% r.h.), increased inactivation was observed for K. rhizophila (up to 5·2 log10). Furthermore, a dependency of the antimicrobial effect on the radiation intensity and the inoculation density was identified. Conclusions: Antimicrobial surfaces and coatings based on titanium dioxide have the potential to effectively inactivate vegetative micro-organisms. Significance and impact of the study: Knowledge about the antimicrobial efficiency of titanium dioxide was gained. This is a prerequisite for industrial applications to improve hygiene, food quality and safety. [ABSTRACT FROM AUTHOR]

Aims: To investigate the effect of relative gas humidity on the inactivation efficiency of a cascaded dielectric barrier discharge (CDBD) in air against Aspergillus niger and Bacillus subtilis spores on PET foils. Methods and Results: The inactivation kinetics as a function of treatment time were determined using synthetic air with different relative humidity as the process gas. Spores of A. niger and B. subtilis respectively were evenly sprayed on PET foils for use as bioindicators. In the case of A. niger, increased spore mortality was found at a high relative gas humidity of 70% (approx. 2 log10). This effect was more evident at prolonged treatment times. In contrast, B. subtilis showed slightly poorer inactivation at high gas humidity. Conclusions: Water molecules in the process gas significantly affect the inactivation efficiency of CDBD in air. Significance and Impact of the Study: Modifying simple process parameters such as the relative gas humidity can be used to optimize plasma treatment to improve inactivation of resistant micro-organisms such as conidiospores of A. niger. [ABSTRACT FROM AUTHOR]

Aims: To investigate the microbial inactivation efficiency of a newly developed cascaded dielectric barrier discharge (CDBD) set-up against various micro-organisms on polyethylene terephthalate (PET) foils. Methods and Results: Inactivation kinetics in dependency of time were produced with air as process gas and test strains like Salmonella serotype Mons, Staphylococcus aureus and Escherichia coli and spores of Bacillus atrophaeus, Aspergillus niger and Clostridium botulinum, which were homogeneously distributed on the sample surface by a spray method. Highest count reduction was observed for the vegetative cells with at least 6·6 log10 within 1 s. Aspergillus niger was the most resistant test strain with an inactivation rate of about 5 log10 in 5 s. Conclusions: For industrial applications it is necessary to evaluate new sterilization methods against a broad range of different micro-organisms. Significance and Impact of the Study: CDBD plasma is a fast and effective technology for decontamination of heat sensitive materials in few seconds. [ABSTRACT FROM AUTHOR]

The impact of the fluence regulation on the inactivation efficiency of pulsed light (PL) surface disinfection treatments was investigated. E. coli and L. innocua were exposed to PL on a gel surface under variation of the applied voltage, the number of light flashes as well as the distance between the flash lamp and the sample surface. The results revealed deviations from the reciprocity law when the total fluence striking the sample surface was not applied at once, but subdivided into several successive light flashes. No differences were found when the fluence was delivered with only single light flashes, irrespective of the applied voltage. The pulse frequency did not have an impact on the microbial reduction within 1–5 Hz. Furthermore, the sensitivities of various bacterial strains, endospores and conidiospores were compared. Differences occurred for vegetative bacteria without a clear pattern, while bacterial endospores were more resistant. Dark pigmented mold spores were slightly more resistant than bacterial endospores. All dose-response curves exhibited a downward concavity, except for P. aeruginosa . Industrial relevance This study shows that the inactivation of bacteria on e.g. food surfaces by pulsed light systems depends on the way of fluence dosage. While it is irrelevant whether the fluence is regulated by the discharge voltage or the distance between the flash lamp and the treated surface, it is more effective to apply only single light flashes of high fluence instead of several consecutive light flashes. There is furthermore no distinct trend regarding the sensitivity of bacteria to PL, variations occur on species and strain level. Bacterial spores are in general more resistant while pigmented conidiospores show a slightly higher resistance than bacterial endospores. [ABSTRACT FROM AUTHOR]

Nonthermal disinfection technologies are gaining increasing interest in the field of minimally processed food in order to improve the microbial safety or to extend the shelf life. Especially fresh-cut produce or meat and fish products are vulnerable to microbial spoilage, but, due to their sensitivity, they require gentle preservation measures. The application of intense light pulses of a broad spectral range comprising ultraviolet, visible and near infrared irradiation is currently investigated as a potentially suitable technology to reduce microbial loads on different food surfaces or in beverages. Considerable research has been performed within the last two decades, in which the impact of various process parameters or microbial responses as well as the suitability of pulsed light (PL) for food applications has been examined. This review summarizes the outcome of the latest studies dealing with the treatment of various foods including the impact of PL on food properties as well as recent findings about the microbicidal action and relevant process parameters. [ABSTRACT FROM AUTHOR]

This study evaluated the Pulsed Light technology (PL) for its efficiency to reduce the microbial loads on mung bean sprouts and endive salad during a simulated wash process for up to 60 s. The microbicidal action of PL proved to be more efficient than the sanitizers electrolyzed water (40 ppm free chlorine) and chlorine dioxide (15 ppm) within the same treatment time. Reductions of the microbial count up to 2.5 log were found in case of PL treated endive salad while both sanitizers only caused maximum reductions by about 1.5 log. A combination of PL and sanitizers did not have pronounced additional effect for both endive salad and mung bean sprouts. Overall, the decontamination treatments were more effective in case of endive salad compared to mung bean sprouts. It was also shown that the microbial loads in the washing water may be kept on a low level during PL treatments as count reductions of approx. 3 log were found in relation to simply washing in tap water. This study reveals that PL may be a suitable approach to reduce microbial hazards of industrially manufactured fresh produce. The application during the washing process not only reduces microbial loads on the product surface but also efficiently inactivates suspended microorganisms in the wash water and may therefore be an alternative to sanitizers for the prevention of cross contaminations. [ABSTRACT FROM AUTHOR]

Aims The objective of this study was a comprehensive characterization of physiological changes of Salmonella enterica induced by intense broad spectrum pulsed light (PL). After exposing the bacteria to this nonthermal decontamination technology on a gel surface, multiple viability parameters beyond culturability were assessed. Methods and Results By applying flow cytometry, a luciferin-luciferase bioluminescence assay and a microplate assay to measure the current redox activity, the impact of pulsed light on the membrane potential, membrane integrity, esterase activity, efflux pump activity, expression of the green fluorescent protein (GFP), respiration activity and ATP-content of Salm. enterica ATCC BAA-1045 was determined. These culture-independent methods for assessing the bacterial activity were compared to the ability to grow on tryptic soy agar. It is shown that this strain is rather sensitive to PL considering colony count reductions, while on the other hand unculturable bacteria still exhibit significant cellular energetic functions. However, this residual activity after PL exposure significantly decreases during sample storage in buffer for 24 h. This study also shows that the GFP expression of PL-treated cells which have rendered unculturable is severely reduced. Conclusions This study reveals that although not all cellular functions of Salm. enterica are immediately shut down after PL exposure, the synthesis of new GFP is strongly reduced and affected to a similar extent as the culturability. Significance and Impact of the Study It is shown for the first time, that even there is significant bacterial activity measurable after PL exposure, it is likely that nongrowing pathogenic bacteria like Salm. enterica are unable to express proteins, which is of great importance regarding their pathogenicity. [ABSTRACT FROM AUTHOR]

Aims Pulsed light ( PL) is an upcoming nonthermal decontamination technology mainly used for surface sterilization. The objective of this study was to investigate the extent of cellular damage caused by PL treatments of Listeria innocua and Escherichia coli on a polysaccharide surface in order to gain knowledge about the main inactivation pathways. Methods and Results The impact of PL on the cellular ATP level was investigated as well as the bacterial ability to take up fluorescently labelled glucose (2- NBDG). Furthermore, the extent of DNA damages was assessed by qPCR. The ability of L. innocua and E. coli to photorepair under artificial daylight exposure was quantified. Finally, the induction of reactive oxygen species ( ROS) and lipid peroxidation were studied by fluorometric detection of ROS and thiobarbituric acid reactive substances ( TBARS). It is shown that intracellular ATP levels and glucose uptake ability do not correlate with the immediate loss of bacterial reproducibility, which indicates that cellular activity and energy may remain on a relatively high level, although growth on tryptic soy agar is not observable. Sequence specific investigation of PL induced DNA damages by qPCR revealed distinct differences between L. innocua and E. coli although the observed inactivation efficacy of PL by the culture based method was similar. Photoreactivation has been observed for both bacteria, a higher recovery rate of up to 2 log was seen in case of E. coli. Intracellular ROS and lipid peroxides were both detectable at relatively high fluencies with E. coli so the contribution of oxidative damage to microbial inactivation of PL cannot be excluded. Conclusions Escherichia coli as well as L. innocua cells have proven to maintain residual cellular activity after having been exposed to PL even when they are not able to reproduce any more. High proportions of sublethal damages were also obvious with regard to occurring photoreactivation. The destruction of bacterial DNA seems to be the primary mechanism of inactivation of PL but the involvement of other factors like oxidative stress cannot be excluded. Significance and Impact of the Study The observed data underline that bacteria are not immediately inactivated after exposure to PL as different indicators of cellular energy are still detectable even when cells do not reproduce on solid media any more. DNA is the primary target of PL, but as the extent of damage among different bacteria may not reveal their actual sensitivity, other destructive effects should also be considered. [ABSTRACT FROM AUTHOR]

The objective of this study was the determination of the efficiency of pulsed light (PL) treatments for the decontamination of endive salad and mung bean sprouts, as well as the assessment of quality changes in relation to discoloration and alteration of respiration activity. Produce samples were artificially inoculated with two bacterial test strains Escherichia coli (DSM 498) and Listeria innocua (DSM 20649) and exposed to PL at different energy doses. The inactivation efficiency with regard to the naturally occurring microbiota was also investigated. Besides microbiological investigations, color changes were determined as well as the produce respiration during chilled storage. The results indicated that inactivation of more than 2 log was possible with one flash in the case of fresh-cut salad, while the reduction on mung bean sprouts was limited to approximately 1.6 log with one flash, irrespective if the natural flora or inoculated E. coli or L. innocua were considered. The UV part of the PL proved to be exclusively responsible for the inactivation of microorganisms. Significant lower levels of microbial counts of treated compared with untreated samples were maintained for up to 6 days. In the case of endive salad, a dose-dependent progressive discoloration and increase in respiration was diminished by applying optical bandpass filters, which only slightly affected the inactivation efficiency. In contrast, PL treatments showed a positive effect on color and general appearance of mung bean sprouts, while the respiration was almost unaffected. However, care must be taken with regard to efficiency-limiting matrix effects and impact on food quality. These aspects have to be assessed for each treated product. The integration of PL in industrial food processing plants could be an alternative way to improve the microbial quality of fresh produce, and therefore have a positive impact on public health by reducing the risk of contaminations with pathogenic bacteria. [ABSTRACT FROM AUTHOR]

Aims: In case of biological hazards and pandemics, personal protective equipment of rescue forces is currently manually decontaminated with harmful disinfectants, primarily peracetic acid. To overcome current drawbacks regarding supply, handling and disposal of chemicals, the use of plasma processed air (PPA) represents a promising alternative for surface decontamination on site. In this study, the sporicidal efficiency of a portable plasma system, designed for field applications, was evaluated. Methods and Results: The developed plasma device is based on a dielectric barrier discharge (DBD) and operated with ambient air as process gas. PPA from the plasma nozzle was flushed into a treatment chamber (volume: 300 l) and bacterial endospores (Bacillus subtilis and Bacillus atrophaeus) dried on different surfaces were treated under variable conditions. Reductions in spores by more than 4 log10 were found within 3 min of PPA exposure. However, the presence of endospores in agglomerates or in an organic matrix as well as the complexity of the respective surface microstructure negatively affected the inactivation efficiency. When endospores were embedded in a dried protein matrix, mechanical wiping with swabs during exposure to PPA increased the inactivation effect significantly. Gaseous ozone alone did not provide a sporicidal effect. Significant spore inactivation was only obtained when water vapour was injected into the PPA stream. Conclusion: The results show that endospores dried on surfaces can be reduced by several orders of magnitude within few minutes in a treatment chamber which is flushed with PPA from of a DBD plasma nozzle. Significance and Impact of the Study: Plasma processed air generated on site by DBD plasma nozzles could be a suitable alternative for the disinfection of various surfaces in closed rooms. [ABSTRACT FROM AUTHOR]

Aims The objective of this study was the fundamental investigation of the antimicrobial efficiency of various hop extracts against selected foodborne pathogens in vitro, as well as their activity against Listeria monocytogenes in a model meat marinade and on marinated pork tenderloins. Methods and Results In a first step, the minimum inhibitory concentrations ( MIC) of three hop extracts containing either α- or β-acids or xanthohumol were determined against test bacteria including L. monocytogenes, Staphylococcus aureus, Salmonella enterica and Escherichia coli by a colorimetric method based on the measurement of bacterial metabolic activity. Moreover, the influence of either lactic or citric acid on the antimicrobial activity of the hop extracts was evaluated. The efficiency of hop extracts as a natural food preservative was then tested in a model meat marinade at 2 and 8°C, respectively, and finally on marinated pork. The experiments showed that Gram-positive bacteria were strongly inhibited by hop extracts containing β-acids and xanthohumol ( MIC values of 6·3 and 12·5 ppm, respectively), whereas the antimicrobial activity of the investigated α-acid extract was significantly lower ( MIC values of 200 ppm). Gram-negative bacteria were highly resistant against all tested hop extracts. Acidification of the test media led to a decrease of the MIC values. The inhibitory activity of the hop extracts against L. monocytogenes was strongly reduced in a fat-containing model meat marinade, but the efficiency of β-acids in this matrix could be increased by lowering pH and storage temperatures. By applying 0·5 % β-acids at pH = 5 in a model marinade, the total aerobic count of pork tenderloins was reduced up to 0·9 log10 compared with marinated pork without hop extract after 2 weeks of storage at 5°C. Conclusions β-acid containing hop extracts have proven to possess a high antimicrobial activity against Gram-positive bacteria in vitro and in a practice-related application for food preservation. Significance and Impact of the Study Antimicrobial hop extracts could be used as natural preservatives in food applications to extend the shelf life and to increase the safety of fresh products. [ABSTRACT FROM AUTHOR]

Contamination of cold cuts with Listeria monocytogenes pose a risk to human health and frequently cause recalls of affected products. In order to avoid chemical additives for the preservation of ready-to-eat meat products, plant based antimicrobials are currently in demand. Beta acids from the hop plant are known for their strong antimicrobial effects especially against gram-positive bacteria like L. monocytogenes, making them a promising candidate as a functional ingredient. In this study, the antimicrobial activity of a beta acid rich hop extract in combination with sodium nitrite was characterized in vitro, at which the different hurdles of packaged cured boiled sausages were simulated. A complete growth inhibition of L. monocytogenes was found at a minimum inhibitory concentration of 0.2 μg/ml (MIC) when the hop extract was applied in combination with a reduced water activity (a w 0.970), a slightly acidic environment (pH 6) and anaerobic conditions. Under optimal growth conditions (a w 0.995, pH 7, aerobic incubation), the MIC was 16-fold higher (3.2 μg/ml). Sodium nitrite showed a comparably low antimicrobial activity against L. monocytogenes in vitro (MIC > 100 μg/ml). The presence of 1% sunflower oil negatively affected the antimicrobial activity of the hop extract, leading at least to a 32-fold increase of the MIC. The hop extract was subsequently added to a standard recipe of pork bologna at two concentrations. The pork bologna was produced by use of two different cutter processes and then sliced, inoculated on the surface with a two strain mixture of L. monocytogenes and stored at 7 °C under modified gas atmosphere for 28 days. At 0.4 g/kg of hop extract, L. monocytogenes populations were reduced up to 3 orders of magnitude in relation to bologna without hop extract while 0.8 g/kg of hop extract either prevented the growth of L. monocytogenes or resulted in at least 4 orders of magnitude lower final populations. There was no significant sensory deviation of hop bologna according to performed triangle tests (α = 0.05) and the product color remained unaffected. Based on the presented results, the use of beta acid rich hop extracts can be proposed as an additional hurdle to inhibit the propagation of L. monocytogenes on packaged ready-to-eat cold cuts like bologna. • Hurdle concept increases antimicrobial effect of hop extract. • Hop extract in bologna prevents growth of Listeria monocytogenes. • Hop extract could be used as functional ingredient in bologna. [ABSTRACT FROM AUTHOR]

Abstract: Experiments on laboratory scale carried out by use of different microwave-driven plasma sources proved that low-pressure plasmas represent an excellent means to efficiently sterilise materials for all kind of applications. Based on experimental results obtained for four different test spores, more detailed experiments on Bacillus subtilis with initial contaminations between 106 and 107 spores and varying spore densities were carried out showing the adaptability of the process parameters microwave power, continuous wave and pulsed power supply, and distance between plasma source and substrate to the individual requirements of the aspired sterilisation process. Spore reduction kinetics reproduced by a low-pressure microwave plasma source designed for industrial applications demonstrated the easy scalability of this plasma sterilisation technique. [Copyright &y& Elsevier]

The emission of UV light as well as chemical reaction in plasmas allow them to be used for decontamination of food packaging. Sterilization efficiency of different dielectric barrier discharge (DBD) setups at atmospheric pressure was investigated for spores of B. subtilis and A. niger sprayed onto PET foils. In normal DBDs the efficiency of spore reduction in different gases (nitrogen, argon, synthetic air) can be related to the UV spectra of these gases in the discharge. With special so-called cascaded dielectric barrier discharges (CDBDs) a fast reduction of viable cells by more than four orders of magnitude is possible within few seconds, even for UV resistant cells. The sealing properties of commonly used PE-PET-laminate can be maintained in CDBD which is not observed for single-gap DBD. [ABSTRACT FROM AUTHOR]