Combined effect of nisin and carvacrol at different pH and temperature levels on the viability of different strains of Bacillus cereus

Chemical Composition and Phytotoxic and Antibiofilm Activity of the Essential Oils of Two Moroccan Retama Species

This study reports chemical composition, phytotoxic and antibiofilm activities of essential oils (EOs) of R. dasycarpa and R. sphaerocarpa from Morocco. EOs were analyzed by GC/MS and their phytotoxicities were evaluated against germination and seedling growth of Lolium multiflorum, Sinapis alba and Raphanus sativus. The antimicrobial and anti-biofilm activities were studied against Gram-negative (Pseudomonas aeruginosa, Escherichia coli and Acinetobacter baumannii) and Gram-positive bacteria (Staphylococcus aureus and Listeria monocytogenes). Both EOs were abundant in oxygenated monoterpenes (40.01% and 23.57 %, respectively). Carvacrol is the predominant component in R. dasycarpa EO (17.80 %), and it also represents an appreciable amount in R. sphaerocarpa (8.96 %). R. sphaerocarpa showed total inhibition at high doses against all seeds. S. alba seeds were the most sensitive to all EOs. Minimum inhibitory concentration (MIC) values indicated significant inhibition for R. sphaerocarpa, between 24 and 30 μg/mL, with a remarkable antibacterial potential and biofilm formation inhibition. R. sphaerocarpa EO showed significant biofilm inhibition with variable efficacy depending on the strain and concentration, except for S. aureus. R. dasycarpa exhibited activity against all bacterial strains and effect on metabolism with activity also on mature biofilms. Results suggest that Retama EOs could have potential applications in the fields of food and health.

Study on synergistic effects of curcumin and bixin against foodborne pathogens

Various studies have shown that natural colorants, in addition to their coloring attributes, have valuable biological effects such as antioxidant, anti-inflammation, and anticarcinogenic properties. Moreover, their use as a food colorant can restrict the potential disadvantages of synthetic additives and turn foods into functional products. In this study, in vitro antimicrobial activities of two natural colorants of bixin and curcumin against some important foodborne pathogens: Staphylococcus aureus (S. aureus), Listeria innocua (L. innocua), and Escherichia coli (E. coli) were investigated by disk diffusion method. Minimum inhibitory concentration and minimum bactericidal concentration values were determined by agar dilution and broth microdilution methods. The synergistic activity of the colorants against selected microorganisms was assayed by the checkerboard microdilution method. The results showed that the inhibitory effects of bixin against S. aureus were more pronounced than E. coli and L. innocua. The lowest concentration of curcumin (0.6 mg/mL) in the disk diffusion method was not inhibited by any tested bacteria. However, it was effective at the higher concentrations against three microorganisms, but its diameter of inhibition zones was lower than gentamicin in all concentrations. Synergetic effects were observed by curcumin and bixin combination against S. aureus (FICI ≤ 0.5), but they act as an antagonist against E. coli and L. innocua. The results of the synergy test were confirmed by the isobologram curves.

Biodegradable Polymers and Polymer Composites with Antibacterial Properties

Antibiotic resistance is one of the greatest threats to global health and food security today. It becomes increasingly difficult to treat infectious disorders because antibiotics, even the newest ones, are becoming less and less effective. One of the ways taken in the Global Plan of Action announced at the World Health Assembly in May 2015 is to ensure the prevention and treatment of infectious diseases. In order to do so, attempts are made to develop new antimicrobial therapeutics, including biomaterials with antibacterial activity, such as polycationic polymers, polypeptides, and polymeric systems, to provide non-antibiotic therapeutic agents, such as selected biologically active nanoparticles and chemical compounds. Another key issue is preventing food from contamination by developing antibacterial packaging materials, particularly based on degradable polymers and biocomposites. This review, in a cross-sectional way, describes the most significant research activities conducted in recent years in the field of the development of polymeric materials and polymer composites with antibacterial properties. We particularly focus on natural polymers, i.e., polysaccharides and polypeptides, which present a mechanism for combating many highly pathogenic microorganisms. We also attempt to use this knowledge to obtain synthetic polymers with similar antibacterial activity.

Antibacterial and anti-biofilm properties of carvacrol alone and in combination with cefixime against Escherichia coli

BACKGROUND

Plant-derived compounds can be used as antimicrobial agents in medicines and as food preservatives. These compounds can be applied along with other antimicrobial agents to strengthen the effect and/or reduce the required treatment dose.

RESULTS

In the present study, the antibacterial, anti-biofilm and quorum sensing inhibitory activity of carvacrol alone and in combination with the antibiotic cefixime against Escherichia coli was investigated. The MIC and MBC values for carvacrol were 250 μg/mL. In the checkerboard test, carvacrol showed a synergistic interaction with cefixime against E. coli (FIC index = 0.5). Carvacrol and cefixime significantly inhibited biofilm formation at MIC/2 (125 and 62.5 μg/mL), MIC/4 (62.5 and 31.25 μg/mL) and MIC/8 (31.25 and 15.625 μg/mL) for carvacrol and cefixime, respectively. The antibacterial and anti-biofilm potential effect of carvacrol confirmed by the scanning electron microscopy. Real-time quantitative reverse transcription PCR revealed significant down-regulation of the luxS and pfs genes following treatment with a MIC/2 (125 μg/mL) concentration of carvacrol alone and of only pfs gene following treatment with MIC/2 of carvacrol in combination with MIC/2 of cefixime (p < 0.05).

CONCLUSIONS

Because of the significant antibacterial and anti-biofilm activity of carvacrol, the present study examines this agent as an antibacterial drug of natural origin. The results indicate that in this study the best antibacterial and anti-biofilm properties are for the combined use of cefixime and carvacrol.

A review of potential antibacterial activities of nisin against Listeria monocytogenes: the combined use of nisin shows more advantages than single use

Listeria monocytogenes is a foodborne pathogen causing serious public health problems. Nisin is a natural antimicrobial agent produced by Lactococcus lactis and widely used in the food industry. However, the anti-L. monocytogenes efficiency of nisin might be decreased due to natural or acquired resistance of L. monocytogenes to nisin, or complexity of the food environment. The limitation of nisin as a bacteriostatic agent in food could be improved using a combination of methods. In this review, the physiochemical characteristics, species, bioengineered mutants, and antimicrobial mechanism of nisin are reviewed. Strategies of nisin combined with other antibacterial methods, including physical, chemical, and natural substances, and nanotechnology to enhance antibacterial effect are highlighted and discussed. Additionally, the antibacterial efficiency of nisin applied in real meat, dairy, and aquatic products is evaluated and analyzed. Among the various binding treatments, the combination with natural substances is more effective than the combination with physical and chemical methods. However, the combination of nisin and nanotechnology has more potential in terms of the impact on food quality.

A Review of Essential Oils as Antimicrobials in Foods with Special Emphasis on Fresh Produce

ABSTRACT

Consumer safety concerns over established fresh produce washing methods and the demand for organic and clean-label food has led to the exploration of novel methods of produce sanitization. Essential oils (EOs), which are extracted from plants, have potential as clean-label sanitizers because they are naturally derived and act as antimicrobials and antioxidants. In this review, the antimicrobial effects of EOs are explored individually and in combination, as emulsions, combined with existing chemical and physical preservation methods, incorporated into films and coatings, and in vapor phase. We examined combinations of EOs with one another, with EO components, with surfactants, and with other preservatives or preservation methods to increase sanitizing efficacy. Components of major EOs were identified, and the chemical mechanisms, potential for antibacterial resistance, and effects on organoleptic properties were examined. Studies have revealed that EOs can be equivalent or better sanitizing agents than chlorine; nevertheless, concentrations must be kept low to avoid adverse sensory effects. For this reason, future studies should address the maximum permissible EO concentrations that do not negatively affect organoleptic properties. This review should be beneficial to food scientists or industry personnel interested in the use of EOs for sanitization and preservation of foods, including fresh produce.

HIGHLIGHTS

Temperature-Dependent Antimicrobial Activity of Menhaden Fish Oil In Vitro and on Pet Food Kibbles against Salmonella

ABSTRACT

Fish oil inclusion into a dry pet food provides a source of long-chain omega-3 fatty acids. Polyunsaturated fatty acids in fish oil have antibacterial activity against various foodborne pathogens, such as Salmonella and pathogenic Escherichia coli. The purpose of this study was to determine the effect of temperature applied to dry pet food kibbles on the antimicrobial activity of menhaden fish oil against Salmonella spp. Sterile menhaden oil was inoculated with ∼8 log of a Salmonella cocktail (∼3% moisture; Salmonella Enteritidis, Salmonella Heidelberg, and Salmonella Typhimurium) and incubated at 25, 37, and 45°C. Microbiological evaluation of the water phase was done after 2 h on tryptic soy agar. Sterile kibbles were coated with fish oil (7.0%, w/w). Canola oil coating was kept as a control. One hour after coating, the kibbles were inoculated with ∼9 log of Salmonella and incubated at the respective temperature. The microbiological evaluation was conducted at 0, 2, 6, 12, and 24 h. The oil phase of the fish oil system was negative for Salmonella after 2 h of incubation and confirmed by enrichment and PCR. From the water phase, 8.1 and 7.3 log were recovered at 25 and 37°C, respectively, and no Salmonella was detected at 45°C. On the kibble, menhaden oil had higher antimicrobial (P ≤ 0.05) activity after 12 h at 25°C and throughout the experiment at 37°C. At 45°C, the fish oil had a superior antimicrobial activity against the Salmonella cocktail after 2 h. When the fish oil alone was compared at different temperatures, a higher antimicrobial activity was observed at 37 and 45°C across all time points. The results indicate antimicrobial activity of menhaden oil increases with temperature. This is an important finding to the pet food industry: a higher fat holding temperature (∼45°C) and the application process may help mitigate Salmonella on extruded kibbles.

HIGHLIGHTS

Assessment of the Antibacterial Mechanism of Pterostilbene against Bacillus cereus through Apoptosis-like Cell Death and Evaluation of Its Beneficial Effects on the Gut Microbiota

Foods contaminated by harmful substances such as bacteria and viruses have caused more than 200 kinds of diseases, ranging from diarrhea to cancer. Among them, Bacillus cereus (B. cereus) is a foodborne pathogen that commonly contaminates raw meat, fresh vegetables, rice, and uncooked food. The current chemical preservatives may have adverse effects on food and even human health. Therefore, natural antibacterial agents are sought after as alternative preservatives. Stilbene compounds, including pterostilbene (PT), pinostilbene (PS), and piceatannol (PIC), which have many health benefits and exhibit antibacterial activity, were tested against B. cereus. The minimum inhibitory concentrations (MICs) and minimum bactericidal concentrations (MBCs) of PT, PS, and PIC against B. cereus ranged from 25 to 100 μg/mL. From the time-kill curve assay, PT reduced B. cereus cell survival, increased intracellular reactive oxygen species (ROS), and induced apoptosis-like cell death (ALD) in a dose-dependent manner. The quantitative real-time polymerase chain reaction (qPCR) results confirmed that treatment with PT induced genetic changes related to ALD, such as an increase in RecA gene expression and a decrease in LexA gene expression. In addition, PT showed a beneficial effect on the gut microbiota that increased the abundance of Bacteroidetes and lowered the abundance of Firmicutes. Taken together, our results showed that PT has antibacterial effects against B. cereus via ALD and is beneficial for promoting healthy gut microbiota that is worthy for the development of antibacterial agents for the food industry.

Bactericidal effect of marinades on meats against different pathogens: a review

Marinades are seasoned liquids used to improve tenderness, palatability, flavor, color and/or texture of different meats. In addition to contribute to the sensory characteristics, marinates can inactivate food microorganism as well. The purpose of this study was to assess the current state of knowledge regarding the effect of marinades on meats and important food pathogens. Using a systematic review of literature, different types of marinades were evaluated, identifying its ingredients, concentrations, temperature, marinating time and their effect on Salmonella, Escherichia coli, Listeria monocytogenes, Campylobacter and Vibrio. Findings demonstrated that the use of marinades on meats not only prevents the growth of pathogens but also inactivates food pathogens. Most marinades were able to reduce < 3 log CFU/g of pathogens, and Vibrio populations demonstrated the highest reductions (> 4 log CFU/g). The pH was the most pronounced parameter influencing the pathogens inactivation, however, ingredients and storage temperature also affected pathogen reduction in marinades.

Risk of Bacillus cereus in Relation to Rice and Derivatives

Rice is a very popular food throughout the world and the basis of the diet of the citizens of many countries. It is used as a raw material for the preparation of many complex dishes in which different ingredients are involved. Rice, as a consequence of their cultivation, harvesting, and handling, is often contaminated with spores of Bacillus cereus, a ubiquitous microorganism found mainly in the soil. B. cereus can multiply under temperature conditions as low as 4 °C in foods that contain rice and have been cooked or subjected to treatments that do not produce commercial sterility. B. cereus produces diarrhoeal or emetic foodborne toxin when the consumer eats food in which a sufficient number of cells have grown. These circumstances mean that every year many outbreaks of intoxication or intestinal problems related to this microorganism are reported. This work is a review from the perspective of risk assessment of the risk posed by B. cereus to the health of consumers and of some control measures that can be used to mitigate such a risk.

Application of bacteriocins in food preservation and infectious disease treatment for humans and livestock: a review

Infectious diseases caused by bacteria that can be transmitted via food, livestock and humans are always a concern to the public, as majority of them may cause severe illnesses and death. Antibacterial agents have been investigated for the treatment of bacterial infections. Antibiotics are the most successful antibacterial agents that have been used widely for decades to ease human pain caused by bacterial infections. Nevertheless, the emergence of antibiotic-resistant bacteria has raised awareness amongst public about the downside of using antibiotics. The threat of antibiotic resistance to global health, food security and development has been emphasized by the World Health Organization (WHO), and research studies have been focused on alternative antimicrobial agents. Bacteriocin, a natural antimicrobial peptide, has been chosen to replace antibiotics for its application in food preservation and infectious disease treatment for livestock and humans, as it is less toxic.

Heat sensitization of hepatitis A virus and Tulane virus using grape seed extract, gingerol and curcumin

Human noroviruses (HNoV) and hepatitis A virus (HAV) are predominantly linked to foodborne outbreaks worldwide. As cell-culture systems to propagate HNoV in laboratories are not easily available, Tulane virus (TV) is used as a cultivable HNoV surrogate to determine inactivation. Heat-sensitization of HAV and TV by "generally recognized as safe'' (GRAS) substances can potentially reduce their time-temperature inactivation parameters during processing to ensure food safety. Curcumin, gingerol (from ginger), and grape seed extract (GSE) reportedly have anti-inflammatory, immune-modulating and antiviral properties. The objective of this study was to determine and compare the D-values and z-values of HAV and TV at 52-68 °C with or without curcumin (0.015 mg/ml), gingerol (0.1 mg/ml), or GSE (1 mg/ml) in 2-ml glass vials. HAV at ~7 log PFU/ml and TV at ~6 log PFU/ml were diluted in phosphate buffered saline (PBS) and added to two sets of six 2-mL sterile glass vials. One set served as the control and the second set had the three extracts individually added for thermal treatments in a circulating water bath for 0-10 min. The D-values for TV in PBS ranged from 4.55 ± 0.28 to 1.08 ± 0.16 min, and for HAV in PBS ranged from to 9.21 ± 0.24 to 0.67 ± 0.19 min at 52-68 °C. Decreased D-values (52-58 °C) for TV with curcumin ranging from 4.32 ± 0.25 to 0.62 ± 0.17 min, gingerol from 4.09 ± 0.18 to 0.72 ± 0.09 min and GSE from 3.82 ± 0.18 to 0.80 ± 0.07 min, with similar trends for HAV were observed. The linear model showed significant differences (p < 0.05) between the D-values of HAV and TV with and without plant extracts for most tested temperatures. This suggests that GRAS substances can potentially lower temperature and time regimens needed to inactivate HAV and TV.

Antimicrobial action of octanoic acid against Escherichia coli O157:H7 during washing of baby spinach and grape tomatoes

We investigated the antimicrobial efficacy of octanoic acid (OA) against Escherichia coli O157:H7 inoculated on the surface of baby spinach and grape tomatoes during simulated washing processes. 3 mM OA at 45 °C achieved >6 log CFU/g reduction from the surface of tomatoes within 2 min. However, washing baby spinach with 6 mM OA at 5 °C resulted in <1 log CFU/g reduction, highlighting the role of surface properties in inactivation efficacy. OA significantly (p < 0.05) reduced the risk of cross-contamination during washing of spinach as well as tomatoes. Also, total mold and yeast population on surface of spinach was significantly reduced immediately after OA wash and inhibited during following 14 days. Baby spinach and grape tomatoes washed with OA did not cause significant (p > 0.05) difference in color compared to the control and no residual OA was detected in most cases following rinsing of produce in water. OA at the concentrations above 2 mM and temperature higher than 25 °C induced severe membrane damage along with release of ATP and other intracellular constituents resulting in bacterial death. OA can be an attractive natural decontamination agent for washing fresh produce.

Interactions of resveratrol with other phenolics and activity against food-borne pathogens

The aim of this study was to investigate the antibacterial activity of individual phenolics and their binary mixtures with resveratrol against selected food-borne pathogens. The antibacterial activity was quantified using the broth microdilution method by the determination of minimal inhibitory concentrations (MICs). Interactions between compounds in the binary phenolic mixtures were determined by calculating the fractional inhibitory concentration index (FICI). The influence of the number of OH groups in the phenols' structure on their antibacterial activity was assessed by principal component analysis (PCA). The most effective compounds were flavone luteolin and flavonol rutin, while the weakest antimicrobial activity was observed for phenolic acid and flavan-3-ols (catechin and epicatechin). The synergistic effect (FICI ≤0.5) of equimolar mixture of resveratrol with kaempferol was confirmed against Staphylococcus aureus, Bacillus cereus, and Escherichia coli, while the mixture of rutin with resveratrol proved synergistic only against S. aureus. The increasing concentrations of resveratrol in the mixtures with kaempferol and rutin resulted in a loss of synergism which indicates that only selected phenolic mixtures, with optimal concentrations of their individual components, result in synergistic antibacterial activity. We did not find an association between total number of OH groups and antibacterial activity of either individual phenolics or their mixtures.

Shelf life extension of mozzarella cheese contaminated with Penicillium spp. using the antifungal compound ɛ-polylysine

Molds are one of the most important spoilage organisms on cheese which can lead to economic loss as well as raising public health concerns due to the production of mycotoxins. This study investigates the use of ɛ-polylysine as natural antimicrobial to inhibit fungal growth. The minimal inhibitory concentrations and minimal fungicidal concentrations of ɛ-polylysine were determined against Penicillium roqueforti, Penicillium nordicum, and Penicillium solitum. Then, polylysine was tested as surface antimicrobial for the preservation of mozzarella slice cheese inoculated with these Penicillium spp. and stored in plastic trays during 25 days. The minimal inhibitory concentrations calculated for the three fungi tested were of 60 mg/l whereas the minimal fungicidal concentrations detected were of 125-10,000 mg/l. The shelf life observed for the control experiments was of 15 days, and just using the ɛ-polylysine at 0.00625, 0.0125, and 0.025% was evidenced a shelf life increment in comparison with the control of 1-3 days.

Nisin in Combination with Cinnamaldehyde and EDTA to Control Growth of Escherichia coli Strains of Swine Origin

Post-weaning diarrhoea (PWD) due to enterotoxigenic Escherichia coli (ETEC) is an economically important disease in pig production worldwide. Although antibiotics have contributed significantly to mitigate the economic losses caused by PWD, there is major concern over the increased incidence of antimicrobial resistance among bacteria isolated from pigs. Consequently, suitable alternatives that are safe and effective are urgently required. Many naturally occurring compounds, including the antimicrobial peptide nisin and a number of plant essential oils, have been widely studied and are reported to be effective as antimicrobial agents against pathogenic microorganisms. Here, we evaluate the potential of nisin in combination with the essential oil cinnamaldehyde and ethylenediaminetetraacetic acid (EDTA) to control the growth of E. coli strains of swine origin including two characterized as ETEC. The results reveal that the use of nisin (10 μM) with low concentrations of trans-cinnamaldehyde (125 μg/mL) and EDTA (0.25–2%) resulted in extended lag phases of growth compared to when either antimicrobial is used alone. Further analysis through kill curves revealed that an approximate 1-log reduction in E. coli cell counts was observed against the majority of targets tested following 3 h incubation. These results highlight the potential benefits of combining the natural antimicrobial nisin with trans-cinnamaldehyde and EDTA as a new approach for the inhibition of E. coli strains of swine origin.

Bacteriocins as food preservatives: Challenges and emerging horizons

The increasing demand for fresh-like food products and the potential health hazards of chemically preserved and processed food products have led to the advent of alternative technologies for the preservation and maintenance of the freshness of the food products. One such preservation strategy is the usage of bacteriocins or bacteriocins producing starter cultures for the preservation of the intended food matrixes. Bacteriocins are ribosomally synthesized smaller polypeptide molecules that exert antagonistic activity against closely related and unrelated group of bacteria. This review is aimed at bringing to lime light the various class of bacteriocins mainly from gram positive bacteria. The desirable characteristics of the bacteriocins which earn them a place in food preservation technology, the success story of the same in various food systems, the various challenges and the strategies employed to put them to work efficiently in various food systems has been discussed in this review. From the industrial point of view various aspects like the improvement of the producer strains, downstream processing and purification of the bacteriocins and recent trends in engineered bacteriocins has also been briefly discussed in this review.

Use of enhanced nisin derivatives in combination with food-grade oils or citric acid to control Cronobacter sakazakii and Escherichia coli O157:H7

Cronobacter sakazakii and Escherichia coli O157:H7 are well known food-borne pathogens that can cause severe disease. The identification of new alternatives to heating to control these pathogens in foods, while reducing the impact on organoleptic properties and nutritional value, is highly desirable. In this study, nisin and its bioengineered variants, nisin V and nisin S29A, are used alone, or in combination with plant essential oils (thymol, carvacrol and trans-cinnamaldehyde) or citric acid, with a view to controlling C. sakazakii and E. coli O157:H7 in laboratory-based assays and model food systems. The use of nisin variants (30 μM) with low concentrations of thymol (0.015%), carvacrol (0.03%) and trans-cinnamaldehyde (0.035%) resulted in extended lag phases of growth compared to those for corresponding nisin A-essential oil combinations. Furthermore, nisin variants (60 μM) used in combination with carvacrol (0.03%) significantly reduced viable counts of E. coli O157:H7 (3-log) and C. sakazakii (4-log) compared to nisin A-carvacrol treatment. Importantly, this increased effectiveness translated into food. More specifically, sub-inhibitory concentrations of nisin variants and carvacrol caused complete inactivation of E. coli O157:H7 in apple juice within 3 h at room temperature compared to that of the equivalent nisin A combination. Furthermore, combinations of commercial Nisaplin and the food additive citric acid reduced C. sakazakii numbers markedly in infant formula within the same 3 h period. These results highlight the potential benefits of combining nisin and variants thereof with carvacrol and/or citric acid for the inhibition of Gram negative food-borne pathogens.

Listeria monocytogenes behaviour and quality attributes during sausage storage affected by sodium nitrite, sodium lactate and thyme essential oil

The effects of the addition of nitrite at 200 ppm (N), sodium lactate 1.5% (L) and thyme essential oil at 100 ppm (T1) on Listeria monocytogenes behaviour and ATPase activity inhibition were evaluated, as well as lipid oxidation through the quantification of malonaldehydes, in sausage stored at 8 ℃ for 41 days and at 30 ℃ for 14 days. The changes in the colour profile were performed during storage time at 8 ℃. Quantitative descriptive sensory analyses were performed after two days at 4 ℃. At 8 ℃, the treatments with the highest inhibition on L. monocytogenes were L and N, without significant differences. In turn, at 30 ℃, the bacterium was most inhibited with treatment L, followed by T1 and N, without significant differences. A 44.1% and 19% inhibition of ATPase activity was detected in L and T1 treatments, respectively. At 8 ℃ and 30 ℃, malonaldehydes content was not different between the treatments. N presented the highest values of a* and concentration of metmyoglobin after 41 days at 8 ℃. The panel detected differences between T1 and N for the aroma in the descriptors spices and herbal.

Combined Effect of Nisin, Carvacrol and Thymol on the Viability of Bacillus Cereus Heat-Treated Vegetative Cells

The influence of mild heat pretreatment on the bactericidal action of nisin, carvacrol and thymol on stationary and exponential phase cells of two Bacillus cereus strains was studied. Carvacrol or thymol concentrations of 0.3 mmol/L had no bactericidal effect on unheated, and a minor effect on heated B. cereus cells either in stationary or exponential growth phases. Nisin (0.15 mg/mL) alone decreased the viable counts in all cases (unheated and heated cells in stationary and exponential phase) although the two strains tested showed different sensitivity to this natural antimicrobial between them. When carvacrol or thymol were combined with nisin, it resulted in a greater loss of viability of heated cells than when nisin was applied alone. There was a synergistic effect of nisin and both essential oils with a mild heat pretreatment on the viability of B. cereus cells. This study pointed out the potential use of nisin alone and in combination with carvacrol or thymol applied after a mild heat pretreatment for preservation of minimally processed foods.

Effect of nisin and perilla oil combination against Listeria monocytogenes and Staphylococcus aureus in milk

In the present study, in vitro interaction of nisin and perilla oil (PO) against 20 food-borne isolates of L. monocytogenes and S. aureus were assessed using a checkerboard microdilution method. Synergism was observed in tested strains with the fractional inhibitory concentration indexs (FICIs) ranges from 0.125-0.25 and 0.19-0.375, respectively. Scanning electron microscopy was carried out to investigate the effect of nisin and PO on the integrity of cell wall and membrane of L. monocytogenes and S. aureus. The results showed that nisin and PO were more effective in damaging cell wall and membrane in combination.

Essential oils as natural food antimicrobial agents: a review

Food-borne illnesses pose a real scourge in the present scenario as the consumerism of packaged food has increased to a great extend. Pathogens entering the packaged foods may survive longer, which needs a check. Antimicrobial agents either alone or in combination are added to the food or packaging materials for this purpose. Exploiting the antimicrobial property, essential oils are considered as a "natural" remedy to this problem other than its flavoring property instead of using synthetic agents. The essential oils are well known for its antibacterial, antiviral, antimycotic, antiparasitic, and antioxidant properties due to the presence of phenolic functional group. Gram-positive organisms are found more susceptible to the action of the essential oils. Essential oils improve the shelf-life of packaged products, control the microbial growth, and unriddle the consumer concerns regarding the use of chemical preservatives. This review is intended to provide an overview of the essential oils and their role as natural antimicrobial agents in the food industry.

Latent Ice Recrystallization Inhibition Activity in Nonantifreeze Proteins: Ca2+-Activated Plant Lectins and Cation-Activated Antimicrobial Peptides

Organisms living in polar regions have evolved a series of antifreeze (glyco) proteins (AFGPs) to enable them to survive by modulating the structure of ice. These proteins have huge potential for use in cellular cryopreservation, ice-resistant surfaces, frozen food, and cryosurgery, but they are limited by their relatively low availability and questions regarding their mode of action. This has triggered the search for biomimetic materials capable of reproducing this function. The identification of new structures and sequences capable of inhibiting ice growth is crucial to aid our understanding of these proteins. Here, we show that plant c-type lectins, which have similar biological function to human c-type lectins (glycan recognition) but no sequence homology to AFPs, display calcium-dependent ice recrystallization inhibition (IRI) activity. This IRI activity can be switched on/off by changing the Ca2+ concentration. To show that more (nonantifreeze) proteins may exist with the potential to display IRI, a second motif was considered, amphipathicity. All known AFPs have defined hydrophobic/hydrophilic domains, rationalizing this choice. The cheap, and widely used, antimicrobial Nisin was found to have cation-dependent IRI activity, controlled by either acid or addition of histidine-binding ions such as zinc or nickel, which promote its amphipathic structure. These results demonstrate a new approach in the identification of antifreeze protein mimetic macromolecules and may help in the development of synthetic mimics of AFPs.

Impact of Moderate Heat, Carvacrol, and Thymol Treatments on the Viability, Injury, and Stress Response of Listeria monocytogenes

The microbial safety and stability of minimally processed foods are based on the application of combined preservative factors. Since microorganisms are able to develop adaptive networks to survive under conditions of stress, food safety may be affected, and therefore understanding of stress adaptive mechanisms plays a key role in designing safe food processing conditions. In the present study, the viability and the sublethal injury of Listeria monocytogenes exposed to moderate heat (55 °C) and/or essential oil compounds (carvacrol and thymol, 0.3 mM) treatments were studied. Synergistic effects were obtained when combining mild heat (55 °C) with one or both essential oil compounds, leading to inactivation kinetics values three to four times lower than when using heat alone. All the treatments applied caused some injury in the population. The injury levels ranged from around 20% of the surviving population under the mildest conditions to more than 99.99% under the most stringent conditions. Protein extracts of cells exposed to these treatments were analysed by two-dimensional gel electrophoresis. The results obtained revealed that stressed cells exhibited differential protein expression to control cells. The proteins upregulated under these stressing conditions were implicated, among other functions, in stress response, metabolism, and protein refolding.

Synergistic antibacterial activity of the essential oil of Cuminum cyminum L. seed and nisin in a food model

AIMS

To investigate effects of various concentrations of the essential oil of Cuminum cyminum L. seed alone and in combination with nisin on survival of vegetative forms of Bacillus cereus and Bacillus subtilis in a food model (commercial barley soup) and their ultrastructure.

METHODS AND RESULTS

Gas chromatography-mass spectrometry analysis indicated that cumin aldehyde (29·02%) and α-terpinen-7-al (20·70%) constituted the highest amount of the essential oil. The lowest concentration of the essential oil significantly affected the growth of the bacteria at 8°C but not at 25°C. Synergistic effect of the essential oil in combination with the lowest concentration of nisin was observed on the bacteria at 8°C. Evaluation of the sensory properties showed that concentration of 0·15 μl ml−1 of the essential oil was the most acceptable.

CONCLUSIONS

 The essential oil of C. cyminum L. seed showed the most bactericidal effects on B. cereus at 8°C. Ultrastructural studies of vegetative cells confirmed the synergistic destructive effects of the essential oil and nisin on membrane and cell wall of the bacteria.

Antimicrobial Activities of the Combined Use of Cuminum Cyminum L. Essential Oil, Nisin and Storage Temperature Against Salmonella typhimurium and Staphylococcus aureus In Vitro

Background:

Foodborne diseases are considered as major health problems in different countries. Concerns over the safety of some chemical preservatives and negative consumer reactions to them have prompted interest in natural alternatives for the maintenance or extension of food shelf life. In this respect, the combination of a plant essential oil and nisin has used for controlling the growth of foodborne pathogens as natural food preservative using the mathematical model.

Objectives:

The purpose of this study was to determine the effect of different concentrations of Cuminum cyminum L. essential oil (0, 15, 30 and 45 µL/100 mL) and nisin (0, 0.5 and 1.5 µg/mL) combination at different temperatures (10, 25 and 35°C) on growth of Salmonella typhimurium and Staphylococcus aureus in the Brain-Heart Infusion (BHI) broth model. The concentrations of 0 µL/100 mL for essential oil and 0 µg/mL for nisin imply the negative control.

Materials and Methods:

A multivariate variance experiment was performed. To assess the effect of essential oil, nisin and the incubation temperature on growth probability (log P%) of S. typhimurium and S. aureus, four concentrations of C. cyminum L. essential oil (0, 15, 30 and 45 µL/100 mL), three concentrations of nisin (0, 0.5 and 1.5 µg/mL) and three storage temperatures (10, 25 and 35°C) were considered.

Results:

The growth of S. typhimurium was significantly decreased by the concentration of essential oil ≥ 30 µL/100 mL in combination with nisin ≥ 0.5 µg/mL at temperature = 10°C (P < 0.05). Also, in combination of the essential oil ≥ 15 µL/100 mL and nisin ≥ 0.5 µg/mL at temperature ≤ 25°C, the growth of S. aureus was significantly reduced (P < 0.05).

Conclusions:

These results indicate that the combination of essential oil and nisin inhibits the growth of S. typhimurium and S. aureus bacteria and there is the possibility of using them as substitutes for chemical food preservatives. Moreover, the model (log P%) in this study can be a good tool for the reduction of microbiological hazards in food industry.

Efficacies of nisin A and nisin V semipurified preparations alone and in combination with plant essential oils for controlling Listeria monocytogenes

The food-borne pathogenic bacterium Listeria is known for relatively low morbidity and high mortality rates, reaching up to 25 to 30%. Listeria is a hardy organism, and its control in foods represents a significant challenge. Many naturally occurring compounds, including the bacteriocin nisin and a number of plant essential oils, have been widely studied and are reported to be effective as antimicrobial agents against spoilage and pathogenic microorganisms. The aim of this study was to investigate the ability of semipurified preparations (SPP) containing either nisin A or an enhanced bioengineered derivative, nisin V, alone and in combination with low concentrations of the essential oils thymol, carvacrol, and trans-cinnamaldehyde, to control Listeria monocytogenes in both laboratory media and model food systems. Combinations of nisin V-containing SPP (25 μg/ml) with thymol (0.02%), carvacrol (0.02%), or cinnamaldehyde (0.02%) produced a significantly longer lag phase than any of the essential oil-nisin A combinations. In addition, the log reduction in cell counts achieved by the nisin V-carvacrol or nisin V-cinnamaldehyde combinations was twice that of the equivalent nisin A-essential oil treatment. Significantly, this enhanced activity was validated in model food systems against L. monocytogenes strains of food origin. We conclude that the fermentate form of nisin V in combination with carvacrol and cinnamaldehyde offers significant advantages as a novel, natural, and effective means to enhance food safety by inhibiting food-borne pathogens such as L. monocytogenes.

Combined effect of a nanoemulsion of D-limonene and nisin on Listeria monocytogenes growth and viability in culture media and foods

The present work evaluated the antibacterial effect of nanoemulsions from natural compounds d-limonene and nisin against Listeria monocytogenes in tryptic soy broth growth medium, chicken broth, and vegetable cream. Experiments were performed by means of optical density growth curves and studies of viability in culture media and foods. Stability of nanoemulsions was evaluated by a Mastersizer 2000 equipment. Results showed greater effectiveness when applying D-limonene in form of nanoemulsion than when applying it directly, and when using both compounds together, both directly and in the form of nanoemulsion. Concentration of L. monocytogenes decreased at least in three log cycles in all the culture media and foods used within the first 90 min after the addition of the natural antimicrobials combined in form of nanoemulsion. Moreover, the growth of L. monocytogenes was inhibited with the combination of antimicrobials in the four weeks that the experiment lasted. Nanoemulsion technology would solve present problems of solubility and stability of oily antimicrobials in the food industry.

Antibacterial peptide nisin: a potential role in the inhibition of oral pathogenic bacteria

Although the antimicrobial peptide nisin has been extensively studied in the food industry for decades, its application in the oral cavity remains to develop and evaluate its feasibility in treating oral common diseases. Nisin is an odorless, colorless, tasteless substance with low toxicity and with antibacterial activities against Gram-positive bacteria. These biologic properties may establish its use in promising products for oral diseases. This article summarizes the antibacterial efficiency of nisin against pathogenic bacteria related to dental caries and root canal infection and discusses the combination of nisin and common oral drugs.

Adding Molecules to Food, Pros and Cons: A Review on Synthetic and Natural Food Additives

The pressing issue to feed the increasing world population has created a demand to enhance food production, which has to be cheaper, but at the same time must meet high quality standards. Taste, appearance, texture, and microbiological safety are required to be preserved within a foodstuff for the longest period of time. Although considerable improvements have been achieved in terms of food additives, some are still enveloped in controversy. The lack of uniformity in worldwide laws regarding additives, along with conflicting results of many studies help foster this controversy. In this report, the most important preservatives, nutritional additives, coloring, flavoring, texturizing, and miscellaneous agents are analyzed in terms of safety and toxicity. Natural additives and extracts, which are gaining interest due to changes in consumer habits are also evaluated in terms of their benefits to health and combined effects. Technologies, like edible coatings and films, which have helped overcome some drawbacks of additives, but still pose some disadvantages, are briefly addressed. Future trends like nanoencapsulation and the development of "smart" additives and packages, specific vaccines for intolerance to additives, use of fungi to produce additives, and DNA recombinant technologies are summarized.

Efficacy of commercial natural antimicrobials alone and in combinations against pathogenic and spoilage microorganisms

Microbial control strategies are needed in the food industry to prevent foodborne illnesses and outbreaks and prolong product shelf life. The aim of this study was to investigate and compare the efficacy of the commercial natural antimicrobials white mustard essential oil (WMEO), citrus flavonoid and acid blend (CFAB), olive extract (OE), Nisaplin (a compound containing nisin), and lauric arginate (LAE) alone and in combinations against foodborne pathogens and spoilage microorganisms. MICs of individual and combined antimicrobials against Escherichia coli, Salmonella Enteritidis, Enterobacter aerogenes, Bacillus cereus, Listeria monocytogenes, and Staphylococcus aureus were determined at pH 6.0 and 25 °C. WMEO was most effective against B. cereus and S. aureus, with MICs of 250 and 500 mg/liter, respectively. CFAB inhibited all tested microorganisms, requiring only 12 to 35 mg/liter for gram-positive bacteria. For OE, 2,000 mg/liter was needed to achieve microbial inhibition. Nisaplin at 400 to 1,200 mg/liter inhibited only gram-positive bacteria. LAE was effective at low concentrations and required only 20 to 50 mg/liter to inhibit all tested microorganisms. When WMEO was combined with other antimicrobials, the effects were usually additive except for WMEO plus Nisaplin and WMEO+OE, which had synergistic activity against L. monocytogenes and Salmonella Enteritidis, respectively. An antagonistic effect was observed for WMEO+CFAB against E. aerogenes. For WMEO+LAE+CFAB, additive antimicrobial effects were noted against all strains tested except S. aureus, where a synergistic effect occurred. These findings suggest that these commercial natural antimicrobials have potential to enhance food safety by inhibiting foodborne pathogens and extending product shelf life.

Combined effect of nisin, carvacrol and a previous thermal treatment on the growth of Salmonella enteritidis and Salmonella senftenberg

The aim of this study was to evaluate the combined effect of a previous mild heat treatment (15 min at 55 ) with the use of antimicrobials, nisin and carvacrol, on the growth of Salmonella enteritidis and Salmonella senftenberg. Natural antimicrobials, alone or combined with a previous mild heat treatment, affected the growth of these two serovars in Tryptone Soy Broth at 37 . Increasing concentrations of carvacrol had a significant effect on both growth rate and lag phase duration of both strains. The time to reach stationary phase was almost doubled in the case of S. enteritidis when a concentration of 0.77 mM in carvacrol was added. For S. senftenberg the effect was smaller. The effect of nisin and of heat, applied individually, was lower for both microorganisms. A combination of 1.2 µM nisin with 0.77 mM carvacrol significantly delayed the growth of heat treated cells, compared to the control without antimicrobials, showing additive effects.