Naturally occurring antimicrobials in food

An In-Depth Study on the Chemical Composition and Biological Effects of Pelargonium graveolens Essential Oil

The essential oil of Pelargonium graveolens (PGEO) is identified in the literature as a rich source of bioactive compounds with a high level of biological activity. This study aimed to examine the chemical profile of PGEO as well as its antioxidant, antibacterial, antibiofilm, and insecticidal properties. Its chemical composition was analyzed using gas chromatography-mass spectrometry (GC-MS), achieving comprehensive identification of 99.2% of volatile compounds. The predominant identified compounds were β-citronellol (29.7%) and geraniol (14.6%). PGEO's antioxidant potential was determined by means of DPPH radical and ABTS radical cation neutralization. The results indicate a higher capacity of PGEO to neutralize the ABTS radical cation, with an IC50 value of 0.26 ± 0.02 mg/mL. Two techniques were used to assess antimicrobial activity: minimum inhibitory concentration (MIC) and disk diffusion. Antimicrobial evaluation using the disk diffusion method revealed that Salmonella enterica (14.33 ± 0.58 mm), which forms biofilms, and Priestia megaterium (14.67 ± 0.58 mm) were most susceptible to exposure to PGEO. The MIC assay demonstrated the highest performance of this EO against biofilm-forming S. enterica (MIC 50 0.57 ± 0.006; MIC 90 0.169 ± 0.08 mg/mL). In contrast to contact application, the assessment of the in situ vapor phase antibacterial activity of PGEO revealed significantly more potent effects. An analysis of antibiofilm activity using MALDI-TOF MS demonstrated PGEO's capacity to disrupt the biofilm homeostasis of S. enterica growing on plastic and stainless steel. Additionally, insecticidal evaluations indicated that treatment with PGEO at doses of 100% and 50% resulted in the complete mortality of all Harmonia axyridis individuals.

A review of food additives to control the proliferation and transmission of pathogenic microorganisms with emphasis on applications to raw meat-based diets for companion animals

Raw meat-based diets (RMBDs) or sometimes described as biologically appropriate raw food (BARFs) are gaining in popularity amongst dog and cat owners. These pet guardians prefer their animals to eat minimally processed and more “natural” foods instead of highly heat-processed diets manufactured with synthetic preservatives. The market for RMBDs for dogs and cats is estimated at $33 million in the United States. This figure is likely underestimated because some pet owners feed their animals raw diets prepared at home. Despite their increasing demand, RMBDs have been plagued with numerous recalls because of contamination from foodborne pathogens like Salmonella, E. coli, or Campylobacter. Existing literature regarding mitigation strategies in RMBD's for dogs/cats are very limited. Thus, a comprehensive search for published research was conducted regarding technologies used in meat and poultry processing and raw materials tangential to this trade (e.g., meats and poultry). In this review paper, we explored multiple non-thermal processes and GRAS approved food additives that can be used as potential antimicrobials alone or in combinations to assert multiple stressors that impede microbial growth, ultimately leading to pathogen inactivation through hurdle technology. This review focuses on use of high-pressure pasteurization, organic acidulants, essential oils, and bacteriophages as possible approaches to commercially pasteurize RMBDs effectively at a relatively low cost. A summary of the different ways these technologies have been used in the past to control foodborne pathogens in meat and poultry related products and how they can be applied successfully to impede growth of enteric pathogens in commercially produced raw diets for companion animals is provided.

Ethnobotanical, phytochemical and antimicrobial activity of Halexylon salicornicum (Ramth) as a graze and promising shrub against selected animal microbes

Folk medicine, including plants, has been utilized for humans and animals since the dawn of civilization. Because of the widespread problem of antimicrobial resistance around the world, one of the mainly significant challenges in microbiological research is to achieve a replacement antibiotic with the fewest adverse effects. Camel and ruminant grazing were provided by the wild shrub Halexylon salicornicum (Ramth). However, despite prior research demonstrating its antimicrobial action against human diseases, no investigations on its antimicrobial activity against animal pathogens have been conducted to far. The goal of this study is to investigate whether Halexylon salicornicum aqueous and solvent extracts have antimicrobial activity on a variety of animal pathogens isolated from cattle and poultry using the agar well diffusion method (Enterococcus faecium, Shigella flexneri, Bacillus Cereus, Klebsiella pneumoniae, Staphylococcus aureus, Escherichia coli, Streptococcus pyogens, Pseudomonas aerogenes, Salmonella typhimurium, and Candida albicans) moreover it's ethnobotanical and phytochemical. All of the extracts tested had antimicrobial efficacy against tested strains and included bioactive chemicals, particularly the acetone extract, had the highest antibacterial activity. As a result, it can be stated that Halexylon salicornicum is a promising important shrub that might be used as a natural antimicrobial alternative for animals or as a food additive.

Antimicrobial and Anti-Inflammatory Effects of the Ethanol Extract of Polygonum cuspidatum as a Mouthwash Component

Polygonum cuspidatum (PC) has been used as traditional Korean medicine to treat various diseases including asthma, hypertension, cancer, and arteriosclerosis. In this study, we assessed the antibacterial and anti-inflammatory effects of PC ethanol extract. Persistent antibacterial activity against Streptococcus mutans for up to 23 days was observed when the extract was used at a concentration of 10 mg/mL. The minimum inhibitory concentration of PC against S. mutans was 0.2 mg/mL and the minimum bactericidal concentration was 10 mg/mL. We compared the antimicrobial activities of S. mutagens cultured with or without PC. Bacterial activity was observed only in the group where RE was not added. The anti-inflammatory effect of PC on RAW264.7 cells was assessed using the MTT assay; changes in nitric oxide (NO) production and inflammatory cytokine levels (tumor necrosis factor [TNF]-α and interleukin [IL]-6) were measured in the presence of PC. In lipopolysaccharide-induced RAW264.7 cells, PC inhibited NO production by 68.6% when used at a concentration of 50 µg/mL. The expression of TNF-α and IL-6 was reduced by PC in a concentration-dependent manner. These results suggest that the ethanol extract of PC could be used as a mouthwash component with antibacterial and anti-inflammatory effects.

Antimicrobial activity of gaseous Citrus limon var pompia leaf essential oil against Listeria monocytogenes on ricotta salata cheese

Contamination by Listeria monocytogenes is a particularly challenging problem in the food industry due to the ability of the bacterium to develop under conditions normally used for food preservation. Here, we show that the gaseous phase of Citrus limon var pompia leaf essential oil (hereafter PLEO) exerts specific anti-Listeria activity on ricotta salata cheese stored at 5 °C. The synergic effect of gaseous PLEO treatment and refrigeration was first confirmed in vitro on L. monocytogenes strains treated for 3 h with gaseous PLEO and then stored at 5 °C. Ricotta cheese was then inoculated with L. monocytogenes strains and subjected to hurdle technology with different concentrations of gaseous PLEO. Cell counts revealed gaseous PLEO to exert a bactericidal effect on L. monocytogenes 20600 DSMZ and a bacteriostatic effect on a mix of L. monocytogenes strains. Scanning and transmission electron microscopy analyses of L. monocytogenes cells suggested that gaseous PLEO targets the bacterial cell wall and plasma membrane. Chemical analyses of the liquid and vapor phases of PLEO indicated linalyl acetate to be the predominant compound, followed by limonene and the two isomers of citral, whereas EO composition analysis, although generally in line with previous findings, showed the presence of linalyl acetate for the first time. Solid-phase microextraction coupled with gas chromatography confirmed the presence of all crude oil components in the headspace of the box.

A Novel Discovery: Holistic Efficacy at the Special Organ Level of Pungent Flavored Compounds from Pungent Traditional Chinese Medicine

Pungent traditional Chinese medicines (TCMs) play a vital role in the clinical treatment of hepatobiliary disease, gastrointestinal diseases, cardiovascular diseases, diabetes, skin diseases and so on. Pungent TCMs have a vastness of pungent flavored (with pungent taste or smell) compounds. To elucidate the molecular mechanism of pungent flavored compounds in treating cardiovascular diseases (CVDs) and liver diseases, five pungent TCMs with the action of blood-activating and stasis-resolving (BASR) were selected. Here, an integrated systems pharmacology approach is presented for illustrating the molecular correlations between pungent flavored compounds and their holistic efficacy at the special organ level. First, we identified target proteins that are associated with pungent flavored compounds and found that these targets were functionally related to CVDs and liver diseases. Then, based on the phenotype that directly links human genes to the body parts they affect, we clustered target modules associated with pungent flavored compounds into liver and heart organs. We applied systems-based analysis to introduce a pungent flavored compound-target-pathway-organ network that clarifies mechanisms of pungent substances treating cardiovascular diseases and liver diseases by acting on the heart/liver organ. The systems pharmacology also suggests a novel systematic strategy for rational drug development from pungent TCMs in treating cardiovascular disease and associated liver diseases.

Simultaneous determination of synthetic food additives in kimchi by liquid chromatography-electrospray tandem mass spectrometry

A new analytical method was developed for the simultaneous determination of seven food additives (Ponceau 4R, Allura Red AC, Amaranth, 4-hydroxymethyl benzoic acid, ethyl-4-hydroxybenzoate, butyl-4-hydroxybenzoate, and saccharin sodium) in kimchi using high-performance liquid chromatography-electrospray ionization tandem mass spectrometry. The linearity, sensitivity, selectivity, precision, and accuracy of the method were validated. The limit of detection was 0.00004-0.24 μg/mL, and the limit of quantification was 0.00012-0.8 μg/mL. Recoveries ranged from 85.65 to 120.82%. The method was successful and may help to ensure food safety.

Microencapsulation of reuterin to enhance long-term efficacy against food-borne pathogen Listeria monocytogenes

The aim of this study was to microencapsulate the reuterin produced by Lactobacillus reuteri BPL-36 strain for its long-term efficacy against food-borne pathogen Listeria monocytogenes. Lactobacillus reuteri BPL-36 strain previously isolated from a human infant fecal sample in lab was selected for the present study based on its ability to produce reuterin. The organism displayed a broad-spectrum antimicrobial activity. Reuterin concentration of 89.63 mM was obtained in the MRS-glycerol medium after 16 h incubation at 37 °C. The reuterin concentration required to inhibit the growth of Pseudomonas aeruginosa, Escherichia coli O157: H7, Salmonella typhi, Staphylococcus aureus, and Listeria monocytogenes was found to be 1.0, 2.0, 2.0, 4.0, and 10.0 AU/mL, respectively. Microencapsulation of reuterin to enhance long-term efficacy against food-borne pathogens was done. Results in this study indicated that the release characteristics of reuterin from the encapsulated particles were pH dependent. The release characteristics were unaffected by the storage of encapsulated reuterin at 4 °C for 2 weeks. The anti-listerial efficacy of the encapsulated reuterin was tested against L. monocytogenes in the BHI medium adjusted to pH 5.0 with a reuterin content equivalent to 16 mM, similar to un-encapsulated (free) reuterin. Encapsulated reuterin demonstrated enhanced efficacy against L. monocytogenes for longer duration of time when compared with un-encapsulated (free) reuterin. The present work demonstrated a novel antimicrobial delivery system that ensured much better capability of inhibiting the growth of L. monocytogenes throughout 24 h incubation at 37 °C.

Antibacterial Activity of Subtilosin Alone and Combined with Curcumin, Poly-Lysine and Zinc Lactate Against Listeria monocytogenes Strains

In this paper, the antibacterial effects of the Bacillus amyloliquefaciens-produced bacteriocin subtilosin, both alone and in combination with curcumin, ε-poly-L-lysine (poly-lysine), or zinc lactate, were examined against Listeria monocytogenes. Results indicated that subtilosin inhibits both of the studied bacterial strains, Scott A (wild-type, nisin sensitive) and NR30 (nisin resistant). However, L. monocytogenes Scott A was more sensitive to subtilosin and pure curcumin. In addition, subtilosin was more active at an acidic pH. Subtilosin in combination with encapsulated curcumin displayed partial synergy against L. monocytogenes ScottA. It also had synergistic activity against both L. monocytogenes Scott A and L. monocytogenes NR30 when combined with zinc lactate. Only an additive effect was observed for subtilosin when combined with non-encapsulated curcumin or poly-lysine against the mentioned strains. Thus, using the combination of subtilosin with curcumin, poly-lysine, or zinc lactate, a lower effective dose can be used to control L. monocytogenes infection. Our findings suggest that subtilosin could be used as alternative bacteriocin to nisin, providing an opportunity to use a novel natural and efficacious biopreservative against L. monocytogenes in food preservation. This is the first report on the effects of the combination of subtilosin with natural antimicrobials on L. monocytogenes.

Antimicrobial Efficacy of an Array of Essential Oils Against Lactic Acid Bacteria

The essential oils of clove bud, cinnamon bark and thyme, and their individual compounds including allyl isothiocyanate (AIT), carvacrol, cinnamaldehyde, cinnamic acid, eugenol, and thymol were initially assessed for antimicrobial activity against 9 lactic acid bacteria (LAB) species. Carvacrol and thymol were the most inhibitory with MICs of 0.1% (v/v and w/v, respectively). Cinnamaldehyde, cinnamon bark oil, clove bud oil, eugenol, and thyme oil were moderately inhibitive (MICs = 0.2% v/v), while cinnamic acid required a concentration of 0.5% (w/v). AIT was not effective with MICs in excess of concentrations tested (0.75% v/v). The bactericidal capability of the oil components carvacrol, cinnamaldehyde, eugenol, and thymol were further examined against Pediococcus acidilactici, Lactobacillus buchneri, and Leuconostoc citrovorum. Thymol at 0.1% (w/v) was bactericidal against L. citrovorum (>4-log reduction), but resulted in a 2-log CFU/mL reduction against L. buchneri and P. acidilactici. Cinnamaldehyde at 0.2% to 0.25% (v/v) was effective against L. citrovorum, L. buchneri, and P. acidilactici, resulting in a >2-log reduction. All 3 organisms were susceptible to 0.2% carvacrol with >3-log reduction observed after exposure for 6 h. Eugenol was the least effective. Concentrations of 0.2% and 0.25% (v/v) were needed to achieve an initial reduction in population, >3-log CFU/mL after 6 h exposure. However, at 0.2%, P. acidilactici and L. buchneri recovered to initial populations in 48 to 72 h. Results indicate essential oils have the capacity to inactivate LAB that are commonly associated with spoilage of shelf stable low-acid foods.

Effect of Selected Volatiles on Two Stored Pests: The Fungus Fusarium verticillioides and the Maize Weevil Sithophilus zeamais

New agronomic practices and technology enabled Argentina a larger production of cereal grains, reaching a harvest yield of 26.5 million metric tons of maize, of which, about 40% was exported. However, much of the maize production is lost annually by the attack of fungi and insects (2.6 million tons). In this study, the antifungal effect of selected volatiles on Fusarium verticillioides, its mycotoxin production, and the repellent and insecticidal activities against the weevill Sithophilus zeamais, an insect vector of F. verticillioides, were evaluated. The compounds tested were (2E)-2-hexenal, (2E)-2-nonenal, (2E,6Z)-2,6-nonadienal, 1-pentanol, 1-hexanol, 1-butanol, 3-methyl-1-butanol, pentanal, 2-decanone, and 3-decanone, which occur in the blend of volatile compounds emitted by various cereal grains. The most active antifungals were the aldehydes (2E)-2-nonenal, (2E)-2-hexenal, and (2E,6Z)-2,6-nonadienal (minimum inhibitory concentration values of <0.03, 0.06, and 0.06 mM, respectively). The occurrence of fumonisin B1 also was prevented because these compounds completely inhibited fungal growth. The best insecticidal fumigant activities against the maize weevil were shown by 2-decanone and 3-decanone (lethal concentration ≤ 54.6 μL/L (<0.28 mM)). Although, all tested compounds showed repellent activity against S. zeamais at a concentration of 4 μL/L, (2E,6Z)-2,6-nonadienal was the most active repellent compound. These results demonstrate the potential of (2E,6Z)-2,6-nonadienal to be used as a natural alternative to synthetic pesticides on F. verticillioides and S. zeamais.

Controlled fermentation of kimchi using naturally occurring antimicrobial agents

Kimchi is a traditional Korean fermented food. Since it ferments continuously during distribution and storage, the extension of shelf life by preventing over-acidification is a major concern in the kimchi industry. One of the most frequently attempted ways to delay fermentation is to add naturally occurring antimicrobial agents. Many researchers have investigated ways to delay over-acidification by adding minor ingredients, fruits or fruit seed extracts, extracts of medicinal herbs, culinary herbs and spices, and other miscellaneous substances to kimchi. The addition of naturally occurring antimicrobial agents may enhance the acceptability of kimchi to consumers over a longer period of time but may also have a disadvantage in that it may cause changes in sensory quality, especially if added in large amounts. To avoid undesirable sensory changes, application of hurdle technologies (i.e., multifactor preservative systems) which involve using combinations of low amounts of various naturally occurring antimicrobial agents as ingredients should be explored with the goal of controlling fermentation. If synergistic or additive antimicrobial effects can be achieved using small amounts of a combination of natural agents, changes in sensory qualities will be minimized, thereby prolonging shelf life. Research findings summarized in this review provide a basis for developing effective hurdle technologies using naturally occurring antimicrobial agents to extend shelf life of kimchi and perhaps other types of traditional fermented foods.

Spices as functional foods

Spices and aromatic herbs have been used since antiquity as preservatives, colorants, and flavor enhancers. Spices, which have long been the basis of traditional medicine in many countries, have also been the subject of study, particularly by the chemical, pharmaceutical, and food industries, because of their potential use for improving health. Both in vitro and in vivo studies have demonstrated how these substances act as antioxidants, digestive stimulants, and hypolipidemics and show antibacterial, anti-inflammatory, antiviral, and anticancerigenic activities. These beneficial physiological effects may also have possible preventative applications in a variety of pathologies. The aim of this review is to present an overview of the potential of spices and aromatic herbs as functional foods.

Antibacterial interactions of monolaurin with commonly used antimicrobials and food components

Monolaurin is a nontraditional antimicrobial agent that possesses better antimicrobial activities but causes no health problems to consumers, but the use of monolaurin in the food industry as a preservative is still limited. Using a microtiter plate assay, the minimum inhibitory concentrations for monolaurin were 25 microg/mL against Escherichia coli, 12.5 microg/mL against Staphylococcus aureus, and 30 microg/mL against Bacillus subtilis. The interaction with commonly used antimicrobials revealed that monolaurin and nisin acted synergistically against the test microorganisms, monolaurin in combination with sodium dehydroacetate or ethylenediaminetetraacetic acid was synergistic against E. coli and B. subtilis but not S. aureus, and monolaurin combined with calcium propionate or sodium lactate showed no synergistic effects against any test microorganism. The interaction with food components revealed that the antibacterial effectiveness of monolaurin was reduced by fat or starch while the monolaurin activity remained unchanged in the presence of protein. This study contributes to a better understanding on the use of monolaurin as a nontraditional preservative in food products. Results from this study suggest the potential use of monolaurin as a nontraditional preservative in combination with commonly used antimicrobials, such as nisin, sodium dehydroacetate, or ethylenediaminetetraacetic acid, and suggest that the antibacterial effectiveness of monolaurin may be reduced significantly in high-fat or low-starch food products.

Effect of α-Cyclodextrin–Cinnamic Acid Inclusion Complexes on Populations of Escherichia coli O157:H7 and Salmonella enterica in Fruit Juices

Cinnamic acid (CA), a naturally occurring organic acid found in fruits and spices, has antimicrobial activity against spoilage and pathogenic bacteria, but low aqueous solubility limits its use. The purpose of this study was to determine the effectiveness of solubility-enhancing α-cyclodextrin–CA inclusion complexes against Escherichia coli O157:H7 and Salmonella enterica serovars suspended in apple cider or orange juice at two different incubation temperatures (4 and 26°C). Two concentrations (400 and 1,000 mg/liter) of α-cyclodextrin-CA inclusion complex were aseptically added to apple cider inoculated with E. coli O157:H7 (7 log CFU/ml) and orange juice inoculated with a cocktail of six Salmonella enterica serovars (7 log CFU/ml). Samples were extracted at 0 min, at 2 min, and at 24-h intervals for 7 days, serially diluted in 0.1% peptone, spread plated in duplicate onto tryptic soy agar, and incubated at 35°C for 24 h. Populations of E. coli O157:H7 in apple cider were significantly reduced (P ≤ 0.05) during the 7-day sampling period in all solutions regardless of temperature. Compared with the controls, populations were significantly reduced by the addition of 400 and 1,000 mg/liter inclusion complex, but reductions were not significantly different (P ≥ 0.05) between the two treatment groups (400 and 1,000 mg/liter). Salmonella was significantly reduced in all solutions regardless of temperature. There were significant differences between the control and each inclusion complex concentration at 4 and 26°C. Coupled with additional processing steps, α-cyclodextrin–CA inclusion complexes may provide an alternative to traditional heat processes.

Inhibition of growth and ochratoxin A biosynthesis in Aspergillus carbonarius by flavonoid and nonflavonoid compounds

The effect of naturally occurring phenolic compounds on Aspergillus carbonarius growth and ochratoxin A (OTA) production was studied. Caffeic acid and the flavonoids, rutin and quercetin, were added to Czapek Yeast Extract agar at concentrations ranging between 50 and 500 mg/l. All phenolic compounds had a significant influence on growth rate and lag phase of A. carbonarius at 250 mg/l. The growth was completely inhibited with 500 mg/l. In comparison with the control, a significant decrease in OTA production was observed with all phenolic compounds. In general, effect on growth was less evident than effect on toxin production. An inhibitory effect on growth and OTA production, as concentration was increased was observed in all cases. The response of A. carbonarius to the flavonoids, rutin and quercetin, was similar. The inhibitory effect of these natural phenolic compounds on fungal growth and OTA production could be an alternative to the use of chemical fungicides.

Application of natural antimicrobials for food preservation

In this review, antimicrobials from a range of plant, animal, and microbial sources are reviewed along with their potential applications in food systems. Chemical and biochemical antimicrobial compounds derived from these natural sources and their activity against a range of pathogenic and spoilage microorganisms pertinent to food, together with their effects on food organoleptic properties, are outlined. Factors influencing the antimicrobial activity of such agents are discussed including extraction methods, molecular weight, and agent origin. These issues are considered in conjunction with the latest developments in the quantification of the minimum inhibitory (and noninhibitory) concentration of antimicrobials and/or their components. Natural antimicrobials can be used alone or in combination with other novel preservation technologies to facilitate the replacement of traditional approaches. Research priorities and future trends focusing on the impact of product formulation, intrinsic product parameters, and extrinsic storage parameters on the design of efficient food preservation systems are also presented.

Control of Listeria monocytogenes on frankfurters by dipping in hops beta acids solutions

Hops beta acids (HBA) are parts of hops flowers used in beer brewing and have shown antilisterial activity in bacteriological broth. The U.S. Department of Agriculture, Food Safety and Inspection Service has approved HBA for use to control Listeria monocytogenes on ready-to-eat meat products. This study evaluated the effects of HBA as dipping solutions to control L. monocytogenes during storage of frankfurters. Frankfurters (two replicates and three samples each) were inoculated (1.9 +/- 0.1 log CFU/cm2) with L. monocytogenes (10-strain mixture), dipped (2 min, 25 +/- 2 degrees C) in HBA solutions (0.03, 0.06, and 0.10%) or distilled water, and then vacuum packaged and stored at 4 or 10 degrees C for up to 90 and 48 days, respectively. Samples were periodically analyzed for microbial survival and growth on tryptic soy agar plus 0.6% yeast extract and PALCAM agar. Dipping in HBA solutions caused immediate L. monocytogenes reductions (P < 0.05) of 1.3 to 1.6 log CFU/cm2, whereas distilled water reduced counts by 1.0 log CFU/cm2. Pathogen growth was completely suppressed (P < 0.05) for 30 to 50 (4 degrees C) or 20 to 28 (10 degrees C) days on frankfurters dipped in HBA solutions, with antilisterial effects increasing with higher concentrations (0.03 to 0.10%). Fitting the data with the Baranyi model confirmed that the lag-phase duration of the pathogen was extended, and the growth rate was decreased on samples dipped in HBA solutions. Therefore, HBA may be considered for use to improve the microbial safety of ready-to-eat meat products, provided that future studies show no adverse effects on sensory qualities and that their use is economically feasible.

CYP53A15 of Cochliobolus lunatus, a target for natural antifungal compounds

A novel cytochrome P450, CYP53A15, was identified in the pathogenic filamentous ascomycete Cochliobolus lunatus. The protein, classified into the CYP53 family, was capable of para hydroxylation of benzoate. Benzoate is a key intermediate in the metabolism of aromatic compounds in fungi and yet basically toxic to the organism. To guide functional analyses, protein structure was predicted by homology modeling. Since many naturally occurring antifungal phenolic compounds are structurally similar to CYP53A15 substrates, we tested their putative binding into the active site of CYP53A15. Some of these compounds inhibited CYP53A15. Increased antifungal activity was observed when tested in the presence of benzoate. Some results suggest that CYP53A15 O-demethylation activity is important in detoxification of other antifungal substances. With the design of potent inhibitors, CYP53 enzymes could serve as alternative antifungal drug targets.

Susceptibility of food-borne bacteria to binary combinations of antimicrobials at selected awand pH

AIM

To evaluate the antibacterial susceptibilities of food-borne bacteria to individual and binary mixtures of a synthetic antimicrobial agent with a natural phenolic compound.

METHODS AND RESULTS

Antibacterial susceptibilities of Escherichia coli, Listeria innocua, Salmonella Typhimurium and Staphylococcus aureus to individual and binary mixtures of potassium sorbate with a phenolic compound (thymol, carvacrol, or eugenol) were evaluated, at selected water activity (a(w); 0.99 or 0.97) and pH (5.5 or 4.5). The bacteria studied were susceptible to the action of the antimicrobials individually with minimal inhibitory concentrations that varied from 800-ppm potassium sorbate for Staph. aureus at a(w) 0.99, and pH 5.5 to 100-ppm thymol or carvacrol for the four studied bacteria at a(w) 0.97 and pH 4.5. Several binary mixtures of potassium sorbate with thymol, carvacrol or eugenol inhibited bacterial growth. Antimicrobial agent inhibitory concentrations in the mixture varied among bacteria, additionally depending on the a(w) and the pH tested.

CONCLUSIONS

Synergistic binary mixtures with fractional inhibitory concentration index <0.6 include 100- or 200-ppm potassium sorbate with 50- or 100-ppm thymol, carvacrol or eugenol.

SIGNIFICANCE AND IMPACT OF THE STUDY

The synergistic combinations could be useful in reducing the amounts of antimicrobials needed to inhibit growth, thus diminishing consumer concerns regarding chemical preservatives.

Aspergillus flavus growth in the presence of chemical preservatives and naturally occurring antimicrobial compounds

The combined effects of water activity ([a(w)] 0.99 or 0.95), pH (4.5 or 3.5) and antimicrobial agent (potassium sorbate, sodium benzoate, sodium bisulfite, carvacrol, citral, eugenol, thymol, or vanillin) concentration (0, 100, 200 up to 1800 ppm) on the growth of Aspergillus flavus were evaluated in potato dextrose agar (PDA). Mold spore germination time and radial growth rates (RGR) were significantly (p<0.05) affected by the variables. For equal antimicrobial concentration, reduction in pH or a(w) had important effects, lowering RGR and delaying germination time. Depending on a(w) and pH, increase in antimicrobial concentration slightly reduced RGR until a critical concentration where RGR was drastically reduced or mold growth was inhibited. Germination time increased as antimicrobial agent concentration increased and when a(w) and pH decreased. Important antimicrobial differences were observed, being, in general, the natural antimicrobials less pH-dependent than chemical preservatives. A. flavus exhibited higher sensitivity to thymol, eugenol, carvacrol, potassium sorbate, sodium bisulfite, and sodium benzoate (at pH 3.5) than to vanillin or citral.