The antimicrobial paradox: why preservatives lose activity in foods

Chemical profiles and bioactivities of polyphenolic extracts of Lavandula stoechas L., Artemisia dracunculus L. and Ocimum basilicum L

This study assessed the chemical profiles and bioactivities of the infusions, decoctions and hydroethanolic extracts of tarragon, basil and French lavender. The extracts were chemically characterised (HPLC-DAD-ESI/MS) and their bioactivities were evaluated in vitro. All extracts revealed antimicrobial, antifungal and antioxidant properties. French lavender extracts showed higher total phenolic content, regardless of the extraction method used, and antioxidant and antitumour capacities, but no anti-inflammatory action. All basil and two of the tarragon extracts revealed anti-inflammatory power. Thus, tarragon, basil and French lavender extracts may be considered for inclusion in foods, as preservatives or functional ingredients. Nonetheless, further studies must be conducted to evaluate the pharmacokinetic parameters of the bioactive compounds.

Relationships between the inhibitory efficacy and physicochemical properties of six organic acids and monolaurin against Bacillus weihenstephanensis KBAB4 growth in liquid medium

Organic acids are widely used in foodstuffs to inhibit pathogen and spoiler growth. In this study, six organic acids (acetic, lactic, propionic, phenyllactic, caprylic, and lauric acid) and monolaurin were selected based on their physicochemical properties: their molecular structure (carbon chain length), their lipophilicity (logP), and their ability to dissociate in a liquid environment (pKa). The relation between these physicochemical properties and the inhibitory efficacy against B. weihenstephanensis KBAB4 growth was evaluated. After assessing the active form of these compounds against the strain (undissociated, dissociated or both forms), their MIC values were estimated in nutrient broth at pH 6.0 and 5.5 using two models (Lambert & Pearson, 2000; Luong, 1985). The use of two models highlighted the mode of action of an antibacterial compound in its environment, thanks to the additional estimation of the curve shape α or the Non-Inhibitory Concentration (NIC). The undissociated form of the tested acids is responsible for growth inhibition, except for lauric acid and monolaurin. Moreover, long-carbon chain acids have lower estimated MICs, compared to short-chain acids. Thus, the inhibitory efficacy of organic acids is strongly related to their carbon chain length and lipophilicity. Lipophilicity is the main mechanism of action of a membrane-active compound, it can be favored by long chain structure or high pKa in an acid environment like food.

Effect of the Addition of Dandelion (Taraxacum officinale) on the Protein Profile, Antiradical Activity, and Microbiological Status of Raw-Ripening Pork Sausage

The study evaluated the effect of adding dandelion extract on the characteristics of raw-ripening pork sausages while reducing the nitrite addition from 150 to 80 mg/kg. The sausages were made primarily from pork ham (80%) and pork jowl (20%). The process involved curing, preparing the meat stuffing, forming the links, and then subjecting the sausages to a 21-day ripening period. Physicochemical parameters such as pH, water activity, and oxidation-reduction potential were compared at the beginning of production and after the ripening process. The study also examined the impact of ripening on protein metabolism in pork sausages and compared the protein profiles of different sausage variants. The obtained research results indicate that dandelion-leaf extract (Taraxacum officinale) were rich in phenolic acids, flavonoids, coumarins, and their derivatives (LC-QTOF-MS method). Antiradical activity test against the ABTS+* and DPPH radical, and the TBARS index, demonstrated that addition of dandelion (0.5-1%) significantly improved the oxidative stability of raw-ripening sausages with nitrite content reduction to 80 mg/kg. A microbiological evaluation of the sausages was also carried out to assess the correctness of the ripening process. The total number of viable bacteria, lactic acid bacteria, and coliforms were evaluated and subsequently identified by mass spectrometry.

Recent advances on erythorbyl fatty acid esters as multi-functional food emulsifiers

Over the past few decades, food scientists have investigated a wide range of emulsifiers to manufacture stable and safe emulsion-based food products. More recently, the development of emulsifiers with multi-functionality, which is the ability to have more than two functions, has been considered as a promising strategy for resolving rancidification and microbial contamination in emulsions. Erythorbyl fatty acid esters (EFEs) synthesized by enzymatic esterification of hydrophilic erythorbic acid and hydrophobic fatty acid have been proposed as multi-functional emulsifiers since they simultaneously exhibit amphiphilic, antioxidative, and antibacterial properties in both aqueous and emulsion systems. This review provides current knowledge about EFEs in terms of enzymatic synthesis and multi-functionality. All processes for synthesizing and identifying EFEs are discussed. Each functionality of EFEs and the proposed mechanism are described with analytical methodologies and experimental details. It would provide valuable insights into the development and application of a multi-functional emulsifier in food emulsion chemistry.

Date (Phoenix dactylifera L.) seed oil is an agro-industrial waste with biopreservative effects and antimicrobial activity

Antimicrobial resistant (AMR) infections are a leading health threat globally. Previous literature has underscored the farm-to-fork continuum as a potential focal point for the emergence and spread of AMR. In the present study, date (Phoenix dactylifera L.) seed oil was investigated for its chemical composition and antimicrobial activity against common foodborne pathogens including Escherichia coli O157:H7, Salmonella enteritidis, Salmonella typhimurium, Listeria monocytogenes, and Staphylococcus aureus in vitro, and in ultra-high-temperature (UHT) milk as a food model at storage temperatures of 37 °C (24 h) and 10 °C (7 days). GC-MS analysis of the seed oil revealed 20 compounds, with octadecane (52.2-55.4%) as the major constituent, and the fatty acid analysis revealed 17 fatty acids, with oleic acid (42.3-43.1%) as the main constituent, followed by lauric acid (19.8-20.3%). The antimicrobial activity of date seed oil was determined using the microdilution method. A significant inhibition against gram-negative bacteria was noted in microbiological media and UHT milk, with a log reduction ranging from 4.3 to 6.7 (at 37 °C/24 h) and 5.7 to 7.2 (at 10 °C/7 days), respectively, at oil concentrations ranging between 10 and 15 µl/ml. The oil showed a similar significant inhibitory effect against St. aureus in the microbiological media (2.0-6.0 log reduction), whereas the inhibitory effect against L. monocytogenes was not statistically significant, with a maximum log reduction of 0.64 achieved at a concentration of 10 µl/ml. AFM imaging of the bacteria showed that oil treatment led to morphological changes in the bacteria including the formation of distorted shapes, surface blebs, indentations, stiffness, and swelling. Present findings suggest that date seed oil can be a promising by-product with potential antimicrobial activity and a food preservative.

Food matrix design can influence the antimicrobial activity in the food systems: A narrative review

Antimicrobial agents are safe preservatives having the ability to protect foods from microbial spoilage and extend their shelf life. Many factors, including antimicrobials' chemical features, storage environments, delivery methods, and diffusion in foods, can affect their antimicrobial activities. The physical-chemical characteristics of the food itself play an important role in determining the efficacy of antimicrobial agents in foods; however the mechanisms behind it have not been fully explored. This review provides new insights and comprehensive knowledge regarding the impacts of the food matrix, including the food components and food (micro)structures, on the activities of antimicrobial agents. Studies of the last 10 years regarding the influences of the food structure on the effects of antimicrobial agents against the microorganisms' growth were summarized. The mechanisms underpinning the loss of the antimicrobial agents' activity in foods are proposed. Finally, some strategies/technologies to improve the protection of antimicrobial agents in specific food categories are discussed.

Minimum Inhibitory Concentration (MIC) of Propionic Acid, Sorbic Acid, and Benzoic Acid against Food Spoilage Microorganisms in Animal Products to Use MIC as Threshold for Natural Preservative Production

Some preservatives are naturally contained in raw food materials, while in some cases may have been introduced in food by careless handling or fermentation. However, it is difficult to distinguish between intentionally added preservatives and the preservatives naturally produced in food. The objective of this study was to evaluate the minimum inhibitory concentration (MIC) of propionic acid, sorbic acid, and benzoic acid for inhibiting food spoilage microorganisms in animal products, which can be useful in determining if the preservatives are natural or not. The broth microdilution method was used to determine the MIC of preservatives for 57 microorganisms. Five bacteria that were the most sensitive to propionic acid, benzoic acid, and sorbic acid were inoculated in unprocessed and processed animal products. A hundred microliters of the preservatives were then spiked in samples. After storage, the cells were counted to determine the MIC of the preservatives. The MIC of the preservatives in animal products ranged from 100 to 1,500 ppm for propionic acid, from 100 to >1,500 ppm for benzoic acid, and from 100 to >1,200 ppm for sorbic acid. Thus, if the concentrations of preservatives are below the MIC, the preservatives may not be added intentionally. Therefore, the MIC result will be useful in determining if preservatives are added intentionally in food.

Genetic, physiological, and cellular heterogeneities of bacterial pathogens in food matrices: Consequences for food safety

In complex food systems, bacteria live in heterogeneous microstructures, and the population displays phenotypic heterogeneities at the single-cell level. This review provides an overview of spatiotemporal drivers of phenotypic heterogeneity of bacterial pathogens in food matrices at three levels. The first level is the genotypic heterogeneity due to the possibility for various strains of a given species to contaminate food, each of them having specific genetic features. Then, physiological heterogeneities are induced within the same strain, due to specific microenvironments and heterogeneous adaptative responses to the food microstructure. The third level of phenotypic heterogeneity is related to cellular heterogeneity of the same strain in a specific microenvironment. Finally, we consider how these phenotypic heterogeneities at the single-cell level could be implemented in mathematical models to predict bacterial behavior and help ensure microbiological food safety.

Application of essential oils in packaging films for the preservation of fruits and vegetables: A review

Fruits and vegetables are highly perishable in nature. Several factors could affect the quality and shelf life of fruits and vegetables. Packaging materials (usually made up of polymers, proteins, lipids, polysaccharides, etc.,) are incorporated with essential oil (EO) which is high in antimicrobial and antioxidant compounds that can enhance the shelf life of fruits and vegetables without affecting their quality. However, the use of EO for postharvest preservation can alter the organoleptic properties of fresh produce. Exploiting synergistic interactions between several EOs, encapsulation of EO, or combining EO with non-thermal techniques such as irradiation, UV-C, cold plasma, ultrasound, etc., may help in preventing the spoilage of food products at lower concentrations without altering their organoleptic properties. This review aims to discuss the overview and current scenario of packaging film with EO for the preservation of fruit and vegetables. We have also discussed the spoilage mechanism of fruits and vegetables, mode of action of EOs, and the effect of EO with packaging film on antimicrobial and sensory properties of fruits and vegetables.

Nanotechnology as a Novel Approach in Combating Microbes Providing an Alternative to Antibiotics

The emergence of infectious diseases promises to be one of the leading mortality factors in the healthcare sector. Although several drugs are available on the market, newly found microorganisms carrying multidrug resistance (MDR) against which existing drugs cannot function effectively, giving rise to escalated antibiotic dosage therapies and the need to develop novel drugs, which require time, money, and manpower. Thus, the exploitation of antimicrobials has led to the production of MDR bacteria, and their prevalence and growth are a major concern. Novel approaches to prevent antimicrobial drug resistance are in practice. Nanotechnology-based innovation provides physicians and patients the opportunity to overcome the crisis of drug resistance. Nanoparticles have promising potential in the healthcare sector. Recently, nanoparticles have been designed to address pathogenic microorganisms. A multitude of processes that can vary with various traits, including size, morphology, electrical charge, and surface coatings, allow researchers to develop novel composite antimicrobial substances for use in different applications performing antimicrobial activities. The antimicrobial activity of inorganic and carbon-based nanoparticles can be applied to various research, medical, and industrial uses in the future and offer a solution to the crisis of antimicrobial resistance to traditional approaches. Metal-based nanoparticles have also been extensively studied for many biomedical applications. In addition to reduced size and selectivity for bacteria, metal-based nanoparticles have proven effective against pathogens listed as a priority, according to the World Health Organization (WHO). Moreover, antimicrobial studies of nanoparticles were carried out not only in vitro but in vivo as well in order to investigate their efficacy. In addition, nanomaterials provide numerous opportunities for infection prevention, diagnosis, treatment, and biofilm control. This study emphasizes the antimicrobial effects of nanoparticles and contrasts nanoparticles' with antibiotics' role in the fight against pathogenic microorganisms. Future prospects revolve around developing new strategies and products to prevent, control, and treat microbial infections in humans and other animals, including viral infections seen in the current pandemic scenarios.

Evaluation of antimicrobial activities of plant aqueous extracts against Salmonella Typhimurium and their application to improve safety of pork meat

Nine odorless laboratory-collected hydro-distilled aqueous extracts (basil, calendula, centrifuged oregano, corn silk, laurel, oregano, rosemary, spearmint, thyme) and one industrial steam-distilled oregano hydrolate acquired as by-products of essential oils purification were screened for their in vitro antimicrobial activity against three Salmonella Typhimurium strains (4/74, FS8, FS115) at 4 and 37 °C. Susceptibility to the extracts was mainly plant- and temperature-dependent, though strain dependent effects were also observed. Industrial oregano hydrolate eliminated strains immediately after inoculation, exhibiting the highest antimicrobial potential. Hydro-distilled extracts eliminated/reduced Salmonella levels during incubation at 4 °C. At 37 °C, oregano, centrifuged oregano, thyme, calendula and basil were bactericidal while spearmint, rosemary and corn silk bacteriostatic. A strain-dependent effect was observed for laurel. The individual or combined effect of marinades and edible coatings prepared of industrial hydrolate and hydro-distilled oregano extracts with or without oregano essential oil (OEO) was tested in pork meat at 4 °C inoculated with FS8 strain. Lower in situ activity was observed compared to in vitro assays. Marinades and edible coatings prepared of industrial oregano hydrolate + OEO were the most efficient in inhibiting pathogen. Marination in oregano extract and subsequent coating with either 50% oregano extract + OEO or water + OEO enhanced the performance of oregano extract. In conclusion, by-products of oregano essential oil purification may be promising alternative antimicrobials to pork meat stored under refrigeration when applied in the context of multiple hurdle approach.

Oregano and Thyme Essential Oils Encapsulated in Chitosan Nanoparticles as Effective Antimicrobial Agents against Foodborne Pathogens

The use of natural compounds with biocidal activity to fight the growth of bacteria responsible for foodborne illness is one of the main research challenges in the food sector. This study reports the preparation and physicochemical characterization of chitosan nanoparticles loaded with Thymus capitatus (Th-CNPs) and Origanum vulgare (Or-CNPs) essential oils. The nanosystems were obtained by ionotropic gelation technique with high encapsulation efficiency (80-83%) and loading capacity (26-27%). Nanoparticles showed a spherical shape, bimodal particle size distribution, and good stability (zeta potential values > 40 mV). The treatment of the nanosuspensions at different temperatures (4 and 40 °C) and storage times (7, 15, 21, and 30 days) did not affect their physicochemical parameters and highlights their reservoir ability for essential oils also under stressful conditions. Both Or-CNPs and Th-CNPs exhibited an enhanced bactericidal activity against foodborne pathogens (S. aureus, E. coli, L. monocytogenes) than pure essential oils. These ecofriendly nanosystems could represent a valid alternative to synthetic preservatives and be of interest for health and food safety.

Encapsulation of phenolic compounds within nano/microemulsion systems: A review

Phenolic compounds (phenolics) have received great attention in the food, pharmaceutical and nutraceutical industries due to their health-promoting attributes. However, their extensive use is limited mainly due to their poor water dispersibility and instability under both processing conditions and/or gastrointestinal interactions, affecting their bioavailability/bioaccessibility. Therefore, different nanocarriers have been widely used to encapsulate phenolics and overcome the aforementioned challenges. To the best of our knowledge, besides many research studies, no comprehensive review on encapsulation of phenolics by microemulsions (MEs) and nanoemulsions (NEs) has been published so far. The present study was therefore attempted to review the loading of phenolics into MEs and NEs. In addition, the fundamental characteristics of the developed systems such as stability, encapsulation efficiency, cytotoxicity, bioavailability and releasing rate are also discussed. Both MEs and NEs are proved as appropriate vehicles to encapsulate and protect phenolics which may expand their applications in foods, supplements and pharmaceuticals.

The antimicrobial activity of silver nanoparticles biocomposite films depends on the silver ions release behaviour

This study aimed to investigate the release of silver ions from the packaging, their diffusion within a food hydrogel and the effect on the growth of Pseudomonas fluorescens. Biosorbed-silver nanoparticles (BSNPs) were synthesized using a plant extract and were incorporated into chitosan or poly (vinyl alcohol) polymer to prepare biocomposite films. The addition of BSNPs improved the physical and antimicrobial properties of the films as shown by tensile strength and inhibition of P. fluorescens in hydrogels, respectively. PVA based BSNPs film showed a stronger antimicrobial effect, compared to chitosan based BSNPs film and this correlated with a higher amount of silver ions release from the PVA film into the hydrogel. Results suggest that the strength of the interaction between BSNPs and the film polymer is the key factor leading to the difference in the release behaviour of the antimicrobials, which in turn determines the antimicrobial activity of the active packaging.

Nanoemulsion-Based Technologies for Delivering Natural Plant-Based Antimicrobials in Foods

There is increasing interest in the use of natural preservatives (rather than synthetic ones) for maintaining the quality and safety of foods due to their perceived environmental and health benefits. In particular, plant-based antimicrobials are being employed to protect against microbial spoilage, thereby improving food safety, quality, and shelf-life. However, many natural antimicrobials cannot be utilized in their free form due to their chemical instability, poor dispersibility in food matrices, or unacceptable flavor profiles. For these reasons, encapsulation technologies, such as nanoemulsions, are being developed to overcome these hurdles. Indeed, encapsulation of plant-based preservatives can improve their handling and ease of use, as well as enhance their potency. This review highlights the various kinds of plant-based preservatives that are available for use in food applications. It then describes the methods available for forming nanoemulsions and shows how they can be used to encapsulate and deliver plant-based preservatives. Finally, potential applications of nano-emulsified plant-based preservatives for improving food quality and safety are demonstrated in the meat, fish, dairy, and fresh produce areas.

A critical review on intelligent and active packaging in the food industry: Research and development

The emergence of many new food products on the market with need of consumers to constantly monitor their quality until consuming, in addition to the necessity for reducing food corruption during preservation time, have led to the development of some modern packaging technologies such as intelligent packaging (IP) and active packaging (AP). The benefits of IP are detecting defects, quality monitoring and tracking the packaged food products to control the storage conditions from the production stage to the consumption stage by using various sensors and indicators such as time-temperature indicators (TTIs), gas indicators, humidity sensors, optical, calorimetric and electrochemical biosensors. While, AP helps to increase the shelf-life of products by using absorbing and diffusion systems for various materials like carbon dioxide, oxygen, and ethanol. However, there are some important issues over these emerging technologies including cost, marketability, consumer acceptance, safety and organoleptic quality of the food and emphatically environmental safety concerns. Therefore, future researches should be conducted to solve these problems and to prompt applications of IP and AP in the food industry. This paper reviews the latest innovations in these advanced packaging technologies and their applications in food industry. The IP systems namely indicators, barcoding techniques, radio frequency identification systems, sensors and biosensor are reviewed and then the latest innovations in AP methods including scavengers, diffusion systems and antimicrobial packaging are reviewed in detail.

Rapid assessment and prediction of the efficiency of two preservatives against S. aureus in cosmetic products using High Content Screening-Confocal Laser Scanning Microscopy

Most cosmetic products are susceptible to microbiological spoilage due to contaminations that could happen during fabrication or by consumer’s repetitive manipulation. The composition of cosmetic products must guarantee efficient bacterial inactivation all along with the product shelf life, which is usually assessed by challenge-tests. A challenge-test consists in inoculating specific bacteria, i.e. Staphylococcus aureus, in the formula and then investigating the bacterial log reduction over time. The main limitation of this method is relative to the time-consuming protocol, where 30 days are needed to obtain results. In this study, we have proposed a rapid alternative method coupling High Content Screening—Confocal Laser Scanning Microscopy (HCS-CLSM), image analysis and modeling. It consists in acquiring real-time S. aureus inactivation kinetics on short-time periods (typically 4h) and in predicting the efficiency of preservatives on longer scale periods (up to 7 days). The action of two preservatives, chlorphenesin and benzyl alcohol, was evaluated against S. aureus at several concentrations in a cosmetic matrix. From these datasets, we compared two secondary models to determine the logarithm reduction time (Dc) for each preservative concentration. Afterwards, we used two primary inactivation models to predict log reductions for up to 7 days and we compared them to observed log reductions. The IQ model better fits datasets and the Q value gives information about the matrix level of interference.

Incorporation of nanoencapsulated garlic essential oil into edible films: A novel approach for extending shelf life of vacuum-packed sausages

The efficacy of chitosan (CH) and whey protein (WP) films impregnated with garlic essential oil (GEO, 2% v/v) or nanoencapsulated GEO (NGEO, 2% v/v) to extend the shelf life of refrigerated vacuum-packed sausages were assessed and compared during 50 days. The primary evaluation of GEO and NGEO showed that GEO had a considerable amount of active compounds diallyl sulfide derivatives (~67%) and the mean size and zeta potential of NGEO were 101 nm and -7.27 mV, respectively. Based on the microbiological and lipid stability analysis of the sausages, all active films retarded lipid oxidation and the growth of main spoilage bacterial groups compared to the control, and CH film containing NGEO exhibited the best result with the peroxide value, thiobarbituric acid reactive substances and aerobic plate count of 0.37 (meq/kg lipid), 0.47 (mg malondialdehyde/kg) and 3.69 (log CFU/g), respectively, on day 50. The nanoencapsulation of GEO made no significant differences in the sensory properties comparing to free-GEO samples (P < .05).

Influence of Protein Type on the Antimicrobial Activity of LAE Alone or in Combination with Methylparaben

The cationic surfactant Lauric arginate (LAE) has gained approval for utilization in meat products (limit: 200 mg/kg). However, as for other antimicrobials, its activity is reduced when applied to complex food matrices. The current study therefore aims to better understand protein-antimicrobial agent-interactions and their influence on the antimicrobial activity of (i) LAE and (ii) methylparaben against Listeria innocua and Pseudomonas fluorescens in defined model systems (pH 6). Antimicrobials were utilized alone or in combination with nutrient broth containing either no protein or 2% bovine serum albumin, whey protein isolate, or soy protein hydrolysate. LAE was found to form complexes with all proteins due to electrostatic attraction, determined using microelectrophoretic and turbidity measurements. Minimal lethal concentrations of LAE were remarkably increased (4-13 fold) in the presence of proteins, with globular proteins having the strongest impact. Combinations of LAE (0-200 µg/mL) with the less structure-sensitive component methylparaben (approved concentration 0.1%) remarkably decreased the concentrations of LAE needed to strongly inhibit or even kill both, L. innocua and P. fluorescens in the presence of proteins. The study highlights the importance of ingredient interactions impacting microbial activity that are often not taken into account when examining antimicrobial components having different structure sensitivities.

Evaluation of antimicrobial activity of rambutan (Nephelium lappaceum L.) peel extracts

Microbial safety in food products is not always adequately controlled. Chemical antimicrobials which are recognized as hazards to human health are gradually replaced by natural antimicrobial compounds. In the current study, the antimicrobial activity against some Gram-positive and Gram- negative bacteria by the methanolic extract from rambutan fruit peels was evaluated using both in vitro (medium) and in situ (food matrices i.e. raw chicken breast and pangasius fillet fish) methods. Methanolic rambutan peel extract (lyophilized to powder with total phenolic content of 310 ± 14.5 mg GAE/g) with geraniin, ellagic acid, rutin, quercetin, and corilagin as main phenolic compounds was a potent inhibitor towards E. coli, V. campbellii, V. parahaemolyticus, V. anguillarum, P. aeruginosa, S. enteritidis, St. aureus, L. monocytogenes, and C. albicans using in vitro tests. In in situ tests, the extract inhibited S. enteritidis in raw chicken breast during 14 days of cold storage at 4 °C. Even though food matrices partly protected bacteria, the extract showed a 1.5 log CFU/g reduction of V. parahaemolyticus in fish during 10 days of cold storage. These results provide useful information on the utilization of rambutan fruit peel as natural antimicrobial agent in food products.

Antifungal Activity of Selected Natural Preservatives against Aspergillus westerdijkiae and Penicillium verrucosum and the Interactions of These Preservatives with Food Components

The present study examined the influence of primary food components on the antifungal activity of the essential oil of Origanum vulgare, carvacrol, thymol, eugenol, and trans-cinnamaldehyde against Penicillium verrucosum and Aspergillus westerdijkiae. The MIC was determined in food model media enriched with proteins (1, 5, or 10%), carbohydrates (1, 4, or 6%), or oil (1, 5, or 10%). Proteins increased the antifungal activity of O. vulgare essential oil, carvacrol, thymol, and eugenol, whereas the effect of trans-cinnamaldehyde decreased with increasing protein content. The presence of carbohydrates diminished the inhibitory effect of the natural preservatives on A. westerdijkiae; for P. verrucosum, their inhibitory effect increased with carbohydrates. Only the antifungal activity of trans-cinnamaldehyde did not depend on the carbohydrate content. The presence of oil had the strongest influence. At a concentration of 1% oil, the antifungal activity decreased significantly, and at 10% oil, almost no inhibition was observed. To investigate the effect of the antifungal agents on the morphology of the target molds, they were grown on malt extract agar containing carvacrol and trans-cinnamaldehyde and were examined by scanning electron microscopy. The hyphae, conidiophores, vesicles, and phialides were severely altered and deformed, and spore formation was clearly suppressed.

Impact of ripening inhibitors on molecular transport of antimicrobial components from essential oil nanoemulsions

The objective of this study was to provide insights into the mechanisms involved in the mass transport of antimicrobial compounds from essential oil nanoemulsions to bacterial cell membranes. Origanum oil-in-water nanoemulsions were produced using spontaneous emulsification by titrating a mixture of essential oil, ripening inhibitor, and surfactant (Tween 80) into 5 mM sodium citrate buffer (pH 3.5). Stable nanoemulsions containing relatively small droplets (d < 60 nm) were produced using this low-energy method. The nature of the ripening inhibitor used in the oil phase of the nanoemulsions affected the antimicrobial activity of the nanoemulsions: corn (LCT) > medium-chain triglycerides (MCT). Differences in antimicrobial activity were attributed to the differences in the rate of transfer of hydrophobic antimicrobial constituents from the nanoemulsion to the MCT emulsion, which was used to mimic the hydrophobic region of the bacterial cell membranes. Each antimicrobial nanoemulsion was separated from the MCT emulsion by a dialysis tubing. Dialysis tubing with two different pore sizes was used, one excluding nanoemulsion droplet and micelle delivery, allowing the delivery of antimicrobial compounds only through the aqueous phase and the other by both the aqueous phase and micelles. For origanum oil nanoemulsions, the delivery of all antimicrobial agents occurred more efficiently when micelles were present.

Antimicrobial activity of bioactive starch packaging films against Listeria monocytogenes and reconstituted meat microbiota on ham

Contamination with spoilage organisms and Listeria monocytogenes are major concerns for quality and safety of cooked ready-to-eat (RTE) meat products. Thus, the objective of this study was to investigate the use of antimicrobial starch packaging films to control competitive microbiota and L. monocytogenes growth on a RTE ham product. Starch packaging films were prepared with different bioactives, gallic acid, chitosan, and carvacrol, using subcritical water technology. The viability of the incorporated strains on ham in contact with different antimicrobial starch packaging films was examined during 28-day storage period at 4 °C. Starch films with gallic acid had the least effect on ham antimicrobial activity; starch films with chitosan and carvacrol fully inhibited L. monocytogenes growth throughout 4 weeks of storage. RTE meat microbiota was more resistant to the antimicrobials than L. monocytogenes. Starch films loaded with chitosan or chitosan and carvacrol did not fully inhibit growth of RTE meat microbiota but delayed growth of RTE meat microbiota by one to two weeks. Moreover, competitive meat microbiota fully inhibited growth of L. monocytogenes. Therefore, antimicrobial starch packaging films prepared by subcritical water technology used in this study showed a promising effect on inhibiting L. monocytogenes in RTE ham.

Ferulic Acid and Eugenol Have Different Abilities to Maintain Their Inhibitory Activity Against Listeria monocytogenes in Emulsified Systems

Natural phenolic compounds are found in large quantities in plants and plant extracts and byproducts from agro-industries. They could be used to ensure food quality and safety due to their antimicrobial properties demonstrated in systems such as culture media. The aim of this study was to evaluate the ability of two natural phenolic compounds, ferulic acid and eugenol, to maintain their inhibitory activity against the growth of Listeria monocytogenes in an oil-in-water emulsion, simulating a complex food system. The minimum inhibitory concentration (MIC) of each phenolic compound was first determined in culture medium, consisting of TS broth and an added emulsifier. Whey proteins and Tween 80 increased the MIC of the antimicrobial activity of eugenol. The MIC of ferulic acid was less affected by the addition of Tween 80. The inhibitory activities of both phenolic compounds were then compared at the same concentration in emulsions and their corresponding aqueous phases by following the growth of L. monocytogenes by plate counting. In emulsified systems, eugenol lost the high inhibitory activity observed in the aqueous phase, whereas ferulic acid retained it. The partition coefficient (logP_oct/wat) appears to be a key factor. Eugenol (logP_oct/wat = 2.61) dispersed in the aqueous phase intercalates into the bacterial membrane and has high antimicrobial activity. In contrast, it likely preferentially partitions into the lipid droplets when dispersed in an emulsion, consequently losing its antimicrobial activity. As ferulic acid is more hydrophilic, a higher proportion probably remains in the aqueous phase of the emulsion, retaining its antimicrobial activity.

Plants of Genus Mentha: From Farm to Food Factory

Genus Mentha, a member of Lamiaceae family, encompasses a series of species used on an industrial scale and with a well-described and developed culture process. Extracts of this genus are traditionally used as foods and are highly valued due to the presence of significant amounts of antioxidant phenolic compounds. Many essential oil chemotypes show distinct aromatic flavor conferred by different terpene proportions. Mint extracts and their derived essential oils exert notable effects against a broad spectrum of bacteria, fungi or yeasts, tested both in vitro or in various food matrices. Their chemical compositions are well-known, which suggest and even prompt their safe use. In this review, genus Mentha plant cultivation, phytochemical analysis and even antimicrobial activity are carefully described. Also, in consideration of its natural origin, antioxidant and antimicrobial properties, a special emphasis was given to mint-derived products as an interesting alternative to artificial preservatives towards establishing a wide range of applications for shelf-life extension of food ingredients and even foodstuffs. Mentha cultivation techniques markedly influence its phytochemical composition. Both extracts and essential oils display a broad spectrum of activity, closely related to its phytochemical composition. Therefore, industrial implementation of genus Mentha depends on its efficacy, safety and neutral taste.

Antifungal activity of nanoemulsions encapsulating oregano (Origanum vulgare) essential oil: in vitro study and application in Minas Padrão cheese

The objective of this study was to evaluate the antifungal activity of nanoemulsions encapsulating essential oil of oregano (Origanum vulgare), both in vitro and after application on Minas Padrão cheese. Nanodispersions were obtained by the phase inversion temperature method. Cladosporium sp., Fusarium sp., and Penicillium sp. genera were isolated from cheese samples and used to evaluate antifungal activity. Minimal inhibitory concentrations of non-encapsulated and encapsulated oregano essential oil were determined, and they were influenced by the encapsulation of the essential oil depending on the type of fungus. The antifungal activity of the nanoencapsulated oregano essential oil in cheese slices showed no evidence of an effect of the MICs, when applied in the matrix. On the other hand, an influence of contact time of the nanoemulsion with the cheese was observed, due to the increase in water activity. It was concluded that nanoencapsulated oregano essential oil presented an inhibitory effect against the three genera of fungi evaluated. If environmental parameters, such as storage temperature and water activity, were controlled, the inhibitory effect of nanoemulsions of oregano oil could possibly be greatly improved, and they could be presented as a potential alternative for the preservation of Minas Padrão cheese against fungal contamination.

Combined effects of oregano essential oil and salt on the growth of Escherichia coli in salad dressing

There is a broad research interest in the search for alternatives to chemical additives for use as natural food preservatives. Although many natural compounds have biological in vitro properties evidenced, in situ studies are still scarce. This study evaluated the effect of oregano essential oil (OEO) and salt (NaCl) concentrations against Escherichia coli (ATCC 8739), in salad dressing, using the response surface methodology. The experiment included a 2² central composite rotatable design (CCRD) in a total of 11 formulations of salad dressings. Oregano essential oil was characterized by gas chromatography and salad dressings by ash, lipids, proteins and moisture. OEO was composed mainly by carvacrol (65.1%) and p-cymene (12.0%). Salad dressings showed similar chemical profiles. A mathematical model for the prediction of the antibacterial activity in salad dressing was obtained. The results revealed that the interaction between OEO and salt showed effect on the bacterial count. However, the effect of salt was negative suggesting that the highest NaCl concentrations decreases the bacterial count. Therefore, within the parameters studied, the use of OEO to control E. coli in salad dressing can be considered promising and allows reduction in the levels of salt to be incorporated in food.

A review on influencing factors on the minimum inhibitory concentration of essential oils

With growing interest in essential oils as natural preservatives in the food industry, the literature is expanding enormously. To understand the antimicrobial activity of essential oils, the antimicrobial mechanism of individual essential oil (EO) compounds, and their minimum inhibitory concentrations (MICs), are interesting starting points for research. Therefore, and to get insight into the factors influencing their antimicrobial activities, the Web of Science was searched for MICs of EO compounds (1995-2016). Many MICs for individual EO compounds have already been reported in the literature, but there is large variability in these data, even for the MIC of the same compound against the same species. No correlation was found between the tested structural parameters of EO compounds (polarity, water solubility, dissociation constant, molecular weight and molecular complexity) and their MICs against all microorganisms, Gram-negative bacteria, Gram-positive bacteria and fungi. Few clear differences in sensitivity between microorganisms could be found. Based on this review it is clear that different incubation conditions, culture media and the use of emulsifiers/solvents have an influence on the MIC, causing big variance. This review points out the need for a good international standard method to assess the antimicrobial activity of EO compounds for better comparability between studies.

Use of Foodomics for Control of Food Processing and Assessing of Food Safety

Food chain, food safety, and food-processing sectors face new challenges due to globalization of food chain and changes in the modern consumer preferences. In addition, gradually increasing microbial resistance, changes in climate, and human errors in food handling remain a pending barrier for the efficient global food safety management. Consequently, a need for development, validation, and implementation of rapid, sensitive, and accurate methods for assessment of food safety often termed as foodomics methods is required. Even though, the growing role of these high-throughput foodomic methods based on genomic, transcriptomic, proteomic, and metabolomic techniques has yet to be completely acknowledged by the regulatory agencies and bodies. The sensitivity and accuracy of these methods are superior to previously used standard analytical procedures and new methods are suitable to address a number of novel requirements posed by the food production sector and global food market.

The Challenges of Eliminating or Substituting Antimicrobial Preservatives in Foods

Consumers' criteria for evaluating food safety have evolved recently from considering the food's potential to cause immediate physical harm to considering the potential long-term effects that consumption of artificial ingredients, including antimicrobial preservatives, would have on health. As bacteriostatic and bactericidal agents to prevent microbial spoilage, antimicrobials not only extend shelf life, but they also enhance the product's safety. Antimicrobials and their levels that may be used in foods are specified by regulatory agencies. This review addresses the safety of antimicrobials and the potential consequences of removing those that are chemically synthesized or replacing them with antimicrobials from so-called natural sources. Such changes can affect the microbiological safety and spoilage of food as well as reduce shelf life, increase wastage, and increase the occurrence of foodborne illnesses.

Atividade antisséptica do óleo essencial de Lippia origanoides Cham. (Alecrim-pimenta) na presença de leite bovino

Resumo: Objetivou-se determinar atividade antisséptica do óleo essencial de Lippia origanoides na presença de leite bovino. A composição química do óleo essencial de alecrim pimenta foi determinada por cromatografia gasosa acoplada à espectrometria de massas (CG-EM), sendo detectados 53 compostos, dos quais 16 foram identificados (>0,1% área total). O carvacrol (32,7%), p-cimeno (23%), timilmetil éter, cariofileno (7,98%) e o γ-terpineno (5,40%) foram os componentes mais abundantes. A concentração inibitória mínima para Staphylococcus aureus ATCC 25923 e E. coli ATCC 8739 foi de 60μL/mL, enquanto para Salmonella Choleraesuis ATCC 35640 foi de 90μL/mL. A concentração bactericida mínima foi de 120μL/mL para as três bactérias. Avaliou-se a atividade antisséptica do óleo essencial na concentração de 120μL/mL na presença de leite bovino sobre as mesmas cepas bacterianas. O óleo em estudo apresentou efeito inibitório do crescimento das cepas em diferentes tempos de ação (p<0,05). S. aureus apresentou maiores índices de inibição após 5 min de contato e Escherichia coli e Salmonella Choleraesuis após 15 min. O óleo essencial de alecrim-pimenta revelou ser um potencial antimicrobiano natural, mesmo na presença de matéria orgânica constituída de uma matriz nutricional complexa que é o leite bovino.