Reverse micelles as nano-carriers of nisin against foodborne pathogens. Part II: The case of essential oils

Multiple potential strategies for the application of nisin and derivatives

Nisin is a naturally occurring bioactive small peptide produced by Lactococcus lactis subsp. lactis and belongs to the Type A (I) lantibiotics. Due to its potent antimicrobial activity, it has been broadly employed to preserve various food materials as well as to combat a variety of microbial pathogens. The present review discusses the antimicrobial properties of nisin and different types of their derivatives employed to treat microbial pathogens with a detailed underlying mechanism of action. Several alternative strategies such as combination, conjugation, and nanoformulations have been discussed in order to address several issues such as rapid degradation, instability, and reduced activity due to the various environmental factors that arise in the applications of nisin. Furthermore, the evolutionary relationship of many nisin genes from different nisin-producing bacterial species has been investigated. A detailed description of the natural and bioengineered nisin variants, as well as the underlying action mechanisms, has also been provided. The chemistry used to apply nisin in conjugation with natural or synthetic compounds as a synergetic mode of antimicrobial action has also been thoroughly discussed. The current review will be useful in learning about recent and past research that has been performed on nisin and its derivatives as antimicrobial agents.

Effects of conjugates of ε-polylysine-dextran created through Maillard reaction on quality and storage stability of the chicken gel

The present study mainly focused on the effects of the conjugates of PL-dextran produced through the Maillard reaction on the quality and storage stability of chicken gel for 5 days at 4 ℃. According to the results of the texture profile, water retention capacity (WRC), low-field nuclear magnetic resonance (LF NMR), aerobic plate count (APC), and total volatile basic nitrogen (TVBN), ε-polylysine (PL) could improve chicken gel storage stability while decreasing the quality of protein gels (p < 0.05). Additionally, adding dextran with high or low molecular weight could significantly increase the quality of gel during storage (p < 0.05), whereas decreased storage stability could be obtained (p < 0.05). In general, conjugates formed by PL and dextran with high molecular weight were beneficial for quality maintenance. In comparison, the polymers produced from the low molecular weight of dextran could modify the storage stability of gels. Adding conjugates of dextran and PL benefited the structure formation of protein gel, while PL would retain part of antibacterial activity when crosslinked with dextran. Therefore, it could be concluded that the quality improvement effect of PL-dextran addition on gel quality was greater than its antibacterial effect, which would impact the formulation design of novel emulsion-type meat products.

Antimicrobial Impacts of Microbial Metabolites on the Preservation of Fish and Fishery Products: A Review with Current Knowledge

Microbial metabolites have proven effects to inhibit food spoilage microbiota, without any development of antimicrobial resistance. This review provides a recent literature update on the preservative action of metabolites derived from microorganisms on seafood. Fish and fishery products are regarded as a myriad of nutrition, while being highly prone to spoilage. Several proven controversies (antimicrobial resistance and health issues) related to the use of synthetic preservatives have caused an imminent problem. The demand for minimally processed and naturally preserved clean-label fish and fishery products is on rise. Metabolites derived from microorganisms have exhibited diverse preservation capacities on fish and fishery products' spoilage. Inclusions with other preservation techniques, such as hurdle technology, for the shelf-life extension of fish and fishery products are also summarized.

Plant Extracts for the Control of Listeria monocytogenes in Meat Products

The antimicrobial activity of garlic (Allium sativum L.) and onion (Allium cepa L.) plant active extracts was determined against Listeria monocytogenes in two meat products. Samples of sausages “cacciatore” and cooked ham in vacuum-packaged slices were artificially contaminated, and the presence of Listeria was evaluated during the sausages ripening and throughout the shelf-life of the cooked ham. The test carried out on sausages did not show differences among treated and untreated samples. The antagonistic activity of the plant extracts against the pathogen was probably hidden by the competition from the sausages microbial flora and the pH and the water activity (aw) decrease. On the other hand, the plant extracts determined an initial reduction of about 1.00 log cfu/g of the L. monocytogenes viable count in the cooked ham slices contaminated with 103 cfu/g, but the best result was obtained with the contamination of 102 cfu/g of L. monocytogenes. In addition to the pathogen’s initial decrease, we observed an extension of the lag phase and a reduction of the Listeria growth rate. Considering that the presence of L. monocytogenes during the slicing phase of the cooked ham does not exceed 10 cfu/g, the use of plant extracts can lead to complete pathogen elimination.

Morphological and metabolomics impact of sublethal doses of natural compounds and its nanoemulsions in Bacillus cereus

Microbiological safety in food industry are always a concern regarding sublethal tolerance in bacteria for common and natural sanitizers. Natural bacteriocins, such as nisin (NIS), may negatively interfere in the efficiency of major compounds of essential oils against foodborne pathogenic bacteria. However, nanoemulsioned forms increase the bactericidal potential of natural compounds acting synergistically. In this study, cinnamaldehyde (CIN), citral (CIT), and linalool (LIN) were evaluated independently, associated with NIS, and in nanoemulsions (NEs) against Bacillus cereus using untargeted-metabolomics. Results revealed morphological changes in the structure of B. cereus treated with NEs of CIN and CIT, both NIS-associated. In addition, sensibility tests and UHPLC-QTOF-MS analyses indicated that NIS might react together with CIT reducing the bactericidal efficiency, while the nanoemulsion of CIT effect was enhanced by NIS in nanoemulsioned forms. This study highlights the importance of prudent administration of natural compounds as antimicrobial agents to prevent sublethal tolerance in pathogenic bacteria.

Natural antimicrobial-loaded nanoemulsions for the control of food spoilage/pathogenic microorganisms

Both consumers and producers of food products are looking for natural ingredients and efficient formulation strategies to improve the shelf life of final products. Natural antimicrobial ingredients such as essential oils can be applied as alternatives to synthetic preservatives, but their main challenge is low stability, adverse effects on sensory properties, low solubility, high needed doses, etc. Formulation of these bioactive compounds into nanoemulsions can be an efficient strategy to improve their properties and practical applications in food products. In this review, after an overview on nanoemulsion formulation, ingredients and fabrication methods, different types of natural antimicrobial agents have been discussed briefly. In addition, properties and action mechanisms of antimicrobial-loaded nanoemulsions, along with their application in preservation and shelf life improvement of different food products have been explained. Finally, safety and regulatory issues of antimicrobial delivery via nanoemulsions have been examined. As a conclusion antimicrobial-loaded nanoemulsions can be promising candidates and alternatives for common synthetic preservatives in real food systems.

Biocompatible Solvents and Ionic Liquid-Based Surfactants as Sustainable Components to Formulate Environmentally Friendly Organized Systems

In this review, we deal with the formation and application of biocompatible water-in-oil microemulsions commonly known as reverse micelles (RMs). These RMs are extremely important to facilitate the dissolution of hydrophilic and hydrophobic compounds for biocompatibility in applications in drug delivery, food science, and nanomedicine. The combination of two wisely chosen types of compounds such as biocompatible non-polar solvents and ionic liquids (ILs) with amphiphilic character (surface-active ionic liquids, SAILs) can be used to generate organized systems that perfectly align with the Green Chemistry concepts. Thus, we describe the current state of SAILs (protic and aprotic) to prepare RMs using non-polar but safe solvents such as esters derived from fatty acids, among others. Moreover, the use of the biocompatible solvents as the external phase in RMs and microemulsions/nanoemulsions with the other commonly used biocompatible surfactants is detailed showing the diversity of preparations and important applications. As shown by multiple examples, the properties of the RMs can be modified by changes in the type of surfactant and/or external solvents but a key fact to note is that all these modifications generate novel systems with dissimilar properties. These interesting properties cannot be anticipated or extrapolated, and deep analysis is always required. Finally, the works presented provide valuable information about the use of biocompatible RMs, making them a green and promising alternative toward efficient and sustainable chemistry.

Sustainable sources for antioxidant and antimicrobial compounds used in meat and seafood products

The contribution of food in promotion of health has become of most importance. The challenges that lie before the global food supply chain, such as climate changes, food contamination, and antimicrobial resistance may compromise food safety at international scale. Compounds with strong antimicrobial and antioxidant activity can be extracted from different natural and sustainable sources and may contribute to extend the shelf life of meat and seafood products, enhance food safety and enrich foods with additional biologically active and functional ingredients. This chapter describes the use of bioprotective cultures, essential oils, plant extracts, seaweed extracts and grape pomace compounds in production of value-added meat and seafood products with improved shelf life and safety, following the requests from the market and consumers.

Emulsions Incorporated in Polysaccharide-Based Active Coatings for Fresh and Minimally Processed Vegetables

The consumption of minimally processed fresh vegetables has increased by the consumer's demand of natural products without synthetic preservatives and colorants. These new consumption behaviors have prompted research on the combination of emulsion techniques and coatings that have traditionally been used by the food industries. This combination brings great potential for improving the quality of fresh-cut fruits and vegetables by allowing the incorporation of natural and multifunctional additives directly into food formulations. These antioxidant, antibacterial, and/or antifungal additives are usually encapsulated at the nano- or micro-scale for their stabilization and protection to make them available by food through the coating. These nano- or micro-emulsions are responsible for the release of the active agents to bring them into direct contact with food to protect it from possible organoleptic degradation. Keeping in mind the widespread applications of micro and nanoemulsions for preserving the quality and safety of fresh vegetables, this review reports the latest works based on emulsion techniques and polysaccharide-based coatings as carriers of active compounds. The technical challenges of micro and nanoemulsion techniques, the potential benefits and drawbacks of their use, the development of polysaccharide-based coatings with natural active additives are considered, since these systems can be used as alternatives to conventional coatings in food formulations.

Innovative Seafood Preservation Technologies: Recent Developments

Fish and fishery products are among the food commodities of high commercial value, high-quality protein content, vitamins, minerals and unsaturated fatty acids, which are beneficial to health. However, seafood products are highly perishable and thus require proper processing to maintain their quality and safety. On the other hand, consumers, nowadays, demand fresh or fresh-like, minimally processed fishery products that do not alter their natural quality attributes. The present article reviews the results of studies published over the last 15 years in the literature on: (i) the main spoilage mechanisms of seafood including contamination with pathogens and (ii) innovative processing technologies applied for the preservation and shelf life extension of seafood products. These primarily include: high hydrostatic pressure, natural preservatives, ozonation, irradiation, pulse light technology and retort pouch processing.

Strategies for reducing Ostwald ripening phenomenon in nanoemulsions based on thyme essential oil

BACKGROUND

White thyme essential oil, which can be incorporated in clean-label and food emulsion-based products, is a natural antimicrobial agent. However, emulsions containing essential oils commonly undergo Ostwald ripening as the main destabilization process. The main objective of this work was to evaluate various strategies for the inhibition of Ostwald ripening so as to develop stable nanoemulsions containing white thyme essential oil as food preservative and Kolliphor EL as surfactant.

RESULTS

In a first approach, the influence of the surfactant/dispersed phase ratio and the number of cycles through a microfluidizer on droplet size distribution was evaluated. Unfortunately, these emulsions underwent Ostwald ripening, which was demonstrated by the application of the Lifshitz-Slyozov-Wagner theory. In order to reduce this destabilization mechanism, two different techniques based on the modification of the formulation (addition of rosin gum or Aerosil COK84) were analysed using laser diffraction and multiple light scattering techniques. The addition of rosin gum inhibited the Ostwald ripening mechanism, but only partially. Conversely, the incorporation of Aerosil COK84 to the continuous phase led to a gel-like rheological behaviour which seemed to practically avoid Ostwald ripening.

CONCLUSIONS

Aerosil particles cover the droplets and form a three-dimensional network suggesting a Pickering stabilization, which was confirmed using transmission electronic microscopy. The results confirmed the role of Aerosil COK84, not only as a thickener or gelling agent, but also as an Ostwald ripening inhibitor. © 2019 Society of Chemical Industry.

An Overview of Micro- and Nanoemulsions as Vehicles for Essential Oils: Formulation, Preparation and Stability

The interest around essential oils is constantly increasing thanks to their biological properties exploitable in several fields, from pharmaceuticals to food and agriculture. However, their widespread use and marketing are still restricted due to their poor physico-chemical properties; i.e., high volatility, thermal decomposition, low water solubility, and stability issues. At the moment, the most suitable approach to overcome such limitations is based on the development of proper formulation strategies. One of the approaches suggested to achieve this goal is the so-called encapsulation process through the preparation of aqueous nano-dispersions. Among them, micro- and nanoemulsions are the most studied thanks to the ease of formulation, handling and to their manufacturing costs. In this direction, this review intends to offer an overview of the formulation, preparation and stability parameters of micro- and nanoemulsions. Specifically, recent literature has been examined in order to define the most common practices adopted (materials and fabrication methods), highlighting their suitability and effectiveness. Finally, relevant points related to formulations, such as optimization, characterization, stability and safety, not deeply studied or clarified yet, were discussed.

Oil-In-Water Microemulsions for Thymol Solubilization

Essential oil compounds (EOCs) are molecules with well-known antimicrobial and antipest activity. However, such molecules possess limited solubility in water, making their handling difficult. This work aimed to enhance the distribution of a solid essential oil compound, thymol, using oil-in-water (o/w) microemulsions for its solubilization. The use of mixtures formed by an alkyl polyglucoside (APG) and soybean lecithin (SL) allowed for stabilization of the o/w microemulsions in a broad range of compositions, with the total concentration of the mixture of the two surfactants (APG+SL) and the APG:SL ratio both being essential for controlling the nature of the obtained dispersions. The microemulsions obtained using oleic acid as the oil phase and with compositions far from those corresponding to the onset of the emulsion region showed a good efficiency for thymol solubilization. This is an advantage from a stability point of view, as well as for ease of thymol preparation. The present work opens new alternatives for designing eco-sustainable formulations for EOC solubilization, with the possibility of preparing the formulations at the place of use, thereby saving transport costs and reducing the emission of pollutants.

Food Safety through Natural Antimicrobials

Microbial pathogens are the cause of many foodborne diseases after the ingestion of contaminated food. Several preservation methods have been developed to assure microbial food safety, as well as nutritional values and sensory characteristics of food. However, the demand for natural antimicrobial agents is increasing due to consumers' concern on health issues. Moreover, the use of antibiotics is leading to multidrug resistant microorganisms reinforcing the focus of researchers and the food industry on natural antimicrobials. Natural antimicrobial compounds from plants, animals, bacteria, viruses, algae and mushrooms are covered. Finally, new perspectives from researchers in the field and the interest of the food industry in innovations are reviewed. These new approaches should be useful for controlling foodborne bacterial pathogens; furthermore, the shelf-life of food would be extended.

Natural products with preservative properties for enhancing the microbiological safety and extending the shelf-life of seafood: A review

Seafood is highly perishable, presenting a rapid loss of its quality soon after capture. Temperature is the critical parameter that impacts on seafood shelf-life reduction, allowing the growth of foodborne pathogens and spoilage microorganisms. In recent years, the search by additional methods of preserving seafood has increased, able to ensure quality and safety. Several natural preservatives have highlighted and gained considerable attention from the scientific community, consumers, industry, and health sectors as a method with broad action antimicrobial and generally economical. Natural preservatives, from different sources, have been widely studied, such as chitosan from animal sources, essential oils, and plant extracts from a plant source, lactic acid bacteria, and bacteriocins from microbiological sources and organic acid from different sources, all with great potential for use in seafood systems. This review focuses on the natural preservatives studied in seafood matrices, their forms of application, concentrations usually employed, their mechanisms of action, factors that interfere in their use and the synergistic effect of the interactions among the natural preservatives, with a focus for maintenance of quality and ensure of food safety.

Hydroxytyrosol encapsulated in biocompatible water-in-oil microemulsions: How the structure affects in vitro absorption

Over the last years, the incorporation of natural antioxidants in food and pharmaceutical formulations has gained attention, delaying or preventing oxidation phenomena in the final products. In order to take full advantage of their properties, protection in special microenvironments is of great importance. The unique features of the natural phenolic compound hydroxytyrosol (HT) - including antioxidant, anti-inflammatory, antiproliferative and cardioprotective properties - have been studied to clarify its mechanism of action. In the present study novel biocompatible water-in-oil (W/O) microemulsions were developed as hosts for HT and subsequently examined for their absorption profile following their oral uptake. The absorption of HT in solution was compared with the encapsulated one in vitro, using a coculture model (Caco-2/TC7 and HT29-MTX cell lines). The systems were structurally characterized by means of Dynamic Light Scattering (DLS) and Electron Paramagnetic Resonance (EPR) techniques. The diameter of the micelles remained unaltered after the incorporation of 678 ppm of HT but the interfacial properties were slightly affected, indicating the involvement of the HT molecules in the surfactant monolayer. EPR was used towards a lipophilic stable free radial, namely galvinoxyl, indicating a high scavenging activity of the systems and encapsulated HT. Finally, after the biocompatibility study of the microemulsions the intestinal absorption of the encapsulated HT was compared with its aqueous solution in vitro. The higher the surfactants' concentration in the system the lower the HT concentration that penetrated the constructed epithelium, indicating the involvement of the amphiphiles in the antioxidant's absorption and its entrapment in the mucus layer.

Essential Oils as an Intervention Strategy to Reduce Campylobacter in Poultry Production: A Review

Campylobacter is a major foodborne pathogen and can be acquired through consumption of poultry products. With 1.3 million United States cases a year, the high prevalence of Campylobacter within the poultry gastrointestinal tract is a public health concern and thus a target for the development of intervention strategies. Increasing demand for antibiotic-free products has led to the promotion of various alternative pathogen control measures both at the farm and processing level. One such measure includes utilizing essential oils in both pre- and post-harvest settings. Essential oils are derived from plant-based extracts, and there are currently over 300 commercially available compounds. They have been proposed to control Campylobacter in the gastrointestinal tract of broilers. When used in concentrations low enough to not influence sensory characteristics, essential oils have also been proposed to decrease bacterial contamination of the poultry product during processing. This review explores the use of essential oils, particularly thymol, carvacrol, and cinnamaldehyde, and their role in reducing Campylobacter concentrations both pre- and post-harvest. This review also details the suggested mechanisms of action of essential oils on Campylobacter.