Spray-dried zein capsules with coencapsulated nisin and thymol as antimicrobial delivery system for enhanced antilisterial properties

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.

Levofloxacin HCl-Incorporated Zein-Based Solvent Removal Phase Inversion In Situ Forming Gel for Periodontitis Treatment

Zein is composed of nonpolar amino acids and is a water-insoluble protein used as the matrix-forming agent of localized in situ forming gel (ISG). Therefore, this study prepared solvent removal phase inversion zein-based ISG formulations to load levofloxacin HCl (Lv) for periodontitis treatment using dimethyl sulfoxide (DMSO) and glycerol formal (GF) as the solvents. Their physicochemical properties were determined, including viscosity, injectability, gel formation, and drug release. The topography of dried remnants after drug release was revealed using a scanning electron microscope and X-ray computed microtomography (μCT) to investigate their 3D structure and % porosity. The antimicrobial activities were tested against Staphylococcus aureus (ATCC 6538), Escherichia coli ATCC 8739, Candida albicans ATCC 10231, and Porphyromonas gingivalis ATCC 33277 with agar cup diffusion. Increasing zein concentration or using GF as the solvent notably enhanced the apparent viscosity and injection force of the zein ISG. However, its gel formation slowed due to the dense zein matrix barrier's solvent exchange: the higher loaded zein or utilization of GF as an ISG solvent prolonged Lv release. The SEM and μCT images revealed the scaffold of dried ISG in that their % porosity corresponded with their phase transformation and drug release behavior. In addition, the sustainability of drug diffusion promoted a smaller antimicrobial inhibition clear zone. Drug release from all formulations was attained with minimum inhibitory concentrations against pathogen microbes and exhibited a controlled release over 7 days. Lv-loaded 20% zein ISG using GF as a solvent exhibited appropriate viscosity, Newtonian flow, acceptable gel formation and injectability, and prolonged Lv release over 7 days with efficient antimicrobial activities against various test microbes; thus, it is the potential ISG formulation for periodontitis treatment. Consequently, the Lv-loaded solvent removal zein-based ISGs proposed in this investigation offer promising potential as an efficacious drug delivery system for periodontitis treatment by local injection.

Nano-enabled plant-based colloidal delivery systems for bioactive agents in foods: Design, formulation, and application

Consumers are becoming increasingly aware of the impact of their dietary choices on the environment, animal welfare, and health, which is causing many of them to adopt more plant-based diets. For this reason, many sectors of the food industry are reformulating their products to contain more plant-based ingredients. This article describes recent research on the formation and application of nano-enabled colloidal delivery systems formulated from plant-based ingredients, such as polysaccharides, proteins, lipids, and phospholipids. These delivery systems include nanoemulsions, solid lipid nanoparticles, nanoliposomes, nanophytosomes, and biopolymer nanoparticles. The composition, size, structure, and charge of the particles in these delivery systems can be manipulated to create novel or improved functionalities, such as improved robustness, higher optical clarity, controlled release, and increased bioavailability. There have been major advances in the design, assembly, and application of plant-based edible nanoparticles within the food industry over the past decade or so. As a result, there are now a wide range of different options available for creating delivery systems for specific applications. In the future, it will be important to establish whether these formulations can be produced using economically viable methods and provide the desired functionality in real-life applications.

Microencapsulation of Natural Food Antimicrobials: Methods and Applications

The global demand for safe and healthy food with minimal synthetic preservatives is continuously increasing. Some natural food antimicrobials with strong antimicrobial activity and low toxicity have been considered as alternatives for current commercial food preservatives. Nonetheless, these natural food antimicrobials are hardly applied directly to food products due to issues such as food flavor or bioavailability. Recent advances in microencapsulation technology have the potential to provide stable systems for these natural antibacterials, which can then be used directly in food matrices. In this review, we focus on the application of encapsulated natural antimicrobial agents, such as essential oils, plant extracts, bacteriocins, etc., as potential food preservatives to extend the shelf-life of food products. The advantages and drawbacks of the mainly used encapsulation methods, such as molecular inclusion, spray drying, coacervation, emulsification, supercritical antisolvent precipitation and liposome and alginate microbeads, are discussed. Meanwhile, the main current applications of encapsulated antimicrobials in various food products, such as meat, dairy and cereal products for controlling microbial growth, are presented.

Satureja montana Essential Oil, Zein Nanoparticles and Their Combination as a Biocontrol Strategy to Reduce Bacterial Spot Disease on Tomato Plants

Tomato bacterial spot (Bs), caused by Xanthomonas spp., including X. euvesicatoria (Xeu) remains a major threat for tomato production. The emergence of copper resistance strains of Xeu calls urgently for eco-friendly phytosanitary treatments as sustainable green alternatives for disease control. Satureja spp. essential oil (EO) has antimicrobial activity against xanthomonads and combined with zein nanoparticles (ZNPs), might offer a viable option for field applications. This study aims to evaluate the effects of S. montana EO, of ZNPs, and their combination in a nanoformulation, on Xeu quantity, and how these compounds modulate molecular and physiological changes in the pathosystem. Uninfected and infected tomato plants (var. Oxheart) were treated with EO; ZNPs and nanoformulation (EO + ZNPs). Treatments reduced Xeu amount by a minimum of 1.6-fold (EO) and a maximum of 202-fold (ZNPs) and improved plants’ health. Nanoformulation and ZNPs increased plants’ phenolic content. ZNPs significantly increased GPX activity and reduced CAT activity. Overall treatments upregulated transcripts of the phenylpropanoid pathway in infected plants, while ZNPs and nanoformulation upregulated those transcripts in uninfected plants. Both sod and aao transcripts were downregulated by treatments in infected plants. These findings demonstrate that S. montana EO, ZNPs and their nanoformulation are suitable to integrate tomato bacterial spot management strategies, mainly due to their antimicrobial activity on Xeu, however further field studies clarifying the long-term action of these products are required. These results also support the prophylactic potential of ZNPs on tomato bacterial spot.

A Systematic Review on Nanoencapsulation Natural Antimicrobials in Foods: In Vitro versus In Situ Evaluation, Mechanisms of Action and Implications on Physical-Chemical Quality

Natural antimicrobials (NA) have stood out in the last decade due to the growing demand for reducing chemical preservatives in food. Once solubility, stability, and changes in sensory attributes could limit their applications in foods, several studies were published suggesting micro-/nanoencapsulation to overcome such challenges. Thus, for our systematic review the Science Direct, Web of Science, Scopus, and Pub Med databases were chosen to recover papers published from 2010 to 2020. After reviewing all titles/abstracts and keywords for the full-text papers, key data were extracted and synthesized. The systematic review proposed to compare the antimicrobial efficacy between nanoencapsulated NA (nNA) and its free form in vitro and in situ studies, since although in vitro studies are often used in studies, they present characteristics and properties that are different from those found in foods; providing a comprehensive understanding of primary mechanisms of action of the nNA in foods; and analyzing the effects on quality parameters of foods. Essential oils and nanoemulsions (10.9–100 nm) have received significant attention and showed higher antimicrobial efficacy without sensory impairments compared to free NA. Regarding nNA mechanisms: (i) nanoencapsulation provides a slow-prolonged release to promote antimicrobial action over time, and (ii) prevents interactions with food constituents that in turn impair antimicrobial action. Besides in vitro antifungal and antibacterial, nNA also demonstrated antioxidant activity—potential to shelf life extension in food. However, of the studies involving nanoencapsulated natural antimicrobials used in this review, little attention was placed on proximate composition, sensory, and rheological evaluation. We encourage further in situ studies once data differ from in vitro assay, suggesting food matrix greatly influences NA mechanisms.

Nanoencapsulation of Essential Oils as Natural Food Antimicrobial Agents: An Overview

The global demand for safe and healthy food with minimal synthetic preservatives is continuously increasing. Natural food antimicrobials and especially essential oils (EOs) possess strong antimicrobial activities that could play a remarkable role as a novel source of food preservatives. Despite the excellent efficacy of EOs, they have not been widely used in the food industry due to some major intrinsic barriers, such as low water solubility, bioavailability, volatility, and stability in food systems. Recent advances in nanotechnology have the potential to address these existing barriers in order to use EOs as preservatives in food systems at low doses. Thus, in this review, we explored the latest advances of using natural actives as antimicrobial agents and the different strategies for nanoencapsulation used for this purpose. The state of the art concerning the antibacterial properties of EOs will be summarized, and the main latest applications of nanoencapsulated antimicrobial agents in food systems will be presented. This review should help researchers to better choose the most suitable encapsulation techniques and materials.

Natural Plant-Derived Chemical Compounds as Listeria monocytogenes Inhibitors In Vitro and in Food Model Systems

Listeria monocytogenes is a foodborne pathogen, sporadically present in various food product groups. An illness caused by the pathogen, named listeriosis, has high fatality rates. Even though L. monocytogenes is resistant to many environmental factors, e.g., low temperatures, low pH and high salinity, it is susceptible to various natural plant-derived antimicrobials (NPDA), including thymol, carvacrol, eugenol, trans-cinnamaldehyde, carvone S, linalool, citral, (E)-2-hexenal and many others. This review focuses on identifying NPDAs active against L. monocytogenes and their mechanisms of action against the pathogen, as well as on studies that showed antimicrobial action of the compounds against the pathogen in food model systems. Synergistic action of NDPA with other factors, biofilm inhibition and alternative delivery systems (encapsulation and active films) of the compounds tested against L. monocytogenes are also summarized briefly.

Invited review: Advances in nisin use for preservation of dairy products

Dairy product safety is a global public health issue that demands new approaches and technologies to control foodborne pathogenic microorganisms. Natural antimicrobial agents such as nisin can be added to control the growth of pathogens of concern in dairy foods, namely Listeria monocytogenes and Staphylococcus aureus. However, several factors affect the antimicrobial efficacy of nisin when directly added into the food matrix such as lack of stability at neutral pH, interaction with fat globules, casein, and divalent cations. To overcome these limitations, new and advanced strategies are discussed including nisin encapsulation technology, addition to active packaging, bioengineering, and combination with other antimicrobials. This review highlights advanced technologies with potential to expand and improve the use of nisin as a dairy preservative.

Stability and Antimicrobial Activity of Nisin-Loaded Mesoporous Silica Nanoparticles: A Game-Changer in the War against Maleficent Microbes

Antimicrobial agents, such as nisin, are used extensively in the food industry. Here, we investigated various approaches to load nisin onto mesoporous silica nanoparticles (MSNs, 92 ± 10 nm in diameter), to enhance its stability and sustained release. The morphology, size, and surface charge of the as-prepared nanoparticles were analyzed using scanning transmission electron microscopy, dynamic light scattering, and ζ potential measurement. Nisin was either physically adsorbed or covalently attached to the variously functionalized MSNs, with high loading capacities (>600 mg of nisin g^-1 of nanoparticles). The results of antibacterial activity analysis of nisin against Staphylococcus aureus showed that, despite the very low antibacterial activity of nisin covalently conjugated onto MSNs, the physical adsorption of nisin onto the unfunctionalized nanoparticles enhances its antimicrobial activities under various conditions, with no significant cytotoxicity effects on mouse fibroblast L929 cells. In conclusion, MSNs can be recommended as suitable carriers for nisin under various conditions.

Preparation, characterisation and antioxidant activities of rutin-loaded zein-sodium caseinate nanoparticles

Novel rutin-loaded zein-sodium caseinate nanoparticles (ZP) with antioxidant activity in aqueous medium were investigated. The results showed that the sodium caseinate concentrations, dosages of rutin and ethanol volume fractions significantly affected the zein nanoparticles’ characteristics. Concerning the antioxidant properties, the highest values of rutin loaded ZP obtained using 2, 2-diphenyl-1-picrylhydrazyl scavenging and 2 and 2'-azino-bis (3-ethylbenzothiazoline-6-sulphonic acid) decolourisation assays were 52.7% and 71.2%, respectively, and the total antioxidant capacity was 0.40 nmol g^-1. The results suggest that zein-sodium caseinate nanoparticles can be used as a new nano carrier system for rutin or other water insoluble active ingredients.

Thymol Ameliorates Cadmium-Induced Phytotoxicity in the Root of Rice (Oryza sativa) Seedling by Decreasing Endogenous Nitric Oxide Generation

Thymol has been developed as medicine and food preservative due to its immune-regulatory effect and antimicrobial activity, respectively. However, little is currently known about the role of thymol in the modulation of plant physiology. In the present study, we applied biochemical and histochemical approaches to investigate thymol-induced tolerance in rice (Oryza sativa) seedlings against Cd (cadmium) stress. Thymol at 20 μM recovered root growth completely upon CdCl₂ exposure. Thymol pronouncedly decreased Cd-induced ROS accumulation, oxidative injury, cell death, and Cd²⁺ accumulation in roots. Pharmaceutical experiments suggested that endogenous NO mediated Cd-induced phytotoxicity. Thymol decreased Cd-induced NO accumulation by suppressing the activity of NOS (nitric oxide synthase) and NR (nitrate reductase) in root. The application of NO donor (SNP, sodium nitroprusside) resulted in the increase in endogenous NO level, which in turn compromised the alleviating effects of thymol on Cd toxicity. Such findings may helpful to illustrate the novel role of thymol in the modulation of plant physiology, which may be applicable to improve crop stress tolerance.

Corn-based vaccines: current status and prospects

Corn is an attractive host for vaccine production and oral delivery. The present review provides the current outlook and perspectives for this field. Among seed-crops, corn represents a key source of biomass for food, fuel production, and other applications. Since the beginning of the development of plant-based vaccines, corn was explored for the production and delivery of vaccines. About a dozen of pathogens have been studied under this technology with distinct degrees of development. A vaccine prototype against enterotoxigenic Escherichia coli was evaluated in a phase I clinical trial and several candidates targeting bacterial and viral diseases are under preclinical evaluation. The present review provides an updated outlook on this topic highlighting the employed expression strategies; perspectives for the field are also provided.

Enhanced antimicrobial activity of essential oil components immobilized on silica particles

The antimicrobial activity of essential oils components (EOCs) is well-known. However, their high volatility and powerful aroma limit their application in the formulation of a wide range of food products. In this context, the antimicrobial activity of carvacrol, eugenol, thymol and vanillin grafted onto the surface of three silica supports with different morphologies, textural properties and chemical reactivities (fumed silica, amorphous silica and MCM-41) was evaluated herein. Materials characterization revealed a good immobilization yield and all the devices showed a micro-scale particle size. Sensory evaluation revealed that sensory perception of EOCs decreases after covalent immobilization. Moreover, immobilization greatly enhanced the antimicrobial activity of the essential oil components against Listeria innocua and Escherichia coli compared to free components. The incorporation of EOCs immobilized on silica particles into pasteurized milk inoculated with L. innocua demonstrated their effectiveness not only for in vitro conditions, but also in a real food system.

Nanocarriers from GRAS Zein Proteins to Encapsulate Hydrophobic Actives

One factor limiting the expansion of nanomedicines has been the high cost of the materials and processes required for their production. We present a continuous, scalable, low cost nanoencapsulation process, Flash Nanoprecipitation (FNP) that enables the production of nanocarriers (NCs) with a narrow size distribution using zein corn proteins. Zein is a low cost, GRAS protein (having the FDA status of "Generally Regarded as Safe") currently used in food applications, which acts as an effective encapsulant for hydrophobic compounds using FNP. The four-stream FNP configuration allows the encapsulation of very hydrophobic compounds in a way that is not possible with previous precipitation processes. We present the encapsulation of several model active compounds with as high as 45 wt % drug loading with respect to zein concentration into ∼100 nm nanocarriers. Three examples are presented: (1) the pro-drug antioxidant, vitamin E-acetate, (2) an anticholera quorum-sensing modulator CAI-1 ((S)-3-hydroxytridecan-4-one; CAI-1 that reduces Vibrio cholerae virulence by modulating cellular communication), and (3) hydrophobic fluorescent dyes with a range of hydrophobicities. The specific interaction between zein and the milk protein, sodium caseinate, provides stabilization of the NCs in PBS, LB medium, and in pH 2 solutions. The stability and size changes in the three media provide information on the mechanism of assembly of the zein/active/casein NC.

Impact of starch-based emulsions on the antibacterial efficacies of nisin and thymol in cantaloupe juice

The use of antimicrobial compounds to prevent foodborne pathogens from contaminating fresh-cut produce has received broad attentions; however, the applications of these compounds are hindered by their rapid depletion in foods. To prolong their efficacies, the use of delivery systems is essential. In this study, oil-in-water emulsions formed using starch octenyl succinate (starch-OS) were used to stabilize nisin and thymol in cantaloupe juice-containing fluid. Listeria monocytogenes V7 and Salmonella enterica serovar Typhimurium were used as model pathogens to evaluate the antimicrobial activities of nisin and thymol formulations in cantaloupe juice. The results showed that the emulsions had much greater capability to retain nisin and thymol over the storage and displayed much greater effect to inhibit Listeria and Salmonella than non-emulsion, aqueous formulations. Starch-OS based emulsions not only retained nisin and thymol activities separately, but also exhibited their cooperative antibacterial effects.

Characterization and Antilisterial Effect of Phosphatidylcholine Nanovesicles Containing the Antimicrobial Peptide Pediocin

Encapsulation may provide increased stability and antimicrobial efficiency to bacteriocins. In this work, the antilisterial peptide pediocin was encapsulated in nanovesicles prepared from partially purified soybean phosphatidylcholine. The maintenance of antimicrobial activity and properties of free and encapsulated pediocin was observed during 13 days at 4 °C, and after this period, the encapsulated pediocin retained 50 % its initial activity. The maintenance of the bioactive properties of free and encapsulated pediocin was observed against different species of Listeria, inhibiting Listeria monocytogenes, Listeria innocua and Listeria ivanovii. The size of vesicles containing pediocin was determined by dynamic light scattering as an average of 190 nm, with little change throughout the observation period. Polydispersity index values were around 0.201 and are considered satisfactory, indicating an adequate size distribution of liposomes. The efficiency of encapsulation was 80 %. Considering these results, the protocol used was appropriate for the encapsulation of this bacteriocin. Results demonstrate the production of stable nanoparticulate material. The maintenance of the properties of pediocin encapsulated in liposomes is fundamental to prospect the stability in different conditions of the food matrix.

Formation, characterization and release kinetics of chitosan/γ-PGA encapsulated nisin nanoparticles

To improve its efficiency, nisin was encapsulated in a γ-PGA and chitosan nanoparticles using self-assembly method. The release of nisin from the nanoparticles exhibited a pH-dependent pattern, and the release mechanism was an anomalous behavior.

Antimicrobial Peptide-Conjugated Graphene Oxide Membrane for Efficient Removal and Effective Killing of Multiple Drug Resistant Bacteria

According to the World Health Organization (WHO), multiple drug-resistant (MDR) bacterial infection is a top threat to human health. Since bacteria evolve to resist antibiotics faster than scientists can develop new classes of drugs, the development of new materials which can be used, not only for separation, but also for effective disinfection of drug resistant pathogens is urgent. Driven by this need, we report for the first time the development of a nisin antimicrobial peptide conjugated, three dimensional (3D) porous graphene oxide membrane for identification, effective separation, and complete disinfection of MDR methicillin-resistant Staphylococcus aureus (MRSA) pathogens from water. Experimental data show that due to the size differences, MRSA is captured by the porous membrane, allowing only water to pass through. SEM, TEM, and fluorescence images confirm that pathogens are captured by the membrane. RT-PCR data with colony counting indicate that almost 100% of MRSA can be removed and destroyed from the water sample using the developed membrane. Comparison of MDR killing data between nisin alone, the graphene oxide membrane and the nisin attached graphene oxide membrane demonstrate that the nisin antimicrobial peptide attached graphene oxide membrane can dramatically enhance the possibility of destroying MRSA via a synergestic effect due to the multimodal mechanism.

Plant protein-based delivery systems for bioactive ingredients in foods

The application of food-grade delivery systems for the encapsulation, protection and controlled release of bioactive food ingredients have recently gained increasing interest in the research fields of functional foods and pharmaceutics. The preparation and application of bifunctional particles provide a novel perspective for the design of plant protein-based delivery system.

Antimicrobial properties of nisin after glycation with lactose, maltodextrin and dextran and the thyme oil emulsions prepared thereof

To clarify the reported conflicting antimicrobial activities of nisin after glycation, nisin was glycated with lactose, maltodextrin, and dextran at 70 °C and 50% relative humidity for 1-24 h. Nisin before and after glycation was studied for the first time to prepare thyme oil emulsions. The activity of glycated nisin and the thyme oil emulsions was tested in both tryptic soy broth (TSB) and 2% reduced fat milk. Results showed that nisin glycated with a smaller saccharide for a longer duration had a higher degree of glycation and the reduced number of positive charges lowered its antibacterial activity. The emulsified thyme oil had an additive effect with either glycated or native nisin against Listeria monocytogenes Scott A and Bacillus subtilis in TSB and 2% reduced fat milk. However, emulsions were less effective against L. monocytogenes Scott A in milk than same units of native nisin and same concentration of free thyme oil, likely due to the reduced availability of thymol and carvacrol, the main components of thyme oil. These results showed that glycation of nisin cannot broaden its antimicrobial activity and nisin is not a good compound to prepare emulsions of essential oils.