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Natural products as antimicrobial agents.
Food Control, 46, Jamali, H. Detection and isolation of Listeria spp. Food Control, 32 1 , Kimura, H. Novel bacteriocin of Pediococcus sp. ISK-1 isolated from well-aged bed of fermented rice bran. Annals of the New York Academy of Sciences, 1 , Lou, Z. Maistro, L. Microbiological quality and safety of minimally processed vegetables marketed in Campinas, SP - Brazil, as assessed by traditional and alternative methods.
Food Control, 28 2 , Malik, N. Phenolic compounds and fatty acid composition of organic and conventional grown pecan kernel. Journal of the Science of Food and Agriculture, 89 13 , Motta, A. Characterization of an antimicrobial peptide produced by Brevibacterium linens. Journal of Applied Microbiology, 92 1 , Hepatoprotective effects of pecan nut shells on ethanol-induced liver damage.
Experimental and Toxicologic Pathology, 65 , Prado, A. Effect of the extraction process on the phenolic compounds profile and the antioxidant and antimicrobial activity of extracts of pecan nut [ Wangenh C. Koch] shell. Carya illinoinensisIndustrial Crops and Products, 52, Antimicrobial properties of phenolic compounds from berries. Journal of Applied Microbiology, 90 4 , Reckziegel, P.
Oxidative stress and anxiety-like symptoms related to withdrawal of passive cigarette smoke in mice: beneficial effects of pecan nut shells extract, a byproduct of the nut industry. Ecotoxicology and Environmental Safety, 74 6 , Moreover, combining the selected strains with natural antimicrobials produced a further increase in the shelf-life of these products without detrimental effects on the organoleptic qualities. Links to Text. DOI Actions on this item.
Application of both extracts and EOs of plant-based antimicrobials could be a potential alternative to synthetic preservatives. By the other hand, when developing novel packaging concepts that have never been used and are produced by new processes, there is the need to ensure the safety and benefits of such food packaging solutions. Min, B. The consumers disliked the very intensive and aggressive smell of the carvacrol. However, this effect could not be observed on or after day 4 of the storage period.
Spices and EOs are used as natural agents for extending the shelf life of foods in food industry. A variety of plant and spice-based antimicrobials is used for eliminating food-borne pathogens such as Salmonella, Listeria monocytogenes, Escherichia coli, Bacillus cereus, Staphylococcus aureus and increasing the overall quality of food products.
More than plants with defined antimicrobial compounds, and above 30, components have been isolated from phenol group-containing plant-oil compounds, used in the food industry. Commercially based plant-origin antimicrobials are most commonly produced by SD steam distillation and HD hydro distillation methods, and alternative methods such as SFE supercritical fluid extraction from aromatic and volatile oily liquids from flowers, buds, seeds, leaves, twigs, bark, herbs, wood, fruits and roots of plants.
The most common source of EOs are oregano, clove, cinnamon, citral, garlic, coriander, rosemary, parsley, lemongrass, sage and vanillin serve as antimicrobial, antioxidant compounds and widely used in smart or bioactive packaging material to prevent surface growth of microorganisms in foods  . Spices and herbs are tremendous sources of antioxidants and have a long history of safe usage. Over years ago, the ancient Egyptians used a blend of spices such as cumin, cinnamon and onion and herbs in their food, for medicinal purposes and for mummification .
Various Gram-positive and Gram-negative bacteria secreted bacteriocins are ribosomally synthesised antimicrobial peptides or complex proteins. Without showing toxicity, bacteriocins from many bacteria have been reported to be active against human and animal microbial pathogens, including methicillin-resistant Staphylococcus aureus MRSA and vancomycin-resistant Enterococci VRE. Several bacteriocins have been recovered for their significant potential as food preservatives or as therapeutic or bio-controlling agents  .
In this regard, the application of natural antimicrobials is dramatically important as natural preservative strategies to protect and extend the shelf-life of food  . Chitosan represent another group of natural antimicrobial compound that received considerable interest for commercial applications.
It has been used in food, medical, agricultural, and chemical industry, mostly because of its high biodegradability and antimicrobial properties. It is produced from crab and shrimp shell wastes, with diverse deacetylation grades and molecular weights. It has been reported to possess a film-forming property for use as edible film or coating, to decline water vapor and oxygen transmission, reduce respiration rate and increase shelf-life of fruit .
Essential oils are natural, volatile and complex liquids known as volatile odoriferous oils characterized by an intense smell and flavor that varies depending on the type of constituents that form the oil. They are isolated from aromatic plants as secondary metabolites, especially by plants generally located in warm areas such as tropical and Mediterranean areas. EOs perform a major role in plants defense, working as antibacterial, antifungal and antiviral agents. They have originally been added to food in order to change or improve the flavor, their antimicrobial actions make them good candidates to replace chemical preservatives and suitable alternatives to antibiotics  .
Chemically the EOs consist of terpene compounds, alcohols, acids, esters, epoxides, aldehydes, ketones, amines and sulfides  . Components contained in EOs can be divided into two groups are: terpenes monoterpenes and sesquiterpenes and terpenoids monoterpenoids. At present, more than EOs are known, with of them having a commercial interest in food, pharmaceutical, sanitary or cosmetic industries. Various terpene components of EOs e.
The main sources of well-known EOs are ginger, oregano, rosemary, sage, thyme, mint, and many other aromatic plants. EOs can be isolated by means of water distillation, water and steam distillation, or steam distillation alone. These are the most conventional and commonly used method of extraction. Another method, namely cohobation, can be used when the solubility of a certain essential oil in water is high, as in the case of geranium, rose, or lavender.
Maceration and enfleurage processes are also used for obtaining EOs, as well more modern techniques such as extraction with solvents or supercritical fluids and ohmic assisted hydrodistilation. When the yield from distillation is poor maceration method can be used, while enfleurage and solvent extraction is suitable for costly, fragile, and thermally unstable materials  .
The foremost bioactive compounds are alcohols, aldehydes, phenylpropanoids, terpenes and ketones that have been found in EOs and are related to their antioxidant. Apart from the antioxidant activities, the incorporated EOs could provide antibacterial properties, including Staphylococcus aureus, Enterococcus faecalis, Escherichia coli, Clostridium perfringens, Clostridiumsporogenes in several meat products .
Usually terpenoids and phenylpropanoids are among the major components of common EOs in the food industry. EOs are used in a broad range of consumer goods such as confectionery food products, soft drinks, and distilled alcoholic beverages. As well as their extensive use as a flavoring material, they are used in the nutritional and agricultural fields for their reported antibacterial, antifungal, antiviral, nematicidal, insecticidal, and antioxidant.
Due to this, their use as antioxidants and preservatives in food has been recommended, either incorporated into the food stuff packaging material or as plant and crop protectants  . Inappropriate extraction conditions can damage or alter the chemical property of the EOs  . Thus, appropriate extraction method and extraction technique are important considerations in producing an EO with desirable characteristics.
Therefore, new extraction techniques of EOs are recently proposed as alternatives to the traditional methods   .
Essential oils can be extracted by several different methods are shown below:. Steam Distillation: In this process, water is boiled, and plant sample is exposed to the resulting steam. The heat applied is the major cause of burst and break down of cell structure of plant material. As a consequence, the volatile aromatic compounds or EOs from plant material are released by steam and transported into a tube where the resulted vapor cool down to produce a mixture of distilled water and EO.
Later, the EOs are separated from aqueous phase due to the differences in their specific gravity. Steam temperature, pressure and extraction duration are the most important considerations in the steam distillation process. In addition, steam distillation is a time-consuming process that sometimes involves a redistillation of the EO  . Besides, one disadvantage of this conventional extraction method is the degradation of some volatile compounds as a result of long extraction times and relatively high temperatures .
Hydrodistillation: Hydrodistillation is one of the oldest and standard method of EO extraction technique . In this process, EOs are extracted from the fragile parts of the plants through a solid-liquid extraction between plant material and hot water in a distillation container equipped with a Clevenger apparatus.
The plant sample and water mixtures are boiled to get a vapor phase in the condenser section and collect the isolated EO in a receiver flask. This extraction method requires several disadvantages, such as long extraction times, which could promote hydrolysis of some heat sensitive components of the EOs and produce unwanted compounds .
Moreover, process parameters such as, process temperature and time, are difficult to control which may result in incomplete or prolonger extraction. So, researchers are looking for alternatives to this tedious extraction technique   . Hydrodiffusion: It is a one kind of steamdistillation, which is only different in the inlet way of steam intothe container of still.
This method is suitable for use when the plant materialhas been dried and is not damaged at boiling temperature . In this process, steam is applied from the top of plant material, while steam is entered from the bottom for steam distillation method. Hydrodiffusion method is better than steam distillation due to shorter processing time and a higher oil yield with less steam used .
Solvent Extraction: This process is used when plant materials are delicate or cannot bedistilled by other techniques. The purpose of solvent extraction is extracting the odoriferous lipophilic materials from the original plant by food grade solvents like methanol, ethanolor hexane . It is important to select proper extraction solvents in this process, and the experts avoid solvents that can interfere with the extraction process or react with the extract.
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At first, plant samples are washed with the extraction solvent breaking the material or centrifuging in a rotating drum and the solvent is filtered and subjected to vacuum distillation to remove solid plant materials. The resulting mixture contains the aromatic and lipid-soluble compounds. After that, a second solvent usually alcohol is used to remove non-aromatic fractions.
Lastly, another vacuum distillation is operated to eliminate the second solvent and obtain a pure mixture. Innovative Extraction Techniques: EOs are thermo-labile. So, high temperatures can alter their structures hydrolyse, isomerization, oxidation and inversely affect their antioxidant and antimicrobial properties during traditional extraction methods. Several alternative methods have been developed and proposed recently to solve these issues .
Besides, the combination of these innovative extraction techniques could improve the performance of the extraction process and increase the extraction yield . Supercritical Fluid Extraction: This process occupies the supercritical fluids, such as carbondioxide, as an inert solvent to separate the volatile compounds from medicinal plants. The CO 2 gas reaches a supercritical state under low pressure and temperature, becoming a liquid which can diffuse throughout plant material to extract aromatic compounds.
The resulting extracts are considered as high quality, clean and pure, have a great similarity to the aroma of the original plant before extraction process . Though supercritical fluid extraction is expensive, it is very efficient due to its low viscosity and high diffusivity. The use of shorter extraction times around 25 minutes and the versatility of this method compared to conventional extraction ones, offers the possibility of selecting the characteristics of the resulting EO by modifying the temperature, pressure and extraction duration.
In addition, this method can be considered as an environment-friendly extraction technique for the extraction of bioactive ingredients . Microwave-Assisted Extraction: Microwave-assisted extraction is basically a combination of microwave heating and a conventional extraction method such as solvent extraction and hydrodistillation . In this process, the plant material is extracted without any organic solvent or water. This technique is considered as superior to traditional methods because it can reduce the extraction time and energy .
Ultrasound-Assisted Extraction: This technique releases the EOs from aromatic plants mostly through the cavitation phenomenon, which develops the penetration of the solvents in the plant material . Cavitation occupies the formation, expansion, and growth of small liquid-free zones or bubbles which collapse strongly producing mechanical forces as well as local high temperatures and pressure at ambient conditions, therefore allowing the release and dissolution of intracellular materials such as EOs.
This process can enhance the quality of the extract by minimizing thermal degradation of the EO components at a reduced temperature . Spices come from different parts of a plant except leaves whereas herbs come from leaves of a plant. According to flavor, spices and herbs can be classified into 4 groups: hot spices black and white peppers, cayenne pepper, mustard, chillies , mild flavor spices paprika, coriander , aromatic spices clove, cumin, dill fennel, nutmeg, mace, cinnamon and aromatic herbs and vegetables thyme, basil, bay leaf, marjoram, shallot, onion, garlic.
Based on taxonomic classification, spices and herbs fall under the class Angiospermae or the flowering plants . Spices and herbs are rich sources of phytochemicals and powerful antioxidants as they contain effective compounds that have been shown to impart antioxidative effect in food. For more than years, spices and herbs have been used as flavor, color and aroma. Phytochemicals are a large group of bioactive compounds derived from plants which have capability to protect against diseases.
This group contains flavonoids and other phenolic compounds, carotenoids, plant sterols, glucosinolates and other sulphur-containing compounds. More than flavonoids are identified.
Phenolic compounds play a major role in the plant such as structural, defense, as attractants for pollinators and seed-dispersing animals. These substances help plants to protect themselves against UV light for their survival and for adaptation to their environment. Due to their phytochemicals, they have also been used for preservation of foods and beverages primarily.
A large amount of spices have eastern origins; however, some of them have been introduced after invention of the New World spices such as chili peppers, sweet peppers, allspice, annatto, chocolate, epazote, sassafras, and vanilla, which have been used for food flavoring and medicinal purposes. In India, clove, cinnamon, mustard, garlic, ginger and mint are still applied as alternative health remedies. Plant extracts and spices also act against Gram-positive pathogens such as Listeria monocytogenes. They can also increase storage stability using active components including phenols, alcohols, aldehydes, ketones, ethers and hydrocarbons, especially in such spices as cinnamon, clove, garlic, mustard, and onion.
In the s, the first scientific studies were reported about preservation potential of spices, describing antimicrobial activity of cinnamon oil against spores of anthrax bacilli. Furthermore, clove was used as a preservative to cloak spoilage in meat, syrups, sauces and sweetmeats. In the s, cinnamon and mustard were shown to be useful in preserving applesauce. Later some other spices, such as allspice, bay leaf, caraway, coriander, cumin, oregano, rosemary, sage and thyme, have been reported to have considerable bacteriostatic properties  .
Several microbes such as, Pediococcous spp. Bacteriocins are abundant, have large diversity and a type of ribosomal synthesized antimicrobial peptides or proteins which can kill or inhibit other closely-related narrow spectrum or non-related broad spectrum microbiotas, but will not harm the bacteria themselves by specific immunity proteins.
Bacteriocins were first discovered by Gratia in Due to the specific characteristics of huge diversity of structure and function, natural resource and being stable to heat; bacteriocins are considered to be one of the weapons against micro-organisms. They are commonly used in agriculture, veterinary medicine as a therapeutic, in food science to extend food preservation duration which reduce pathogen infection of animal diseases, pharmaceutical industry and medical society to treat cancer therapy   .
Nowadays public is more aware of the importance of food safety, as many of the chemical additives used in food may elicit toxic concern; thus, it is beneficial to claim natural resources and health benefits of diets. However, a good number of commercially available preservatives and antibiotics are produced by chemical synthesis and long-term consumption of such products may have an adverse impact on the human body as they decrease the number of bacteria in the gut. Besides, the use of antibiotics or residues in food is considered as illegal.
So, bacteriocins may be used as a potential drug candidate for replacing antibiotics to treat multiple drugs resistance pathogens in the future.
Bacteriocins are considered as natural food additives because they are produced by bacteria present in many types of foods since ancient times, such as cheeses, yogurts, and Portuguese fermented meat. Usually, most common methods are agar-spot deferred test and agar-well diffusion assay . In the first method, producer strains are allowed to grow overnight on the surface of the optimal agar medium. Then indicator strain is inoculated into the optimal soft agar medium and poured on the plate where growth of the producers occurred.
After incubation, bacteriocin inhibition is indicated by the presence of a detectable clearing zone around the colony of the producer strain. In the second method, the agar base medium is overlaid with soft agar medium containing the indicator strain, as above.
After that, wells are cut into the agar and the cell-free supernatant of the bacteriocin producer strains is placed into each well. Agar-based antagonistic assays of bacteriocin detection may be replaced by quicker tools. In addition, PCR Polymerase Chain Reaction methods have also been used to detect genes coding for bacteriocins in pure cultures  and fermentation broth .