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The Application of Natural Antimicrobials as a Preservative Measure on Food
In the food industry it is imperative that the appropriate precautions be taken to prevent the possible contamination by bacteria, yeast or fungi. These microorganisms not only have a negative impact on flavor, odor, color, textual properties of food, and spoilage, but can also lead to harmful food borne illness and economic loss associated with food. These possible harmful microorganisms can contaminate food from the moment it is established to when it is harvested and transported to the consumer. In the United States alone each year there is approximately forty-eight million cases of foodborne illnesses each year (Barberis, Sonia.) With the modern consumer becoming more health conscious and the growing demand for higher quality, minimally processed, ready to eat foods, the food industry is looking to alternatives to the commonly used chemical preservatives.
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The most common chemical preservative agents that have been used in food manufacturing are weak organic acids . These weak acids includes, acetic, lactic, benzoic and sorbic acids. These molecules prevent the growth of bacterial and fungal cells with sorbic acid preventing gemination and growth of bacterial spores(Khosravan, Mehrji, Shoshtari, and Hoseinchi).These agents are not only known for their preservative values but also for possible their life-threatening side effects. Depending on the individual’s general health conditions, chemical preservative such as sulphites can cause allergic reaction in hypersensitive individuals ranging from large scale asthma to anaphylactic shock (Pisoschi, Magdalena). With these health risk in mind some consumer are calling for the use and application of more natural means. As a healthier and what some might say a more cost-effective approach to food preservation, a look at alternatives to the commonly used chemical and thermal preservation techniques that still maintains the integrity and quality of the foods have led to an increase in research and application of a more natural approach, Bioperservation.
Bioperservation is the use of natural preservatives that are derived from sources like bacteria, fungi, plants, animals and their ability to use their naturally occurring antimicrobial components to protect foods from a variety of foodborne pathogens. Lactic bacterial and its corresponding antibacterial compounds like lactic acid, bacteriocins , which are a part of plants and animals’ preservative natural microflora, have been proved to be able to not only extend the shelf life of foods but also inhibit colour loss and ensure food security(Pisoschi, Magdalena). In its application on raw and cooked meats that requires the use of natural extracts derived from herbs, spices, fruits and vegetables, have been effective in inhibiting lipid oxidation, preserving colour and extending shelf stability. These successes have been attributed to the bioactive compounds like phenolics (flavonins and non-flavonoids), phenolic terpenes and tannins.
It has been found that several herbs and vegetal extracts behaves like antioxidants, antimicrobials, anti-diabetics, anti-carcinogens, flavorings, and repellents. Properties which can be beneficial in the application in food manufacturing. Plant based derivatives contain two different bioactive compounds that have been categorized to two different groups. The first being vegetable or essential oils. These essential oils are commonly extracted from olive, canola, soy, sunflower, linseed, avocado, grape seed, oregano, rosemary, and coriander seed. The second category being extracts, from the likes of grape seed, green tea, olive leaf, cranberry, pomegranate, broccoli cocoa leaf, and lemon balm.
To inhibit the growth of possible harmful microorganisms in foods, antimicrobials can be either directly added, coated on the surface, or incorporated in to the packaging material (Del Nobile, Alessandro) the incorporation of antimicrobials of active agents in food can result in an immediate but short term reduction of the bacterial population. Whereas coating helps to maintain their activity longer. The main natural plant-based derived compounds are essential oils, enzymes from animal sources, bacteriocins from microbial sources, organic acids, and naturally occurring polymers. Out of these natural alternatives, essential oils is the forerunner.
Despite the sometimes overwhelming sensorial aspect of most essential oils, the odor can be masked with the use of approved aroma compounds. The bioactive compound from a variety of berries such as cranberry, cloudberry, raspberry, strawberry and bilberry contain the organic acids and polyphenolics that possess clear antimicrobial effects against human pathogens such as Helicobacter pylori, L.monocytogense, Salmonella spp,. S.aureus, E.coli, and Campylobacter spp. (Barberis, Sonia, et al).Essential oils are attractive to the food industry because they are Generally Recognized as Safe (GRAS), and they possess potential decontaminating agents. The active components, commonly found in the essential oil fractions are well established and they have a wide variety of antimicrobial activates against foodborne pathogens and spoilage bacteria. Oils of clove, oregano, rosemary, thyme, sage and vanillin that have the phenolic groups are the most effective (Gyawali, Rabin, and Ibrahim). The antimicrobial component of mustard and horseradish oil, Ally-isothiocyanate which is effective on Gram-negative bacteria is limited but it has been shown to be effective in the inhibition of E.coli.
There is limited research on the function and structure of these compounds, their chemical composition in regards to their antimicrobial activity is not currently fully understood. What is known is that their effectiveness against pathogenic microorganism might be in part due to their polyphenolic compounds. Phenolic compounds are secondary plant metabolites, natural phenols have excellent properties as food preservatives while also exhibiting an important role in the protection against a variety pathological disturbances as well as many industrial applications. (Ignat, Ioana, Volf, and Popa)Thus the antimicrobial activity of essential oils is due to their chemical structure, particularly the presence of its hydrophobic component, rendering them more effective on Gram-positive bacteria than Gram-negative. Which is most likely due to the difference in the cell membrane composition.
There has also been peaked interest in the use of bacteriocin-producing lactic acid bacteria. Bacteriocins bacterial peptides have shown strong antimicrobial activity activity against closely related bacteria. Nisin which is produced by Lactococcus lactis spp, has been approved as a food additive with GRAS status in over fifty countries. With its seemingly broad spectrum of activity against various lactic acid bacteria and other Gram-negative bacteria, it is particularly effective against heat resistant bacterial spores of Clostridium botulinum and against foodborne pathogens such as L. monocytogenes, and S.aureus. It is the only antimicrobial peptinde that is currently used as food preservative. (Brul, and P. Coote.)Lytic enzymes another natural compound that has been shown to have vaild application in food preservation, is well known for its bactericidal activity against Gram-positive bacteria. Lysozyme a lytic enzyme that is found foods such as milk and eggs are commercially used to prevent late blowing in semi-hard cheeses, caused by Clostridium tyrobutyrucum.( Del Nobile, Alessandro,)
Figure 1: Plant compounds structural variation that alter their antimicrobial activity.
The structural diversity of plant-derived compounds is overwhelming and its antimicrobial action on microorganisms depends on their structural configuration (Fig 1). Phenolic compounds have a great deal of structural variation and is one of the most diverse groups of secondary metabolites. Their hydroxyl (-OH) groups are said to cause inhibitory actions that can interact with the cell membranes of bacteria to disrupt membrane structure and cause the leakage of cellular components.( Gyawali, Rabin, and Ibrahim).The active groups such as –OH not only promote the delocalization of electrons which act as proton exchangers that reduces the gradient across which the cytoplasmic membrane bacterial cell but it also will cause the collapse of the proto motive force and deplete the ATP pool, resulting in cell death.
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The use of effective extraction and purification procedures are critical for both the isolation and application of natural antimicrobials that are intended for food related usage. Initially, the preparation techniques were mainly represented by steam and hydro distillation. Recently more nonconventional methods like superficial fluid extraction, which provided more improved solubility and mass transfer are being applied. Other methods that are being implemented includes microwave assisted extraction and ultrasound extraction that has been shown to decrease extraction time. These extraction techniques provides a more efficient way of obtaining better quantities and quality yield of volatile oils (Pisoschi, Magdalena,).
The essential oils that are obtained from plants including herbs and spices feature antimicrobial potential are obtained by a variety of methods such as dry, cold, seam or vacuum distillation. Polyphenols and essential oils were extracted by classical methods until the past two or three decades (Ignat, Ioana, Irina Volf, and Valentin I. Popa). Relatively recently new and high performance extraction methods were translated form laboratory to industrial scale, with major advantages being the extraction time, quality, and yield. It is known that extraction techniques that utilize chemical or thermal treatments can not only alter the active ingredients, yields, functionality and natural features, but it can also result in unsafe compounds. The direct extraction method that is applied to fruits and vegetables is a very straightforward process and can preserve the natural integrity, structure, and composition of active ingredients. Direct extractions from guava and xoconstle pear have confirmed their efficacy against Salmonella spp. And E.coli.O157:H7. (Tajkarimi, M. M., Salam A. Ibrahim, and D. O. Cliver).
Mechanical treatment used for extractions from fruits and vegetables, do not use any chemical treatment, heating, or concentrations. Water extraction is used to extract mainly phenolic from seeds and leaves. With thermal treatment of hydro soluble muscadine, seed extracts resulted in enhanced antimicrobial activity and acidity resulting in total increase in phenolic (Smid, Eddy and Gorris)Alternative methods to extraction that rely on ultrahigh temperatures, far infrared radiation, or enzyme treatment may determine the he breakdown of polymeric compounds. This disassociation resulted in subsequent release of low molecular weight components that may lead to an overall reduction in the antimicrobial efficiency. Direct or juice extraction may preserve the structure and activity of natural antimicrobials.
Like with anything else during the production of foods, there is a large amount of byproduct that is generated waste such as fruit pomace, sees, pulps, unused flesh, husks of defendant fruits and vegetables which have proven to be valuable source of components such as phenolic compounds and organic acids. They not only have a wide range of antimicrobial properties but also exhibit an array of attractive economical and commercial exploitations to enhance food safety as a natural food preservative (Barberis, Sonia).Byproducts from the likes of grape, olive, pomace, olive juice, pomegranate bergamot, almond peels, jackfruit, papaya, plum, guava, and tamarind, tomatoes, mustard seeds, coconut, walnut, and coffee husks, buck wheat, and legume hulls, and pulp tea extract powders have inhibited spoilage and pathogenic bacteria including Aeromonas hydrophila, B. ceres, Enterobacter aerogenes, E. faecalis, E.coli O157:H7, M. smegmais, Proteus vulgaris, P. aeruginosa , Pseuomonas fluorescens, Salmonella eneritidis, S. typhimurmim, S. aureus and Yersinia enterocolitica (Barberis, Sonia).
Along with the food safety concerns that are associated with the use of chemical preservatives, the focus towards natural antimicrobials is justified due to the incorrect handling of antibiotics that have led to the development of multidrug resistant organisms, including foodborne pathogens that are unaffected b he conventional applied food processing and preservation techniques.( Tiwari, Brijesh). We are at the forefront of the quest for natural biopreservatives that have antimicrobial effects.
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