1Department of Food Science and Post Harvest Technology, Wachemo University College of Agricultural Sciences, Hosanna, EthiopiaFind articles by
Potentials of Natural Preservatives to Boost the Safety and Shelf Life of Foods
Traditional food preservation methods are ineffective in reducing the spread of food-borne viruses in food items. The growing desire for chemical-free food has paved the way for the use of antimicrobials in the food sector [12]. Antimicrobials are a novel technology used by the food industry to extend the shelf life of food and address quality and safety concerns [13].
2. Natural Antimicrobial Agents
Primary metabolites serve an essential purpose in the organism, whereas secondary metabolites may be waste products or play an essential role in production. Natural antimicrobials are secondary metabolites with antimicrobial action. Plants (fruits, vegetables, seeds, herbs, and spices), animals (eggs, milk, and tissues), and microorganisms (fungi and bacteria) can all be used to extract them [14, 15]. Secondary metabolites have been discovered to be beneficial substances that act as antimicrobials or disease-controlling agents in plants [16]. Due to the antibacterial ability of secondary metabolites against pathogenic and spoilage microorganisms, they are becoming increasingly important for use in food items [17]. They are believed to be a superior option for food preservation to synthetic preservatives because they have antibacterial and antioxidant characteristics at the same time.
Natural antimicrobials can be found in raw vegetables, fruits, and herbs/spices. Fruits and vegetables (garlic, pepper, onion, cabbage, and guava), seeds and leaves (olive leaves, parsley, caraway, nutmeg, fennel, and grape seeds), and herbs and spices (marjoram, basil, oregano, rosemary, thyme, sage, clove, and cardamom) all include natural plant-derived chemicals [18]. Essential oils (Eos) and extracts derived from plants have long been used as food additives to improve taste and impart distinct flavors, and extend the shelf life of foods by preventing rancidity and controlling microbiological contamination. Indeed, these chemicals can limit or impede the growth of harmful bacteria because of their high presence of secondary metabolites, primarily phenolic compounds, iso-flavonoids, terpenes, ketones, aliphatic alcohols, acids, and aldehydes [19].
The antimicrobial activity of plant-derived compounds mainly depends on microorganism type, inoculum size, culture medium, extraction method, and method for antimicrobial activity determination [18]. Plant-based compounds, such as polyphenols, terpenes, and alkaloids, are produced from natural sources. Because of their biocidal effects against bacteria or herbivore repellence, plants have a diverse range of secondary metabolites that protect them from predators and microbial pathogens [20]. The phenolic and polyphenolic groups are two of the significant classes found in secondary metabolite compounds. Flavonoids, quinones, coumarins, phenolic acids, tannins, phenols, flavones, and flavonols are some of the subgroup chemicals important for inhibiting microbial activity. Phenol is a hydroxyl (-OH) group-containing chemical. The amount and locations of phenol groups present in the substance correlate with their relative microbial toxicity.
Many Eos have been classified as generally recognized as safe (GRAS) by the US Food and Drug Administration (FDA) and may be used as food preservatives [21]. Eos is the most crucial phytochemical employed in food preservation [22]. Eos are highly volatile, sweet-smelling molecules with an oily consistency, produced by plants. EOs can be extracted from various plant components, including flowers, seeds, and leaves. Essential oils can be extracted from various portions of aromatic plants using a variety of processes, including distillation, supercritical fluid, and many more. The Eos antibacterial properties are oxygenated terpenoids (such as alcohol and phenolic terpenes). Several hydrocarbons, such as aliphatic, monoterpene, and sesquiterpene hydrocarbons, have characteristics that make them microbially active [20].
Herbs and spices are used as antibacterial agents. Eos extracted from plants, spices, and herbs has a high vapor pressure and can reach microbes via liquid and gas phases [5]. Eos hydrophobic qualities react with lipids in the microbes cell membrane, causing the cell wall to disintegrate. As a result, the cells permeability will grow, and the cytoplasmic membrane will be damaged. There will be cell content leakage and cytoplasm coagulation. As a result, the cells original structure will be disrupted [23].
Bitencourt et al. [21] found that by employing a two-fold dilution of mint essential oil, the inhibition of Escherichia coli and Salmonella enteritidis could be resolved using the usual broth dilution approach. The use of an edible coating containing mint essential oil prevented the growth of Escherichia coli and Salmonella enteritidis; the higher the mint essential oil concentration, the lower the microbiological activity. Matan [24] found that using anise oil, which includes multiple active chemicals including trans-anethole, -trans-bergamotene, and limonene, inhibits bacteria such as Salmonella typhimurium, Staphylococcus aureus, and Vibrio parahaemolyticus was adequate. These bacteria are commonly found in seafood. Furthermore, anise oil may prevent spore germination.
Furthermore, according to Matan [24], cinnamon and clove oil include a variety of active chemicals such as cinnamaldehyde, eugenol, and linalool. As a result, both oils reduce the growth of yeasts and molds, and extend the shelf life of dried fish. According to Rehman et al. [25], citrus peel essential oils have various uses in bread. According to the findings, the oils impacted sensory properties and slowed microbial growth. Spraying peel essential oil has the most inhibitory impact against molds and germs. To extend the shelf life of gluten-free sliced bread, researchers used active packaging using cinnamon essential oil and modified atmosphere packaging (MAP). The active packaging outperformed MAP by increasing product shelf life since it reduced microbial development while retaining the gluten-free breads sensory qualities [26].
Aronian berry, asparagus, bell pepper, beet, blackberry, blueberry, broccoli, carrot, cucumber, cherry, cranberry, garlic, ginger, grape, red onion, red cabbage, rhubarb, raspberry, pomegranate, spinach, strawberry, and green tea have all been studied for their antibacterial effects [27]. According to the authors, all green vegetables have no antibacterial action against Staphylococcus epidermidis and Klebsiella pneumonia, while all purple and red vegetables and fruit juices have. Pomegranate juice has reduced E. coli O157: H7 growth [28].
Fruits, vegetables, nuts, seeds, stems, flowers, and leaves contain saponin and flavonoids [29]. Saponins and flavonoids obtained from plants such as Bersama engleriana (Melianthaceae) have been shown to have antibacterial activity when extracted from roots, stems, bark, leaves, and wood [30, 31]. The antimicrobial activity of thiosulfinate has also been demonstrated against Gram-negative bacteria. Glucosinolates are secondary metabolites found in mustards, cabbage, cauliflower, brussels sprouts, broccoli, kohlrabi, kale, horseradish, and radishes, among other plants [32]. Hydrolysis products of glucosinolates have been shown to exhibit substantial antibacterial activity against Gram-positive bacteria, Gram-negative bacteria, and fungus, either alone or in combination with other substances [32].
Pathogenic bacteria and fungi were tested on olive leaves. The aqueous extract of an olive leaf at 0.6 percent (w/v) destroyed practically all bacterium cells in three hours. However, Dermatophytes and Candida albicans required 1.25 percent and 15 percent (w/v) olive leaf extract, respectively [33]. Olive leaf extract also has potent antibacterial and antifungal properties [34]. Olive leaves antibacterial and antifungal properties are attributed to phenolic substances such as caffeic acid, verbascoside, oleuropein, luteolin 7-O-glucoside, rutin, apigenin 7-O-glucoside, and luteolin 4-O-glucoside, according to the authors [34]. As a result, the authors indicated that olive leaf extract could be used as a nutraceutical, particularly as a source of phenolic chemicals. shows some of the beneficial effects of plant-derived extracts in food systems.
| Antimicrobial compound | Target microorganism | Concentration | Antimicrobial effects | Product (food) | Reference |
|---|---|---|---|---|---|
| Satureja horvatii EO | Listeria monocytogenes | 10 and 20 mg/mL | Total inhibition | Pork meat | Bukvicki et al. [35] |
| Thyme EO | L. monocytogenes | 0.8% and 1.2% | Reduction of viable count below 2 logs (CFU/g) from day six until the end of storage | Minced fish meat | Pellegrino and Tirelli [36] |
| Oregano and cinnamon cassia Eos | L.monocytogenes | 500 ppm | The growth rate was reduced by 19 and 10 percent with oregano and cinnamon cassia EOs, respectively | Ham | Dussault et al. [37] |
| Bay leaf EO | Coliforms | 0.1 g/100 g | A 2.8 log reduction in total coliforms count on day 12 | Fresh Tuscan sausage | da Silveira et al. [38] |
| Vervain Eos | Monilinialaxa, M. fructigena | 1000 ppm | Reduction of brown rot lesions diameter | Peaches | Elshafie et al. [39] |
| Thyme Eos Lemon EO | E. coli O157: H7 | 500 ppm75 μL/L + thermal treatment at 54°C for 10 min | A 5-log reduction in the initial population | Apple juice | Espina et al. [40] |
| Lemon EO | E. coli O157: H7 | 0.1 mL/100 g | A 1.7 log reduction in E. coli O157: H7 | Chocolate | Kotzekidou et al. [41] |
| Olive leaves extract | Total viable count | 2% (w/v) | A 2-log reduction in the initial population | Raw peeled undeveined shrimp | Ahmad et al. [7] |
| Chestnut inner shell extract | Campylobacter jejuni | 2 mg/g | Total inhibition of C. jejuni at an inoculum level of 3 logs (CFU/g) | Chicken meat | [42] |
Animals also contain antibacterial compounds that are safe for humans to consume. Antimicrobial compounds produced from animal sources are employed for various applications, as shown in . The utilization of chitosan, which is commonly used in the food industry, is cited as an example. Chitosan is a polycationic biopolymer typically found in crustacean exoskeletons such as crabs and lobsters. Because of its features, such as its inability to dissolve in neutral conditions and a higher pH value, chitosans utility in food preservation is limited [49]. Chitosan is now commonly used in edible coatings and films to reduce water vapor content, limit oxygen transmission, and lengthen the shelf life of fruits. As a result, food spoilage will be avoided [50].
| Antimicrobials | Source | Food bio-preservation | References |
|---|---|---|---|
| Lysozyme | Naturally found as part of a living organism for defence. | Used as antimicrobials in dairy foods and inhibits Gram-positive bacterial species | [43] |
| Lactoferrin | A type of natural protein seccteted in milk, especially in the whey part. | Antimicrobial activity because of its iron binding property, as well as its antibacterial potency it inhibits B. stearothermophilus, L. monocytogenes, E. coli, and B. subtilis | [44] |
| Lactoperoxidase | An antimicrobial system that originated from milk | Effective against gram-negative bacteria | [45] |
| Ovotransferrin | Produced by hydrolysis of natural proteins. | Inhibits bacterial growth due to iron deprivation | [46] |
| Protamine | A type of protein found in the sperm of fish (salmon and other species of fish) and birds. | Used as antimicrobial properties inhibits the Gram-positive, as well as Gram-negative bacterias and some species of fungi used as a preservative in a wide variety of foods ranging from confection items to fruits and rice | [19] |
| Pleurocidin | An antimicrobial peptide secreted in the skin of winter flounder | Inhibits various species of fungus and bacteria including L. monocytogenes, E. coli O157: H7, V. Parahemolyticus S. cerevisiae, and P. expansum | [47] |
| Chitosan | P produced from chitin for commercial purposes and extracted from exoskeletons of arthropods and crustaceans | Used as antibacterials and antifungals inhibits the growth of B. cereus, S. typhimurium, S. aureus, L, monocytogenes, and Shigella dysenteriae | [48]. |
Apart from chitosan, lysozyme, which is found in eggs and milk, can also be utilized as an antibacterial of animal origin and is widely accepted as safe. The lysozyme enzyme, found in eggs, is often used as an antibacterial and preservative in chicken, meat, and fruits. Because of its ability to hydrolyze the β-1,4 connection between N acetylmuramic acids and N-acetyl glucosamine at the microbial cell wall, lysozyme possesses antibacterial characteristics [49]. Lysozyme is well-known commercially used to prevent Clostridium tyrobutyricum-induced late blowing in semihard cheese. Gram-positive bacteria are frequently susceptible to lysozyme but Gram-negative bacteria are not. A lipopolysaccharide layer on the cell membranes surface causes this effect [50].
Lactoferrin is one of the natural antimicrobial agents found in mammalian secretions such as saliva, milk, and tears, according to Murdock et al. [51], and it is one of the most effective antimicrobial agents in milk. Lactoferrin will help to reduce the amount of iron in the environment. As a result, the bacteria cells development will be hampered by this circumstance. Lipopolysaccharides will then be released from Gram-negative bacterias outer membrane, causing the outer membrane to deform. Pores, or “blebs,” will form as a result. Lactoferrin has been shown to suppress the microbiological activity of Escherichia coli and Listeria monocytogenes.
Antimicrobial peptides are also naturally found in milk. Lactoperoxidase, for example, is a common enzyme found in milk that has been demonstrated to have potent antibacterial properties against bacteria, fungi, and viruses [45]. Cow milk, ewe milk, goat milk, buffalo milk, pig milk, and human milk all include lactoperoxidase [45]. The dairy industry utilizes the lactoperoxidase system to maintain microbiological purity in cow milk. Lactoperoxidase-mediated food preservation affects Gram-negative bacteria more than Gram-positive bacteria.
The antimicrobial activity of animal lipids against various microorganisms has also been reported [52]. Gram-positive and Gram-negative bacteria and fungi may be rendered inactive by milk lipids [53]. Lipids in food may help prevent pathogenic and spoilage microbes from proliferating in food matrixes. Other components found in animals, such as eicosapentaenoic acid and docosahexaenoic acid, have been shown to have antibacterial properties against Gram-positive and Gram-negative bacteria [53].
Microorganisms such as bacteria, fungi, and mold produce various chemicals that are potentially harmful to other microorganisms. Bacteria that fight other bacteria produce a variety of chemicals. Those active bacteria can thwart and prevent the growth of microbes that can cause food deterioration [54]. shows some of the microbial-based preservatives used in the food system. Bacteriocin, a protein molecule, is a crucial component that can function as an antibacterial agent against spoilage or microbial pathogens. Gram-positive and Gram-negative bacteria can create bacteriocins [49]. These proteinaceous molecules permeate the cytoplasmic membrane, allowing intracellular metabolites to flow out. As a result, membrane depletion may be taking place. Other active bacteria, such as reuterin and pediocin, can successfully limit the growth of spoilage germs in addition to bacteriocins [19]. Food-borne pathogens such as Clostridium botulinum, Enterococcus faecalis, and Listeria monocytogenes can be inhibited by bacteriocins. Bacteriocins are also safe to employ in bio preservatives because they are protease-degradable [60].
| Antimicrobials | Source | Food bio-preservation | References |
|---|---|---|---|
| Organic acids | Main end products of fermentation. | Decrease the pH of the surrounding environment, creating a selective barrier against nonacidophiles. Lactic acid exerts an antimicrobial effect by disruption of the cytoplasmic membrane and interference with membrane potential. | [55] |
| Carbon dioxide | Produced by fermentation of sugar by-products using heterofermentative lactic acid bacteria | It creates an anaerobic creation of anaerobic conditions it has antagonistic effects on aerobic bacteria and produces carbonic acid. | [19] |
| Diacetyl (2,3-butanedione) | A type of low molecular weight compound produced as a metabolic by-product of lactic acid bacteria | Inhibits both Gram-positive and Gram-negative bacterias including Bacillus cereus, Staphylococcus aureus, Escherichia coli, Salmonella anatum, Listeria monocytogenes Yersinia, and Aeromonas. | [19] |
| Hydrogen peroxide | Produced by LAB in the presence of oxygen and action of flavoprotein oxidases or NADH peroxidase. | The antibacterial effect through oxidative damage of proteins and increase of membrane permeability | [56] |
| Reuterin | A kind of antimicrobial compound with low molecular weight; it is produced by Lactobacillus reuteri by anaerobic metabolism of glycerol. | Effective against Listeria monocytogenes | [57] |
| Reutericyclin | Produced and isolated from Lactobacillu reuteri | Antibacterial and it effectively inhibits Gram-positive bacteria including B. cereus, B. subtilis, E. faecalis Listeria innocua S. aureus, and Clostridium difficile. | [58]; [19] |
| Nisin | Nisin synthesized by some strains of Lactococcus lactis is a heat-stable bacteriocin peptide | Nisin inhibits target cells via specific binding to the cell wall precursor lipid II, followed by the formation of pores in the bacterial cell membrane and subsequent loss of intracellular constituents | [59] |
Nisin is a well-known bacteriocin that is often listed in European food additives and by the FDA in the United States. Nisin is commonly used in cheese and sausage preparation [61]. Lactococcus lactis produces nisin, made up of amino acids such as lanthionine, dehydroalanine, and aminobutyric acid [60]. Nisin can inhibit a wide range of Gram-positive bacteria. Nisin will be connected to the microbes cell membrane, and a pore will form due to the ionic contact with the C-terminus. For example, nisin should be used with chelators such as ethylene diamine tetra-acetic (EDTA) [51]. Nisin is used to make cheese because it inhibits the bacteria Staphylococcus aureus, which is found in raw milk [23].
Because of its powerful oxidizing effect on the bacterial cell and destruction of basic molecular structures of cell proteins, hydrogen peroxide has significant antibacterial activity [56]. Lactic acid bacteria (LAB) are the main biocontrol agents used to extend the life of perishable products. It acts as an antimicrobial and a probiotic [62]. The antimicrobial activities of lactic acid bacteria are due to their potential to produce various antimicrobials such as hydrogen peroxide, organic acids, carbon dioxide, bacteriocins, reuterin, and ethanol [60]. Lactic acid bacteria (LAB) are thought to produce hydrogen peroxide as their major metabolite [63]. Another antibacterial molecule produced by heterofermentative lactic acid bacteria (LAB) during fermentation is diacetyl (2,3-butanedione). However, due to its buttery aroma and the high concentration required for food preservation, diacetyls usage as a food preservative has been limited [64]. Acetaldehyde, produced by heterofermentative LAB, has also been demonstrated to have an antibacterial effect against various pathogenic bacteria.
Lactobacillus reuteri produces reuterin and reutericyclin, both of which are active antimicrobials against Gram-positive bacteria. The antimicrobial activity of Reuterin was discovered against Gram-negative bacteria, yeasts, molds, and protozoa. Reuterin (-hydroxy propionaldehyde) is a nonproteinaceous glycerol metabolite that is water-soluble [65]. L. monocytogenes, E. coli O157: H7, S. choleraesuis subsp. Choleraesuis, Yersinia enterocolitica, Aeromonas hydrophila subsp. Hydrophila, and Campylobacter jejuni have all been found to have high antimicrobial activity [66]. Reuters antibacterial action against Gram-negative bacteria was not boosted when it was tested in combination with nisin [66].
Pediocin, a heat-stable bacteriocin generated by Pediococcus species such as Pediococcus acidilactici and Pediococcus pentosaceus, is another heat-stable bacteriocin. Most of these peptides are thermostable and active across a broad pH range (pH 2 to 8). Pediocin, unlike nisin, has a relatively narrow range of activity. Overall, pediocins are active against some Enterococcus, Clostridium, Lactobacillus, Carnobacterium, Pediococcus, and Leuconostoc and Streptococcus species as Leuconostoc and Streptococcus, yet they have vigorous antimicrobial activity against L. monocytogenes [67]. Pediocins have been employed as preservatives in various foods, including cheese and meat-based foods. In this regard, Rodriguez et al. [68] found that pediocin preparations from Lactobacillus lactis CL1 and L. lactis CL2 reduced E. coli O157: H7 counts by 0.83 and 1.66 log units, S. aureus counts by 0.98 and 0.40 log units, and L. monocytogenes counts by 2.97 and 1.64 log units, respectively, when compared to control cheese at day 30.