With consumer awareness about food safety and quality, there is a high demand for the preservative (synthetic)-free foods and use of natural products as preservatives. Natural antimicrobials from different sources are used to preserve food from spoilage and pathogenic microorganisms. Plants (herbs and spices, fruits and vegetables, seeds and leaves) are the main source of antimicrobials and contain many essential oils that have preservation effect against different microorganisms. Mainly, herb and spices contain many essential oils and the examples include rosemary, sage, basil, oregano, thyme, cardamom, and clove. These essential oils are very effective against many pathogenic and spoilage microorganisms like Salmonella, Escherichia coli, Listeria monocytogenes, Campylobacter spp., and Staphylococcus aureus and help to increase their quality and shelf stability. These antimicrobial compounds are also used in combination with edible food coatings and inhibit the ability of microorganisms to grow on the surface of food and food products.
- essential oils
- antimicrobial edible coatings
Today, food safety is everybody’s concern and it is very hard to find anyone who has not encountered an unpleasant moment of food-borne illness at least once in the past year. According to the report of WHO in 2005, there were about 1.8 million deaths caused by diarrhea (food-borne illness), and these diseases were due to the use of contaminated food and water . The main cause of food-borne illnesses is the use of food contaminated by microbial pathogens, toxins, or radioactive components. When certain bacteria or pathogens contaminate food, they can cause food-borne illness or sometimes called “food poisoning.” Food-borne illnesses are mild but sometimes they can even be deadly .
Food-borne pathogens (
There is an increase in the consumption of fresh food with the consumer demand for the ready-to-eat food and the desire to lead a healthy lifestyle. The challenges associated with the consumption of fresh food are short storage life and its association with food-borne diseases. To avoid these challenges, there is a commercial pressure of using chemical preservatives that prevent the growth of food spoilage agents, but the increase in the use of these chemical preservatives is negatively perceived by the consumer .
2. Antimicrobial agents and food safety
Traditional food preservation methods are less efficient in reducing the growth of food-borne pathogens in food products, and the ever-increasing demand for chemical-free food has paved the way for antimicrobials to be used in food industry . The use of antimicrobials is a new technology by the food industry to increase the shelf life of food and overcome the issues of food quality and safety. These antimicrobials could be of natural or synthetic type, but natural antimicrobials are gaining much importance than synthetic ones. Even though synthetic preservatives are approved by government agencies for human use, many of these preservatives still threaten our health. Thus, researchers give more importance toward the potential of natural products for their antimicrobial activities [8–10].
3. Natural antimicrobial agents
Chemical compounds having pharmacological and biological activity and produced by living organisms are called natural products. Living organisms produce primary and secondary metabolites [11–13]. Primary metabolites are the products that have essential function in the organism, while secondary metabolites could simply be waste products or could have some important function in their producers. Secondary metabolites can be used as drugs against diseases such as cancer, inflammation (swelling), and so on and also have antimicrobial activity [1, 14]. Secondary metabolites possessing antimicrobial activity are called the natural antimicrobials and could be extracted from different sources like plants (fruits, vegetables, seeds, herb, and spices), animals (eggs, milk, and tissues), and microorganisms (fungi and bacteria) [15–17]. With special reference to plants, secondary metabolites are found to be healthy ingredients that work as antimicrobials or disease-controlling agents . Owing to the potential of antimicrobials against pathogenic and spoilage microorganisms, these secondary metabolites gain much importance for the application in food products [18–20]. They contain the properties of antimicrobials and antioxidants at the same time and so are considered as a better option for food preservation as compared to synthetic preservatives .
Several researches have been conducted to find out the antimicrobial potential of natural products, especially the plant sources like fruits, vegetables, herbs, and spices because they are enriched with compounds having antimicrobial activity. Nowadays, there are more than 1350 plants with antimicrobial activities and more than 30,000 antimicrobial components have been extracted from plants . However, many studies have also been conducted on antimicrobial potential of microorganisms and animals. Food applications of antimicrobials have also been investigated.
Nowadays, plant extracts and essential oils (EOs) have gained much importance due to their flavoring as well as antimicrobial potential . Research conducted on the antimicrobial activity of the extracts from different fruit peels like banana, apple, pomegranate, sweet lime, orange, mango, and papaya indicated that fruit peel extracts have mild inhibitory effect against pathogenic bacteria [24–29]. Plants secondary metabolites contain many antimicrobial agents, so they have a greater inhibitory effect against Gram-positive and Gram-negative bacteria [14, 27, 30–32]. The chemical composition, concentration, and structure of the antimicrobial component determine their efficacy. Antimicrobial components of plant origin include flavonoids, thiosulfinates, glucosinolates, phenolics, organic acids, flavonoids, and saponins [31, 33, 34]. However, the main compounds with antimicrobial activity are phenols which include terpenes, aliphatic alcohols, aldehydes, ketones, acids, and isoflavonoids [35–38].
Antimicrobial components in plant materials are commonly found in herbs and spices (rosemary, sage, basil, oregano, thyme, cardamom, and clove), fruits and vegetables (guava, pepper, cabbage, garlic, and onion, citrus), seeds and leaves (grape seeds, fennel, nutmeg, parsley, and olive leaves) [39–42].
In this chapter, we discuss the role of antimicrobials from different sources with special reference to meat and meat products. Consumption of meat is important for the growth, development, and maintenance of health in human beings. Meat is an animal origin food and is a rich source of proteins, vitamins, minerals, and so on which is why the safety of meat and meat products is of much importance [43, 44]. Proteins of meat are of much importance with a high amount of essential amino acids being available and of biological value. Meat and meat products are at a high risk of microbial spoilage and also cause losses to economy . Although food industry has developed several new techniques for hygienic slaughtering and production of meat products, a major concern related to meat consumption is the presence of pathogenic microorganisms that cause food-borne diseases, for which raw meat provides an ideal substrate [46, 47].
Essential oils, as plant extracts possessing antimicrobial agents and also antioxidative and flavoring properties, can be considered as healthy ingredients to be used in meat and meat products. If essential oils are used in meat products, they can reduce the chances of food-borne diseases and can retard the oxidation of lipids in meat [52–54].
4. Antimicrobials from plant sources
4.1. Herbs and spices
Herbs and spices have long been used by human beings for different reasons like food additives, flavorings, and preservatives. They are considered the most commonly used natural antimicrobials against different pathogens. The antimicrobial activity of herbs and spices depends on the type of essential oil present in it, food type in which it has to be used, and the type of microorganism [11, 55–57].
The efficiency of essential oils from herbs and spices depends upon their chemical structure, in particular to the presence of hydrophilic functional groups such as hydroxyl groups . Essential oils from clove, oregano, rosemary, thyme, sage, and vanillin are the most effective containing the phenolic groups . They possess inhibitory activity against Gram-positive than Gram-negative bacteria [59, 60]. Essential oils have high vapor pressure and are able to reach pathogenic microorganism through gas or liquid phases. Many investigations have proved the antimicrobial efficiency of essential oils against several pathogenic and spoilage microflorae. However, the efficiency of essential oils depends upon the pH, storage temperature, and concentration of oxygen .
Some of the antimicrobial compounds that are present in spices and herbs are eugenol, thymol, thymol and carvacrol, vanillin, allicin, cinnamic aldehyde, and allyl isothiocyanate that are, respectively, present in cloves, thyme, oregano, vanilla, garlic, cinnamon, and mustard .
Essential oils possess antimicrobial activities against several pathogenic microorganisms present in meat, including both Gram-positive and Gram-negative bacteria . Many studies have been conducted to analyze the effects of essential oils extracted from sources such as oregano, rosemary, thyme, basil, garlic, and clove, when used alone or in combination with other essential oils [4, 63].
Essential oils extracted from herbs and spices were found to be effective against several pathogenic microorganisms. Studies showed the antimicrobial activities of 14 essential oils (clove, oregano, rosemary, pepper, nutmeg, liquorice, turmeric, aniseed, cassia bark, fennel, prickly ash, round cardamom, dahurian angelipca root, and angelica) against four meat spoilage and pathogenic bacteria (
The oregano essential oils have antibacterial activities against
Sodium nitrite has been used as a preservative in meat and meat products, but researches showed that if it is used in combination with oregano essential oils, it will slow down the growth of bacteria more efficiently than sodium nitrite alone . The amount of EOs used in meat and meat products should be higher than the dose used in in vitro conditions because of the interaction with components of meat. Antimicrobial essential oils can be used directly or as polyethylene oxide (PEO)-based antimicrobial packaging .
Another research showed that the addition of oregano essential oils at a concentration of 0.7% will provide antimicrobial activity in minced sheep meat against
When applying the antimicrobials in meat or meat products, depending upon the properties and type of pathogen, some EOs are more effective than others. Eugenol, coriander, clove, oregano, and thyme oils were found to be effective at levels of 5–20 μl/g in inhibiting
Thyme essential oils have high antimicrobial activity owing to the presence of different compounds. The most prominent of all identified compounds of thyme essential oils were thymol (50%), followed by p-cymene (24%), linalool (4.6%), γ-terpinene (4.1%), and 1,8-cineole (4.3%). Thyme oils are effective against
Extensive research has been conducted to analyze the efficiency of essential oils against
Research has been conducted to find out the antimicrobial activity of clove oil against
Sage essential oil is used at a concentration of 0.3% in minced beef in combination with soy protein. Rosemary or Chinese mahogany (500, 1000, and 1500 ppm) is used to increase fresh chicken sausage [14, 69, 79].
4.1.1. Safety aspect of essential oils
Antimicrobial agents, though very effective against microbial population and able to extend the quality and shelf life of meat and meat products, should be added with care because they can cause some side effects. Many essential oils like thymol and eugenol can cause mucous membrane irritation, if used in higher concentrations. In vitro studies of various essential oils like carvacrol, carvone, thymol, and so on show a mild to moderate toxic effects . Some essential oils can cause allergy or some can have photoactive molecules which can cause phototoxic reactions [80, 81].
4.2. Fruits and vegetables
Many fruits and vegetables are nowadays well known to have antimicrobial effect against different pathogenic and spoilage microbes due to their contents of phenolic and organic acids. Fruit peels that are mostly discarded also contain antimicrobial compounds [30, 82].
Research showed that the antimicrobial activity of orange peel and capsicum was due to the presence of phenolic compound (coumaric acid) . In minced beef, the extracts of capsicum annum have inhibitory effect against
Pomegranate extract reduces the growth of
Citrus peel extract, lemon grass, and lime peel extracts were investigated for their antimicrobial activities in meat and meat products. The extracts showed high potential of antibacterial activity against
Garlic is a potential inhibitor for food pathogens. Foods contaminated with pathogens pose a potential danger to the consumer’s health. The use of garlic can increase the shelf life and decrease the possibilities of food poisoning and spoilage in processed foods. Garlic extract has antimicrobial activity due to the presence of an organic sulfur compound allicin, which acts as a growth inhibitor for both Gram-positive and Gram-negative bacteria including
The antimicrobial effect of onion extract on the fresh beef fillet meat was investigated. Beef fillet samples were cut into pieces and treated with 5, 10, 20, and 50% onion-water extract (v/v) and stored in refrigeration conditions at 4°C. Microbiological quality of the samples was investigated during storage for 9 days. Increasing concentrations of onion extract significantly affected
Antimicrobial efficacy of curcumin, one of the active components of the
5. Antimicrobial edible coatings
Today, many fresh products are available commercially with best nutritional profile and low cost of production. Consumers also prefer consuming fresh meat and meat products, but a limit for the commercial availability of fresh meat is its low storage life because of high moisture contents that cause the growth of pathogenic and spoilage microorganisms .
To avoid this, the spoilage use of antimicrobials is one of the best ways to increase the shelf life of these perishable food products especially meat and meat products. The use of antimicrobial films and coatings dates back to twelfth century. The only difference between film and coating is its thickness. There are many ways of applying these antimicrobials on food products to enhance the natural appearance and safety of fresh meat and meat products like spray or spread of antimicrobials on meat [88, 89].
By the combination of different preservation techniques, researchers have been successful in achieving the objectives related to microbial quality storage life of perishable products. The addition of natural antimicrobials in combination with modified atmosphere packaging and refrigeration has proven to show the best results. Antimicrobials can also be added in coatings and films to be used in meat and meat products [88, 90].
The use of antimicrobials in edible films and coatings is an emergent technique that is helpful in enhancing the quality and safety aspect of food. This technique includes a control release of antimicrobial agents in effective concentration in the food product, when required.
The use of oregano essential oil (EO) as natural antimicrobial in combination with modified atmosphere packaging and refrigeration highly enhances the storage life of fresh beef or chicken during storage. Whey protein isolate coatings containing antimicrobial agents like oregano EO, 3-polylysine, or sodium lactate were used on fresh beef under refrigeration, which was evaluated against the progression of microflora like
The effect of soy protein isolate films containing up to 5% of oregano and/or thyme EO was evaluated to be effective against coliform and
Whey protein isolates-based edible films were evaluated for antimicrobial activities with different essential oils. These films showed high effectiveness against
Similarly, milk protein coatings are used in beef in combination with oregano essential oils against
Chitosan coatings in different molecular weights and viscosities (14, 57, or 360 mPa) were used in Atlantic cod fish against psychotropic bacteria. Whey protein coatings were used in smoked fish in combination with Lactoperoxidase system (0–0.5%, w/v) against
All the researches and studies conducted till now have proved that the use of synthetic preservatives to increase the shelf life of food and food products is in any way harmful for the human health, so there is a call for the use of natural products as preservatives to increase the quality and shelf stability of the food and food products. Natural antimicrobials contain all the qualities to be used as preservatives especially in meat and meat products, and plants are the main source of these antimicrobials.
Plant essential oils have great antimicrobial activity against Gram-positive and Gram-negative bacteria owing to the potential of phenolic compounds. Essential oils from herbs and spices like clove, oregano, rosemary, thyme, sage, and vanillin are the most effective against spoilage and pathogenic microorganisms like
To increase the shelf life of meat and meat products, a new trend is the use of antimicrobial in edible films and coatings in combination with different packaging techniques. Oregano essential oils in combination with modified atmosphere packaging highly increase the shelf life of chicken and beef. Whey protein isolate coatings added with oregano essential oils in combination with refrigeration were very effective against