Review on the extension of shelf life for fruits and vegetables using natural preservatives

Abstract

Fruits and vegetables are important for the nutrition and health of individuals. They are highly perishable in nature because of their susceptibility to microbial growth. Foodborne pathogens create a significant problem for consumers, food businesses, and food safety. Postharvest factors, including transportation, environment, and preservation techniques, cause a reduction in product quality. The present world is using synthetic preservatives, which have negative impacts on consumer health. Food safety and demand for healthy foods among consumers, the scientific community, and the food industry resulted in the exploitation of natural preservatives, which play an important role in their effectiveness, prolonged shelf life, and safety. Natural preservatives include plants, animals, and microbiological sources with polymers to extend shelf life, improve quality, and enhance food safety. This review specifically focuses on mechanism of action of natural preservatives, spoilage of fruit and vegetables, the importance of edible film and coating on fruits and vegetables.

Introduction

Fresh fruits and vegetables are high on consumer purchase priorities because of their vitamins, minerals, antioxidants, and fibers, as they play an essential part in a healthy diet (Jafarzadeh et al., 2021). Fruits and vegetables provide numerous health benefits for humans and are an important part of a balanced diet (Ziv and Fallik, 2021). Their consumption can help minimize a wide range of health issues, including chronic diseases, strokes, malignancies, osteoporosis, and neurological diseases (Ribeiro et al., 2021). Fruits and vegetables represent around 40–50% of food losses, which leads to an annual loss of US$750 billion (Perumal et al., 2022). Such food products become more susceptible to contamination, enzymatic browning, unwanted volatile production, and texture changes, each of which diminishes their health advantages (Ribeiro et al., 2021). Maintaining quality in terms of color, flavor, weight, and nutritional content has become more challenging over time. The biochemical changes involve variations in total soluble solids (TSS), titratable acidity (TA), pH, phenolics, flavonoids, increased oxidative stress, phytohormones, antioxidant enzymes [superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT)], color values, organoleptic properties, firmness, defence response-related enzymes (PAL, β-1,3-glucanase, and chitinase), excessive temperatures, and spoilage by microbes (Perumal et al., 2022). Water loss is an important factor that leads to the degradation of vegetable and fruit quality, which causes nutritional value loss, soft texture, flaccidity, shriveling, and wilting (Al-Tayyar et al., 2020). However, the main problem regarding preserving fruits and vegetables is their short shelf life due to their high moisture content (75–95%), which results in quick deterioration and disintegration of such foods and also contributes to their undesirable appearance (Jafarzadeh et al., 2021). Fruits and vegetables possess various physical attributes such as color, texture, shape, and size, which can serve as distinguishing factors for efficient classification. Fruits and vegetables exhibit a multitude of inter and intraclass variances and similarities. The interclass differences refer to significant changes, such as alterations in color, texture, and shape. On the other hand, the intraclass variations are typically more subtle and difficult to distinguish, such as tiny variations in features among different types of mangoes or apples (Hameed et al., 2018). Fresh fruits and vegetables include apple, strawberries, guava, avocado, litchi, blackberry, banana, lemon, figs, berfruit, kiwifruit, tomato, melon, Duke blueberries, capsicum, potatoes, and eggplant. Fresh-cut fruits and vegetables such as pears, pineapples, strawberries, apple cubes, sliced mango, and apricot pulp. Factors such as enzymatic degradation, microbiological spoilage, or unfavorable storage conditions can trigger postharvest deterioration of fruits and vegetables. During storage, fruits undergo a reduction in quality, leading to undesirable changes in flavor, softening of the outer surface, browning and loss of water, and disintegration of surface textures (Das et al., 2021). Scientific research has shown that the quantity of fruits and vegetables lost after harvest is approximately 10–15% in developed nations and about 20–40% in developing nations. These losses can be even higher for certain specialized crops (El Khetabi et al., 2022). Fresh-cut fruits and vegetables that have been recently sliced are more susceptible to deterioration as a result of several biochemical reactions, such as alterations in color, texture, and the rapid ripening process. During the storage of fresh-cut produce, several undesirable processes occur, including moisture loss, discoloration, the development of an unpleasant scent, and microbial deterioration (Firdous et al., 2023). Cellular respiration is a mechanism by which plants, such as vegetables and fruits, constantly use oxygen while emitting carbon dioxide. Sugars, carbohydrates, proteins, and organic acids are reduced and degraded during the metabolic process in the respiratory system. Following the digestion of substrates and carbohydrates, the plants separate from the vegetables or fruit, making replenishment challenging (Romanazzi and Moumni, 2022). Numerous methods are available, such as synthetic preservatives and conventional food preservation techniques, to preserve these fruits and vegetables. However, these methods still have limitations in the inhibition of microbial reactions and lipid oxidation. Hence, preservatives are used to sustain quality, safety, and protection from spoilage. Synthetic preservatives are easily available and economical. However, they come with severe health issues and side effects. Therefore, bio-preservatives have evolved to decrease the application of processes and preservation methods. Bio-preservatives are natural preservatives obtained from plants, animals, and microorganisms that extend the shelf life of fruits and vegetables (Batiha et al., 2021).

Natural preservatives are safe, non-toxic, and cost-effective and have been touted as an alternative to synthetic preservatives. Consumers also believe that they are healthier and continuously discover new natural preservatives. It is exploited as an edible coating and film technique as a novel way to preserve fresh fruits and vegetables and fresh-cut fruits and vegetables from physical, chemical, and biological deterioration (Valencia-Chamorro et al., 2011). Biopolymers are Generally Recognized as Safe (GRAS), biocompatible, environment-friendly, and biodegradable. Biopolymers are characterized into three types: polysaccharides (gums, starch, pectin, and cellulose derivatives), lipid components (fatty acids, acylglycerol, and wax), and protein coatings (gluten, gelatin, zein, whey, and soy) (Ribeiro et al., 2021). The processed food packaging market (based on protein, lipids, polysaccharides, and others) will be estimated at USD 2.14 billion by 2030, with a Compound Annual Growth Rate (CAGR) of 6.79 percent (2022–2030), up from USD 783,32 million in 2021, according to Market Research Futures (MRFR) (Kumar et al., 2022a, 2022b). Among the previously published review articles, only very few summarized about the incorporation of natural extracts as edible films and coatings in the preservation of whole fruits and vegetables and fresh-cut fruits and vegetables. There is a lack of knowledge regarding the impact of active substances on the functional, mechanical, and sensory properties of edible coatings in wrapping fruits and vegetables. Although the current study of literature examines the separate advantages of natural preservatives and edible films to prolong the shelf life and maintain the quality of food, there is a lack of review articles on their combined use. This work addresses the problem by examining both the individual effectiveness of natural preservatives and edible films, as well as their potential synergistic effects when combined. To attain innovation through the creation of new formulations that maximize the preservation of fruits and vegetables while also emphasizing safety and minimizing any negative effects on the environment. Moreover, the study investigates the impact of these combined substances on the security and sensory characteristics of packed fruits and vegetables, offering significant knowledge for both business stakeholders and customers. This work fulfills a literature review in the field of food packaging technology and promotes sustainable practices in food preservation. Therefore, the object of the review covers the current works on edible film and coatings and involves the investigation of recent advances, which include natural preservatives in fruits and vegetables, fresh-cut fruits and vegetables, and spoilage in fruits and vegetables. Future perspectives for researchers, technologists, and industry management include an extensive understanding that could be useful for effective food preservation methods and also ensure food safety.

Sources of contamination of fruits and vegetables

Microbial spoilage

The spoilage of fruits and vegetables is a significant food concern that has yet to receive as much research attention as produce-related foodborne illnesses and processed technologies, despite its socioeconomic, food quality, and food security consequences (Alegbeleye et al., 2022). Spoilage refers to the development of undesired modifications in the color, flavor, texture, and odor of fruits and vegetables, resulting in a deterioration in their overall quality (Perumal et al., 2022). Fruit and vegetable deterioration is mainly caused by two processes: (1) physiological deterioration, which encompasses water loss, softening, ripening, and leaf shedding; and (2) microbiological decay, which results from pathogenic bacteria, yeasts, or molds. Each of those processes relies extensively on environmental circumstances and significantly impacts each other (Ziv and Fallik, 2021). The most important physical factors contribute to the deterioration of fruits and vegetables, including temperature, water activity, nutritional availability, humidity, pH levels, and air exposure (Perumal et al., 2022). Gram-positive bacteria, Gram-negative bacteria, and fungi, mainly yeasts and molds, are frequently responsible for the microbiological decay of fruits and vegetables. Microorganisms that cause spoilage can enter plant tissues during the development of the fruit, typically through the calyx (flower or blossom end) or stem scar. In rare cases, they may also enter through the stomata and lenticels (Alegbeleye et al., 2022). Microorganisms can colonize or contaminate fruits and vegetables at any time during the production, distribution, processing, packaging, or preparation of food (Mostafidi et al., 2020). The predominant pathogen that affects harvested crops post-harvest is Colletotrichum gloeosporioides. This pathogen is responsible for causing anthracnose, a common illness that occurs frequently and reduces the quality and longevity of fruits such as mango, avocado, papaya, and other tropical fruits throughout their storage, transportation, and market processes (Perumal et al., 2022). Fruits are categorized into two classes based on the underlying mechanisms that desire the ripening process. This perspective allows for the classification of fruits as either climacteric or non-climacteric. Fruits in the second group do not undergo further ripening after being harvested. Conversely, fruits in the first group can continue to ripen even after being harvested and emit more ethylene than non-climacteric fruits. As a result, they are more susceptible to deterioration caused by bacteria (Mitelut et al., 2021).

The sources of contamination can be categorized into two main groups: preharvest and postharvest sources of contamination. Regarding preharvest sources of contamination, research has demonstrated that the soil used for cultivated the fruits and vegetables can be the potential source. Figure 1 illustrates the contamination of fruits and vegetables and indicates that water used for irrigation, as well as for apply the insecticides and fungicides, can also contribute to contamination. Other sources include faeces, dust, improperly composted manure and human contact with these vegetables at different stages of production. Postharvest factors contributing to contamination involve a variety of aspects, such as faecal matter, harvesting machinery, interaction with humans, insects, both wild and domesticated animals, transportation methods, dust from processing machines and water used for rinsing (Balali et al., 2020). The majority of harvested products are extremely perishable because of their high moisture content and the presence of plant hormones that regulates their growth and maturation. These factors interact with the surrounding environment, leading to rapid spoilage. Therefore, it is necessary to preserve post-harvest products from harmful conditions (Armghan Khalid et al., 2022). Historically, a wide range of chemical preservatives, additives and low-temperature storage methods have been employed to inhibit deterioration in various types of food, particularly vegetables. Nevertheless, these preservation techniques can induce a wide variety of allergic reactions and the incorporated of such compounds represents a significant risk to the individual's health (Liu et al., 2021). Antimicrobial and antioxidant substances can extended the life span in vegetables and fruits remains fresh by inhibited oxidation and prevented from microbial decay. Since natural antimicrobials are considered Generally Recognized as Safe (GRAS), their usage remains unregulated in several countries (Lucera et al., 2012).

Fig. 1.

Illustration of the contamination of fruits and vegetables

Enzymatic browning

Browning is an enzymatic reaction that causes the formation of brown color in food. Enzymatic browning takes place when oxygen, enzymes, and phenol molecules are combined. Post-harvest storage is known to induce significant detrimental alterations in the nutritional, functional, biochemical, and sensory characteristics of fruits and vegetables. Enzymatic browning is primarily induced by the actions of PPO (polyphenol oxidases) that naturally occur in foods. It reduced the number of days in which fresh-cut fruits and vegetables could be stored (Navina et al., 2023). It contributed to huge economic losses in the worldwide market during transportation and storage. Browning, which in turn stimulates the occurrence of enzymatic browning reactions, leads to the waste of over 50% of food products (Shrestha et al., 2020). The enzyme PPO's activity is affected mainly by the presence of oxygen and the amount and type of endogenous phenol molecules (Moon et al., 2020). The following substances play a crucial role in preventing enzymatic browning.

The browning reaction in food products is typically categorized into enzymatic and non-enzymatic browning based on the underlying mechanism. Two different methods, physical and chemical, accomplish the reduction of enzymatic browning. Physical techniques for controlling enzymatic browning include thermal processing, oxygen exclusion, refrigeration, and irradiation. Chemical techniques to impede PPO activity involve acidification or decrease through the use of antioxidants, chelating agents, or natural extracts (Moon et al., 2020). The incorporation of active compounds, such as antioxidants, texture enhancers, and antimicrobials, aims to mitigate enzymatic browning, texture deterioration, and the presence of foodborne pathogens on the surface of the food (Ghidelli and Pérez-Gago, 2018; Bizymis and Tzia, 2022). Antioxidants effectively limit enzymatic browning by carrying out a reaction with endogenous phenols or other intermediates, thereby interrupting the chain reaction involved in pigment formation. Antioxidants are substances that minimize cell damage by impeding oxidation reactions. They can inhibit the enzymatic oxidation processes in fresh fruit and vegetable harvests by reacting with unstable molecules that have the potential to damage cells. The impact of antioxidants on fruits and vegetables is mostly influenced by environmental conditions, including pH, temperature, atmospheric composition, and light availability (Navina et al., 2023).

The non-enzymatic browning reaction is a chemical reaction that produces a brown-colored substance in food. A single ingredient or multiple components can induce this reaction without the involvement of any enzymes. In fruit and vegetable products, non-enzymatic browning can be prevented by limiting the amount of reducing sugars present in the products. Regulates the water activity in desiccated food products by utilizing sulfites, provides glucose oxidase therapy, decreases the amount of amino nitrogen present in the products, stores the items in a refrigerator, and utilizes oxygen scavengers to package products (Armghan Khalid et al., 2022). The non-enzymatic browning reactions include the Maillard reaction, Caramelization, and Ascorbic acid oxidation. In food products, these reactions occur mostly in combination rather than as isolated reactions because food is composed of complex constituents. Caramelization, also known as sugar browning, is the process that takes place while various types of sugar are exposed to high temperatures over their melting point, resulting in the development of a flavor similar to caramel. The release of volatile compounds during the caramelization process results in the development of a distinct caramel-like flavor. When the amine group of a free amino acid interacts with the carbonyl group of a reducing sugar, usually with heat present, the Maillard reaction takes place (Moon et al., 2020). In addition to that, the anti-browning agents from natural sources have been reported to be fruits (30%), vegetables (17%), plants, and herbs (43%), and the remaining 10% are from miscellaneous sources (Hamdan et al., 2022). To ensure a reasonable shelf life for these food products, it is imperative to utilize appropriate packaging, coating, and film technologies.

Edible film and coating for preservation of fruits and vegetables

Consumers have recently become more aware of packaging materials that can be considered edible and biodegradable, as well as environmentally friendly. One innovative solution to reduce this issue is the utilization of edible packaging, coatings, or films (Murugan et al., 2022). These may be used as an additional layer of protection for perishable products, effectively extending their shelf life by inhibiting microbial deterioration along with providing moisture and gas barrier capabilities. In the food sector, there are two distinct methods to utilize edible packaging. Edible coatings can be directly applied to the food product or wrapped around it as a prefabricated film (Mitelut et al., 2021). Typically, manufacturers use edible films and coatings with a thickness of less than 0.3 mm to preserve and enhance the quality of the final product, which consumers can consume as an integral component (Murugan et al., 2022). The main function of edible film and coatings is to inhibit the loss of moisture, oxygen, aroma, fragrance, and oil between food and the surrounding environment. Edible coatings can reduce moisture content, solute migration, and gas exchange, extend shelf life, lower respiration rates, and mitigate oxidative reactions to alleviate physiological illnesses (Kumar et al., 2022a, 2022b). Additionally, it can decrease discoloration, microbial proliferation, flavor alteration, and ultimately browning in fresh-cut fruits and vegetables. Hence, the food processing industry utilizes edible coatings or films as packaging materials to effectively preserve fruits and vegetables for extended periods. The edible films function by developing a semipermeable protective barrier around the vegetables and fruit, which effectively minimizes the loss of quality characteristics (Mitelut et al., 2021). Edible coatings and films have gained significant interest from scholars and the food industry as preservation techniques due to their biodegradability, biocompatibility, and antibacterial and antifungal properties (Armghan Khalid et al., 2022). These techniques have proven highly effective in preserving food while maintaining its nutritional and sensory qualities. The market share of edible packaging has undergone an ongoing increase, reaching a value of $697 million in 2016. It is estimated to further develop to $1097 million by 2023 (Mitelut et al., 2021). Jongsri et al. (2016) reported that edible coatings should provide a partial impediment to the transport of water, thereby minimizing moisture loss. Simultaneously, these coatings can alter the surrounding atmosphere of the fruit by acting as a barrier to gas exchange (Abdul Khalil et al., 2018).

Currently, researchers are using natural biopolymer matrices to create edible films or coatings that enhance the postharvest quality of fruits and vegetables. Biopolymers have various advantages, including biodegradability, recyclability, and sustainability (Kumar et al., 2022a, 2022b). The qualities indicated remain due to the abundance of biopolymers, such as starch, pectin, carrageenan, alginate, chitosan, and xanthan gum. The production of edible films and food coatings widely uses these biopolymers. The study focuses on improving the shelf life of fruits and vegetables by applying various coating materials such as chitosan, carboxymethylcellulose, seaweed gel, pullulan, pectin, starch, sago, carrageenan, gelatine, soy protein isolate, and whey protein. Additionally, researchers use plasticizers like glycerol and sorbitol, along with herbal extracts, to enhance the functional properties of these edible coatings (Murugan et al., 2022; Mitelut et al., 2021). Ayala-Zavala et al. (2013) created a pectin-based film that contains cinnamon leaf essential oil. This film has a high level of antioxidants and successfully decreases the growth of bacteria on freshly cut peaches (Abdul Khalil et al., 2018). The creation of edible films and coatings, often made from biocompatible, biodegradable, low-toxicity, and GRAS components, can address environmental concerns. Several industries have focused their efforts on developing commercially feasible and environmentally friendly packaging applications for food utilizing different biopolymers.

Studies found that blueberries, when packaged in PLA (polylactic acid) containers (VersaPack^®, Wilkinson Industries Inc., Fort Calhoun, NE) or PET clamshell containers, had a postharvest shelf life of 9 days at a temperature of 23 °C. Renewable resources like corn starch or sugar cane are the source of PLA, a thermoplastic polymer. It is the second-most widely used material for the production of biodegradable films. PLA has a significant drawback due to its low glass transition temperature, rendering PLA-based plastic cups inappropriate for containing hot liquids and other substances. Combinations of PDLA (dpoly-D-lactide) and PLLA (poly-L-lactide) can optimize temperature stability. PLA is limited by its inherent brittleness; however, this can be resolved by using an appropriate plasticizer (Abdul Khalil et al., 2018). The use of plant extracts, such as extracts from barks, stems, roots, essential oils, herbal extracts, and plant sap, in edible coating technology has introduced the concept of using nutrient-rich, antioxidant plant-based products and their extracts to prevent browning and inhibit the enzyme tyrosinase, thus extending the shelf-life of food (Navina et al., 2023). Antimicrobial compounds, such as essential oils, have a hydrophobic tendency. Therefore, including them in a biodegradable film can lead to reduced water vapor permeability compared to untreated films. Moreover, antimicrobial compounds can enhance the gas barrier characteristics of bio-based films (Abdul Khalil et al., 2018).

The application of both natural preservatives and edible film for packaging fruits and vegetables can provide synergistic effect of natural preservatives and film (Diaz-Montes and Castro-Muñoz, 2021). For instance, the inclusion of antimicrobial agents from natural preservatives in the edible film can help prolong the shelf life of the food (Fadiji et al., 2023). The impacts, interactions, or unintended consequences of these components primarily rely on their distinct characteristics and concentrations. The combination of particular film materials with specific natural preservatives can enhance their ability to preserve products through the production of synergistic effects. Nevertheless, it is crucial to take into account potential negative effects, such as changes in the taste, consistency, or appearance of agricultural products (Teshome et al., 2022). The utilization of natural preservatives and film constituents for fruit and vegetable packaging can be included directly in the packaging material or applied as a distinct layer. The selection is based on variables such as the preferred quantity of preservation, the suitability of the product, and production techniques (Amit et al., 2017). It is essential to verify that the packaging supplies are of food-grade quality and meet safety regulations. Thorough testing and evaluation should be carried out to determine any potential hazards related to the usage of natural preservatives and edible films in contact with fruits and vegetables (Alamri et al., 2021).

Natural preservatives

The major emphasis on human health depends on the quality and safety of our food. To preserve food quality and prevent decay, preservation methods are implemented. Food with these qualities requires the use of health-safe preservatives. The public is increasingly demanding food products produced with natural preservatives. An increase in public awareness of food security has resulted in the development of new consumer demands for natural food (Naufalin, 2094). The incorporation of artificial preservatives occurs frequently throughout the food preparation procedure, which might result in adverse health effects if consumed routinely. Utilizing natural preservatives provides benefits due to their perceived higher level of safety for consumption. This trend has led to an increased demand for natural preservatives as alternatives to artificial preservatives. Natural preservatives function by impeding the growth of microorganisms, preventing oxidation, and delaying specific enzymatic reactions that take place in food products. Typically, they are derived from plants, animals, and microorganisms (Teshome et al., 2022).

Classification of natural preservatives

1. Antimicrobials

Antimicrobials have been utilized to control and avoid the natural deterioration caused by microbes.

• 2. Antioxidants

Antioxidants are utilized as preservatives that minimize or prevent the biological and chemical deterioration of foods by decreasing the auto-oxidation of colors, tastes, lipids, and vitamins.

• 3. Antibrowning

Antibrowning is used to inhibit the enzymatic browning of food, which may occur at any stage of handling, processing, or storage (Novais et al., 2022; Murugan et al., 2022). Figure 2 represents the flow diagram of the classification of natural preservatives.

Fig. 2.

Flow diagram of the classification of natural preservatives

Positive and negative impacts on natural preservatives

There are several advantages to natural preservatives, such as: (1) Safety: Preservatives of natural origin are commonly produced from plants, herbs, and other natural sources, which generally gives them a perception of being safer than synthetic preservatives. (2) Health benefits: Several natural preservatives provide health benefits because of their antioxidant and antibacterial capabilities, which could improve the nutritional content of food. (3) Consumer appeal: Since there is an increasing desire for natural and organic products, food that is preserved using natural substances can be attractive to consumers and emphasize their health. (4) Environmental sustainability: Commonly, natural preservatives can be biodegradable and derived from renewable resources, thus promoting environmental sustainabiliy. (5) Minimal processing: It may require less processing compared to artificial preservatives, thereby maintaining the naturally occurring characteristics and tastes of the food (Teshome et al., 2022; Gundala and Singh, 2021). The main disadvantages of natural preservatives are: (1) Limited effectiveness: While natural preservatives may not possess the same level of efficacy as their synthetic equivalents in preventing rotting and prolonging the shelf life of products, they can result in reduced product stability. (2) Variable quality: The wide range in the quality and efficacy of natural preservatives is influenced by factors such as their source, extraction technique, and storage conditions, resulting in inconsistent outcomes. (3) Cost: Using natural preservatives instead of synthetic replacements might result in higher production costs and potentially lead to an increase in the final retail price of products. (4) Flavor: Certain natural preservatives can impart unique flavors or aromas to the food, although they might not always be desirable or suitable for the product's taste character. (5) Regulatory changes: These changes in regulations can make it hard to follow the rules when using natural preservatives in some markets (Baptista et al., 2020; Rathee et al., 2023).

Plant origin

Plants, herbs, and spices, together with their obtained essential oils or extracts and compounds isolated from various extracts, contain an extensive range of compounds that are widely recognized for their ability to inhibit the metabolic activity of bacteria, yeasts, and molds (Abdul Khalil et al., 2018). For several decades, plant extracts and essential oils have been utilized for the preservation of food and therapeutic purposes. The plant preservatives, derived from phenolics, polyphenols, essential oils, and plant antimicrobial peptides (pAMPs), are referred to as GRAS (Varghese et al., 2022). Plant-based preservatives exhibit less toxicity, minimal side effects, and more cost-effectiveness when compared to synthetic preservatives. Researchers have specifically focused on using plant essential oils (EOs) and plant extracts as food preservatives (Burt, 2004; Dhifi et al., 2016; Falleh et al., 2020). The majority of the 33,054 manuscripts consisted of research articles (23,030) and reviews (6625), with a focus on natural antimicrobials. The total number of publications published in English is 22,134, with almost 40% of these articles being published over the recent four-year period (2020–2023) (Sar et al., 2023). Eos are volatile organic compounds (VOCs) that have a pleasant aroma and oily texture. They are synthesized by plants (Teshome et al., 2022). Eos are volatile substances produced by aromatic plants as a protective function. These substances are considered safe and are commonly known as GRAS. They possess antifungal and antibacterial characteristics and have the potential to replace synthetic preservatives in food. (Silva Rios et al., 2022). Additionally, it helps to inhibit the growth of foodborne pathogens by assisting antioxidants in preventing the deterioration and degradation of food products. Antioxidants possess stability and can transfer electrons to less stable compounds. These antioxidants interact with unstable compounds termed free radicals and reactive oxygen species (ROS) to prevent the chain reaction that may destroy food products (Lobo et al., 2010). Antioxidants effectively inhibit the enzymatic browning process of cut fruits, hence enhancing consumer satisfaction (Ghidelli et al., 2013; Kumar et al., 2022a, 2022b). Researchers have identified over 3000 different types of essential oils. However, only 300 of these are considered to be industrially important, particularly for their use in the food industry, namely in the flavor and fragrance market (Falleh et al., 2020). It is important to emphasize that Eos have been accepted by consumers because of their significant volatility, transient quality, and biodegradability (Falleh et al., 2020). Consequently, the food sector began to utilize a significant quantity of natural and safe essential oils as part of an "organic or green strategy." This approach represents an innovative method to ensure the eradication of pathogens from a specific food component.

Edible coating and film are the most popular carriers that have been used to deliver EOs on fruits and vegetables (Grande-Tovar et al., 2018; Delshadi et al., 2021). Figure 3A indicates the edible film and coating techniques to preserve the fruits and vegetables using natural preservatives. Awad et al. (2022) have successfully developed active films using plant extracts to extend the shelf life of products. Consumers, manufacturers, and researchers are becoming more aware of the potential benefits of natural antimicrobial agents as effective ways to prolong the shelf life and improve the appearance of food by preventing spoilage (Lee and Paik, 2016). Estimated development of the natural preservatives market in North America, Europe, Asia–Pacific, and LAMEA (Latin America, Middle East & Africa) regions between 2018 and 2026 (Mordor Intelligence). The worldwide market value of the natural food preservatives industry was USD 796.1 million in 2018 and is estimated to reach around USD 1068.1 million in 2026. It is considered a potentially safe approach to enhancing the quality of fresh products by incorporating natural resources into the composition of edible coatings (Hamdan et al., 2022). Various plant extracts and essential oils used to increase the shelf life of fruits and vegetables are given in Table 1 and the plant compounds used to preserve fruits and vegetables using edible film and coating are given in Table 2. According to Raybaudi-Massilia et al. (2006), lemongrass essential oil (EO) and geraniol demonstrated efficacy in controlling Escherichia coli, Listeria sp., and Salmonella sp. in melon, pear, and apple juices. The Arabic gum-based guava fruit coating contains Ocimum sanctum extract, which serves as an active agent and contains polyphenols and flavonoids as its active ingredients (Murmu and Mishra, 2017). When Aloe vera gel was coated on the tomatoes and kept at a temperature of 11 °C, the tomatoes remained within the acceptable firmness range even after being stored for 14 days (Chrysargyris et al., 2016). Murmu and Mishra (2018) found that the application of five distinct combinations of gum arabic, sodium caseinate, cinnamon, and lemongrass essential oil as an edible coating resulted in a significant extension of the shelf life of guava. The coated guava samples remained fresh for up to 40 days, but the untreated ones survived for seven days. Adiamo et al. (2019) assessed the efficacy of gum Arabic as a coating to prolong the shelf life of blanched and sun-dried tomato slices during low-temperature storage at 4 °C. Additionally, it decreased the water activity (a_w) and increased the dry matter (DW) throughout the storage period. Researchers have conducted studies to explore the potential of several native plants as natural preservatives, a process known as bioprospecting. This situation presents novel prospects for the development and production of natural preservatives (Naufalin, 2019).

Fig. 3.

(A) Edible film and coating techniques to preserve the food products using natural preservatives. (B) Schematic diagram of antimicrobial mechanism for the essential oil

Table 1.

List of plant-based preservatives used as edible coating or film for fruits and vegetables and their benefits

S. No.	Plant source	Methodology	Fruits and vegetables	Main benefits	Reference
1	Cinnamon essential oil	Coating	Pineapple	Reduced weight and firmness loss Inhibited growth of fungi and yeast Extended the storability up to 15 days at 5 °C Decreased water loss	Basaglia et al. (2021)
2	Lemongrass with alginate	Coating	Pineapple	Decreased growth of E. coli	Amiri et al. (2021)
3	Cinnamon essential oil	Coating	Bananas	Reduced the growth of decay-causing fungi Increased shelf life up to 21 days Reduced disease incidence significantly Maintained fruit quality	Mastanjevic et al. (2022)
4	Mulberry leaf extract with pectin	Coating	Capsicum	Extended the storability up to 12 days Improved mechanical and water barrier properties Enhanced antioxidative and antibacterial properties Retarded fruit quality deterioration Delayed senescence	Shivangi et al. (2021)
5	Combination of gum arabic, Aloe vera gel, ginger and garlic extract	Coating	Guava	Suppressed browning Decreased weight loss Improved ascorbic acid and titratable acidity Preserved the quality	Anjum et al. (2020)
6	Olive waste (leaves and pomace)	Film	Strawberries and Apples	Prolonged shelf life of apples 35 days and strawberries 16 days at 4 °C Reduced decay and acidity loss Decreased water solubility Prevented weight loss in both fruits Enhances postharvest quality	Khalifa et al. (2016)
7	Combination of moringa leaf extract, chitosan and carboxymethylcellulose	Coating	Avocado	Reduced respiration rate Minimized weight and firmness loss Improved fruit quality	Tesfay and Magwaza (2017)
8	Mimusopsis comersonii extract	Coating	Apple and Potatoes	Extended shelf life up to 15 days Decreased enzymatic browning Inhibited the growth of aerobic mesophiles	Lima et al. (2022)
9	Ginko biloba extract and anthocyanin and Lysimachi foenum-graecum extract	Coating	Litchi	Reduced weight loss and decay Lowered enzymatic activities: PPO (polyphenol oxidase) and POD (peroxidase) and lipid peroxidation Delayed the color changes Decreased enzymatic browning	Li et al. (2021)
10	Chitosan or starch or roselle extract	Film	Blackberry	Extended shelf life for 21 days Retarded moisture loss Increased antimicrobial properties and contact angle	Paredes et al. (2023)
11	Moth bean starch or gelatin and Murraya koenigii leaves extract	Film and Coating	Eggplant	Retained firmness and moisture loss Preserved the color Slowed down the increment in total soluble solid during storage Extended shelf life of up to 16 days	Kumar et al. (2021)
12	Garlic and ginger extract, gum arabic and Aloe vera gel	Coating	Guava	Delayed ripening during storage Maintains fruit quality Showed higher antioxidant activity Inhibited weight loss Decreased sugar contents Extended shelf life up to 15 days	Zaidi et al. (2023)

Table 2.

List of plant preservatives, polysaccharides, phytocompounds used as edible coating or film for fruits and vegetables and their benefits

Antimicrobial mechanism of plant preservatives

The mechanism of action of plant extracts and essential oils, which act as antimicrobials, is often unclear or poorly understood. Plant substances affect microorganisms through various mechanisms, such as attack on the cell membrane, disruption of enzymatic activity, compromise of the genetic material of bacterial cells, and formation of fatty acid hydroperoxide through oxygenation of unsaturated fatty acids (Amit et al., 2017). Figure 3B illustrates the antimicrobial mechanism of essential oils. Essential oils have several targets on the cell, where the results of hydrophobicity reactions with lipids on bacterial and fungal cell membranes disturb the structures, increase membrane permeability, and also cause leakage of cytoplasmic constituents such as metabolites and ions. Bacteria are usually killed by disruption of their cell membrane, dissipation of proton motive force, and inhibition through membrane-associated enzyme activity (Lee and Paik, 2016). Mostly, pAMPs include the cell membranes of target microorganisms and are induced by net positive charge, flexibility, and hydrophobicity, which allow the interaction of bacterial membranes. The antifungal mechanism also takes place through cell lysis, permeabilization, attachment with ergosterol or cholesterol in the membrane, depolymerization of the actin cytoskeleton, and involvement in fungal cell wall synthesis and mitochondria in target intracellular organelles (Jenssen et al., 2006).

Animal origin

Animal-derived foods are an important source of nutrients for the human diet, particularly protein, which has a high biological value and contains essential amino acids (Batiha et al., 2021). Lysozyme, lactoferrin, ovotransferrin, pleurocidin, defensins, chitosan, and other similar substances derived from animals may serve as antimicrobials (Novais et al., 2022). Edible coatings and films have incorporated chitosan, a polycationic biopolymer derived from the exoskeletons of crabs or lobsters. This incorporation helps decrease the amount of water vapor, prevent moisture loss, and slow down the transmission of oxygen. As a result, it prolongs the shelf life of fruits and vegetables (Munoz-Tebar et al., 2023). Chitosan is composed of polymers of glucosamine and N-acetyl glucosamine. It is non-toxic, compatible, and degradable, and it has antibacterial properties, thus making it suitable for use in natural food products (Amiri et al., 2021). Chitosan coatings act as effective barriers against oxygen and slow down the processes of transpiration and ripening in fruits and vegetables (Munoz-Tebar et al., 2023). The fruits and vegetables to which chitosan was added to increase their shelf life are listed in Table 3. Shahbazi (2018) reported that the combination of carboxymethyl cellulose and chitosan with Mentha spicata essential oil resulted in a decrease in spoilage and an extension of the shelf life of strawberries by 12 days. Lysozyme is an enzyme and natural antibacterial agent that breaks down the chemical interactions between N-acetylmuramic acid and N-acetylglucosamine in peptidoglycan. Peptidoglycans make up 90% of the cell wall of Gram-positive bacteria, making them susceptible to lysozyme (Amiri et al., 2021). Hence, it functions as a natural antimicrobial (Irkin and Esmer, 2015). Gram-negative bacteria exhibit resistance to lysozyme due to the presence of a lipopolysaccharide layer that prevents the access of lysozyme to the peptidoglycan layer. Nevertheless, this enzyme can also impact G-negative bacteria in the presence of membrane-disrupting substances such as detergents and chelating chemicals. Lysozyme displays exceptional thermal and pH stability, making it suitable for incorporation into edible active films (Bayarri et al., 2014). Lactoferrin, a natural antimicrobial component, is applied in the food industry to inhibit the growth of spoilage and pathogenic microbes (Jenssen and Hancock, 2009). Chitosan-derived films and coatings improve the shelf life of fruits and vegetables and protect against oxidative deterioration, which excludes antimicrobial and antioxidant properties.

Table 3.

List of animal-based preservatives used as edible coating or film for fruits and vegetables and their benefits

S. no.	Animal source	Methodology	Fruits and vegetables	Main benefits	References
1	Chitosan	Coating	Dried mulberry	Minimized weight loss Decreased the quality deterioration in fresh and dried fruits Retained sensory quality	Gunes and Erçetin (2022)
2	Calcium chitosan	Coating	Kiwifruit	Extended storability upto 10 days at 5 °C Decreased the growth of microorganisms Maintains the sensory quality Delayed the fruit senescence	Kumarihami et al. (2020)
3	Chitosan enriched with citrus lemon peel extracts and Ocimum tenuiflorum leaf extracts	Coating	Bananas	Enhances antioxidant activity, ascorbic acid content and soluble solids Retained phenolic content Decreased ripening process Extended shelf life up to 16 days	Deb Majumder and Sarathi Ganguly, (2020)
4	Chitosan-carboxymethylcellulose	Layer-by- layer	Lemon	Retained fruit firmness Postponed senescence Preserved vitamin C content during storage Reduced weight loss Maintains the fruit quality Provided excellent water vapor permeability, puncture strength and elasticity properties	Chen et al. (2020)
5	Chitosan	Coating	Ber fruit	Controlled fruit decay Prevented fruit shriveling and water loss Extended shelf life up to 28 days Prevented rot appearance of fruits Improved soluble solid content, vitamin C and acidity	Hesami et al., ( 2021)
6	Esterified lactoferin (ELF) and lactoferin (LF)	Coating	Apple	Controlled the blue mold of P. expansum growth at 25 °C Lowered the enzyme activities: PPO (polyphenol oxidase) POD (peroxidase), chitinase and β1,3-glucanase	Wang et al. (2012)
7	Chitosan	Coating	Figs	Decreased weight loss, color change, respiration rate and anthocyanin content Inhibited A. alternata during 21 days at 5 °C Maintains fruit quality Retained antioxidant properties	Saavedra et al. (2020)
8	Chitosan with sodium hypochlorite	Coating	Kiwifruits	Preserved the sensory quality Slowed down the fruit senescence Inhibited growth of microorganisms Decreased mass loss, firmness, respiration rate and total solids	Vivek and Subbarao (2018)
9	Chitosan	Coating	Sliced mango	Restricted water loss Enhances fruit quality Improved soluble solid content, titratable acidity and ascorbic acid Lowered fruit decay Decreased growth of microorganisms	Chien et al. (2007)

Antimicrobial mechanism of animal preservatives

Antimicrobial peptides (AMPs), lipids, and transferrins can induce the synthesis of cell membranes and peptides. AMPs are directly involved with the microbial cell membrane and are involved in the separation of cell components (Cole et al., 2000). Mostly, lipids inhibit bacterial cell walls or membranes and intracellular replication. Bacterial cell membranes are inhibited by lysozymes by hydrolyzing β1, 4-glycosidic linkages between N-acetylmuramic acid and N-acetylglucosamine in the bacterial peptidoglycan (Lee and Paik, 2016).

Microbial origin

Bacteriocins are peptides or ribosomal proteins produced by bacteria that can inhibit or kill other bacteria, whether they belong to the same species or different genera (Munoz-Tebar et al., 2023). They are generally produced by lactic acid bacteria (LAB), and their Generally Recognized as Safe (GRAS) status has received significant attention from researchers and the food industry because LAB can be used as an antimicrobial agent to inhibit the growth of undesirable microorganisms, such as spoilage and pathogenic bacteria, in both fermented and non-fermented foods (Settanni and Corsetti, 2008; Munoz-Tebar et al., 2023). Utilizing bacteriocins in food increases customer demand for flavor and promotes chemical preservative-free food products (Teshome et al., 2022). Several bacteriocins, including nisin, enterocin AS-48, bovicin HC5, pediocin, enterocin 416K1, and bificin C6165, have been utilized for food preservation (O’Sullivan et al., 2002). The benefits of bacteriocin in food include a wide range of inhibitory effects, compatibility with food processing, and significant levels of structural variation. Bacteriocin is categorized into two groups according to its inhibitory spectrum. The first category is characterized by its activity specifically targeting the same species of bacteria, known as narrow-spectrum bacteriocin. The second category, known as broad-spectrum bacteriocin, indicates its efficacy against different bacterial species (Rendueles et al., 2022). The use of coatings containing bacteriocins effectively reduces the growth of bacteria, preventing deterioration in perishable fruits and extending their shelf life. Due to their non-toxicity and physical stability, these compounds possess significant promise as food preservatives, primarily due to their antibacterial characteristics. Lactic acid bacteria (LAB) are gram-positive. They are known for their ability to produce substantial quantities of lactic acid, which is the main product resulting from the fermentation of glucose. It includes lactobacillus, lactococcus, streptococcus, enterococcus, cyanobacterium, and propionibacterium (Agriopoulou et al., 2020). Additionally, it is utilized in the food preservation sector because it can produce various antimicrobial by-products, specifically organic acids like propionic, acetic, pyruvic, lactic acid, diacetyl, hydrogen peroxide, and acetaldehyde, as well as other non-protein components with lower molecular weight (reuterin, reutericiclin, and pyroglutamic acid) and bacteriocins (Oluk and Karaca, 2018). Lactic acid bacteria have been categorized as GRAS by the United States Food and Drug Administration (FDA), the Qualified Presumption of Safety (QPS), and the European Food Safety Authority (EFSA). LAB is investigated as a bioprotective agent that prevents the growth of microorganisms in fruits and vegetables. Lactic acid bacteria (LAB) are used to control the growth of Listeria monocytogenes and Salmonella enteritidis in chickens, as well as to prevent the growth of Salmonella typhimurium, Escherichia coli, and Listeria monocytogenes in lettuce and apples (Amiri et al., 2021). Their potential as an antibacterial agent has been increasingly recognized as a natural food preservative. The utilization of bacteriocins in food preservation offers several benefits: (i) they extend the duration of food freshness; (ii) they provide an extra layer of protection to food in cases of temperature mishandling; (iii) they mitigate the risk of transmitting food-borne pathogens and spoilage microorganisms in food distribution systems; (iv) they minimize losses caused by food spoilage; and (v) they decrease reliance on artificially produced preservatives (Naufalin, 2019).

Nisin is synthesized through the fermentation of milk that has been altered by specific strains of L. lactis bacteria. Nisin, a Canadian Food and Drug and Health License, is recognized as a preservative in over 48 countries. Nisin exhibits high efficacy against most Gram-positive bacteria, including L. monocytogenes and S. aureus. Additionally, Ethylenediamine tetraacetic acid (EDTA) can effectively suppress Gram-negative bacteria (Azizi et al., 2021; Campos et al., 2011; Pisoschi et al., 2018). P. acidilactici and P. pentosaceus synthesize pediocins. These components have high heat resistance and are capable of functioning effectively throughout a wide pH spectrum. Pediocins exhibit antibacterial activity against Listeria monocytogenes, Enterococcus faecalis, Staphylococcus aureus, Clostridium perfringens, and Oenococcus oeni. Pediocin has applications in dairy products and can also be utilized as a fill in pulverized ham, fruits, and vegetables (Diez et al., 2012; Juneja et al., 2012). The representation of nisin and bacteriocin from microbial origin used in fruits and vegetables is given in Table 4. A recent study conducted by Chen et al. (2021) revealed that the combination of natamycin-fludioxonil and natamycin-propiconazole showed a synergistic impact, leading to a reduction of over 85.0% in green mold and sour rot. This effective combination minimizes post-harvest fruit deterioration in citrus. Immersing strawberries in a solution containing 20 mg/L of natamycin for 5 min effectively delayed the formation of mold, reduced the rate of respiration, and prevented fruit rot (Meena et al., 2021). Immersing mulberry in a solution of natamycin (0.3 g/L) resulted in a decrease in decay rate (23.3% on the 10th day), malondialdehyde concentration, phenylalanine ammonia-lyase, and polyphenol oxidase activity during storage (Wen et al., 2019). Furthermore, it decreased the overall levels of phenolic compounds, glucose, fructose, and anthocyanins. Also, natamycin has been proven to be advantageous in preserving the overall soluble solids, total acids, sucrose levels, color, and firmness of mulberries throughout storage. The incorporation of natamycin in the solution resulted in an increase in catalase, superoxide dismutase, and peroxidase levels in mulberries. The addition of N-acetylcysteine and glutathione to edible coatings proved to be successful in inhibiting browning reactions in fresh-cut pears for 2 weeks without causing any changes in texture (Nain et al., 2021).

Table 4.

List of microbial-based preservatives used as edible coating or film for fruits and vegetables and their benefits

S.no.	Microbial source	Methodology	Fruits and vegetables	Main benefits	References
1	B.animalis subsp.lactis DSM 10140 with gelatin	Coating	Apple	Enhanced sensory properties Inhibited enzymatic browning Preserved the color Slowed down the pH changes in fruit Extended shelf life up to 12 days at 4 °C	Campaniello et al. (2020)
2	Lactobacillus brevis SM6	Direct and Indirect approach	Apricot pulp and ready-to-serve	Inhibited spoilage microorganisms	Dharwal et al. (2020)
3	Nisin with zein	Coating	Apples	Maintains fruit quality Extended storability for up to 21 days at 15 °C Decreased microbial growth Retained weight and texture loss Delayed firmness loss	Belay et al. (2023)
4	Lactobacillus plantarum	Coating and Film	Dried sliced tomato	Enhanced shelf life up to 7 days and safety Improved quality Reduced water loss during storage Inhibited growth of spoilage bacteria Retained fruit freshness	Mechmeche (2022)
5	Combination of nisin and PLA (3-phenyllactic acid)	Coating	Strawberry	Enhanced antibacterial activity Exhibited high-potential food preservative	Liu et al. (2021)
6	Lactobacillus plantarum TPB21.12 with maize starch, k-carrageenan	Coating	Fresh cut apples	Retained color Decreased browning Minimized mass loss Decreased the quality deterioration Prevented fruit freshness	Kusnadi et al. ( 2023)
7	Lactobacillus plantarum and Lactobacillus fermentum	Coating	Fresh cut pineapples	Inhibited growth of Listeria monocytogenes and Escherichia coli Maintains fruit quality	Russo et al. (2014)

Antimicrobial mechanism of microbial preservatives

The mechanism involved is pore formation in the cytoplasmic membrane of target microorganisms. It causes cell death due to the loss of intracellular molecules and the destruction of the proton motive force (Driessen et al., 1995). When natamycin binds to ergosterol, both cell membrane sterol and fungal membranes show antimicrobial effects. It contains the lactone ring with a lipophilic chain that has conjugated double bonds, and there is a flexible hydrophilic part to tolerate the various hydroxyl groups (Lee and Paik, 2016).

Future perspectives

Edible packaging, including edible films and coatings, is currently undergoing significant research and development, demonstrating great promise as a solution. It suggested a less costly and suitable material for packaging and wrapping food. This suggests that both the film and coating hold potential for commercial use in storage and marketing. Numerous food products incorporate essential oils and other plant-derived compounds as coatings or films due to their antibacterial and antioxidant properties. The study has the potential to provide evidence for maintaining quality in the fruit and vegetable business and to greatly contribute to the use of natural preservatives as a practical resource. This review article provides a significant contribution as it reveals a non-toxic and eco-friendly substitute for commonly used chemical disinfection techniques on fruits and vegetables. The future perspectives provided in this article will assist in pinpointing strategies to prolong the shelf life of fruits and vegetables in open markets, both in India and globally. This study suggests a formulation that could potentially win over a significant number of customers. Furthermore, customers are becoming more aware of the importance of environmental safety, particularly due to the prevalence of single-use plastic in food packaging. Despite these challenges, the food industry and research institutes persist in their efforts to develop edible films and coatings for various food applications. These innovations aim to extend the shelf life of products and minimize environmental concerns. The subsequent steps in the commercialization of edible films and coatings should rely on sensory and consumer research, the utilization and advantages of coatings as carriers of bioactive substances, and accurate disclosure of coating usage with an emphasis on marketing strategies that promote the benefits for consumers of incorporating edible films and/or coatings into food products.

Author contributions

Uma Venkatesan was involved in collecting the literatures. Rajiniraja Muniyan was involved in supervising data collection. Both the authors involved in the preparation of manuscript and the final version read and approved.

Declarations

Conflict of interest

The authors declare that there is no conflict of interest.