Nanotechnology‐enhanced edible coating application on climacteric fruits

Abstract Climacteric fruits continue to ripen after harvest and produce ethylene, coupled with an increase in respiration rate, which contributes to more rapid perishability. Inhibition of ethylene biosynthesis has been shown to be an efficient way to delay the onset of ripening and lengthen shelf life. The use of edible materials as coatings presents an efficient approach in preserving the quality of fruits. Edible coatings have many benefits, such as affordability, ease of application, and use of natural ingredients. Nanotechnology provides interesting approaches to the management of fruit shelf life after harvest. Nanotechnology has the capacity of producing new materials by minimizing the size of components to a nanometric level. These kinds of nanomaterials possess distinct and improved properties for delaying fruit ripening and decay. The main goal of adding nanoparticles to edible coatings is to enhance the biopolymer's mechanical and water vapor barrier properties. Nanoparticles also contain biopolymer‐like features and are thought to have superior antibacterial, antifungal, and antiviral properties than edible coatings. This review is aimed at summarizing recent findings on the application of edible coatings in the form of nanoparticles, and their effect on quality parameters and shelf life extension of climacteric fruits. Peer‐reviewed articles were obtained by using Scopus and science direct. The current materials widely used for coating climacteric fruits are zinc, silver and chitosan nanoparticles. Zinc nanoparticles have been shown to be more effective in delaying ripening significantly by reducing weight and moisture loss and ensuring retention of fruit firmness. Further research is needed to understand their effect on other physicochemical properties of fruits.


| INTRODUC TI ON
Technologies such as ozone treatment (Alencar et al., 2013;Ali et al., 2014), modified atmosphere (Lalel et al., 2005;Lanka et al., 2011;Prange et al., 2013), 1-Methylcyclopropene (De Martino et al., 2007a;De Martino et al., 2007b;Mir et al., 2004;Razzaq et al., 2016), controlled atmosphere storage (Hailu & Worku, 2017), and low-temperature storage (Kudachikar et al., 2011) have been used in controlling ripening in climacteric fruits. For several years up to date, low-temperature storage is used commercially in the supply and marketing chain from precooling at the farm to using refrigerated trucks set at a certain temperature for transportation to cold rooms at the fresh produce market (Zhang et al., 2016). Although low-temperature storage has been successful in controlling ripening in climacteric fruits, storing fruit at suboptimal temperatures can cause chilling injury leading to internal browning and emergence of black spots (Sivankalyani et al., 2015). Other postharvest technologies have also been successful, but some have certain disadvantages, such as a reduction in the volatile esters in fruit and a negative impact on the nutritional properties of fruit (Skog & Chu, 2001).
Furthermore, the application of controlled and modified atmosphere is expensive, and it involves specialized labor, thereby limiting its practical application. Use of 1-Methylcyclopropene on climacteric fruit might induce chilling injury and require additional time to ripen adequately, limiting its economic applicability (Harris et al., 2000;Mir et al., 2004;De Martino et al., 2007a;De Martino et al., 2007b).
Edible coating is another type of technology becoming popular for controlling the ripening of climacteric fruits because coatings are simple to prepare, widely available, relatively low cost and mostly do not need the use of sophisticated atmosphere and temperature control technologies (Jodhani & Nataraj, 2021;Suhaget al., 2020). Edible coatings are thin layers of edible material added on the surface of climacteric fruits to enhance the appearance, maintain quality, prevent microbial growth, reduce respiration, slow maturation, minimize water loss, and extend shelf life (Murmu & Mishra, 2018). Besides, the use of edible coatings in fresh produce has been approved by the US Food and Drug Administration and is considered to meet the GRAS (generally regarded as safe) requirements (Dhall, 2013;Martín-Belloso et al., 2009). To comply with export protocols, all the processes involved in the application of edible coatings must follow the high hygiene requirements and the quantity used must not exceed the amount necessary to achieve the desired physical and nutritional impact on the fruit (Nussinovitch & Nussinovitch, 2003).
However, some edible coatings can pose disadvantages when used on fruits: for instance, edible coating formulated from polysaccharides and proteins exhibits weak water vapor barrier properties while lipids and waxes exhibit poor mechanical characteristics; thus, new alternative methods have been developed to solve these drawbacks.
Nanotechnology is a novel approach for creating new edible coating components for the postharvest management of fresh produce by reducing the size of the edible coating particles to a nanometric scale ranging from 1 to 100 nanometers (Parisi et al., 2015).
The application of nanotechnology has proven to be one of the best strategies for extending the shelf life of fresh fruits and nanoparticles used for edible coatings also possesses unique properties such as antibacterial and antifungal qualities (Bajpai et al., 2018;Lloret et al., 2012;Singh et al., 2020). Recently, there have been studies on the effects of the addition of nanoparticles to edible coatings and these studies have revealed that the addition of nanoparticles to edible coatings has opened new opportunities not only for enhancing higher antimicrobial, antifungal, and antiviral properties, but also to improve the cost-effectiveness of edible coatings (Sorrentino et al., 2007). The reviews by Nor and Ding (2020), Dhaka and Upadhyah (2018), and Ncama et al. (2018) have compiled all possible coatings that are functional for tropical fruits and horticultural produce, highlighting safe concentrations, and the use of commonly consumed plant extracts that have potential to be used on fresh produce. The above reviews cover the use of polysaccharides, proteins, and lipids as edible coatings on popular fruits. The reviews also show that edible coatings are a promising method for extending the postharvest shelf life of tropical fruits. The current review talks specifically to the use of nanoparticle materials in addition to edible coating on climacteric fruits. Recent review studies have reported the successful application of nanotechnology in the food packaging industry, agricultural sector, agri-food sectors as well as in the postharvest disease management of fruits and vegetables (Al-Tayyar et al., 2020;Chawla et al., 2021;Lang et al., 2021;Mahela et al., 2020;Ruffo Roberto et al., 2019;Wahab et al., 2021). As a result of all these studies, the addition of various kinds of nanoparticles to the different edible coatings to maintain the quality of food appears to be a viable consideration. However, there is still limited information about the effectiveness of nanoparticle edible coating material in regard to their application to climacteric fruits. Therefore, this review aims to highlight the most relevant and recent information on the use of edible coatings enriched with chitosan, silver, and zinc nanoparticles in extending postharvest storage life and the overall preservation of the quality of popular climacteric fruit ( Figure 1).

| PROB LEMS FACED BY CLIMAC TERIC FRU ITS
Based on their respiration behavior and ethylene production, fruits such as banana, mango, guava, apricot, pear, papaya, apple, avocado, tomato, and plantain are referred to as climacteric fruits (Atkinson et al., 2011). Climacteric fruits are usually harvested at physiological maturity and remain firm without major changes in peel color, texture, or composition before the beginning of maturation (Mendoza & Aguilera, 2006). After harvesting, the fruits undergo progressive deterioration, resulting in a relatively short postharvest life, increased respiratory rate, autocatalytic ethylene development, increase in susceptibility to various pathogenic infections, and sensory changes such as color, taste, and texture change such as softening (Palapol et al., 2009;Paul et al., 2012).
In postharvest fruit management, the perishability of fruit after harvest is a major challenge faced by the industry influencing | 2151 produce marketability, especially for international trade . Globally, a massive quantity of fruits are wasted before the commodity reaches consumers, with about 50% of those food losses being valuable fruits. The U.S.D.A. Economic Research Service reports that over 34.6% of the loss is directly related to unwanted climacteric maturation, resulting in subsequent spoilage, degradation, mechanical injuries, and physiological disorders in produce (Barth et al., 2009;Kader, 2004). The perishability of the fruits is mainly attributable to adverse physicochemical changes, such as loss of weight due to respiration, softening of the flesh, deterioration of quality due to microbial attack, and changes in the content of sugar and acid. Another big threat to the global fruit supply chain is contamination by fungal pathogens. Postharvest fruit loss due to phytopathogens like fungi now accounts for more than half of all agricultural fruit production (Zhang et al., 2017). The most important factors causing postharvest losses are intrinsic physiological senescence and invasion by fungal pathogens. Anthracnose caused by Colletotrichum spp is one of the common fungal diseases that can result in serious economic and extensive postharvest losses during transportation and storage of climacteric fruits (Bautista-Baños et al., 2013;Pavitra Kumari & Singh, 2017). Symptoms of anthracnose postharvest are sunken black spots that occur on the fruit surface during ripening . Mango anthracnose, caused by Colletotrichum gloeosporioides, is a significant threat to farmers around the world, as it results in massive pre-and postharvest losses in mangoes (Lima et al., 2013;Pavitra Kumari & Singh, 2017). During postharvest preservation and following export, papaya deteriorates, primarily due to anthracnose caused by Colletotrichum fructicola and Colletotrichum gloeosporioides Penz (Madani et al., 2014;Vilaplana et al., 2020). The most damaging postharvest disease of bananas is anthracnose, which is caused by the fungus Colletotrichum musae leading to substantial economic loss (Khaliq et al., 2019). It degrades the fruit's quality and nutritional value and makes it unfit for marketing and consumption, resulting in significant losses for farmers and traders.
The use of synthetic chemical fungicides has resulted in issues with postharvest disease control, including decreased efficacy, increased plant pathogen resistance to active ingredients, F I G U R E 1 Schematic representation of nanoparticle synthesis using green method (Esa & Sapawe, 2020) (Dubey et al., 2007;Kumar & Kudachikar, 2018). Synthetic chemicals have been used to reduce fungi attacks in postharvest storage of fruits, but there are concerns against their safety due to the toxicity of chemicals thus making it an urgent need to find alternative environmentally friendly technologies. With the above-mentioned problems facing climacteric fruits, one of the most preferred solutions includes the application of edible coatings (Romanazzi et al., 2016). Many studies have shown that edible coatings made from a variety of biopolymers can effectively preserve the nutritional properties and extend the shelf life of climacteric fruits.
To suppress decay, improve fruit quality, and prolong the shelf life of climacteric fruits during postharvest storage, edible coatings such as chitosan, aloe vera gel, and gum arabic are widely used (Berumen-Varela et al., 2015;Khaliq et al., 2019;Maqbool et al., 2010).

| FORMUL ATI ON OF ED IB LE COATING S
Generally, films from edible coatings are prepared from polymers such as hydrocolloids (polysaccharides and protein), lipids, a combination of both (referred to as composite coatings), and the addition of plasticizers (Dhall, 2013). Edible coatings can be applied over the food product in liquid form by spraying, extrusion, solvent casting, brushing, or dipping to achieve a thin protective layer (Thakur et al., 2019;Yousuf et al., 2018). A review by Nor and Ding (2020) compiles all possible coatings that are functional for tropical fruit.
The review also covers the fundamentals of coating attributes, materials, and processes, which include the following: the effectiveness of various coating materials such as polysaccharide, protein, lipid, and composite-based coatings has been highlighted, and various application methods, and coating protection. Dhaka and Upadhyay Plant extract-derived edible coatings can delay ripening, improve esthetic appearance by shinning the produce and covering minor scars (Murmu & Mishra, 2018). Also, they are an inexpensive means for maintaining the quality of fresh produce. The use of edible coatings from plant extracts has been proposed to decrease the usage of nonbiodegradable storage polyethylene plastic films and containers, thereby reducing pollution to the environment (Bourtoom, 2008).
Plant extracts with high antioxidant properties can also improve the nutritional qualities of fruits. The effect of plant edible coatings on the quality attributes and nutritional characteristics of various climacteric fruits such as banana, apple, mango, and papaya has been studied. A review by Ncama et al. (2018) gave a comprehensive report on the use of plant extract-derived edible coatings for both climacteric and nonclimacteric fruits. Some of the plants whose extracts are used as edible coatings for climacteric fruits include moringa leaf extract (Tesfay & Magwaza, 2017), corn starch and rice starch (Razak & Lazim, 2015;Thakur et al., 2019), aloe vera (Khaliq et al., 2019), and gum arabic (Maqbool et al., 2011). The use of natural edible coating extracts is one of the most promising technologies to enhance the protection and quality of fruits because it is considered as being environmentally friendly and acceptable for consumers (Janisiewicz & Korsten, 2002).

| Unique features of edible coatings
The edible coating serves as a barrier to control moisture loss and gas exchange (CO 2 and O 2 ) between the fruit and their surrounding environment thereby slowing down the rate of respiration, retarding the physiological ripening process, and preventing the loss of natural volatile flavor compounds (Khatri et al., 2020;Pratiwi et al., 2015;Rojas-Graü et al., 2009). Furthermore, edible coatings can safely be consumed as part of the product and contain health benefits because they are made of food-grade products (Shit & Shah, 2014).
Other advantages of coatings include their edibility and biodegradability, as well as the avoidance of waste and the commercialization of food without preservatives Tavassoli-Kafrani et al., 2016 (Poverenov et al., 2014). It is advisable to use coatings that have been shown to remove respiration peaks efficiently and reduce the output of ethylene to a minimal level.

| The effect of edible coatings on quality attributes in climacteric fruits
The ripening process of climacteric fruit shows a dramatic increase in ethylene production and respiration rate at the onset of ripening. Various parameters such as weight loss, firmness, total soluble solids, total phenols, and antioxidant activity, decay rate, and shelf life have been used to assess quality in climacteric fruits (Hudina et al., 2012). The efficacy of using edible coatings has been demonstrated by increasing evidence from numerous studies. In a study that investigated the effect of shellac and gelatin composite coatings for extension of shelf life of a banana, Soradech et al. (2017) observed 60% of shellac and 40% gelatin act as an effective physical barrier around the fruit, resulting in a slow decrease in weight loss, and softening. The quality was maintained for more than 30 days compared with uncoated banana. A report by Jaiswal et al. (2018) indicated that the incorporation of citric acid and neem extract improved the effectiveness of aloe vera by maintaining the firmness, color, sensory attribute, and market value of tomato fruit. Aloe vera (40%) plus citric acid gave the best result compared with other concentrations (20%, 60%, and 80%). Recently, a study by Kubheka et al. (2020) showed the effect of gum arabic-and Carboxymethylcellulosecontaining moringa leaf extract on maintaining quality and control of C. gloeosporiodes on maluma avocado at cold storage for 21 days.
Based on the result, 15% gum arabic plus moringa followed by 10% gum arabic and moringa and 1% Carboxymethylcellulose plus moringa were the most effective in reducing weight and firmness loss.
The coatings also delayed color change and inhibited the growth of C. gloeosporiodes respectively compared with the control. shelf life was extended by 3 days in both fruits relative to the control (Joshi et al., , 2018. A report by Abd El-Razek et al. (2019) showed that moringa and green tea extracts act as an antioxidant coating and was effective in reducing vitamin C loss, total soluble solids, total phenols, and antioxidant activity, and a decrease in weight loss was observed in mango fruits at 2, 4, and 6 weeks during two consecutive seasons.
Moringa leaf extracts are also rich in antioxidants and have antibacterial effects against a range of microorganisms. The high phytochemical constituents of moringa plant extracts, which include phenols, alkaloids, and tannins among a few others, have been attributed to the inhibitory effect on the mycelial growth of various pathogens. Furthermore, tea leaves are high in polyphenolic compounds, which have a high antioxidant potential and antimicrobial activity in general; hence, the properties of moringa and green tea make them suitable as coating materials. Natural substances present in moringa and green tea extracts, which are high in antioxidants, serve as electron donors, creating free radicals that minimize normal respiration and transpiration, as well as enhance stomata closure. The reduction of fruit decay caused by the coating of moringa and green tea extracts is linked to a reduction in the activity of cell wall-degrading enzymes, which prolongs the postharvest period and delays fruit ripening. Because of its low oxygen permeability, which decreased enzyme activity and prevented oxidation of vitamin C, moringa and green tea extracts as antioxidant coating treatments were successful in reducing vitamin C loss in mango fruits during all storage periods. The best result to achieve a high value of storability and quality was shown in applying 10% moringa leave extract followed by 5% green tea extract under refrigerated storage.
Shah and Hashmi (2020) investigated the impact of chitosan in combination with aloe vera gel on the storage life of mango fruits.
They found that adding Chitosan to aloe vera lowered weight loss, respiration rate, and ethylene generation more effectively than using chitosan alone or control samples. Furthermore, the combination treatment preserved fruit quality metrics such as titratable acidity, total soluble solids, fruit firmness, ascorbic acid, and peel color.
This study shows that combined application of chitosan and aloe vera synergistically improves the phenolic content of mango fruit, sustaining high ascorbic acid, total phenolic content, and antioxidant activity during storage. This suggests that addition of aloe vera may enhance the barrier of chitosan coating thereby improving antimicrobial properties and decreasing permeability to water and gaseous exchange (Mishra et al., 2010). Jodhani and Nataraj (2021)

| NANOTECHNOLOGY
Nanotechnology is another form of innovation that offers countless postharvest management approaches capable of producing new materials by reducing particle sizes to a nanometric scale (at least one-dimensional ranges of 1-100 nanometers) giving materials with distinct and improved properties compared with larger ones (Magnuson et al., 2011;Parisi et al., 2015). Nanoparticles (NPs

| Synthesis of nanoparticles
Currently, various physical and chemical methods are widely used to synthesize nanoparticles, enabling particles with the necessary characteristics to be obtained. These manufacturing methods can present several drawbacks such as the use of nonbiodegradable stabilizing agents, labor-intensive, usage of toxic chemicals, and are potentially detrimental to the environment and living organisms (MubarakAli et al., 2015;Phanjom & Ahmed, 2015). Therefore, to minimize hazards to the environment, green/biochemical synthesis of nanoparticles offers an appealing means for nanoparticle synthesis and promises to help overcome these physical and chemical disadvantages (Nayak et al., 2015;Shankar et al., 2004). This is due to low synthesis costs, short development time, easy accessibility, eco-friendliness, economic considerations (

| NANOPARTICLE S COMMONLY US ED IN CLIMAC TERIC FRU IT
Several nanoparticles have been used in fruits. The most explored nanoparticles in climacteric fruits are zinc oxide, silver, and chitosan considering their higher antimicrobial activity and stability.
Nevertheless, other nanoparticles such as iron, titanium dioxide, cerium oxide, and copper have been used in various field of the food sector. Titanium dioxide nanoparticle was reported used with chitosan coating to form a film on the surface of mango fruit. It was effective in reducing losses caused by decay, delay respiration, and maintain the firmness of fruits (Xing et al., 2020).

| Chitosan nanoparticle
Chitosan (CS) is one of the promising biopolymers that has been studied as a nanoparticle because of its film-forming capability, biodegradability, biocompatibility, and antimicrobial activity, nontoxic to humans, ease of alteration, and flexible physical and chemical properties (Divya & Jisha, 2018;Jianglian & Shaoying, 2013).
Chitosan derived from the deacetylation of chitin in an alkaline medium is obtained from the waste products of the shellfish industry (Suseno et al., 2014;Xu et al., 2005). Chitosan is considered gener-

| Zinc oxide nanoparticle (ZnONPs)
Zinc has been properly approved by the US Food and Drug Administration (FDA) (Noshirvani et al., 2017;Rasmussen et al., 2010). Due to its excellent mechanical properties, barrier capacities, biocompatibility, and antimicrobial broad-spectrum performances, the zinc oxide nanoparticle (ZnONP) has gained considerable interest in sciences (Yusof & Zain, 2019). The antimicrobial properties of ZnO particles are due to the reactive oxygen species that form on their surface. In addition, recent scientific studies have shown that zinc is a promising coating material due to its being a relatively potent antimicrobial agent with high stability as a comparison to natural-based coating, and there is no possible risk to human health from its use (Sun et al., 2018). And, as stated elsewhere, ZnONP's addition to polysaccharides, lipids, and proteinbased biopolymers can effectively improve the mechanical properties, barrier capacities, and physicochemical properties of edible coatings (Muraleedaran & Mujeeb, 2015;Wu et al., 2019). ZnONPs have highly effective antibacterial activity and are considered as a possible additive to replace hazardous chemicals and physical antibacterial materials (Awwad et al., 2020).

| Silver nanoparticles (AgNPs)
Among nanoparticles, silver nanoparticles (AgNPs) are one of the most studied as they have been shown to be efficient against different microorganisms and are safe for humans (Aadil et al., 2018).
Around the same time, silver has been adopted as an antimicrobial material that is relatively free of adverse effects. A wide variety of antibacterial, antifungal, and antiviral properties are found in silver nanoparticles. Due to its biocidal activity against a wide range of Gram-positive and Gram-negative microorganisms, yeast, molds, and viruses, silver is currently the most researched antibacterial nanoparticle. The release of Ag+ions, which bind to electron donor groups in molecules containing sulfur, oxygen, or nitrogen, is primarily responsible for the antimicrobial activity of silver nanoparticles.
Additionally, AgNPs outperformed metallic silver in antimicrobial properties due to their incredibly large surface area, which allows for better contact with microorganisms (Toker et al., 2013). The safety limit of silver declared by EU safety regulations for foods is 0.05 mg/ kg (Fernández et al., 2009). It is proved that a silver concentration of 0.06 mg/L is acceptable for coating fruits and vegetables . The use of silver nanoparticles, which include a wide variety of compounds that can be used in the formulation of edible coatings, is the most recent breakthrough advancement in the application and development of edible coatings for fresh fruit.

| APPLIC ATION OF NANOPARTICLE-ENHAN CED ED IB LE COATING S ON CLIMAC TERI C FRU ITS
The application of nanoparticle-enhanced edible coatings has been explored in postharvest shelf life research and can be effective in improving color quality, firmness, increase antimicrobial properties, control enzymatic activity, and reducing weight loss of fruits (Table 1).
The incorporation of silver nanoparticle into sodium alginate inhibits the growth of the microbial diseases in pear; because after coating, the silver nanoparticle-incorporated sodium alginate coatings maintain its antibacterial activity against Gram-positive and Gram-negative bacteria. The coated fruit was found to be suitable for up to 10 days in storage as judged by the color and appearance, texture, and aftertaste compared with sodium alginate-coated and -uncoated fruit  Table 1 shows more studies done on the application of nanoparticles to edible coating resulting in keeping the quality of climacteric fruits.

| ADVANTAG E S AND D ISADVANTAG E S OF ADDING NANOPARTICLE S TO EDIB LE COATI N G S
The benefits and drawbacks of the addition of nanoparticles to edible coatings have been studied. The addition of nanoparticles to edible coatings has provided various benefits, such as increased antimicrobial activity, and formation of stronger coating homogeneity on fruit surface (Acevedo-Fani et al., 2017;Severino et al., 2014). Chitosan, zinc oxide, and silver are the most widely used nanoparticles in climacteric fruits that have shown promising effects when applied to edible polysaccharide and protein materials. It has been stated that zinc has better compatibility and heat resistance in climacteric fruits (Table 1). The main goal of adding nanoparticles to edible coatings is to enhance the biopolymer's mechanical properties and water vapor barrier.
Firstly, ZnO-enhanced xanthan hybrid method provides greater health benefits considering zinc requirement in the human body and is healthy in blood compatibility and toxicity tests (Joshy et al., 2020). Zinc oxide metal has been shown to have antimicrobial properties, demonstrating strong effectiveness in inhibiting the growth of pathogenic microorganisms, even when added in small amounts such as 0.1%-0.5% (w/v) (Esparza-González et al., 2016).
Recently, Meindrawan et al. (2018) found that the addition of zinc nanoparticle to carrageenan effectively decreases weight loss and total acidity, preserve firmness, and delay discoloration and decay of mango fruit compared with carrageenan alone. This is because zinc can improve the gas barrier of the coating as compared to carrageenan alone which tends to be hydrophilic. Similarly, zinc significantly improves the quality of cherry tomatoes by suppressing their respiration and water evaporation thus ensuring a better preservative effect at room temperature storage. The addition of zinc to carboxymethylcellulose and cinnamaldehyde not only reduced weight loss and ensured fruit firmness for a longer period but significantly inhibited the tested fungi showing greater antimicrobial activity compared with noncoated or pure carboxymethylcellulose with cinnamaldehyde . Chitosan nanoparticles have demonstrated significant effects as a postharvest treatment in terms of antioxidant, antibacterial, and antifungal activities compared with chitosan (Avelelas et al., 2019;Divya et al., 2017). Compared with the use of chitosan, chitosan nanoparticles are more active and perform better, which is due to smaller particle size and increased nanoparticle contact area (Orellano et al., 2019;Qi et al., 2004). The size reduction of chitosan to a nanoscale can improve the functionality and properties at lower concentrations (Eshghi et al., 2014). The effective concentration of chitosan decreased significantly to 0.5% when used in nanoparticle form as compared to the higher amount suggested in previous studies for coating fruits (Esyanti et al., 2019). Chitosan alone or with other polymer has been used at a concentration as high as 2% on fruit to effectively preserve the quality of fruit, but with the introduction of nanoparticle, a lower amount is required to effectively preserve the quality of fruits (Khatri et al., 2020;Suseno et al., 2014).
As the penetration and absorption of chitosan increase dramatically in the form of nanoparticles, the effective amount of chitosan used for coating fruits can be substantially or greatly reduced (Zahid et al., 2012). Jagana et al. (2017)

| SAFE T Y CON CERN S AND LEG IS L ATI ON IN US ING NANOPARTICLE-ENHAN CED ED IB LE COATING S
Nanoparticles are used in the fruit industry for a variety of reasons, one of which is their unique properties, which are associated with their small size. Small particles, for example, are digested faster, have a greater surface reactivity, and can more efficiently penetrate biological barriers than larger particles. Currently, there is insufficient legislation regarding the use of nanoparticles in fruits, and consumers view emerging innovations as posing a danger to their health and the environment. Legislative barriers and uncertainty about the effectiveness of such systems, as well as their economic and environmental impact, may be the primary reasons for this. While legislation is still in its early stages, it must discuss all aspects of nanotechnology's use in the fruit industry around the world. Only the European Commission (EU) member states of Sweden, France, Denmark, Belgium, and Switzerland have adopted their regulations for nanomaterials or nano-enabled goods at this time (Arts et al., 2015).
Recent EU regulations mandated that any food ingredient derived from nanotechnological applications be subjected to a safety evaluation before being approved for use (Cubadda et al., 2013). Only a few  hence, their combination with nanoparticles helps to improve their physicochemical and biological properties.

| CON CLUS I ON AND FUTURE TRENDS
There is a great potential to extend the use of other nanoparticles such as copper, cerium oxide, and titanium oxide as coating materials as they are of low concern. Also, food-grade nanomaterials such as starch, cellulose, and gums are edible and nontoxic and hence present promising prospects for use in fruit coating. present in fruits to create a healthy nanoparticle that could be used on commercial products.

ACK N OWLED G M ENTS
These authors are thankful to the University of Johannesburg for the Global Excellence and Stature scholarship as financial support, the faculty of science and department of Botany and Plant Biotechnology

CO N FLI C T O F I NTE R E S T
The authors declare that they do not have any conflict of interest.

E TH I C A L A PPROVA L
This study does not involve any human or animal testing.