Polysaccharide-Based Active Coatings Incorporated with Bioactive Compounds for Reducing Postharvest Losses of Fresh Fruits

: This review reports recently published research related to the application of polysaccharide-based biodegradable and edible coatings (BECs) fortiﬁed with bioactive compounds obtained from plant essential oils (EOs) and phenolic compounds of plant extracts. Combinations of polysaccharides such as starches, pectin, alginate, cellulose derivatives, and chitosan with active compounds obtained from clove, lemon, cinnamon, lavender, oregano, and peppermint have been documented as potential candidates for biologically active coating materials for retardation of quality changes in fresh fruits. Additionally, polysaccharide-based active coatings supplemented with plant extracts such as cashew leaves, pomegranate peel, red roselle, apple ﬁber, and green tea extracts rich in phenolic compounds and their derivatives have been reported to be excellent substituents to replace chemically formulated wax coatings. Moreover, EOs and plant polyphenolics including alcohols, aldehydes, ketones phenols, organic acids, terpenes, and esters contain hydroxyl functional groups that contribute bioactivity to BECs against oxidation and reduction of microbial load in fresh fruits. Therefore, BECs enriched with active compounds from EOs and plant extracts minimize physiological and microbial deterioration by reducing moisture loss, softening of ﬂesh, ripening, and decay caused by pathogenic bacterial strains, mold, or yeast rots, respectively. As a result, shelf life of fresh fruits can be extended by employing active polysaccharide coatings supplemented with EOs and plant extracts prior to postharvest storage. the internal oxygen and carbon dioxide levels were measured at room temperature for 4 days. Results indicated that coating thickness varied with viscosity, concentration, density, and draining time of the biopolymer solution. Coating thickness relates to the square root of viscosity and the inverse square root of draining time, which agrees with the theoretical approach for ﬂat plate dip-coating in low-capillary-number Newtonian liquids. These results indicate the possibility of controlling coating thickness data curation, K.A.S. and K.N.; writing—original draft preparation, K.A.S.; writing review and editing, K.A.S., K.N., and W.T.; visualization, K.A.S. and W.T.; supervision, W.T.; project administra-tion, W.T.; funding acquisition, W.T. All authors have read and agreed to the version of the manuscript.


Introduction
Fresh fruits containing essential nutrients, vitamins, and minerals are consumed worldwide in part because of their strong antioxidant potential against chronic diseases [1]. Fresh fruit packaging materials after single use are disposed of in the environment. The application of synthetic and non-biodegradable polymer-tailored packaging materials for fresh fruit has raised potentially alarming consequences for the environment [2]. Conventional packaging materials such as glass, wood, aluminum, tin, and paper have been employed as fresh fruit containers to prevent mechanical damage during bulk transportation [3]. The innovative designs of synthetic packaging materials have been of great convenience to customers in supermarkets [4]. Synthetic packaging materials used for fruits may lack the optimum oxygen and moisture barrier properties to maintain their postharvest quality in the markets [5]. Additionally, the production of synthetic packaging materials may directly have an impact on the sustainability of non-renewable petroleum-based resources [6].
Fresh fruits typically have a short postharvest shelf life due to ongoing physiological and biochemical changes occurring in the living tissues until consumption [7]. Mechanical damages and pathological changes during improper handling and transportation have been associated with heavy economic losses [8]. Conventional synthetic waxes and chemical fungicides have been used as postharvest treatments to minimize losses in fresh

Postharvest Quality Constraints of Fresh Fruits
Fruits are commonly harvested on the basis of conventional extrinsic factors such as firmness, color, size, and shape. More recently, intrinsic factors such as nutritional and functional attributes have been considered, including minerals, vitamins, dietary fibers, and other polyphenolic constituents that exhibit beneficial health properties [27]. During postharvest handling, transportation, and bulk storage, fruits may be highly susceptible to biological and/or mechanical hazards that can affect both intrinsic and extrinsic factors [28]. In addition to improper postharvest handling of fruits, mechanical vibrations may affect the fruit quality during transportation, triggering heavy losses during longer storage periods. The quality problems that emerge in metabolically active fruits during postharvest storage include physiological deterioration and microbial deterioration as evidenced by moisture loss, softening of flesh, ripening, and decay caused by pathogenic bacterial strains, molds, or yeast rots [27,29].

Microbial and Biochemical Causes of Deterioration in Fresh Fruits
Fruits after harvesting from the field may be contaminated with pathogenic microbes, insects, and pests. Fresh fruits in unprocessed and raw form contain infectious germs on the skin of fruits that can lead to food borne diseases [30]. The microbial population is an important factor in considering the quality of the food product [31]. The low pH fruits, like ripe tomatoes, in a pH range (3.9-4.5) could inhibit the human intestinal pathogens such as Shigella and Escherichia coli O157:H7. Melons and soft fruits with a pH of 4-6 can favor the growth and survival of Botrytis cinerea and Penicillium species [32]. Pathogenic organisms are transmitted from the environment mostly during fruit harvesting from plants, post-harvest displacements, processing, and transport movements [33]. Several types of microorganisms, such as bacteria, yeasts, and fungi that cause deterioration may be transmitted during postharvest storage. Approximately 80-90% of microbial contamination in fresh fruits is due to Pseudomonas and Enterobacteriaceae (Klebsiella, Enterobacter, Citrobacter, Salmonella, Escherichia coli, Shigella, Proteus, Serratia, and other species) referred as Gram-negative bacteria [32,34]. Additionally, lactic acid bacteria, which are a natural flora of fruits, are corrosive and develop unpleasant odors [32]. Moreover, fresh fruits contaminated with fungi (Rhizopus, Penicillium, Aspergillus, and Eurotiumand Wallemia) and the yeast (Debaryomyces, Pichia, Candida, Hanseniaspora, Zygo saccharomyces), also have major role in the spoilage of fresh fruits during postharvest handling and storage [32]. The use of chemical disinfectants such as organic acids, chlorine dioxide, hydrogen peroxide, hypochlorite, sodium bisulfite, sulfur dioxide, and ozone has been proposed for reducing the bacterial population during postharvest storage [35]. Such chemical-based disinfectants have limited applications due to ill effects on human health and degradation of sensory quality in fruits [36].
Biochemical quality deterioration may depend on the storage temperature and metabolic processes occurring during respiration of living tissues in postharvest storage of fruits. Temperature is an important factor responsible for controlling metabolism of carbohydrates, lipids, and amino acids in respiring fruits. Temperate fruit crops are commonly stored at temperatures (0-1 • C) compared to the tropical or subtropical fruits that must be stored at higher temperatures (7-15 • C) to avoid losses due to chilling injury (CI) [37]. CI may alter the ripening process by damaging the external peel, inducing internal flesh browning, pitting, loss of firmness, and discoloration evidenced after the removal of fruits from cold temperature storage [37].
Appropriate storage temperatures can extend storage life by approximately 2-4 weeks for crops such as apricots, sweet cherries, and peaches, and up to several months for apples, pears, and kiwifruits [37]. The general effect of low temperature storage upregulates stressresponsive genes, blocks signal transduction of ethylene production processes affecting metabolic changes in vital components of fruits [38,39]. Various commercially important fruits, such as apples, pears, kiwifruits, bananas, and nectarines, at physiological maturity are characterized by high starch content that is converted to sugars at low temperatures during postharvest storage [40]. Induction of chilling tolerance of nectarines stored at near freezing temperatures (−1.4 • C) was shown to reduced activities of sucrose metabolismassociated enzymes that resulted in higher sucrose contents [40]. Moreover, fatty acids are essential cell membrane components forming a selectively permeable barrier between the cells in a fruit matrix. Fruits are composed of different types of fatty acids that show active roles in the biochemical quality degradation during postharvest cold storage. Peaches containing plastidic glycerolipid and triacylglycerides (TAGs) are used as a source of energy during fruit senescence [41]. Phosphatidic acid (PA) is accumulated in pineapple fruit during blackheart development at 10 • C [42]. Increased levels of phospholipase D enzyme activities have been observed in cold stored pears [43,44]. Similarly, chilling injury of "Honeycrisp" apples with soggy flesh showed elevated contents of glycerol and TAGs [45]. During postharvest storage of fruits, proteins may be degraded into free amino acids due to the activation of proteolytic enzymes. Amino acids such as Glu, Gln, Asp, and Asn contents increased in tomatoes stored at 4 • C [46]. Similar results were also documented in kiwifruit that showed increased Thr, Ile, and Val contents [47].
Additionally, temperature fluctuations during turbulent transportation may lead to mechanical bruising of fruits without any postharvest coating, thereby accelerating their decay [48]. In this regard, it is of primary concern to apply different novel coating techniques to delay ripening and senescence in fruits [49]. The aim is to eradicate biochemical quality deterioration during defective cold chain management that may accelerate the rate of respiration in living tissues and induce undesirable ripening (the main cause of senescence), thereby shortening the shelf-life of fruits [50]. Fruit ripening increases the total soluble solids resulting in higher sugar content; it involves several metabolic processes that differ between 'climacteric' and 'non-climacteric' fruits [51]. During the ripening of climacteric fruit, respiration increases until it reaches a peak, which is accompanied by an increase in ethylene production. In contrast, respiration of non-climacteric fruit does not increase during ripening, and ethylene is not required in order to complete the ripening process [52]. Regardless of the type of ripening, this process, as well as other metabolic processes that lead to deterioration, are driven by respiration. After harvest, the fresh produce continues to respire, utilizing food reserves, taking in oxygen, and releasing carbon dioxide and heat from stored carbohydrates [37]. For that reason, postharvest active coating treatments are applied on the fruit surfaces through various methods to reduce respiration, delay deterioration processes, prolong shelf life, and help to maintain produce quality.

Application Methods of Polysaccharide-Based Active Edible Coatings in Fresh Fruits
BECs can be applied to fresh fruits after harvesting from the plants or trees using various methods as shown in Figure 1. The selection of BECs mainly depends on the fruit surface hydrophobicity and roughness and the physical properties of the BEC such as surface tension, viscosity, density, coating emulsion stability, cost, and drying conditions for industrial application [53]. The various methods of BEC application for fresh fruits explained in this reviewed work include conventional spraying, electrospraying, dipping, spreading, brushing, and layer by layer deposition techniques, respectively ( Figure 1). Spraying is a conventional technique for applying low viscous BEC solutions on the fresh fruit surface [54]. A homogenous spray with fine droplets may form a uniform layer on the fruit surface at a high-pressure atomization in the range of 60-80 psi (4.1-5.5 bar) [55]. The desirable layer of coating thickness mainly relies on the lower hydrodynamic diameter of the droplet and atomizer features (spray gun type, operating pressure, and nozzle temperature) as well as the humidity and flow rate of air or liquid in the BEC solution [56]. Conventional spraying methods applied on the rough surfaces of strawberry fruit have shown lower transfer efficiency and coating evenness compared to the electrospraying method of coating [57]. Electrospraying is a novel method of coating in which a coating material is atomized in the presence of a high-intensity electric field, which enables the formation of micrometric and sub-micrometric charged droplets with an extremely narrow size distribution [58,59]. The tip of an emitter causes the formation of a Taylor cone of the nascent charged droplets and destabilizes the liquid surface to generate a cluster of charged droplets [60]. Electrospraying promotes the efficient adhesion to the surface of fresh fruit compared to conventional spraying because of electrostatic interactions of micrometric-sized charged droplets [61]. The droplet size, deposition rate, and coating thickness during electrospraying depend on the conductivity, flow rate, and viscosity of the coating solution [57]. The electrospraying coating method was employed to obtain even distribution of charged coating material droplets containing micro to nano size magnetic cellulose with special affinity to orient under an electric field, forming a compact coating film [62].
BECs applied by the dipping method undergo in three steps. The first step is immersing fresh fruits in the coating solution and holding for 2 to 3 min so the coating material can adhere on the fruit [63]. The last two steps are deposition and drainage of extra adhered BEC solution followed by evaporation and drying of coated fruit either at ambient temperature or flushed with hot air to accelerate drying [64]. Coating thickness and morphology of the coating's material deposited by the dipping method on the surface of fruits depends on various factors such as immersion time, withdrawal speed, dip-coating cycles, density, viscosity, surface tension, and drying conditions [65][66][67]. Hydroxypropyl methylcellulose in a dip-coating solution was analyzed for viscosity, density, and surface tension during coating of Fuji apples, after which the internal oxygen and carbon dioxide levels were measured at room temperature for 4 days. Results indicated that coating thickness varied with viscosity, concentration, density, and draining time of the biopolymer solution. Coating thickness relates to the square root of viscosity and the inverse square root of draining time, which agrees with the theoretical approach for flat plate dip-coating in low-capillary-number Newtonian liquids. These results indicate the possibility of controlling coating thickness and internal gas composition based on coating solution properties [67]. The dipping compared to conventional spraying or electrospraying is more beneficial for coating fruits with complex and rough surfaces, resulting in excellent uniformity [68]. Dipping generally forms a thick coating layer on the fruit surface and may effectively reduce microbial load, contamination, respiration rate, and mechanical damage and prevent physiological changes of coated fruits [69,70].
The brushing method involves the use of a sterile brush for spreading high viscosity BECs on the fruit surface and depends on the wetting degree and the spreading rate parameters followed by a drying process [71]. Brushing of BECs is generally carried out manually by experienced operators and includes several factors to minimize manual error of BEC application and ingredient quality to achieve better coating layer uniformity [15]. The efficiency of BECs is also affected by the roughness of the fruit surface and geometry, viscosity, surface tension, density, drying temperature, and relative humidity [70]. The degree of spreading or wettability of BECs can be characterized on the surface of fruit by contact angle measurements that maintain mechanical equilibrium of the coating drops under the influence of mainly three surface tension forces-solid-liquid, liquid-vapor, and solid-vapor interfaces-to assess the adhesion properties of coating solutions on the fruit surfaces [70,72]. The ideal case of a contact angle value equal to 0 • corresponds to a hydrophilic solid surface where total wetting conditions can be attained by an aqueous solution. A contact angle value between 0 • and 180 • suggests the occurrence of partial wetting, which is higher for a contact angle below 90 • . The ideal case of a contact angle equal to 180 • corresponds to a hydrophobic solid surface, where no wetting conditions occur when in contact with an aqueous medium. The contact angle can be measured directly on the food surface through the sessile drop method or atomic force microscopy to visualize the thickness and adherence of the coated surface [72,73].
BECs applied via the multilayer coating method include layer by layer deposition of coating solutions for better adhesion, especially on the surfaces of fresh-cut fruits [74]. Multilayer coating adhesion exhibits electrostatic interaction of the charged polyelectrolytes with that of the fruit surface [75,76]. The electrostatic interactions between the multilayer coatings of nano size dimensions may form chemical bonds, thereby providing effective control of physiological, mechanical, and functional properties on coated fruit [77]. In the multilayer coating method, coating materials containing oppositely charged polyelectrolytes are deposited through alternate dipping of the fruit in different coating solutions ( Figure 1e). The dipping of fruit in many cycles creates a layer-by-layer deposition of a coating solution that mainly depends on the ionic strength, pH, and charge densities to form a bonded network via electrostatic forces of attraction [74]. Therefore, the application of the multilayer coating method has been reported in polysaccharides and charged polyelectrolytes capable of hydrogen and covalent bonding to increase compactness of the coating layers during postharvest storage of fruits [10,78].

Impact of Polysaccharide-Based Active Edible Coatings Fortified with Essential Oils and Plant Extracts on the Postharvest Quality of Fresh Fruits
The various carboxymethyl cellulose (CMC), chitosan, pectin, alginate, and starchbased active coatings supplemented with EOs and plant polyphenolic extracts have been applied over the past five years in published research work as an active coating material for fresh fruits. The aforementioned active BECs have shown promising results with a diverse combination of other plant-based gums (Tables 1 to 3). Polysaccharides from peach gum with antioxidant and antimicrobial characteristics effectively maintained firmness, inhibited rate of respiration, decreased weight loss, and delayed changes in ascorbic acid, sugar content, and total acidity of cherry tomatoes during refrigerated storage (4 • C) [87] Pullulan Rastali and Chakkarakeli bananas 10% w/v pullulan Dipping Pullulan coating emulsion prepared at 60 • C and dipping time for 10 min 10% w/v level showed reduced weight loss (5.466%), lower color saturation (64.92), minimum browning Index (212.17), decreased peel-pulp ratio (15%), reduced vitamin C content (19%) with augmented firmness (55%) and total sugar contents (12-13%), respectively, in coated bananas stored for 20 days at 25 ± 1 • C and 70% RH. [88] Lemon basil seed mucilage (LBSM) and Chinese quince seed mucilage (QSM) Japanese cucumber fruit (JCF) 0.3% LBSM and 1% QSM Dipping JCF coated with LBSM and QSM showed similar coating thickness, reduced weight loss, and minor changes in texture, pH, and peel color up to 18 days of storage at 11 ± 1 • C and 95% RH, respectively. [89] Commercial CMC (CMCc) and CMC from pineapple core (CMCpc) Cherry tomatoes 2% CMCc and 2% CMCpc Dipping Cherry tomato coated with CMCc and CMCpc had lower weight loss TSS content and higher vitamin C content. Stored for 20 days at 25 • C and 70% RH. [90] Rice starch 'Cavendish' banana fruit Rice starch (3%, w/w), ι-carrageenan and glycerol (1%, w/w)

Dipping
Gum Arabic, oleic acid and CEO delayed browning on guava during cold storage at 10 ± 1 • C and 90% RH for 28 days. [98] Guar gum (GG)

CMC-Based Active Coatings
CMC is a cellulose derivative that is generally odorless and tasteless, flexible, transparent, and non-toxic and can be labelled as an edible coating [115]. CMC usually forms a clear, colorless and tasteless solution. It is cold water soluble and shows tolerance to high concentrations of sugar. I is available in a wide range of viscosities and has good heat stability and film forming properties [116]. Several studies have applied CMC or CMC in combination with other polysaccharides as BECs (Table 1). To provide bioactivity in the CMC coating material against physical, chemical, and microbial deterioration, EOs and plant extracts have been incorporated to form active BECs [117]. In some of the recent studies, garlic EO fortified in CMC coatings maintained higher concentrations of total phenols and anthocyanins in strawberries [118]. CMC coatings containing Mentha spicata EO inhibited Listeria monocytogenes and preserved physicochemical and organoleptic properties of strawberries [119]. CMC-based coatings incorporated with Zataria multiflora Boiss EO and grape seed extract (GSE) retarded changes in chemical, microbial, and sensory characteristics of coated fresh food during low temperature storage [120]. CMC coating enriched with clove EO delayed fungal growth and ripening and also reduced the rate of respiration and weight loss with enhanced commercial acceptability of 'Xinyu' mandarin oranges [121]. CMC reduced decay, weight loss, chilling injury, and hydrogen peroxide and malondialdehyde content in 'Kinnow' mandarin fruits during low temperature storage [122]. CMC along with pistachio (Pistacia atlantica L.) EO supplemented coating material showed higher anthocyanin, antioxidant capacity, phenol, tannin, and titratable acidity with a slight increment in TSS of grape cv. Rasheh during postharvest storage [123]. CMC Impatiens balsamina L. stem extract acted as an antimicrobial barrier to pathogen and gases, reduced the decay rate and weight loss, and inhibited the enzyme activities involved in the biochemical deterioration and softening in "Xinyu" tangerines [124]. CMC acted as a barrier to mold damage by forming a thick layer on the surface of oranges [125]. Methyl cellulose coating with thyme oil retained the higher antioxidant activity and reduced weight loss, total yeast, mold and total plate counts of mesophilic and psychrophilic microorganisms in "Acco" Pomegranate Arils [126].

Chitosan-Based Active Coatings
Chitosan is a renewable biopolymer derived from chitin. The cationic linear structure of chitosan composed of β-(1-4)-linked D-glucosamine (deacetylated unit) and N-acetyl-Dglucosamine (acetylated unit) is derived from crustaceans, fungi, and yeast [76]. Chitosan incorporated with Mentha spicata EO and coated on the surface of strawberries prevented growth of L. monocytogenes and retarded changes in physicochemical and organoleptic properties [119]. Chitosan with Origanum vulgare L. EO reduced the incidence of black mold and soft rot triggered by R. stolonifer and Aspergillus niger in cherry tomato fruit [127]. Chitosan with thymol EO prevented weight loss, retarded the rate of respiration, maintained TSS and the ratio of TSS to TA, lowered fungal decay incidence, and retained firmness, TA, anthocyanin, and sensory characteristics of fresh fig (Ficus carica L.) under low temperature storage [128]. Chitosan with Mentha piperita L. EO delayed changes in peel and pulp color and retained the catechins, procyanidins B1 and B2 in mango cultivar 'Tommy Atkins' during cold storage [129]. Chitosan applied with cinnamon EO reduced weight loss and preserved physical and biochemical quality of jujube fruits during 60 days of cold storage [130]. Clove EO fortified in chitosan inhibited activity of enzymes corresponding to browning of freshly cut lemons [131]. Chitosan-pullulan (50:50) edible coating prepared with pomegranate peel extract (0.02 g/mL) reduced weight loss and maintained TSS, pH, firmness, phenolic content, and antioxidant activity of mango fruits during 18 days of postharvest storage at 4 • C [132]. Chitosan coating incorporated with olive oil residues extracts (2% w/v) showed higher inhibition of Penicillium expansum compared with Rhizopus stolonifer in vitro and in vivo, thereby maintained the fresh quality of apple and strawberry fruits during postharvest storage [133]. Chitosan (1.5% w/v) enriched with hairy fig (Ficus hirta Vahl.) fruit extract coating applied to "Newhall" navel orange showed the lowest decay rate (5.2%), weight loss (5.16%), and malondialdehyde content while enhancing the activities of protective enzyme such as superoxide dismutase, peroxidase, chitinase, and β-1,3-glucanase during 120 days of cold storage [134]. Additionally, chitosan (1% w/v) and alginate (2% w/v) coatings in combination with pomegranate peel extract (1% w/v) recorded reduced losses in ascorbic acid (29%), total phenolics (8%), total flavonoids (12%), and antioxidant activity measured by DPPH (12%) and FRAP (9%) in coated guavas (cv Allahabad safeda) for 20 days at 10 • C [135]. Different chitosan-based coatings with bioactive properties applied to fruits are presented in Tables 2 and 3.

Pectin-Based Active Coatings
Pectin is a complex network-forming biopolymer consisting of high molecular weight glycanogalacturonans in which 1,4-linked α-D-galacturonic acid molecules are linked to a small number of rhamnose and arabinose residues in the main chain and galactose and xylose in the side chains. Pectin is extracted from fruit peels and apples and is widely used as fruit coating material alone or in combination with other polysaccharides and EOs or plant extracts [136]. Apple pectin, cellulose nanocrystals, and lemongrass EO were documented to minimize weight loss and physiological and chemical attributes in coated strawberries (Fragaria Ananassa) [123]. Pectin coatings enriched with citral and eugenol EOs reduced microbial spoilage and maintained sensory attributes of raspberries [137]. Pectin enriched with lemon EO reduced loss of weight and retained higher antioxidant activity of strawberry fruit. Oregano (Lippia graveolens) EO added with pectin delayed the growth of A. alternata under in vitro conditions with an increase in total phenols and antioxidant activity in coated tomatoes [138]. Pectin-based coating incorporated with EO extracted from orange peel showed higher antibacterial and antifungal properties, reduced weight loss, and maintained TSS and ascorbic acid levels in coated oranges [139]. Pectin coating effectively delayed respiration and ripening processes, reduced weight loss, and restricted color change in coated lime (Citrus aurantifolium) [140]. Pectin-coated sapota fruits also recorded minimum weight loss and maintained acidity, TSS, pH, color, ascorbic acid content, and firmness up to 11 days of postharvest storage at room temperature [141].

Alginate-Based Active Coatings
Alginate is a natural polysaccharide commonly obtained from algae and consists of unbranched, linear binary copolymers of β-D-mannuronic acid and α-L-guluronic acid residues linked by 1-4 glycosidic bonds [142]. Alginate combined with citral and eugenol EOs revealed lower microbial and higher sensory acceptability in coated raspberries [143]. Shirazi thyme EO incorporated into alginate increased phenolic content and antioxidant activity and reduced mold and yeast growth in fresh pistachio (Pistacia vera L.) [144]. Alginate mixed with thyme, cinnamon, and oregano EOs in which thyme EO with alginate effectively inhibited the microbial growth, respiration rate, weight loss, firmness, and browning of fresh cut 'Red Fuji' apples [145]. Lemon (Citrus lemon L.), orange (Citrus sinensis L.), and grapefruit (Citrus paradisi L.) coated with sodium alginate edible coating lowered rates of O 2 consumption and CO 2 production and yeast and mold counts. Lemon and orange EOs improved firmness and ascorbic acid content during storage of kiwifruit [146]. Ficus hirta fruit extract with alginate coating retarded the growth of blue mold increased antioxidant content, and activity of defense enzymes in Nanfeng mandarin [147]. Alginate coating incorporated with cinnamon EO effectively reduced the rate of respiration and weight loss, retained original color, increased lightness, and inhibited polyphenoloxidase and peroxidase activity in fresh-cut apple cv Golden Delicious [148]. Rhubarb extract with alginate inhibited Penicillium expansum and preserved the physiological and sensory attributes in coated peaches (Prunus persica) [149]. Sodium alginate with cinnamon EO (0.9%, v/v) inhibited the growth of A. carbonarius on coated sliced apples and pears [150]. Different alginate-based coatings with bioactive properties applied on fruits are presented in Tables 2 and 3.

Starch-Based Active Coatings
Starch is the main component of plant crops such as maize, wheat, edible cassava, potato, amaranth, and quinoa mainly constituted of linear amylose and branched amylopectin fractions amounting to 98-99% of the dry weight [151]. The linear structure of amylose tends to orient itself in a parallel direction to facilitate the hydrogen bonding between hydroxyl groups that increases hydrophobicity in coating films [152]. Starches with higher amylose content have better film-forming properties, i.e., better mechanical strength, elongation, and gas barrier properties [153]. To produce starch-based coatings with a higher amylose content, it can be extracted via selective leaching of starch in hot water (50-70 • C) [154]. Different starches from pea (61-88%), corn (50-85%), potato (21-30%), and tapioca (17%) have been reported with higher amylose content for functionality, barrier, mechanical, and sorption properties of the starch-based coatings [10]. During the retrogradation of starch, the dissociated amylose and amylopectin chains in a gelatinized starch dispersion reunite to form more ordered structures that affect the permeability, solubility, and mechanical properties of starch coating films [155,156]. Additionally, starch-based edible coatings are odorless, tasteless, colorless, non-toxic, act as a good barrier to gases (carbon dioxide, oxygen), and show adequate durability and cohesive strength in coated foods [157]. Rice starch coated on apple (Malus L.) retained color, firmness, total soluble solids, titratable acidity, antioxidant activity, and reduced weight loss, respiration rate, and fruit greasiness [155]. Corn starch with Moringa oleifera extract decreased weight loss and retained firmness and ascorbic acid content in orange (Citrus sinensis L. Osbeck) [158]. The various starch-based coatings incorporated with EOs and plant extracts on the quality of fresh fruits during storage are presented in Tables 1 to 3.
Polysaccharide-based edible coating films added with bioactive compounds from plants have been documented to show excellent barrier, optical, and mechanical properties that play an important role in the postharvest shelf-life of fruits. Barrier properties of polysaccharide coating films include water vapor transmission rate (WVTR) and oxygen or carbon dioxide gas transmission rate (GTR). Chitosan films containing essential oils or other plant extracts addition of carvacrol (0.5, 1.0, and 1.5% v/v) significantly decreased the WVTR of chitosan film [159]. Several reports of decreased WVTR using EOs and plant extracts such as tea tree essential oil, carvacrol, cinnamon essential oil, and turmeric EO were attained in chitosan coating films, possibly due to the hydrophobicity of the EO particles and their ability to occupy the amorphous regions of the films [160][161][162][163]. A gellan gum-chitosan multilayer coating film incorporated with thyme essential oil (TEO) nanoemulsion showed improved elongation at break (EB) and UV blocking ability and increased the water vapor permeability (WVP) of the films with the addition of TEO [163]. The incorporation of turmeric essential oil in chitosan film notably inhibited Aspergillus flavus and prevented biosynthesis of aflatoxin [159]. Generally, the chitosan network interacts with essential oil components via hydrogen and covalent bonds, limiting the accessibility of hydrogen groups in forming hydrophilic bonds with water, which leads to a consequent reduction in affinity of chitosan film to water. The color and opacity of the coating films are important indices regarding the appearance and consumer acceptability of the coated fruits. The opacity of films has also been of interest, as an increase in opacity can be positively related to an improved light barrier property. In addition, the incorporation of rosemary essential oil reduced the light transmission in UV light of the chitosan films by more than 25% [164]. The introduction of thyme essential oil nano-emulsion obviously enhanced the UV blocking property and the yellowness index of chitosan films [165].
Mechanical properties of chitosan coating films have been directly related to the type of essential oil contained in the chitosan matrix. The Young's modulus, strength, and maximum elongation of chitosan increased with higher olive oil concentrations (5, 10, and 15%, w/w) [166]. The tensile strength (TS) of chitosan composite film significantly increased with the incorporation of cinnamon essential oil (CEO) at levels ranging from 0.4%, to 2% (v/v). CEO generated a strong cross-linked effect with chitosan, which reduced the free volume and the molecular mobility of the polymer that forms a compact sheet-like structure resulting in increased TS and decreased elongation in break (EB) [167]. Additionally, intermolecular interaction and molecular compatibility between the functional group of citronella essential oil and cedarwood oil ingredients and hydroxyl and amino groups in the CH matrix could influence the mechanical properties of the films [163]. Therefore, organic compounds in essential oils consist primarily of hydrocarbon molecules such as alcohols, esters, terpenes, ketones, and phenols are categorized as benzene derivatives and terpenes [168]. The most common functional group in essential oils is aromatic that can interact with polysaccharides to exhibit efficient mechanical properties [169].

Conclusions
BECs fortified with EOs and plant extracts as active coating materials could extend the postharvest shelf life of coated fruits to achieve longer storage periods. This review compiled data from recent studies on active edible coatings in which the dipping method was the most reliable on both rough and smooth fruit surfaces compared to other coating methods. The dipping method is an inexpensive manual method and was recommended for small-scale or batch processes in industries for coating of fruits. Polysaccharides like alginate, pectin, CMC, and chitosan added with EOs and plant extracts have been employed over the past decade in fruits and have shown promising results related to the preservation of quality attributes such as firmness, weight loss, delayed ripening, and retardation of the biochemical and microbial changes in coated fruits. EOs and plant extracts containing bioactive compounds are safe additives compared to chemicals additives to be incorporated in BECs. Therefore, this review concludes that polysaccharides fortified with bioactive compounds from plant sources could be a potential means to extend shelf life of fresh fruits during postharvest storage.

Data Availability Statement:
The data presented in this study are available on request from the corresponding author.