Edible Coating of Fruits and Vegetables Using Natural Gums: A Review

ABSTRACT

Water-soluble gums (hydrocolloids) are used for various applications as coating agents, packaging films, texture modifiers, thickeners, stabilizers and emulsifiers. Edible coatings are mostly used to increase food products appearance and extending shelf life of the fruits. Several studies have been carried out showing the potential use of natural gums such as chitosan, alginate, xanthan, gellan, mesquite, psyllium, basil seed, guar, tragacanth and arabic gums in edible coatings formulation and improving their properties. This review summarized the characterization of new biodegradable edible coatings based on natural gums on quality and shelf-life of apple, papaya, carrot, guava, plum, mango, apricot, banana, orange, mushroom and tomato. The edible coatings fabricated from natural gums could provide some benefits such as extended shelf life, delaying ripening, decrease the rate of respiration, biocompatibility and environmentally friendly, economically affordable, good mass transfer barrier characteristics, carriers of foods additives such as antioxidants, vitamins and antimicrobial compounds. The addition of 20% glycerol (w/w) to edible coatings solutions containing 1% gum was sufficient to achieve the high reduction of the fruits and vegetables weight loss.

KEYWORDS:

• Edible coating
• gums
• postharvest
• preservation
• shelf-life

Introduction

The postharvest loss of fresh fruits and vegetables are estimated to be 20–30%. Given the perishable nature of fruits and vegetables, the use of cold storage is necessary to delay changes related to ripening, such as ethylene making, softening, pigment changes, respiration rate, acidity changes and decrease in weight. However, cold storage is not enough to preserve fruits and vegetables quality at optimum levels during transportation and marketing, often leading to the incidence of severe chilling injury symptoms. So, the appropriate postharvest technologies combined with cold storage are needed (Nouri et al., 2017; Salehi, 2017; Salehi et al., 2017; Sayyari et al., 2017; Valero et al., 2013).

Today, due to the nondegradability of synthetic packaging materials, there have been growing study interests toward natural resources to making biodegradable edible coatings. These researches mainly focused on developing edible coatings and improving their properties to apply the main desired features of usual synthetic materials, such as high mechanical strength, lightness, softness, water resistance and transparency. One of the alternatives to plastics, are edible biopolymers including proteins, polysaccharides and lipids (Galus and Kadzińska, 2015; Ganiari et al., 2017; Salehi and Kashaninejad, 2014; Salehi et al., 2014). Biopolymers are biodegradable and environmentally friendly compounds and they can reduce the amount of chemical hazards and home wastes (Avila-Sosa et al., 2010; Nieto, 2009). Various polysaccharides have been used for the making of edible films and coatings including starch, tapioca, corn, cellulose and cellulose derivatives such as HPMC (hydroxyl propyl methyl cellulose), CMC (carboxymethylcellulose), and MC (methylcellulose), quince seed mucilage, Pullulan, alginate, carrageenan, and policaju gum (Ahmadi et al., 2012; Ganiari et al., 2017; Hashemi and Mousavi Khaneghah, 2017).

The term “gum” is used to describe a group of naturally occurring polysaccharides that come across widespread industrial applications due to their ability either to form the gel or make the viscous solution or stabilize the emulsion systems (Salehi and Kashaninejad, 2015; Williams and Phillips, 2000). Water-soluble gums also known as “hydrocolloid” are used for various applications as coating agents, packaging films, texture modifiers, thickeners, gelling agents, stabilizers, emulsifiers and dietary fiber (Barak and Mudgil, 2014; Dick et al., 2015). Edible coatings are useful as postharvest treatments to preserve fruits and vegetables quality, with the additional benefit of reducing the volume of nonbiodegradable packaging materials. Therefore, maintenance of fruits and vegetables quality has been achieved by using some edible coatings based on hydrocolloids (gums), such as chitosan, MC, and HPMC and alginate (Valero et al., 2013). Such edible coatings act as physical barriers on the fruits and vegetables surface and decrease the surfaces of fruits and vegetables permeability to O₂, CO₂ and water vapor, leading to decreasing in respiration rate and transpiration.

Edible coatings act as an extra layer that coats the stomata leading to reducing in transpiration and in turn, to a decrease in weight loss, this being the primary positive effect of edible coatings, as has been demonstrated in a wide range of fruits and vegetables such as apple, papaya, carrot, guava, plum, mango, apricot, banana, orange, mushroom and tomato (Table 1). Moreover, differences in the ability to reduce weight loss are attributed to the different water vapor permeability of the hydrocolloids used in the formulation of the edible coating (Vargas et al., 2008). The addition of glycerol as plasticizer to the edible coating gave good results in terms of decreasing fruits and vegetables moisture loss, consistent with previous reports, in which the addition of 20% glycerol (w/w) to edible coatings solutions containing 1% gum was sufficient to achieve the high reduction of weight loss (Moldão-Martins et al., 2003; Zapata et al., 2008). It is also considered that coatings decrease the rate of respiration and delay the utilization of organic acids. Preservation of titratable acidity has been reported for various fruit treated with edible coatings (Yaman and Bayoindirli, 2002). In addition, edible coating could reduce the postharvest ripening procedure and delay the anthocyanin synthesis (Dong and Wang, 2018).

Table 1. Summary of various gums used as edible coatings for fruits and vegetables and their benefits

Fruit or vegetable	Hydrocolloid	Other compound	Main benefits	References
Apple	Gellan gum, sodium alginate	Sunflower oil	Reduction in the ethylene production, microbiological deterioration, extension of the shelf life, antibrowning effect, maintenance of the initial firmness, retention of the color.	Rojas-Graü et al. (2008)
Apple	Calcium or sodium caseinate	Acetylated monoglicerydes	Increase in the water vapor resistance, reduction in the respiration rate.	Avena-Bustillos et al. (1997)
Apple	Arabic gum	Soybean gum, jojoba wax, glycerol	The apple fruit coated with arabic gum showed significant delay in change of weight loss, ripening, firmness, titratable acidity, total soluble solids, decay and color change during storage.	El-Anany et al. (2009)
Apple	Gellan gum	–	Improving of apple quality properties by pulsed light in combined with gellan gum-based coatings	Moreira et al. (2015)
Apples	Alginate	–	Increasing shelf-life and quality of “Gala” apples.	Olivas et al. (2007)
Apples	Alginate and gellan	–	Edible coatings with alginate can reduce weight loss, preserve quality of apples and prolong its shelf-life.	Rojas-Graü et al. (2007)
Apricot	Methylcellulose	Stearic acid	Decreasing in the water loss.	Ayranci and Tunc (2004)
Apricot	Methylcellulose	–	Improving fruit quality and decreasing in water and vitamin C loss during storage.	Ayranci and Tunc (2004)
Apricot	Chitosan		Increasing quality of apricot during storage.	Ghasemnezhad et al. (2010)
Apricot	Basil seed gum	Essential oils	The new edible coating based on basil seed gum can provide high improvement in terms of quality, odor and overall acceptability of apricot.	Hashemi et al. (2017)
Avocado	Pectin	Beeswax	Slower rate of disease spread and respiration rate, reduction in fruit softening and color changes, beneficial effect on firmness retention.	Maftoonazad et al. (2007)
Banana	Arabic gum	Lemongrass and cinnamon oils	Their results suggest the using 10% arabic gum with 0.4% cinnamon oil as a biofungicide for controlling postharvest anthracnose.	Maqbool et al. (2011)
Banana	Chitosan, modified starch and cellulose	Glycerol and tween-80	Coatings based on chitosan were much superior in increasing and improving the shelf life and quality of banana.	Kittur et al. (2001)
Banana	Chitosan	Cinnamon oil	Increasing quality of banana fruit during storage.	Win et al. (2007)
Button mushrooms	Alginate	–	The use of 2% alginate edible coating under a high oxygen modified atmosphere (100% O2) has the potential to preserve button mushroom quality and increased its postharvest life to 16 days.	Jiang (2013)
Button mushrooms	Tragacanth gum	Zataria multiflora Boiss. essential oil (ZEO)	Mushroom coated with tragacanth gum containing ZEO preserved 93.47% texture firmness and showed decrease in microbial counts from molds and yeasts.	Nasiri et al. (2017)
Carrot	Alginate	–	Edible coatings with alginate can decrease weight loss and natural microbial total counts in carrots.	Amanatidou et al. (2000)
Cherry tomato	Methylcelullose	Beeswax	Extension of the postharvest life by the reduction of gray mold development	Fagundes et al. (2014)
Green peppers	Methylcellulose	–	Improving fruit quality and decreasing in water and vitamin C loss during storage.	Ayranci and Tunc (2004)
Guava	Cashew gum and carboxymethylcellulose	Glycerol	Edible coatings resulted in a decrease of mass loss, protect firmness and delaying surfaces color changes.	Britto et al. (2012)
Guava	Arabic gum	Sodium caseinate and tulsi extract	Increasing shelf-life and quality of guavas.	Murmu and Mishra (2017)
Guava	Arabic gum	Sodium caseinate and essential oil of cinnamon and lemon grass	Edible coatings protect postharvest quality of guavas and reduce its microbial load.	Murmu and Mishra (2018)
Guava	Cassava	Cinnamon essential oil	The guava shelf life increased up to 8 days with the coating based on 2% w/v cassava starch and 0.01% cinnamon essential oil at 25°C and 76% RH.	Botelho et al. (2016)
Guava	Chitosan	Cassava starch and Lippa gracilis Schauer	The guava shelf life increased up to 10 days with the edible coating based on chitosan-cassava starch and Lippa gracilis Schauer at 25°C.	Aquino et al. (2015)
Guava fruit	Mesquite gum	Candelilla wax	Extension of the shelf life, reduction in weight loss and ethylene emission, attractive gloss, retention of the color, limited softening and firmness loss.	Tomas et al. (2005)
Kiwifruit	Pullulan	Stearic acid	Decrease in the senescence and water loss.	Xu et al. (2001)
Mandarin	Locust bean gum	Biocontrol yeasts	Edible coatings can carrying biocontrol yeasts against fungi causal agents of postharvest decay.	Parafati et al. (2016)
Mango	Chitosan	–	Improving quality and shelf-life of sliced mango fruit	Chien et al. (2007)
Mango	Arabic gum	–	Influence on the mango ripening, quality and aroma biosynthesis.	Dang et al. (2008)
Mango	Alginate	–	Application of coating as carrier of anti-browning agents on bioactive compounds and antioxidant activity.	Robles-Sánchez et al. (2013)
Mango	Arabic gum	Calcium chloride	10% arabic gum alone or combined with 3% calcium chloride successfully reduced weight loss, soluble solid concentration, color changes, respiration rate, ethylene production and maintained high firmness, titratable acidity and ascorbic acid.	Khaliq et al. (2015)
Mango	Chitosan	–	Increasing postharvest quality of mango.	Zhu et al. (2008)
Mango	Chitosan, modified starch and cellulose	Glycerol and tween-80	Coatings based on chitosan were much superior in increasing and improving the shelf life and quality of mango.	Kittur et al. (2001)
Melon	Alginate, pectin and gellan	–	They found that gum-based edible coatings prevented the dehydration of fresh-cut melon and in addition inhibited the ethylene producing and triggered the accumulation of total phenol with antioxidant characteristics.	Oms-Oliu et al. (2008)
Melon	Alginate	Cinnamon oil	They reported significant differences in taste, odor, and firmness of fresh-cut melon with edible coating containing cinnamon oil.	Raybaudi-Massilia et al. (2008)
Melon	Xanthan	β-carotene nanocapsules	Combination β-carotene nanocapsules and xanthan gum improves the characteristics of the coatings, and increased shelf time to 21 days at 4 C.	Zambrano-Zaragoza et al. (2017)
Orange	Guar gum	Pea starch and oleic acid	Edible coatings based on guar gum and pea starch can be a useful substitute to common commercial waxes for preservation of quality and storability, and increasing shelf life of orange.	Saberi et al. (2018)
Orange	Chitosan	Bergamot thyme and tea tree essential oils	Fungal decay and increasing shelf life of oranges.	Cháfer et al. (2012)
Orange	Shellac, gelatin and Persian gum	–	The results showed that total soluble solids, weight loss, texture firmness, titratable acidity, pH, ascorbic acid and total phenolic content, total antioxidant capacity and respiration rate were influenced by the coatings.	Khorram et al. (2017)
Oranges	Chitosan and locust bean gum	Pomegranate peel extract	The addition of 0.361 g dry pomegranate peel extract/mL, chitosan and locust bean gum coatings reduced disease incidence by 49 and 28%, respectively	Kharchoufi et al. (2018)
Papaya	Arabic gum	Lemongrass and cinnamon oils	Their results suggest the using 10% arabic gum with 0.4% cinnamon oil as a biofungicide for controlling postharvest anthracnose.	Maqbool et al. (2011)
Papaya	Chitosan	–	They found that control papaya showed early increase in respiration and ethylene producing as compared to 1.5% chitosan coated samples.	Ali et al. (2011)
Papaya	Chitosan and pectin	A microencapsulated β-cyclodextrin and trans-cinnamaldehyde complex	Coated papaya was firmer, maintained color, high β-carotene content, showed lower juice leakage and had the highest organoleptic acceptability.	Brasil et al. (2012)
Papaya	Psyllium gum	–	Improving quality and shelf life of fresh-cut papaya.	Yousuf and Srivastava (2015)
Papaya	Alginate and gellan	–	Improving barrier, texture and nutritional characteristics of fresh-cut papaya	Tapia et al. (2008)
Papaya	Aloe vera	Antimicrobial compounds	Improving of storage life and quality maintenance of papaya.	Marpudi et al. (2011)
Peach	Alginate	Methyl cellulose	The decreased transpiration and respiration rates as a result of coatings were considered responsible for preservation of quality and increasing the shelf life of peaches.	Maftoonazad et al. (2008)
Pears	Xanthan	Cinnamic acid	Edible coating based on xanthan gum (2.5 g/L) and cinnamic acid (1 g/L) slow down surface browning and increase the shelf life of pears slices.	Sharma and Rao (2015)
Pineapple	Alginate	Lemongrass essential oil	Increasing shelf-life and quality of fresh-cut pineapple.	Azarakhsh et al. (2014)
Pineapple	Cassava starch	–	Extension of shelf life and quality of fresh-cut pineapple through edible coatings.	Bierhals et al. (2011)
Plum	Alginate	–	The weight and acidity losses, softening and color changes, were slowing down by the use of alginate edible coating.	Valero et al. (2013)
Raspberry	Alginate	Pectin and essential oils	Edible coatings based on gums and essential oils create a cover around the raspberry fruits surface, and protect them from pathogen spoilage.	Guerreiro et al. (2015)
Shiitake mushroom	Arabic gum	Natamycin	Increasing shelf life and quality of mushroom.	Jiang et al. (2013)
Strawberries	Chitosan	Beeswax	Decrease in the senescence and weight loss, retention of the color and the texture, the titratable acidity, pH, soluble solids and sugars, good visual appearance and taste, enhancement in the antimicrobial properties of chitosan, reduction in the respiration rate.	Velickova et al. (2013)
Strawberries	Chitosan	Oleic acid	Enhancement in the antimicrobial properties of chitosan, reduction of the respiration rate, extension of the shelf life.	Vargas et al. (2006)
Strawberries	Aloe vera	Ascorbic acid	Edible coatings preserve postharvest quality of strawberry and reduce its microbial load.	Sogvar et al. (2016)
Sweet cherry	Alginate	Methylcellulose	Improving fruit quality and bioactive compounds during storage.	Díaz-Mula et al. (2012)
Sweet cherry	Arabic gum	Almond gum	Delay postharvest ripening of sweet cherry and increases its quality during storage	Mahfoudhi and Hamdi (2015)
Sweet cherry	Guar gum	Ginseng extract	Edible coatings based on guar gum and ginseng increased sweet cherries shelf life for about 8 days. Coatings with gums reduced water loss and slow down loss of firmness and of titratable acidity, ascorbic acid and total phenol contents.	Dong and Wang (2018)
Tomato	Alginate	Zein	Delay postharvest ripening process and maintaining tomato quality	Zapata et al. (2008)
Tomato	Arabic gum	–	Enhancing shelf life and improving postharvest quality of tomato.	Ali et al. (2010)
Tomato	Arabic gum	Glycerol	Their results showed that by using 10% arabic gum as coating, the ripening procedure of tomatoes can be decreased and the antioxidant can be preserved for up to 20 days during storage (at 20°C) without any negative effects on quality of tomato.	Ali et al. (2013)
Tomato	Chitosan	–	Decrease in rate of respiration and ethylene producing as a result of coating with films; Increasing the storage life of tomato.	El-Ghaouth et al. (1992)

Gums-based edible coatings have been effective in maintaining postharvest quality of fruits and vegetables. These materials have been widely considered as prospective replacers of synthetic polymers such as plastics. Therefore, this study summarized characterization of new biodegradable edible coatings based on gums on preserving fruits and vegetables quality during postharvest storage.

Apple

Apple represents the fourth most important horticultural fruit for human nutrition in the world. It has very short shelf life due to high moisture content, and it is necessary to use various preservation methods to increase its shelf life (Salehi, 2017). A new approach to extend shelf life of fruits is the use of edible coatings of natural antimicrobial compounds. Edible coatings with alginate can reduce weight loss, preserve quality of apples and prolong its shelf-life (Rojas-Graü et al., 2007). Edible coatings based on gums create a modified atmosphere around the fruit by providing a semi permeable barrier to CO₂ and O₂, thus decreasing respiration and oxidation reaction rates. Gum-based coatings have been used widely to extend the shelf life of fruit (El-Anany et al., 2009; Maqbool et al., 2010). El-Anany et al. (2009) studied the usefulness of arabic gum as an edible coating for apple fruit coating during cold storage. They reported that apple fruit coated with arabic gum showed a significant delay in ripening and as a result, decayed slowly as compared to control sample.

Papaya

Papaya is a rich source of bioactive compounds with high antioxidant activity. Ripe papaya is eaten peeled, seeded, cut in wedges and served. Papaya rapidly loses its freshness.

Edible coatings were used as effective alternative to modified atmosphere packaging for increasing shelf life and improving postharvest quality of fresh-cut papaya because they help to decrease physical damage, improve appearance, and decrease microbial growths (Ali et al., 2011; Brasil et al., 2012; Maqbool et al., 2011; Yousuf and Srivastava, 2015). The multilayered antimicrobial edible coatings based on gums (chitosan and pectin) were used to enhances quality of fresh-cut papaya by Brasil et al. (2012). Coated papaya was firmer, maintained color, high β-carotene content, showed lower juice leakage and had the highest organoleptic acceptability. Their results showed that layer-by-layer assembly with combination of microencapsulated antimicrobial was useful in increasing shelf life and quality of papaya.

Maqbool et al. (2011) used arabic gum (10%) and lemongrass and cinnamon oils for controlling anthracnose and quality of papaya during storage. Their results suggest the using 10% arabic gum with 0.4% cinnamon oil as a biofungicide for controlling postharvest anthracnose of papaya.

Carrot

The carrot is a root vegetable, usually orange, red or yellow in color, with a crisp texture when fresh. It is a rich source of β-carotene, thiamine, vitamin B-complex, riboflavin and minerals (Akubor and Eze, 2012; Heinonen, 1990). Amanatidou et al. (2000) investigated the high O₂ and high CO₂ modified atmospheres for increasing shelf life of carrots. Their results showed that the edible coatings with alginate gum can decrease weight loss and natural microbial total counts in carrots.

Guava

Guava is a tasty sweet fruit native from America. It is a climacteric fruit with high respiratory activity and elevated rate of ethylene producing. Edible coatings such as various gums (xanthan, chitosan, cashew, mesquite and arabic gums), different waxes (carnauba and candelilla), cellulose and CMC, starch and miscellaneous formulations based on gelatin, triacetin and lauric acid have been used for improving quality and shelf life of fresh guavas (Forato et al., 2015; García-Betanzos et al., 2017; Murmu and Mishra, 2017; 2018; Tomas et al., 2005).

Natural gums coatings showed a substantial potential to be incorporated into food packaging applications. Cashew gum is a nontoxic exudates polysaccharide extracted from the Anacardium occidentale tree. This gum is water soluble and can be transformed into transparent and resistant films (Britto et al., 2012). The influence of edible coatings based on cashew gum (1%) and CMC (1 and 2%) in increasing the shelf life of guavas was studied by Forato et al. (2015). Edible coatings resulted in a decrease of mass loss, protect firmness and delaying surfaces color changes. Magnetic resonance imaging (MRI) analysis results showed that tissue decay took place mostly near the peel or around the peduncle region between 8 and 12 days of storage of guavas at room temperature. Edible coating based on arabic gum (0–15%, w/v), sodium caseinate (0–2%, w/v) and tulsi extract (0–5 mL/100 mL) for guava were developed by Murmu and Mishra (2017). Their optimized coating was 5 % arabic gum, 1% sodium caseinate and 2.5 mL/100 mL tulsi extract, and maintained appropriate internal gas composition to slow down ripening, showed high overall acceptability and postharvest shelf-life. The sodium caseinate showed positive effect on carbon dioxide and water vapor transmission rate; tulsi extract showed a significant influence on the CO₂ evolution rate; and its interaction with arabic gum showed significant effects on the O₂ utilization rates of coated guava.

Plum

Plums are very appreciated by consumers, the degree of acceptance depending on organoleptic properties such as texture, color, flavor and aroma. Plum utilization has beneficial health property due to their antioxidant compounds for example vitamin C, polyphenols, carotenoids and anthocyanin (Crisosto et al., 2004; Eum et al., 2009; Navarro-Tarazaga et al., 2008; Valero et al., 2013). Edible coatings fabricated from gums showed many appropriate properties. The influence of edible coating based on alginate gum (1 and 3%) on preserving plum quality during postharvest storage was studied by Valero et al. (2013). The treatments were useful in inhibiting ethylene production, especially when 3% alginate was used. The delay of the ripening process was related to lower carotenoid and anthocyanin accumulation. The changes in fruit quality parameters related to plum postharvest ripening, including weight and acidity losses, softening and color changes, were delayed by the use of alginate edible coating.

Mango

Mango is a tropical climacteric fruit and ripens very fast in harsh climatic conditions. Soft textures of mango fruit limit the postharvest life and enhance susceptibility to various pathogenic infections. Several techniques such as controlled and modified atmosphere, edible coatings and films, low temperature and ionizing radiation have been used to reduce deterioration, increased the shelf life and preserve quality of mango fruits (Khaliq et al., 2015; Singh et al., 2013). Influence of arabic gum (10%) coating combined with calcium chloride (3%) on physicochemical characteristics and quality of mango during low temperature storage was investigated by Khaliq et al. (2015). Arabic gum alone or combined with calcium chloride successfully reduced weight loss, soluble solid concentration, color changes, respiration rate, ethylene production and maintained high firmness, titratable acidity and ascorbic acid. Their results suggest that application of 10% arabic gum edible coating combined with 3% calcium chloride for increasing mango quality during storage.

Apricot

Apricot fruit can take part in human nutrition because of its high fibers, vitamins and mineral content in addition of sugars, phenolic compounds, carotene and lycopene pigments. Spoilage properties such as senescence can be appeared after a short time after harvest of apricots (Salehi et al., 2015).

Composite edible coating based on basil seed gum and Origanum vulgare subsp. viride essential oil

were used to coating of apricots by Hashemi et al. (2017). The addition of essential oil to the formulation reduced water vapor permeability of coatings while increased their moisture content. The used edible coatings decreased total plate count, molds and yeasts populations. The new edible coating based on basil seed gum and essential oils can provide high improvement in terms of quality, odor and overall acceptability of apricot.

Banana

Anthracnose is a disease of banana that results in major economic losses during transportation and storage. Gums being a good emulsifier protected the banana against anthracnose by providing a film onto the fruit surface and creating a modified atmosphere of O₂ and CO₂, delayed the ripening procedure and strengthened the cell wall tissues (Dang et al., 2008; Maqbool et al., 2010). For controlling banana anthracnose, antifungal influences of arabic gum (at four levels of 5, 10, 15 and 20%) and chitosan (at four levels of 0.5, 0.75, 1.0 and 1.5%) were investigated by Maqbool et al. (2010). Chitosan at 1.0% and 1.5% had fungicidal influences on Colletotrichum musae. Arabic gum alone did not show any fungicidal influences while the combination of 1.0% chitosan with all tested arabic gum concentrations had fungicidal effects (Table 2). The potato dextrose agar medium amended with 10% arabic gum incorporated with 1.0% chitosan showed the most promising results among all treatments in suppressing the mycelial growth (100%) and conidial germination inhibition (92.5%). Their results showed the possibility of using 10% arabic gum combined with 1.0% chitosan as a biofungicide for management of anthracnose in banana. In other study, Maqbool et al. (2011) used arabic gum (10%) and lemongrass and cinnamon oils for controlling anthracnose and quality of banana during storage. Their results suggest the using 10% arabic gum with 0.4% cinnamon oil as a biofungicide for controlling postharvest anthracnose of banana. In vivo studies revealed that 10% arabic gum combined with 0.4% cinnamon oil was the best concentration in controlling decay (80%) and (71%), showing a synergistic result in the decrease of C. musae and C. gloeosporioides, respectively.

Table 2. Effects of edible coatings based on gums on physicochemical characteristics of banana, plum, papaya and melon

Fruit or vegetable	Hydrocolloid % (w/v)	Weight loss (%)	Acidity (%)	Soluble solids (%)	Firmness (N)	References
Banana	Chitosan: 0%	30.41	0.17	9.7	39.21	Maqbool et al. (2010)
	Chitosan: 0.5%	25.20	0.23	8.7	42.12
	Chitosan: 0.75%	23.12	0.22	8.5	46.26
	Chitosan: 1.0%	20.34	0.21	8.1	46.78
	Chitosan: 1.5%	19.01	0.21	8.0	47.11
Plum	Alginate:0%	10.8	–	–	–	Valero et al. (2013)
	Alginate:1%	8.4	–	–	–
	Alginate:3%	5.8	–	–	–
Banana	Arabic gum: 0%	31.23	0.18	9.4	39.16	Maqbool et al. (2010)
	Arabic gum: 5%	17.14	0.21	7.8	43.62
	Arabic gum: 10%	16.18	0.20	7.7	47.23
	Arabic gum: 15%	15.82	0.21	7.5	48.30
	Arabic gum: 20%	15.96	0.19	7.3	49.01
Banana	Arabic gum: 0%	32.14	0.16	9.9	39.21	Maqbool et al. (2011)
	Arabic gum: 10%	15.40	0.21	7.64	50.12
Papaya	Arabic gum: 0%	38.12	0.15	11.23	32.18	Maqbool et al. (2011)
	Arabic gum: 10%	22.15	0.18	8.73	54.90
Melon	Xanthan gum: 0%	3.43	0.11	7.28	–	Zambrano-Zaragoza et al. (2017)
	Xanthan gum: 0%	3.16	0.12	7.34	–

Orange

Orange is one of the most plentiful sources of vitamin C amongst fruits and vegetables. Orange is also a good source of essential oils, carotenoids, sugar, flavonoids, fiber and some minerals (Niu et al., 2008). Fernandez-Lopez et al. (2009) suggested that orange is a rich source of flavonoids, with flavanones encompassing 50–80% of the total flavonoid content of oranges. Edible coatings are widely used to preserve the quality and increasing shelf life of citrus. Saberi et al. (2018) used edible coatings based on guar gum and pea starch on quality, storability and shelf life of orange. The integration of hydrophobic compounds into the this composite coatings in general resulted in the high performance in decreasing fruit respiration rate, ethylene producing, weight loss, peel pitting, firmness loss, and fruit decay rate of the coated oranges. Layer-by-layer coating of oranges decreased weight loss and respiration rate and improved firmness retention to a larger extent than the single layer coating. Their results suggested that edible coatings based on guar gum and pea starch can be a useful substitute to common commercial waxes for preservation of quality and storability, and increasing shelf life of orange. Chitosan gum based edible coatings can be used as a carrier to include functional ingredients, such as antioxidant, antimicrobials, minerals and vitamins. Kharchoufi et al.(2018) investigated the application of edible coatings based on chitosan and locust bean gum, incorporated with water and methanol pomegranate peel extract and biocontrol yeast to reduction of fungi (Penicillium digitatum) postharvest decay of oranges. Their experimental results showed that the addition of 0.361 g dry pomegranate peel extract/mL, chitosan and locust bean gum coatings, reduced disease incidence by 49 and 28%, respectively.

Mushroom

Mushrooms have a short shelf life, and lose their commercial value within a few days, due to browning, water loss, senescence and microbial attack. Application of semi-permeable films and coatings has been shown to improve and increases the storage life of various mushrooms (Jiang, 2013; Jiang et al., 2013; Nasiri et al., 2017). Physicochemical responses and microbial properties of shiitake mushroom to arabic gum coating containing natamycin during storage was studied by Jiang et al. (2013). Mushroom coated with arabic gum and natamycin preserved texture firmness and showed decrease in microbial counts from molds and yeasts compared with the control sample. Arabic gum and natamycin coating slow down changes in the total sugar, soluble solids concentration and ascorbic acid. Their study suggests that arabic gum and natamycin has the potential to improve the quality of shiitake mushroom and increased its shelf life up to 16 days. In another study, the influence of alginate coating (1, 2 and 3%) on physicochemical characteristics and sensorial qualities of button mushrooms under a modified atmosphere was studied by Jiang (2013). Their results showed that treatment with 2% alginate coating maintained a high level of firmness, and delayed changes in the respiration rate, weight loss, soluble solids concentration, total sugars, ascorbic acid, texture, color (browning), and percent cap opening of mushrooms. Their study suggests that the use of 2% alginate edible coating under a high oxygen modified atmosphere (100% O₂) has the potential to preserve button mushroom quality and increased its postharvest life to 16 days.

Tomato

Tomato being a climacteric fruit has a relatively short postharvest life. The major factor associated with tomato postharvest shelf life is increased respiration that results in high fruit ripening and deterioration of tomato quality (Bailén et al., 2006). Arabic gum is the most widely used gum in the food industry because it has emulsifying, film and coating forming and encapsulating characteristics (Maqbool et al., 2011). Ali et al. (2010) reported that 10% arabic gum used alone increased the shelf life of tomato up to 20 days during storage and improved its postharvest quality. Their results showed that the tomato coated with 10% arabic gum showed a significant delay in changes of weight, titratable acidity, firmness, ascorbic acid content, soluble solids concentration, high organoleptic acceptability, decay percentage and color change development compared to control sample.

Edible coatings and films can preserve quality of tomatoes by functioning as solute, vapor and gas barriers. Zapata et al. (2008) investigated alginate-based edible coatings on tomato to delay postharvest ripening process and to maintain the quality of tomato. Their results showed positive effects of retarding the ripening process by decreasing the respiration rate and ethylene production, and changes triggered by this plant hormone, such as color change and loss of firmness. Ali et al. (2013) studied the influence of arabic gum as an edible at four levels of 5, 10, 15 and 20%, coating on antioxidant capacity of tomato during storage. Tomatoes coated with 10% arabic gum decreased the ripening procedure by slowing down the rate of respiration and ethylene production and also preserved total antioxidant capacity, lycopene content, total phenol and total carotenoids during storage. Their results showed that by using 10% arabic gum as coating, the ripening procedure of tomatoes can be decreased and the antioxidant can be preserved for up to 20 days during storage (at 20°C) without any negative effects on quality of tomato.

Conclusion

The development of alternative edible biodegradable coatings and films from gums to substitute synthetic polymers has been intensified due to removal and environmental harms with plastic waste. Edible coatings based on gums are potential substitutes for synthetic packaging and have been studied and characterized by several researchers. These papers suggest the efficacy of different gums as an edible coating for delaying ripening and enhancing storage life of various fruits and vegetables. Edible coatings and films based on natural hydrocolloids provide an additional protection for fresh or blanched fruits and vegetables. Natural gum edible coatings provide a promising approach for enhancing quality and prolonging shelf life of fruits and vegetables.