review of literature -...

REVIEW

OF

LITERATURE

CHAPTER 2

Chapter 2 Review of Literature

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The production of tropical fruits has increased in the past few years due to their

attractive sensorial properties and because they supply an optimal mixture of

antioxidants (Yahia, 2010). Among tropical fruits, banana, mango, pineapple, papaya

and guava are the most popular due to their characteristics taste and nutritional value

(Gonzalez-Aguilar et al., 2008). Fruits and vegetables are very important in our day-to-

day living (Sharma et al., 2008). The constituents obtained by the human body from

fruits and vegetables include water, carbohydrates, fats, proteins, fibre, minerals,

organic acids, pigments, vitamins and antioxidants. Fruits and vegetables, especially,

are a good source of fibre, selected minerals, vitamins and antioxidants. They are

relatively low in calories and fat (avocado and olives being the exceptions), they have

no cholesterol, they are rich in carbohydrates and fibre, they contain vitamin C and

carotene and some are a good source of vitamin B. Most fruits and vegetables are

available almost year-round in a wide variety and they not only taste good, but they

also have favorable attributes of texture, color, flavor and ease of use. They can be

fresh, cooked, hot or cold, canned, pickled, frozen or dried (Vicente et al., 2005).

Consumers prefer to buy fruits and vegetables of high quality based on their appearance

(color), sensory quality (texture and taste) and nutritional values (Sharma et al., 2008).

2.1. Postharvest Losses:

Tropical fruits are very susceptible to qualitative and quantitative deterioration

and losses, including sensorial, microbial and nutritional. Major causes of losses are

attributed to fungal decay, chilling injury and rapid maturation that enhance senescence

process (Chan & Tian, 2006). Postharvest decays of fruits and vegetables account for

significant levels of postharvest losses. Losses up to 40% of the total crop have been

reported during the handling of postharvest plant products, differing among products,

production areas and time of year (Aular, 2006). It is estimated that the harvested fruits

and vegetables are lost or abandoned after leaving the farm gate. Huge postharvest

losses result in diminished returns for producers.

2.2. Postharvest Changes:

Fruits undergo several changes during harvesting, transportation and

postharvest storage, which affect the nutritional compounds and enzymes involved in

the metabolism of those compounds. The changes during prolonged storage periods are

related to the taste, nutritional quality and shelf life of the product. Since every


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commodity shows different response through storage, it is difficult to preserve

nutritional quality of all fruits by a single technology. Thus, it is extremely important to

develop sustainable technologies to maintain the quality and shelf life of fruits (Sharma

et al., 2008). In light of the incidence of the huge postharvest losses in the region and

new challenges faced under trade liberalization and globalization, serious efforts are

needed to reduce postharvest losses, especially of fruit and vegetables. Various

technologies have been implemented to prolong horticultural products shelf life,

including ultraviolet light, heat treatment, low temperature storage, plastic packaging

usage aiming to create modified atmospheres, controlled atmospheres, hydrothermal

treatments application, chemical treatments, edible coatings and natural compounds,

among others (Quezada et al., 2003; Gonzalez-Aguilar et al., 2010). In the present

study we have used chemical as well as edible coating treatments, so the present

review of literature is mainly focused on these two aspects.

2.3. Chemical Treatments:

In the past some efforts have been made in this direction by employing certain

chemicals/plant growth hormones to hasten or delay ripening, to reduce losses and to

improve and maintain the color and quality by slowing down the metabolic activities of

the fruit (Sudha et al., 2007). These chemicals are reported to arrest the growth and

spread of microorganisms by reducing the shriveling which ultimately leads to an

increased shelf life and maintain the marketability of the fruit for a longer period

(Sudha et al., 2007).

2.3.1. Calcium Chloride (CaCl2):

Dietary calcium raises concern for consumers and health specialists due to the

number of processes it is involved in, the high amount present in the body, and the

continuous research highlighting the benefits of an adequate intake. Different calcium

salts have been studied for decay prevention, sanitation and nutritional enrichment of

fresh fruits and vegetables. Calcium carbonate and calcium citrate are the main calcium

salts added to foods in order to enhance the nutritional value (Brant, 2002). The

awareness of consumers on the benefits of calcium is relatively high. The calcium

content in the diet is critical in most stages of life (Gras et al., 2003). Other forms of

calcium used in the food industry are calcium lactate, calcium chloride, calcium

phosphate, calcium propionate and calcium gluconate, which are used more when the

objective is the preservation and/or the enhancement of the product firmness (Alzamora


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et al., 2005; Luna-Guzman & Barrett, 2000; Manganaris et al., 2007). CaCl2 has been

widely used as preservative and firming agent in the fruits and vegetables industry for

whole and fresh-cut commodities (Chardonet et al. 2003; Martin-Diana et al., 2007).

Calcium binds to the cell wall and polygalacturonic acid residues of the middle

lamella and thus improving structural integrity (Van-Buren, 1979). The screening of the

literature reveals that many research articles have been published dealing with the

CaCl2 application on fruits and vegetables. As Garcia et al. (1996) reported that

calcium is involved in maintaining the textural quality of produce since calcium ions

from cross-links or bridges between free carboxyl groups of the pectin chains, resulting

in strengthening of the cell wall. Chardonnet et al. (2003) studied the effect of CaCl2 on

fruit firmness after the harvest of whole apples. Mahamud et al. (2008) reported that

postharvest infiltration of calcium at 2.5% has the potential to control disease

incidence, prolong the storage life and preserve valuable attributes of postharvest

papaya, presumably because of its effects on inhibition of ripening and senescence

process and loss of the fruit firmness of papaya. Chuni et al. (2010) studied the effect

of calcium on cell wall enzyme activities of fresh-cut red flesh dragon fruit (Hylocereus

polyrhizus). Effect of calcium chloride treatments on quality characteristics of loquat

fruit during storage is explained by Akhtar et al. (2010). Further Chen et al. (2011)

examined effects of CaCl2 treatment on quality attributes and cell wall pectins of

strawberry fruit. Calcium chloride extends the keeping quality of fig fruit (Ficus carica

L.) during storage and shelf-life is studied by Irfan et al. (2013).

2.3.2. Salicylic Acid (SA):

Salicylic acid (SA) is endogenous signal molecules, playing pivotal roles in

regulating stress responses and plant developmental processes including heat

production or thermogenesis, photosynthesis, stomatal conductance, transpiration, ion

uptake and transport, disease resistance, seed germination, sex polarization, crop yield

and glycolysis (Klessig & Malamy, 1994). Salicylates delay the ripening of fruits,

probably through inhibition of ethylene biosynthesis or action, and maintain

postharvest quality (Srivastava & Dwivedi, 2000). For many years synthetic fungicides

were used to control postharvest decay but, the public concerns about fungicide

residues in fresh horticultural crops and the harmful effects of chemicals on human

health and environment have caused scientists to search for new alternatives to

chemical fungicides (Babalar et al., 2007). Recent studies have shown that SA can be


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introduced as a potent alternative to chemicals (Asghari & Aghdam, 2010). Exogenous

application of SA at nontoxic concentrations to susceptible fruits and vegetables could

enhance resistance to pathogens and control postharvest decay (Babalar et al., 2007;

Asghari et al., 2007 & 2009).

Several researchers have published research articles dealing with the impact of

pre- and post-harvest application of SA on postharvest physiology of horticultural

crops. According to Srivastava and Dwivedi (2000), SA delayed the banana fruit

ripening. They found that SA treatment decreases fruit softening, pulp/peel ratio,

reducing sugar content, invertase activity and also respiration rate. Zhang et al. (2003)

reported a positive correlation between fruit free SA content and firmness in kiwifruit

during ripening. It has been demonstrated that SA decreases ethylene production and

inhibits cell wall and membrane degrading enzymes such as polygalacturonase (PG),

lipoxygenase (LOX), cellulase and pectin methyl esterase (PME) leading to decreasing

the fruit softening rate (Srivastava & Dwivedi, 2000; Zhang et al., 2003). Some

researchers indicated that SA also exhibits direct antifungal effects against pathogens.

According to the result of Qin et al. (2003), SA significantly reduced the incidence of

blue mould (P. expansum) and alternaria rot (A. alternata) in sweet cherry without any

surface injury.

SA in a concentration dependent manner from 1 to 2 mmol L-1

effectively

reduced fungal decay in Selva strawberry fruit as studied by Babalar et al. (2007).

Postharvest treatment of sweet cherry fruits with SA significantly inhibited CAT

activity, but stimulated the activity of SOD and POD, indicated that SA directly or

indirectly activates antioxidant enzymes (Tian et al., 2007). Postharvest treatment of

table grapes with SA before coating with chitosan significantly enhanced the efficacy

of coating and decreased fruit decay (Asghari et al., 2009). Shafiee et al. (2010)

described that addition of SA to nutrient solution combined with postharvest treatments

improved postharvest fruit quality of strawberry. Rao et al. (2011) reported that the SA

and CaCl2 treatments may aid in delaying the softening process, enhancing the keeping

quality while retaining the nutritional quality of sweet peppers more than that of control

fruits in both the storage conditions (25⁰C and 10⁰C). Pre- and postharvest SA

treatments alleviate internal browning and maintain the quality of winter pineapple

fruit, as explained by Lu et al. (2011). Tareen et al (2012) described that SA treatment

significantly maintained the higher level of ascorbic acid and total phenols. In their


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studies they reported that SA at 2.0 mmol L-1

concentration could be used

commercially to preserve peach fruits for up to five weeks without any spoilage. Lolaei

et al. (2012) studied that Pre- and postharvest treatment of SA caused less weight loss,

decay and higher vitamin C and redness than the control strawberry. Further Lolaei et

al. (2012) stated that SA treatment delayed the onset of the climacteric peak of

respiration and also inhibited respiration and ethylene production and increased its

storekeeping quality. Postharvest SA treatment enhances antioxidant potential of

cornelian cherry fruit, as studied by Dokhanieh et al. (2013).

2.3.3. Gibberellic Acid (GA3) and Naphthalene Acetic Acid (NAA):

The exogenous application of various plant bioregulators to different stages of

developing fruits as well as their endogenous levels has highlighted their importance

for fruit development and quality characteristics, as reported by Srivastava & Handa

(2005). Most of these substances are used to control ripening date, improve fruit quality

and increase productivity, thereby increasing the income and the revenues of farmers

(Shafat & Shabana, 1980; Amorós et al., 2004). The discovery of plant hormones and

their ability to regulate all aspects of growth and development were defining moments

in horticulture (Greene, 2010). NAA was found to increase fruit size, weight and delay

ripening of dates (Aboutalebi & Beharoznam, 2006). The treatment with NAA delayed

ripening and anthocyanins accumulation, and decreased PG activity (Villarreal, 2009).

GA3 is a naturally occurring plant growth regulator which may cause a variety of

effects including the stimulation of seed germination in some cases. GA3 is one of the

most important growth stimulating substances used in agriculture since long ago. It

may promote cell elongation, cell division and thus helps in the growth and

development of many plant species. GA3 retards ripening and senescence of fruits by

delaying the chlorophyll degradation and fruit softening (Vendrell 1970; Khader 1992)

and decreases sugar accumulation, TSS and sugar/acid ratio in banana (Ahmed &

Twigwa 1995). GA3 is reported to decrease ethylene production and reduce flesh

softening, thus delaying fruit ripening and fruit senescence (Gholami et al., 2010).

The literature of review reveals that pre- and postharvest application of

bioregulators has been studied by a number of researchers. Postharvest GA3 dips

maintained peel quality of 'Shamouti' oranges (Goldschmidt & Eilati, 1970) and other

citrus fruits (Monselise, 1979). Moustafa & Seif (1996) and Aljuburi et al. (2000)

evaluated the applications of growth regulators and reported that growth regulators may


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translate their influence in retarding fruit ripening process. It has been reported that

NAA at super-optimal rates for control of preharvest drop may advance ripening

(Curry, 2003) and significantly increased fruit yield (Iqbal et al., 2009). Pila et al.

(2010) reported that the post harvest chemical treatment with GA3, CaCl2 and SA has

the potential to control decaying incidence, prolong the storage life and preserve the

valuable attributes of tomato, presumably because of its effect on inhibition of ripening

and senescence processes. The increase in fruit total chlorophyll, TSS and TS, RS and

NRS at rutab or tamar stage and the decrease in TA at rutab stage, as well as the

decrease in fruit carotene content at rutab stage and in fruit acidity at tamar stage

obtained by NAA and GA3, reported by Kassem et al. (2012).

2.3.4. Oxalic Acid (OA) and Boric Acid (BA):

Oxalic acid (OA) is natural identical antibrowning agent and Generally

Recognized as Safe (GRAS) (Suttirak & Manurakchinakorn, 2010). OA’s application

for food preservation has received much attention, as it has been shown not only to be

an anti-browning agent for harvested vegetables (Castaner et al., 1997), banana slices

(Yoruk et al., 2002), and litchi fruit (Zheng & Tian, 2006), but also to be available as a

natural antioxidant in the natural and artificial preservation of oxidized materials

(Kayashima & Katayama, 2002). OA is the most effective antibrowning agent on apple

slices, (Son et al, 2001). Pre-storage OA treatment extends the storage time and

decreases the incidence of mango fruit decay (Zheng et al., 2005). It also contributes in

higher fruit firmness, lower respiration rate, increased activities of antioxidant enzymes

(Zheng & Tian, 2006). Boric acid inhibits the ethylene production, ripening and disease

incidence (Wang & Morris, 1993).

The survey of literature further manifests that many research articles have been

published dealing with the application of OA and BA on fruits. Tian et al. (2006)

reported that OA inhibited the progress of Alternaria rot in harvested pear fruit due to

inducing an increase in defense-related enzymes such as POD, PPO and PAL. Abl El-

Motty et al. (2007) reported that apricot fruit sprayed with 0.5% BA and stored at 0⁰C

exhibited better yield and quality after 40 days of storage. The effects of OA could

contribute to maintaining the membrane integrity and delaying the fruit ripening

process. Increased activities of POD, SOD, and PPO might also possibly be of benefit

to disease resistance during storage (Zheng et al., 2007).


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2.4. Edible Coatings:

Edible coatings have long been used to retain quality and extend shelf life of

some fresh fruits and vegetables, such as citric fruits, apples and cucumbers (Baldwin

et al., 1996; Li & Barth, 1998). Fruits or vegetables are usually coated by dipping in or

spraying with a range of edible materials, so that a semipermeable membrane is formed

on the surface for suppressing respiration, controlling moisture loss and providing other

functions (Ukai et al., 1976; Thompson, 2003b). Most fruits and vegetables possess a

natural waxy layer on the surface, called cuticle. This waxy layer generally has a low

permeability to water vapor. Applying an external coating will enhance this natural

barrier or replace it in cases where this layer has been partially removed or altered

during postharvest handling or processing. Coatings provide a partial barrier to

moisture and gas exchange, improve the mechanical handling property through helping

maintain structural integrity, retain volatile flavor compounds, and carry other

functional food ingredients (Lin & Zhao, 2007).

The growing demand for high quality, ready-to-eat food products with a long

shelf life contributes to the development of new processing technologies, which ensure

that the product’s natural properties and appearance are not significantly affected

(Guilbert et al., 1996). There is a growing interest in edible coatings due to factors such

as environmental concerns, new storage techniques and market development for under-

utilized agricultural commodities. Edible coatings and films prepared from

polysaccharides, proteins and lipids have a variety of advantages such as

biodegradability, edibility, biocompatibility, appearance and barrier properties (Perez-

Perez et al., 2006). In general, edible coatings consist of a thin layer of material which

is formed around the food products as film or which is formed outside of the product

and placed on or between its components (Krochta & de Mulder-Johnston, 1997).

Edible coatings may be applied directly on the surface as additional protection to

preserve product quality and stability (Kokoszka & Lenart, 2007). Any type of material

used for enrobing (i.e. coating or wrapping) various food to extend shelf life of the

product that may be eaten together with or without further removal is considered as an

edible film or coating (Pavlath & Orts, 2009). Two of the most important advantages of

this technology are the reduction of synthetic packaging waste and the incorporation of

preservatives and other functional ingredients into biodegradable raw materials

obtained from natural sources. The latter is in response to the growing demand for safe,


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healthy foods as well as to the increasing concerns over the environment (Vargas et al.,

2008).

Items which are edible should be generally recognized by qualified experts as

being safe under conditions of its intended use, with amount applied in accordance with

good manufacture practices. These food-safe materials must typically are approved for

the Food and Drug Administration (FDA) (Pavlath and Orts, 2009). The United States

is generally considered the leader in worldwide food regulation; thus, when possible,

approval rating based on the U.S. Food and Drug Administration Federal Code of

Regulations (US FDA, 1966) is also given. Generally recognized as safe (GRAS) status

covers direct food additives for their intended use at a quantity not to exceed the

amount reasonably required to accomplish the intended physical, nutritional, or other

technical effect in food, that are of appropriate food grade, and used with good

manufacturing practices (GMP) (US FDA, 1966). However, GRAS status does not

guarantee complete product safety, especially for consumers who have food allergies or

sensitivities, such as lactose intolerance (milk) and celiac diseases (wheat gluten).

Biopolymers such as lipids, polysaccharides and proteins, alone or in combinations,

have been formulated to produce edible coatings (Ukai et al., 1976; Kester & Fennema,

1986). Selection of coating materials is generally based on their water solubility,

hydrophilic and hydrophobic nature, easy formation of coatings, and sensory properties

(Lin & Zhao, 2007). The mechanism by which the coatings retain the quality of fruit

and vegetable is because they create a physical barrier to gases, since they reduce O2

availability and increase CO2 concentrations, producing a MA (Avena-Bustillos et al.,

1997).

2.4.1. Polysaccharide-based Coatings:

Polysaccharides that have been evaluated or used for forming films and coatings

include starch and starch derivatives, cellulose derivatives, alginates, carrageenan,

various plant and microbial gums, chitosan, and pectinates; they were reviewed by

Nisperos-Carriedo (1994), Krochta & Mulder-Johnston (1997), and Debeaufort et al.

(1998). These coatings can be utilized to modify the internal atmosphere, thereby

reducing respiration of fruits and vegetables (Motlagh & Quantick 1988; Nisperos-

Carriedo & Baldwin 1990).

Starch, the reserve polysaccharide of most plants, is one of the most abundant

natural polysaccharides used as food hydrocolloid (Narayan, 1994) because of its wide


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range of functionality and relative low cost. Cellulose is the structural material of plant

cell walls (Nisperos-Carriedo, 1994). The most common commercially produced

cellulose derivatives are carboxymethyl cellulose (CMC), methyl cellulose (MC),

hydroxypropyl cellulose (HPC), and hydroxypropylmethyl cellulose (HPMC).

Alginates are the major structural polysaccharides of brown seaweed known as

Phaeophyceae (Sanderson, 1981). Alginates possess good film-forming property,

producing uniform, transparent, and water soluble films. Carrageenan, extracted from

several red seaweeds, mainly Chondrus crispus (Whistler & Daniel, 1985) and a

complex mixture of several polysaccharides, is another potential coating material for

fruits and vegetables. Other gums, including exudate gums (gum arabic or acacia gum

and gum karaya) and microbial fermentation gums (xanthan gum) have also been

studied as coating materials for fruits and vegetables. Chitosan, a linear polymer of 2-

amino-2-deoxy-ß - D-glucan, is a deacetylated form of chitin, a naturally occurring

cationic biopolymer (Davis et al., 1988; Tharanathan & Kittur 2003).

Ripening and quality changes in mango fruit as affected by coating with edible

film is elucidated by Carrillo-Lopez et al. (2000). Chitosan has been one of the most

promising coating materials for fresh produce because of its excellent film-forming

property, broad antimicrobial activity, and compatibility with other substances, such as

vitamins, minerals and antimicrobial agents (Li et al., 1992; Park & Zhao, 2004;

Durango et al., 2006; Chien et al., 2007; Ribeiro et al., 2007). Aloe vera is a tropical

and subtropical plant that has been used for centuries for its medicinal and therapeutic

properties (Eshun & He, 2004). A. vera gel-based edible coatings have shown to

prevent loss of moisture and firmness, control respiratory rate and maturation

development, delay oxidative browning and reduce microorganism proliferation of

sweet cherries (Martinez-Romero et al., 2006) and table grapes (Valverde et al., 2005).

The perusal of literature manifests that the application of polysaccharide based

edible coatings on postharvest quality of horticultural commodities has been studied by

several researchers. A polysaccharide-based composite coating formulation for shelf

life extension of fresh banana and mango is reported by Kittur et al. (2001). The 2%

alginate and 5% gelatin coatings significantly reduced weight loss, maintained fruit

firmness and freshness in apple fruit, as studied by Moldao-Martins et al. (2003). The

effect of edible coatings on water and vitamin C loss of apricots (Armeniaca vulgaris

Lam.) and green peppers (Capsicum annum L.) is reported by Ayranci & Tunc (2004).


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A commercial edible coating formulation based on CMC and sucrose fatty acid esters,

named semperfreshTM

, has been applied to pears (Zhou et al., 2008), cherries (Yaman

& Bayondirli, 2002) and many other fruits. Published literature reveled that application

of cactus-mucilage coatings leads to increased strawberry shelf life (Del-Valle et al.,

2005). Peach fruit coated with 1% chitosan + 0.5% CaCl2 + polyethylene package +

intermittent warming treatment significantly inhibited POD and PG activities, kept

vitamin C at a high level and reduced fruit sensitivity to chilling injury (Ruoyi et al.,

2005). Quality of cold-stored strawberries as affected by chitosan-oleic acid edible

coatings is explained by Vargas et al. (2006).

Chitosan strongly inhibited spore germination, germ tube elongation and

mycelial growth of Botrytis cinerea and Penicillium expansum in vitro, and damaged

the plasma membranes of spores of both pathogens. Chitosan treatment induced a

significant increase in the activities of PPO, POD and enhanced the content of phenolic

compounds in tomato fruit, as revealed by Liu et al. (2007). Optimization of edible

coating composition to retard strawberry fruit senescence is explained by Ribeiro et al.

(2007). Physiological responses and quality attributes of table grape fruit to chitosan

preharvest spray and postharvest coating during storage are studied by Meng et al.

(2008). Application of pectin, plant gum and starch coating for improvement of quality

and shelf life of raisins is reported by Ghasemzadeh et al. (2008). Shelf life extension

of peaches through sodium alginate and methyl cellulose edible coatings is reported by

Maftoonazad et al. (2008).

Apple fruit coated with jojoba wax, soy gum, glycerol and gum arabic (GA)

showed a significant delay in the change of weight loss, firmness, titratable acidity

(TA), total soluble solids (TSS), decay and colour during cold storage compared to

uncoated ones, as explained by El-Anany et al. (2009). The edible coatings CMC and

whey protein isolate seemed to have a beneficial impact on white asparagus spears

quality retention during refrigerated storage by retarding their weight loss and

maintaining the higher quality (Tzoumaki et al., 2009). Effects of calcium and chitosan

treatments on controlling Anthracnose and postharvest quality of papaya (Carica

papaya L.) are elucidated by Eryani-Raqeeb et al. (2009). Interactive effects of relative

humidity, coating method and storage period on quality of carrot (cv. Nantes) during

cold storage is demonstrated by Rashidi & Bahri (2009). The antimicrobial activity of

films containing 15% guar gum (GG) was comparable to chitosan films against


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Escherichia coli and Staphylococcus aureus. Influence of gamma-irradiation, growth

retardants and coatings on the shelf life of winter guava fruits (Psidium guajava L.) is

examined by Pandey et al. (2010). Composite films obtained from chitosan and GG

reduced environmental problems associated with synthetic packaging (Rao et al.,

2010). Edible coatings viz. zein, gluten and chitosan prolonged the shelf life of

strawberries by prohibiting microbial inhibition and controlling weight loss, when

compared to uncoated strawberries as described by Rehman et al. (2010). Gum arabic

as a novel edible coating for enhancing shelf life and improving postharvest quality of

tomato is examined by Ali et al. (2010). Polysaccharide from Anacardium occidentale

L. tree gum (Policaju) as a coating for Tommy Atkins mangoes is studied by Souza et

al. (2010).

Evaluation of effectiveness of three cellulose derivative-based edible coatings

on changes of physico-chemical characteristics of ‘Berangan’ banana (Musa sapientum

cv. Berangan) during ambient storage is studied by Malmiri et al. (2011). Postharvest

conservation of organic strawberries coated with cassava starch and chitosan is

demonstrated by Campos et al. (2011). Effect of skin coatings on prolonging shelf life

of kagzi lime fruits (Citrus aurantifolia Swingle) is reported by Bisen et al. (2012).

Shellac and aloe-gel-based surface coatings maintained the keeping quality of apple

slices, as explained by Chauhan et al. (2011). Pitaya fruit treated with 3% chitosan had

the least attributes of stomatal conductance, stomatal size in terms of stomatal width,

stomatal length and stomatal aperture. In addition, treatment of 3% chitosan also

showed the lowest wilting percentage and gave the maximum postharvest life, as

studied by Chutichudet & Chutichhudet (2011). Ali et al. (2011) suggested that

chitosan, as a preservative material, delayed the ripening process by inhibiting the

respiration rate in the Eksotika II papaya fruit. Optimization of an edible coating

formulation based on chitosan on ‘Sekaki’ papaya (Carica papaya Cv. Sekaki) to

reduce water loss and delay changes in pH, TSS and firmness is explained by Osman et

al. (2011). Effects of chitosan on increase of antioxidant ability might be beneficial in

delaying ripening process in guava fruit during cold storage, as suggested by Hong et

al. (2012). Effects of alginate edible coating on the quality preservation of four plum

cultivars during postharvest storage is studied by Valero et al. (2013). Benitez et al.

(2013) reported that Aloe vera based edible coatings improve the quality of minimally

processed ‘Hayward’ kiwifruit. Effectiveness of postharvest treatment with chitosan

and other resistance inducers in the control of storage decay of strawberry is examined


Page 26

by Romanazzi et al. (2013). Kou et al. (2013) demonstrated that chitosan, CaCl2 and

pullulan coatings maintained quality of pear and control decline of antioxidant activity.

2.4.2. Protein-based Coatings:

Edible coatings made of plant proteins (such as zein, soy protein, and wheat

gluten) and animal proteins (such as milk protein) exhibit excellent oxygen, carbon

dioxide, and lipid-barrier properties, particularly at low RH (Gennadios et al., 1994;

Baldwin & Baker, 2002). Various types of protein have been used as edible films.

These include gelatin, casein, whey protein, corn zein, wheat gluten, soy protein, mung

bean protein, and peanut protein (Gennadios et al., 2006; Bourtoom, 2008). Protein

based coatings have a variety of applications in the pharmaceutical industry and widely

used to prolong the shelf life of food products (Irissin-Mangata et al., 2001). Better

barrier properties to gases are revealed by the coatings made out of proteins;

nevertheless, the water vapour resistance is lower due to their hydrophilic nature

(Perez-Gago & Krochta, 2002). The addition of compatible plasticizers can improve the

extensibility and viscoelasticity of the films (Brault et al., 1997; Sothornvit & Krochta

2001). Zein and soy protein are the two major plant origin proteins used as coating

materials for fruits and vegetables. Zein is the key storage protein of corn and

comprises approximately 45% to 50% of the proteins in corn (Shukla & Cheryan

2001).

Soy protein concentrate (SPC) or soy protein isolate (SPI) is extracted from

defatted protein meal and contains 65% to 72% and 90% protein on a dry basis,

respectively (Mounts et al., 1987). Wheat gluten is a general term for water-insoluble

protein of wheat flour which is composed of a mixture of polypeptide molecules,

considered to be globular proteins (Bourtoom, 2008). Milk proteins such as whey

protein and casein are important materials for edible films and coatings based on their

numerous functional properties (Chen, 1995 & 2002; Krochta, 2002). Caseins represent

about 80% of the total milk proteins (Dalgleish, 1989). Gelatin is obtained by

controlled hydrolysis from the fibrous insoluble protein, collagen, which is widely

found in nature as the major constituent of skin, bones and connective tissue (Ross,

1987; Bourtoom, 2008).

The review of literature demonstrated that protein based edible coatings are

applied on several fruit and vegetables. Zein coatings were able to retard ripening of

tomatoes (Park et al., 1994a; 1994b), to maintain the original firmness and colour of


Page 27

broccoli florets (Rakotonirainy et al., 2001). Milk protein coatings prevent oxidative

browning of apples and potatoes, as reported by Tien et al. (2001). Bai et al. (2003a)

stated that zein coating is favourable for gloss and other quality. The effect of corn zein

edible film coating on intermediate moisture apricot (Prunus armenica L.) quality is

reported by Baysal et al., (2010). The application of gelatin-starch coatings delayed the

ripening process of avocados, as indicated by a better pulp firmness and retention of

skin colour and lower weight loss of coated fruit in comparison with control avocados,

as studied by Aguilar-Mendez et al. (2008). Lim et al. (2011) reported that the gelatin

film ensured the lowest weight loss in sweet cherries. Shon & Choi (2011) explained

that SPI coating reduced moisture loss in apples and potatoes. Shelf life of apples

coated with WPC-gellan gum edible coatings is studied by Javanmard (2011). Hassani

et al. (2012) studied that edible coating based on whey protein concentrate-rice bran oil

maintained the physical and chemical properties of the kiwifruit (Actinidia deliciosa).

2.4.3. Lipid-based Coatings:

The lipid-based coatings are very efficient to reduce product dehydration; due to

low polarity and low permeability to water vapor (Kester & Fennema, 1986). Lipids

including neutral lipids, fatty acids, waxes and resins are the traditional coating

materials for fresh produce, showing the effectiveness in providing moisture barrier and

improving surface appearance (Hagenmaier & Baker 1995; Morillon et al., 2002).

These coatings have some limitations, such as poor mechanical properties (Garcia et

al., 2000). The gas permeability of shellac and several experimental coating

formulations, including candelilla wax and shellac carnauba were measured by Bai et

al. (2003b). Very abundant reviews on the applications of different types of lipid-based

coatings for fruits and vegetables have been done by Baldwin (1994), Baldwin et al.

(1997), Min & Krochta (2005) and Lin & Zhao (2007). Shellac coating was more

effective in reducing the respiration rate and weight loss and in maintaining the quality

of pears than semperfresh and carboxymethyl coatings, as reported by Zhou et al.

(2008). Postharvest quality of Hunghua pears is maintained by shellac coating as stated

by Zhou et al. (2011).

2.4.4. Emulsion and Bilayer Coatings:

Recent emphasis and interest in the development of edible coatings have been

focused on composite or bilayer coatings, such as integrating proteins, polysaccharides,

and/or lipids together for improving functionality of the coatings. This is based on the


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fact that each individual coating material has some unique, but limited, functions and

that together their functionality can be enhanced (Krochta, 1997). Composite

film/coating can be categorized as a bilayer or a stable emulsion. For bilayer composite

films/coatings, lipid generally forms an additional layer over the polysaccharide or

protein layer, while the lipid in the emulsion composite films/coatings is dispersed and

entrapped in the matrix of protein or polysaccharide (Callegarin et al. 1997). In general,

bilayer films/coatings are more effective water vapor barrier than emulsion

films/coatings due to the existence of a continuous hydrophobic phase in the matrix,

and their moisture-barrier property can be improved by increasing the degree of lipid

saturation and chain length of fatty acids (Kamper & Fennema, 1984a & 1984b;

Hagenmaier & Shaw 1990).

The improved moisture-barrier properties of composite coatings have made

them promising candidates for coating fresh and minimally processed fruits and

vegetables. HPMC–lipid composite coatings consisting of beeswax or shellac

significantly reduced texture loss and internal breakdown of plums (Perez-Gago et al.

2003). Effect of edible wheat gluten-based films and coatings on refrigerated

strawberry (Fragaria ananassa) quality is studied by Tanada-Palmu & Grosso (2005).

An emulsion coating with CMC as the hydrophilic phase and paraffin wax, beeswax, or

soybean oil as the hydrophobic phase also extended shelf life and reduced weight loss

of apples, peaches, and pears (Togrul & Arslan, 2004; 2005). Research article

published by Maqbool et al. (2011) revealed that banana fruit coated with 10% GA plus

1% CH composite coating had very fewer cracks and smooth surface. Further Maqbool

et al. suggested that 10% GA plus 1% CH composite coating can be used commercially

for extending the storage life of banana fruit up to 33 days.

2.4.5. Incorporation of Functional Ingredients into Edible Coating:

A potential viable alternative for fruit and vegetable preservation is the usage of

multicomponent edible coatings, which may be produced with suitable ingredients for

the product to provide the desired barrier protection and also serving as vehicles to

incorporate specific additives that enhance their functionality, such as antioxidants,

dyes, antimicrobials, nutraceuticals, flavor, color agents, which can avoid the pathogen

growth on the surface and enhance food quality, stability and safety of fruits and

vegetables (Cagri et al., 2004; Martin-Belloso et al., 2005; Lin & Zhao, 2007; Ramos-

García et al., 2010). Common antimicrobial agents used in food systems such as


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benzoic acid, sodium benzoate, sorbic acid, potassium sorbate (PS) and propionic acid.

Garcia et al. (1998a) studied that starch-based coatings containing PS were effective in

reducing the microbial growth and extending the storage life of strawberry. In addition,

chitosan coatings containing potassium sorbate were shown to increase antifungal

activity against the growth of Cladosporium and Rhizopus on fresh strawberries (Park

et al., 2005). Chitosan-based coating containing α-tocopheryl acetate significantly

delayed the colour change of fresh and frozen strawberries (Han et al., 2004).

Postharvest control of pericarp browning of litchi fruit (Litchi chinensis Sonn cv Kwai

Mi) by treatment with chitosan and organic acid is reported by Joas et al. (2005).

Essential oils may be considered as the antimicrobial agents incorporated into the

coating formulations (Rodríguez et al., 2005; Rojas, 2006).

Effects of cinnamon extract, chitosan coating, hot water treatment and their

combinations on crown rot disease and quality of banana fruit are studied by Win et al.

(2007). Curative and preventive activity of hydroxypropyl methylcellulose-lipid edible

composite coatings containing antifungal food additives to control citrus postharvest

green and blue molds is reported by Valencia-Chamorro et al. (2009). Features and

performance of edible films, obtained from whey protein isolate formulated with

antimicrobial compounds is elucidated by Ramos et al. (2011). Navarro-Tarazaga et al

(2007) reported a new composite coating containing hydroxypropylmethyl cellulose,

beeswax and shellac for ‘Valencia’ oranges and ‘Marisol’ tangerines. Xing et al. (2011)

studied the effect of chitosan coating enriched with cinnamon oil on qualitative

properties of sweet pepper (Capsicum annum L.). Xing et al. (2011) further reported

that chitosan in combination with oil coating maintained the quality and extended shelf

life of sweet pepper, thus this composition can be considered for commercial

application during storage and marketing. Chitosan–lemon essential oil coatings can be

an alternative method with which strawberry shelf life can be extended as explained by

Perdones et al. (2012).

Edible coating is an excellent vehicle to enhance the nutritional value of fruits

and vegetables by carrying basic nutrients and/or nutraceuticals that are lacking or are

present in only low quantity in fruits and vegetables. The development of chitosan

coatings containing high concentrations of calcium, zinc, or vitamin E also provided

alternative ways to fortify fresh fruits and vegetables that otherwise could not be

accomplished with common processing approaches (Park & Zhao, 2004). A mixed


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coating with hydroxypropylmethyl cellulose, glycerol and stearic acid was developed

by Perez-Gago et al. (2003), aiming to have it implemented in mandarian fruits.

From the foregoing account of review of literature it is clear that there is a great

scope not only to reduce the postharvest losses of fruits and vegetables, but also to

improve or retain the nutritional quality of harvested horticultural products by

employing appropriate technologies, including chemical treatments as well as eco-

friendly edible coatings, which are considered as Generally Regarded as Safe (GRAS).

review of literature -...

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