Use of Chemicals for Shelf-Life Enhancement of Fruits

ASANDA MDITSHWA'", LEMBE S. MACWAZA'-2,

SAMSON Z. TESFAY1, and NOKWAZI C. MBILI3

'Department of Horticultural Science, School of Agricultural,

Earth and Environmental Sciences, University of KwaZulu-Natal, Private Bag XOI, Pietermaritzburg 3201, South Africa

2Department of Crop Science, School of Agricultural,

Earth and Environmental Sciences, University of KwaZulu-Natal, Private Bag XOI, Pietermaritzburg 3201, South Africa

3 Department of Plant Pathology, School of Agricultural,

Earth and Environmental Sciences, University of KwaZulu-Natal, Private Bag X01, Pietermaritzburg 3201, South Africa

*Corresponding author. E-mail: This email address is being protected from spam bots, you need Javascript enabled to view it

ABSTRACT

The development of physiological and pathological disorders during cold chain and storage has an enormous effect on shelf-life of fruits. Increased weight loss as well as the loss of firmness also reduce the shelf-life and overall quality of fruits. Chemicals are commonly used as postharvest phytosanitary treatment in the fruit industry. However, recent research has highlighted the influence of chemical treatments on physiological and physicochemical quality attributes. This chapter presents a comprehensive review on the effect of chemical treatments on enhancing the shelf-life of fruits. Fruits treated with chemicals have shown resistance to microbial growth and decay. Retention of physicochemical quality attributes, such as firmness and color, has also been reported in fruits treated with chemicals. Also, the use of chemical treatments has been closely linked to lower incidences of physiological disorders including bitter pit and internal browning. Although chemical treatments retain postharvest quality and enhance the overall shelf- life of fruits, but there are still some areas that warrant further research. For instance, while chemicals control some physiological disorders, attempts should be made to explain the mechanism of action against such disorders. Health concerns have been raised regarding the use of synthetic chemicals on food stuff; there is a need to adopt more environmentally friendly chemicals for enhancing shelf-life of fruits.

INTRODUCTION

Fruits are important source of nutrients including vitamins, carbohydrates, minerals, dietaiy fiber, phenolics, and antioxidants. Inadequate consumption of fresh fruits is closely linked to various chronic diseases such as certain types of cancer, stroke, and cardiovascular (Joshipura et al., 2001; Lock et al., 2005). Studies by Lock et al. (2005) estimated a global mortality of 2.635 million deaths per annum attributable to insufficient consumption of fruits and vegetables. It is projected that increasing fruit and vegetable consumption to at least 600 g/day/person may reduce the global disease burden by 1.8% while also decreasing heart diseases and stroke by 31% and 19%, respectively (Lock et al., 2005). Interestingly, recent consumer surveys have shown that, following the increased awareness of health benefits associated with fresh produce, the worldwide consumption of fruits has significantly increased over the years (Zheng et al., 2013).

Accordingly, the increased consumption of fruits has also triggered an increase in global production (Olaimat and Holley, 2012). However, fresh fruits are highly perishable during storage and shelf-life. The high water content and very active metabolism increase their susceptibility to microbiological spoilage thereby reducing quality and shelf-life (Rodriguez et al., 2015; Mahajan et al., 2017). In 2008, the World Packaging Organization (WPO) estimated that 10% of fruits and vegetables shipped to the European Union are discarded due to unacceptable postharvest quality and decay (Opara and Mditshwa, 2013). More recently, Food and Agricultural Organization (FAO, 2011) reported that one-third of food intended for human consumption is wasted annually. Firmness loss, fungal infections, physiological disorders, mechanical injuries, such as bruising, are some of the key causes of the reduced quality and shelf-life of fruits (Fig. 10.1). Generally, consumers prefer fruits of high quality without any defects. Fruits that are characterized by poor color development and firmness loss are often rejected by consumers leading high postharvest losses. Immature and overripe fruits have veiy short shelf-life attributable to shriveling, mechanical damage, and mealiness.

Postharvest factors such as temperature and relative humidity (RH) have an intrinsic effect on shelf-life of fruits. Quality deterioration of perishable fresh produce is often high in warm and humid climatic regions of developing countries compared with much cooler and dry environments (Mahajan et al., 2017). Maintaining the quality, extending shelf-life, and reducing postharvest losses are globally one of the pressing issues in the fresh fruit industry. To this effect, through technological advancements, various novel postharvest technologies such as controlled atmosphere (CA), modified atmosphere packaging (MAP), heat and chemical treatments have been developed over the years. Moreover, the potential of emerging postharvest treatments in extending the shelf-life of various fruits has been tested. This chapter focuses on the use of synthetic chemicals such as Methyl salicylate, potassium silicate, 1-methylcyclopropene (1-MCP), and diphenylamine (DPA) to maintain the postharvest quality and extend the shelf-life of fruits.

Postharvest quality attributes affecting the shelf-life of various fruits

FIGURE 10.1 Postharvest quality attributes affecting the shelf-life of various fruits.

FACTORS AFFECTING THE SHELF-LIFE OF FRUITS

There is a number of factors affecting the shelf-life and the overall quality of fresh fruits. Intrinsic factors such as pH, water activity and extrinsic factors including storage temperature and RH have interactive effects on shelf-life of various fruits. For instance, low water activity during storage and shelf-life is known for reducing microbial growth. Due to its effect on respiration rate, regulating storage temperatures can play a critical role in extending the shelf-life of fruits. Various fruits have optimum storage temperature for slowing the ripening process. The ripening of climacteric fruits is characterized by increased ethylene production and cellular respiration, a result, such fruits continue to ripen after harvest. Ethylene is a very important plant- growth regulator, exposing fruits to high ethylene concentrations, increases ripening, and shortens shelf-life (Steele, 2004). Moreover, with its use of available sugars and organic acids, a continuation of respiration results to rapid senescence (Rodriguez et al., 2015).

Fruit shriveling resulting from moisture loss is quite prevalent in high temperature storage and it is closely linked to poor fruit quality (Thompson, 2008). Moisture loss is one of the first signs of quality deterioration noticed by consumers. Consequently, postharvest technologies should also be aimed at reducing the respiration rate and ethylene production. Low cold storage is one of the strategies used to maintain quality and extend shelf-life of fruit. For instance, Shin et al. (2008) reported low firmness and overall quality in “Jewel” strawberries stored at 10°C than fruit stored at 3°C. Ding et al. (1998) studied the effect of storage temperature of the quality of loquat fruit. Their results demonstrated that weight loss increased with increasing temperatures. Notably, respiration rate and ethylene production were significantly reduced in lower storage temperature. However, fruits originating from tropical and subtropical regions are highly susceptible to storage disorders such as chilling injury and freezing damage. Watada and Qi (1999) estimated that about 40% of produce in fresh produce markets is sensitive to chilling temperatures and this often leads to shorter the shelf-life. Studies by Gonzalez-Aguilar et al. (2000) demonstrated that storing “Tommy Atkins” mangoes at 7°C for 21 days and five-day shelf-life increases the risk of chilling injury. Similarly, Gine- Bordonaba et al. (2016) showed that low temperatures induced chilling injury and negatively influenced the consumer acceptability of different peach and nectarine cultivars.

RH is another factor that has the intrinsic effect on quality and shelf-life of fruits. For most fruits, RH should be around 90-95% during storage as fresh fruits stored at lower RH such as 60-65% often transpire more and rapidly lose quality (Mditshwa et al., 2017a). Interestingly, some fruits are not affected by RH. For example, storing strawberries at either 65% or 95% RH had no effect on quality (Shin et al., 2008).

EFFECT OF CHEMICAFS ON PHYSICO-CHEMICAF QUAFITY

Postharvest treatments are essential in reducing quality loss and enhancing the shelf-life of fruits. The effect of chemical treatments on the physicochemical quality parameters, such as firmness, color, and weight loss has extensively been reported.

FIRMNESS

Firmness is one of the key attributes affecting the quality and shelf-life of fruits. In fact, the loss of firmness is the most noticeable change during shelf- life and it is closely linked to water loss and degradation of the cell wall. Developing novel, rapid, and non-destructive technologies for assessing fruit firmness have been one of the research focused in recent years. Fruit firmness is influenced by an array of storage conditions particularly temperature. Cell wall composition has an enormous influence on fruit firmness. Generally, as fruit firmness decreases, pectin polysaccharides are slowly depolymerized and degraded (Liu et al., 2017). Enzymatic activities during storage have also been strongly linked to firmness loss. Notably, polygalacturonase, pectinesterase, and pectolytic enzyme activities have been marked as one of the major factors governing fruit firmness (Hobson, 1965; Ketsa and Daengkanit, 1999). A strong positive correlation between pectolytic activity and firmness has been reported. Vicente et al. (2007) reported that hemicellulose levels decreased in softening blueberries (Vaccimum corymi- bosum). On the other hand, Ketsa and Daengkanit (1999) reported much lower p-galactosidase and cellulase levels in mature durian arils (Dario zibethinus Murr.) compared to immature fruit. These are some of the key enzymes whose activity, due to their enormous effect on firmness, must be monitored and possibly reduced during cold storage and shelf-life.

Various postharvest chemical treatments have shown to be highly effective in retaining firmness of fruits (Table 10.1). For example, Benassi et al. (2003) investigated the potential of 1-MCP to prolong the shelf-life and reduce firmness loss of custard apples (Aunoua squamosal L.) stored at 25°C for four days. Their results demonstrated that fruits treated with 810 nL/L had higher firmness compared to the control treatment. Additionally, non-treated fruit together with fruits exposed to lower 1-MCP concentrations such as 30 or 90 nL/L ripened faster. Interestingly, studies by Jiang et al. (2004) on the effect of the postharvest application of 1-MCP on banana quality showed delayed firmness loss in treated fruit. It is hypothesized that

1-MCP inhibits ripening by occupying ethylene-binding receptors. On the other hand, Moggia et al. (2010) linked the reduced firmness loss in DPA treated ‘Granny Smith’ apples to higher membrane stability compared to the control treatment. Recent research has shown that sodium nitroprusside is also effective in reducing firmness loss. Barman et al. (2014) demonstrated that dipping “Chausa” mango fruit in 1.5 rnM sodium nitroprusside solution before storage reduced firmness loss by 43% compared to the untreated fruit during a 3-day shelf-life at 25°C. Interestingly, the activity of pectin methylesterase and polygalacturonase, the key enzymes affecting cell wall and firmness, was remarkably reduced. Calcium chloride (CaCl,) is another postharvest treatment with the enormous effect on fruit firmness. Studies by Garcia et al. (1996) demonstrated that CaCl, postharvest dips minimize firmness loss in “Tudla” strawberries during the shelf-life of three days at 18°C. Recently, higher firmness retention has also been reported in apricots treated with CaCl, before storage (Liu et al., 2017). The authors closely linked the firmness loss of the untreated fruit to disassembled and degraded nanostructures of cell wall pectin and hemicellulose. On the other hand, calcium (Ca) treatments retarded the degradation of these nanostructures. Notably, water- soluble pectin, sodium carbonate-soluble pectin, and hemicellulose levels were much higher in the treated fruits compared to the untreated fruits.

COLOR

Color is one of the most important attributes determining the postharvest quality and influencing the shelf-life of many fruits. Moreover, fruit color plays a critical role in consumer acceptance of the marketed fruit. The concentration of anthocyanins is the key determinant of color in many red-colored fruit (Allan et al., 2008). Palapol et al. (2009) investigated the relationship between anthocyanin composition and fruit color development. Their findings showed higher anthocyanin content on outer pericarp compared to the inner pericarp, moreover, the anthocyanin content increased with color development. Chemical treatments have a significant role on color development during storage and shelf-life. Recent studies by Chen et al. (2015) have shown that adenosine triphosphate (ATP) is highly effective in retaining the color of longan (Dimocarpus longan Lour.) fruit. In their study, it was demonstrated that exposing longan fruit to 0.8 mM of ATP reduces the loss of chlorophyll and anthocyanin during shelf-life.

The effect of postharvest 1-MCP treatment on fruits has extensively been reported. Notably, the treatments have also been shown to reduce color loss. For instance, Hershkovitz et al. (2005) reported greener peel color and longer shelf-life in “Ettinger” and “Pinkerton” avocados treated with 300 nL/L of 1-MCP before storage. The authors attributed the greener color of the treated fruit to reduce chlorophyllase activity and chlorophyll breakdown. Similarly, Jeong et al. (2002) mentioned that “Simmonds” avocados treated with 0.45 pL/L of 1-MCP were greener and had longer shelf-life compared to the untreated fruit. Shafiee et al. (2010) investigated the effect of salicylic acid dips on the postharvest quality of “Camarosa” strawberries. Their findings showed less redness and higher hue angle in strawberries exposed to 2 mM salicylic acid before storage. The lesser redness in treated fruit showed that the ripening process was significantly delayed by the salicylic acid treatment.

WEIGHT LOSS

Fruit weight is another important factor affecting the quality of fruits. It is particularly important for fruits whose market price is directly dependent on weight. Fruits have more than 75% of water, as a result, any storage environment that promotes respiration and moisture loss significantly increases weight loss. Chemical treatments have been shown to affect the weight loss during storage and shelf-life. For instance, Mahajan et al. (2010) reported reduced weight loss after cold storage and three-day shelf-life in “Pathar- nakh” pears exposed to 1000 ppm of 1-MCP before storage. Recently, postharvest application of ATP has been shown reduced weight loss in “Fuyan” longan fruit stored for five days at 28°C (Chen et al., 2015). Notably, the electrolyte leakage of cell membrane rapidly increased during storage; however, it was much lower in ATP treated fruit. It could be hypothesized that the reduced membrane damage of the pericarp in ATP treated fruit directly delays moisture loss thereby reducing weight loss.

Sodium dehydroacetate is one of the commonly used preservations in the food industry. In their study on the effect of sodium dehydroacetate to control postharvest green and gray molds of Ponkan fruits. Duan et al. (2016) also found reduced weight loss rate in the treated fruit. Although many postharvest chemical treatments are known for reducing weight loss during cold storage and shelf-life, contrary findings have also been reported. For instance, Zhu et al. (2015) demonstrated that weight loss is rapidly increased in epibrassinolide treated satsuma mandarins especially during the first six days of storage. While the treatment did not negatively affect the internal quality, these reports indicate the importance of using acceptable concentrations of chemicals. Recent studies have also shown that CaC 1, and methyl salicylate treatments are effective in minimizing weight loss during storage and shelf-life. For instance, Jan et al. (2016) showed that weight loss in “Red Delicious” apples is significantly minimized by 9% CaCl2 dips before storage. Similarly, mass loss was significantly reduced in “Early Lory” sweet cherry fruit exposed to 1 mM methyl salicylate before cold storage (Gimenez et al., 2016).

TABLE 10.1 The Effect of Postharvest Chemical Treatments on Physico-chemical Quality of Fruits.

Physico

chemical

Chemical

Concentration

Fruits

Effect of treatment

References

Firmness

1-MCP

810 nL/L

Custard apple

High

firmness

retention

Benassi et al. (2003)

1-MCP

200 nL/L

Banana

“Zhonggang”

Delayed firmness loss

Jiang et al. (2004)

1-MCP

1000 ppm

Pear

“Patharnakh”

High

firmness

retention

Mahajan et al. (2010)

1-MCP

1 pL/L

Apples “Empire”

Higher

firmness

DeEU et al. (2005)

1-MCP

0.45 pLL

Avocado

“Simmonds”

Reduced firmness loss

Jeong et al. (2002)

CaCl,

1%

Strawberry

“Tudla”

Retained

firmness

Garcia et al. (1996)

CaCl,

1%

Apricots

“Jinhong”

Reduced firmness loss

Liu et al. (2017)

CaCl,

9%

Apples “Red Delicious”

Retained

firmness

Jan et al. (2016)

Diphenyl-

amine

2000 ppm

Apples “Granny Smith”

High

firmness

retention

Moggia et al. (2010)

Methyl

salicylate

1 inM

Cherry “Early Lory”

Higher fruit firmness

Gimenez et al. (2016)

Salicylic acid

2 mM

Strawberry

“Camarosa”

Higher

firmness

Shafiee et al. (2010)

Salicylic acid

2 mM

“Satsuma”

mandarin

Firmness

retention

Zhu et al. (2016)

Salicylic acid

1.2 imnol/L

Sugar apple

Softness was reduced

Mo et al. (2008)

TABLE 10.1 (Continued)

Physico

chemical

Chemical

Concentration

Fruits

Effect of treatment

References

Sodium

dehydroacetate

0.4 g/L

Ponkan fruit

Minimal effect on firmness

Duan et al. (2016)

Sodium

nitroprusside

1.5 inM

Mango “Chausa”

Higher

firmness

Barman et al. (2014)

Color

1-MCP

300 nL/L

Avocados “Ettinger" and “Pinkerton”

Greener peel color

Hershko- vitz et al. (2005)

1-MCP

0.45 pL/L

Avocado

“Simmonds”

More green color

Jeong et al. (2002)

Salicylic acid

2mM

Strawberry

“Camarosa”

Less redness

Shafiee et al. (2010)

Sodium

dehydroacetate

0.4 g/L

Ponkan fruit

Minor effect on coloration

Duan et al. (2016)

Weight

loss

Adenosine

triphosphate

0.8 mM

Longan “Fuyan”

Reduced weight loss

Chen et al. (2015)

Sodium

dehydroacetate

0.4 g/L

Ponkan fruit

Reduced weight loss rate

Duan et al. (2016)

Salicylic acid

2 mM

Strawberry

“Camarosa”

Less weight loss

Shafiee et al. (2010)

24-epibrassi-

nolide

5 mg/L

Satsuma

mandarin

Increased weight loss

Zhu et al. (2015)

Sodium

nitroprusside

1.5 mM

Mango “Chausa”

Less weight loss

Barman et al. (2014)

1-MCP

0.45 pLL

Avocado

“Simmonds”

Less weight loss

Jeong et al. (2002)

CaCl,

9%

Apples “Red Delicious”

Minimized weight loss

Jan et al. (2016)

Methyl

salicylate

1 mM

Cherry “Early Lory”

Reduced mass loss

Gimenez et al. (2016)

 
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