ABSTRACT
Mango (Mangifera Indica L.) is one of the major fruits produced in Kenya mostly for the domestic market, and to a small extend for export markets. Mango is widely adapted to different Agro-Ecological Zones and its production is mainly by smallholder farmers who depend on it for their livelihoods. However, there are many challenges which have inhibited realization of the full potential of mango in Kenya. High postharvest losses estimated to be 40 – 50% is one of the challenges facing mango value chain actors. The high losses result from various factors including poor harvesting practices, pest and diseases, lack of postharvest technologies, among others. Various postharvest technologies such as controlled atmosphere storage, refrigeration, modified atmospheric packaging, among others have been used with great success, but are out of reach for small holder farmers who are resource constrained. Waxing of fruits is an old practice which has been demonstrated to have benefits on various fresh commodities such as avocados, mangos, citrus, apples, loquats, among others. However, application of waxing technologies in mango fruit has not been tried commercially in Kenya. This study was conducted to evaluate the efficacy of two waxing options on prolonging the shelf life of two popular mango varieties in Kenya under different storage conditions. Fruits for the study were harvested from 6 – 10-year-old trees on commercial farms in Machakos County. In the first experiment, ‘ngowe’ and ‘apple’ mango fruits were harvested at mature green stage and transported in padded crates to the postharvest laboratory where they were sorted for uniformity, washed with disinfected water, brushed gently with Decco Clear (food brush sanitizer), dipped in hot water (45-55C) and placed on wire shelves for air drying. Each variety was then batched into five groups for different treatments. The treatments included Shellac wax (3% and 5%, w/w), Mango wax, Mango wax+prochloraz (fungicide) and untreated (control). The fruits were then packed in open carton boxes and stored in different storage conditions including ambient (25C) and simulated commercial cold storage (12C). A random sample of three fruits was taken from the different treatments and storage environment for analysis of attributes associated with ripening. The ripening attributes measured included physiological (respiration and weight loss) and physical (peel/flesh firmness and peel/pulp color).
In the second experiment, the best performing treatment(s) from each storage option in experiment 1 was selected and applied on the mango fruits (‘ngowe’ and ‘apple’) to establish their effect on postharvest quality attributes. The parameters measured included total titratable acidity (TTA), total soluble solids (TSS), total sugars, beta carotene and vitamin C. Completely Randomized Design with factorial arrangement was used as the study design. Results from the study showed waxing to have a significant (p<0.05) effect on shelf life of mango fruits. Waxed fruits had an extended shelf life of 3 and 4 days at ambient storage conditions for ‘ngowe’ and ‘apple’ mango fruits respectively and for 6 days under cold storage (12C) for both varieties. Waxing suppressed the rate of respiration for both mango varieties in the different storage conditions compared to the control. Under ambient storage conditions, untreated ‘apple’ mango fruits had a high respiratory peak of 85.09ml/kg hr (day 10) compared to a low average peak of 51.55ml/kg hr (day 14) for the treated fruits. Weight loss was significantly reduced by waxing. Control ‘apple’ mango fruits under ambient storage conditions lost 12.4% of the initial weight compared to an average of 7.75% weight loss for the treated fruits by end of the storage period. Similarly, in the case of cold-stored fruits, untreated ‘apple’ mango lost 5.5% compared to an average of 3.7% for the treated fruits by end of storage period. Other ripening related physiological and physical changes followed a trend that correlated positively with water loss and respiratory activity. Wax treated fruits maintained relatively higher hue angles (peel and pulp) and higher firmness (peel and pulp) throughout the storage period compared to control fruits.
In the second experiment, results showed waxing to be effective in delaying the rate of loss of the fruit’s quality attributes for both ‘ngowe’ and ‘apple’ mango fruits. Brix levels for the treated fruits remained relatively low especially for the fruits in the cold storage. Control ‘apple’ mango fruits had a high brix level of 20.88 ºbrix by day 15 compared to a lower average level of 19.05ºbrix for the treated fruits, by end of storage period (day 28). The other parameters (total titratable acidity, vitamin C, beta carotene and sugars) for the waxed fruits were also retained longer, showing a positive correlation with water loss and respiration. The results from this study show that waxing is an effective postharvest technology which can be used as an alternative technology to extend shelf life and maintain postharvest quality of mango fruits during storage, transportation or marketing.
Keywords: Cold storage, Ambient, Mango wax, Shellac wax, Shelf life, Postharvest quality.
TABLE OF CONTENTS
DECLARATION ii
DEDICATION iii
ACKNOWLEDGEMENT iv
LIST OF ACRONYMS AND ABBREVIATIONS v
ABSTRACT ix
CHAPTER ONE
1.0 INTRODUCTION
1.2 PROBLEM STATEMENT AND JUSTIFICATION 3
1.2.1 Problem statement 3
1.2.2 Justification 4
1.3 OBJECTIVES 5
1.3.1 General objective 5
1.4. Hypothesis 6
CHAPTER TWO
2.0 LITERATURE REVIEW
2.1 Background information 7
2.2 Production statistics 7
2.3 Physiological and Biochemical changes during mango ripening 8
2.3.1 Color change 8
2.3.2 Flavor, Aroma and TTA 9
2.3.3 Firmness 10
2.3.4 Total Soluble Solids (TSS) 10
2.4 Challenges of mango farming in Kenya 11
2.4.1 Lack of quality Seedlings 11
2.4.2 Poor prices and lack of market information 11
2.4.3 Poor road network and lack of postharvest handling technology 12
2.4.4 Lack of harvesting tools and techniques 12
2.4.5 Wrong maturity indices 13
2.4.6 Postharvest diseases 13
2.4.7 Poor Relative Humidity and Temperature management 14
2.5 Applicable technologies for shelf life extension and postharvest quality preservation of mango fruits 15
2.5.1 Cold storage 15
2.5.2 Controlled Atmosphere Storage (CAS) and Modified Atmosphere Packaging (MAP) 15
2.5.3 1-Methylcyclopropene (1-MCP) 16
2.5.4 Evaporative Cooling Technologies 17
2.5.5 Waxing and Edible Coatings 17
CHAPTER THREE
3.0 MATERIALS AND METHODS
3.1 Experimental materials 21
3.1.1 Fruit samples 21
3.1.2 Wax and sanitizing material 21
3.1.3 Experimental set up 22
3.2 Evaluation of the Effectiveness of Different Waxing Technologies on Shelf Life of ‘Apple’ and ‘Ngowe’ Mango Fruits Under Different Storage Conditions 22
3.2.1 Evaluation of Physical and Physiological Attributes 23
3.3 Evaluation of the Effect of Waxing on the Postharvest Quality Attributes of ‘Apple’ and ‘Ngowe’ Mango Fruits Stored Under Different Storage Conditions 24
3.3.1 Total Soluble Solids (TSS) 25
3.3.2 Total Titratable Acidity (TTA) 25
3.3.3 Determination of β-carotene content 26
3.3.4 Ascorbic Acid content 26
3.3.5 Simple sugars (fructose, sucrose and glucose) 27
3.4 Statistical Data Analysis 28
CHAPTER FOUR
4.0. RESULTS
4.1 The Effect of Different Waxing Technologies on Shelf Life of ‘Apple’ and ‘Ngowe’ Mango Fruits Stored Under Different Storage Conditions 29
4.1.1 Cumulative weight loss (%) 29
4.1.2 Changes in respiration 31
4.1.3 Changes in peel firmness 33
4.1.4 Changes in pulp firmness 35
4.1.4 Changes in peel hue angle 37
4.1.5 Changes in pulp hue angle 42
4.2 The Effect of Waxing on the Postharvest Quality Attributes of ‘Apple’ and ‘Ngowe’ Mango Fruits Stored Under Different Storage Conditions 45
4.2.1 Changes in Total Soluble Solids (TSS) 45
4.2.2 Total titratable acidity (TTA) 47
4.2.3 Beta-carotene 50
4.2.4 Vitamin C 52
4.2.5 Changes in sugars 55
CHAPTER FIVE
5.0 GENERAL DISCUSION, CONCLUSION AND RECOMMENDATIONS
5.1 Discussion 64
5.2 Conclusion 70
5.3 Recommendations 70
REFERENCES 72
APPENDICES 85
CHAPTER ONE
1.0 INTRODUCTION
Agriculture is the mainstay of the Kenyan economy contributing to about 24% of the Gross Domestic Product (GDP), with an estimated 75% of the population depending on it directly or indirectly (Nnadi et al., 2012). The horticulture sub-sector has continued to experience significant growth and has become a major source of employment and a source of government revenue (HCD, 2016). The livelihoods of many people are significantly impacted by this sector when compared with other sectors in the country. In 2016, the industry generated a total of Kshs. 216.37 billion compared to Kshs. 207.73 billion in 2015, realizing a growth of 4% in a year. Approximately 619,114 hectares of land is under horticulture with a production of 8.127 million tons, compared to 7.983 million tons in 2015. The key produce for export in the industry include vegetables, fruits, flowers, nuts, herbs and spices (HCD, 2016).
Mango is an important fruit ranked first among the export fruits (HCD, 2016). It is adapted to wide agro-ecological zones (AEZs) and this makes it an important crop in Kenya. In the last decade, mango production in Kenya expanded considerably in acreage and geographical spread. The growth in the industry has been stimulated by a continuous increase in demand in the domestic, regional and international markets (HCD, 2016), becoming a major income earner for many smallholder farmers living in dry areas (Arid and Semi-Arid lands). However, mango fruit is highly perishable with a short shelf life of about 4 to 5 days under room temperature and about 3weeks in cold storage (13°C) (Emongor, 2010).
Over the years, different postharvest technologies have been developed to increase shelf life and preserve postharvest quality of perishable commodities such as antioxidants like ascorbic acid, firming agents like calcium derivatives, 1-Methylcyclopropene (1-MCP), Controlled Atmospheres (CAs), Modified Atmosphere Packaging (MAPs), among others. Kader (1999), reported that CA is effective in extending shelf life of mango, however, the technique is not commercially viable especially for the small holder farmers. Also, produce stored under CA has been found to have CO2 injury and with off flavor (Bender et al., 1997; Kader 2008). The use of Active bag® (MAP) has been shown to be effective in extending shelf life of mango fruits (Githiga et al, 2012), however, the packaging is not yet commercialized and there is fear of environmental pollution (Lorevice et al., 2014). Kader (2008), noted that poor balancing of oxygen and carbon dioxide in the film packaging leads to skin discoloration, grayish pulp color and formation of off flavor especially in mangos.
Coating fresh produce, fruits in particular, has been demonstrated to have beneficial effects as the coating helps to stimulate the fruit’s epidermal structure and wax layer of different fruits with improved performance (Abassi et al, 2009). It is also used to replace the natural wax that is lost during washing. Appropriate amounts of the coating when applied forms a thin porous membrane on the surface of fruits reducing transpiration rates, respiration and prevents invasion by micro-organisms (Krochta et al., 1994). Coatings are useful in delaying dehydration, inhibits volatilization of aromatic substances and helps to improve texture of most fruits (Mladenoska, 2012). The use of food coating technology is environmentally friendly (Dhall, 2013) and reduces reliance on synthetic packaging. Other than giving a modified environment like MAP, food coating works to give an additional protective cover on the produce and allows the addition of other active ingredients such as fungicide, antioxidants, spices, among others into the polymer matrix which improves its performance (Mladenoska, 2012).
In pursuit to realize the commercial potential of mango fruit through loss minimization, researchers have developed various postharvest technologies which are affordable, accessible and easy to use. Among these are waxing technologies whose effectiveness and cost benefit can only be realized through research. Hoa et al., (2002), reported positive results on the effect of four wax coating (shellac, carnauba, zein and cellulose) on shelf life of Kent, Lirfa and Tommy Atkins. All coatings reduced rate of CO2 production, development of skin and pulp color and retarded loss of firmness. Banana and tomato fruits which were coated by gum Arabic were reported to have delayed ripening and maintained postharvest quality (Maqbool et al., 2011).
1.2 PROBLEM STATEMENT AND JUSTIFICATION
1.2.1 Problem statement
Mango is a climacteric fruit with a short shelf life of 4-7days depending on harvest maturity and storage conditions (Slaughter, 2009). High perishability and seasonality contribute to high postharvest losses (40-50%) reported in the mango value chain. Postharvest deterioration in climacteric fruits like mango results from various factors including ethylene effects, water loss and respiration. Ethylene is a gaseous plant hormone which is known to trigger ripening and senescence processes leading to a quicker deterioration of perishable commodities. Water is lost from perishables through transpiration process. Cuticle, a waxy layer that prevents water loss to the environment is usually broken or lost during harvesting, handling and washing and this predisposes the fruit to a faster water loss causing withering and senescence (Hagenmaier and Baker, 1997). On the other hand, respiration becomes a dominant process after harvest. Oxygen taken in through lenticelss is used to break down carbohydrates in fruits releasing the energy required for other biochemical processes to occur.
To achieve prolonged shelf life and maintain quality of perishable commodities like mango fruits, various postharvest technologies including cold storage, Controlled Atmosphere (CA), Modified Atmospheric Packaging (MAP), 1-Methylcylopropene (1-MCP), edible coatings, among others have been shown to delay ripening and preserve postharvest quality. However, many of them have not been adopted due to high cost of acquisition and operation and some of them unsuitable for different category of fruit due to CO2 injury (Lorevice et al., 2014). This challenges therefore requires development of alternative affordable postharvest technologies.
Advances in food coating has led to the development of coatings with a wide range of gas permeability characteristics to suit the metabolic characteristics of different produce. Positive results on the use of these coatings include mango coated with pectin and chitosan (Medeiros et al., 2012), tomato and banana coated with gum Arabic (Ali et al., 2010), citrus and apples coated with shellac and carnauba wax, tangerines coated with bees’ wax (Abassi et al., 2009; Bashir et al., 2004; Sabir et al., 2003), among others. There are various waxing technologies whose application requires extensive research to establish their effectiveness on shelf life extension and quality preservation of fresh commodities. Such is shellac wax and mango wax.
Although waxing has been used successfully in various commodities in different countries, its use and registration on Kenyan mango has not been done. Therefore, the current study focused on establishing the effect of different waxing technologies (mango wax and shellac wax) on shelf life and postharvest quality of mango fruits under different storage conditions.
1.2.2 Justification
Various processes that occur after harvest such as water loss, respiration, pathological breakdown, decay and high rates of bruises subjects the fruits to a quick deterioration (Ray and Ravi, 2005). To realize longer shelf life and quality preservation, various postharvest techniques and postharvest technologies must be employed along the value chain. Cuticle, a natural waxy layer on fruit’s surface has a general low permeability to water vapor. Harvesting, packaging and handling of mango fruits along the value chain, causes this natural barrier to be broken or lost and this subjects the fruit to a high-water loss and respiration. Artificial application of wax enhances or replaces the lost cuticle thus providing a partial barrier to moisture loss and gas exchange. Also, the thin layer of wax improves the mechanical handling property by maintaining structural integrity, retention of volatile flavor compounds and addition of functional compounds helps deter pathological breakdown (Mladenoska, 2012).
Successful application of wax delays ripening and retain postharvest quality longer. This can contribute to reduction of the losses and wastage in the mango value chain. The quick deteriorative nature of mango fruits leaves the exporters with the option of air freight in shipping their produce to distant markets. Air freight is very expensive, and this renders the produce uncompetitive in the overseas market. Delayed ripening of mango fruits coated with wax and cold storage gives an opportunity for sea shipping which would help cut down on costs and improve the competitive ability of mango fruits from Kenya.
Evidence of the effectiveness of waxing on shelf life extension and preservation of postharvest quality of mango fruits could lead to its adoption by various actors, especially the mango exporters.
1.3 OBJECTIVES
1.3.1 General objective
To reduce postharvest losses in mango fruits through application of waxing technologies.
1.3.2 Specific objectives
1. To compare the effectiveness of different waxing technologies to extend shelf life of ‘apple’ and ‘ngowe’ mango fruits stored under different storage conditions.
2. To determine the effect of waxing on postharvest quality attributes of ‘apple’ and ‘ngowe’ mango fruits under different storage conditions.
1.4. Hypothesis
(i) The different waxing options on ‘apple’ and ‘ngowe’ mango fruits will have the same effect on shelf life in the different storage conditions.
(ii) The effect of waxing on postharvest quality of ‘apple’ and ‘ngowe’ mangos will be the same in the different storage conditions.
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