ABSTRACT
Mango is a perishable fruit with a limited shelf life once ripe, resulting in significant postharvest losses. The objectives of this study are to determine the efficacy of hexanal treatment in prolonging the shelf life of mango fruits and to determine the effects of hexanal treatment on the physical and biochemical attributes of mango. A laboratory experiment was performed to determine the efficacy of hexanal treatment in different concentrations as a postharvest dip on the physical quality and extension of storage life of mangoes and its interaction with variety and agro ecological zone of production. Further studies were carried out to determine the effects of hexanal treatment on the biochemical attributes of mango. The study was done at two agro ecological zones namely Machakos (AEZ IV) and Meru (AEZ II) and on two varieties namely Apple and Tommy atkins. Fruits were harvested at mature green stage, cleaned, sorted and divided into several batches. A formulation of hexanal also known as Enhanced Freshness Formulation (EFF) was used at two concentrations 2% and 3% as a postharvest dip to treat the mangoes in the laboratory and observed under ambient room temperatures throughout the ripening process. The study also included untreated fruits which were only dipped in plain water to act as control. Various ripening parameters were evaluated at 3 day intervals to determine the effects of the EFF treatments. These parameters include: physiological loss of weight, colour, firmness, ethylene evolution rate and respiration rate. Additionally, Samples from all treatments were taken and refrigerated and later evaluated for several ripening biochemical parameters measured namely, brix, ascorbic acid content, total titratable acidity, Beta carotene and simple sugars (glucose, fructose and sucrose).The results showed that fruits treated with the EFF exhibited slowed ripening rate as compared to untreated fruits by 3 days in the Apple variety and 5 days in the Tommy Atkins variety. Hexanal treatment slowed down the rate of cumulative weight loss by 5% -6%. It also delayed the drop in hue angle by 3-6 days as well as delayed drop in both peel and flesh firmness. This is indicative of slowed down ripening process resulting to prolonged shelf life. It was also observed that mangoes treated with 3% EFF had a longer shelf life by 3 days than those treated with 2% EFF indicating that 3% EFF was highly effective in prolonging the shelf life of the fruits. Hexanal formulation applied as a postharvest dip can therefore be adopted as a solution to reduce postharvest losses and prolong the shelf life of mango fruits for both domestic and commercial use. In all the ripening parameters measured in this study, hexanal treatment was observed to slow down the rate at which the ripening process progressed but did not significantly change the quality of the fruits compared to the untreated fruits. Hexanal treated fruits exhibited a slower ripening rate as well as a higher retention for sugars, vitamin C, Beta carotene and acidity. In some parameters such as TSS, Beta carotene, glucose and fructose content there was no significant difference between fruits from different varieties or even harvested from different zones. However, in parameters such as TTA differences were noted between varieties with Tommy atkins variety recording a higher TTA than apple mangoes. The varietal difference was also noted in sucrose content where apple mangoes had a higher level of sucrose content as compared to the Tommy atkins variety. It was concluded that hexanal treatment indeed prolonged the shelf life of mango fruits without altering the quality and biochemical attributes. Hexanal has been recommended for further studies and later commercialization.
TABLE OF CONTENTS
DECLARATION 2
ACKNOWLEDGEMENT 4
TABLE OF FIGURES 8
LIST OF ABBREVIATIONS 9
APPENDICES 10
ABSTRACT 10
CHAPTER ONE: Introduction
1.1.1 Challenges in mango production 12
1.2 Problem statement 13
1.3 Justification 15
1.4 Objectives 17
1.4.2 Specific objectives 17
1.5 Hypotheses 18
CHAPTER TWO: Literature Review
2.2 The Botany of Mango 20
2.3 Mango Varieties 22
2.3.2 Van dyke 22
2.3.3 Tommy atkins 22
2.3.4 Kent 23
2.3.5 Ngowe 23
2.4 Mango Nutritional Quality 23
2.5 Ecological Requirements for Mango 24
2.5.1 Temperature 24
2.5.2 Light environment 25
2.5.3 Water availability 25
2.5.4 Altitude 26
2.5.5 Soils 26
2.6 Mango Fruit Growth and Maturation 26
2.7 Factors Affecting Maturation of Fruits 27
2.7.2 Cultural practices 28
2.7.3 Varietal differences 31
2.8 Maturity indices for fruits 31
2.9 Maturity indices for mango 33
2.10 Changes in Quality Attributes Associated with Mango Ripening 34
2.10.1 Changes in color 34
2.10.2 Changes in firmness 34
2.10.3 Changes in flavour 35
2.10.4 Ethylene production 35
2.10.5 Changes in soluble sugars 35
2.10.6 Changes in vitamins 36
2.10.7 Changes in β-carotenes 36
2.10.8 Changes in mineral nutrients 36
2.10.9 Changes in acidity 37
2.11 Applicable Post Harvest Technologies in Mango 37
2.11.1 The use of 1-methylcycopropene (1-MCP) 37
2.11.2 Cold chain management 38
2.11.3 Modified Atmosphere Packaging(MAP) 39
2.11.4 Hexanal 40
CHAPTER 3: Efficacy of Hexanal Treatment In Improving The Shelf Life Of Mango (Mangifera Indica L.) Fruits Of Different Varieties Harvested From Different Agro Ecological Zones In Kenya
3.1 Abstract 41
3.2 Introduction 42
3.3 Materials and Methods 45
3.3.2 Samples and treatments 46
3.3.3 Percentage cumulative loss of weight 47
3.3.4 Peel and flesh colour 47
3.3.5 Fruit firmness 47
3.3.6 Rate of ethylene evolution and respiration 47
3.4 Statistical Analysis 48
3.5 Results 48
3.5.2 Flesh colour 50
3.5.3 Peel colour 51
3.5.4 Flesh firmness 53
3.5.5 Peel firmness 55
3.5.6 Rate of respiration 57
3.5.7 Ethylene rate 59
3.6 Discussion 61
3.7 Conclusion 63
CHAPTER 4: The Effects of Hexanal Treatment on the Biochemical Quality Characteristics of Mango Fruits
4.1 Abstract 64
4.1 Introduction 65
4.2 Materials and methods 66
4.4 Measurements of bio chemical attributes of mango 66
4.4.2 Total titratable acidity (TTA) 67
4.4.3 Ascorbic Acid content 67
4.4.4 Beta carotene content 68
4.4.5 Major sugars (fructose, glucose and sucrose) 69
4.5 Data analysis 69
4.6 Results 70
4.6.2 Ascorbic Acid (Vitamin C) 72
4.6.3 Total Titratable Acidity (TTA) 74
4.6.4 Beta Carotene 75
4.6.5 Simple sugars 77
4.6.5.1 Glucose 77
4.6.5.2 Fructose 79
4.6.5.3 Sucrose 81
4.7 Discussion 82
4.8 Conclusion 85
CHAPTER 5: General Discussion, Conclusion and Recommendations
5.1 General Discussion 86
5.2 General Conclusion 87
5.3 General Recommendations 88
References 89
Appendices 103
TABLE OF FIGURES
Figure 1: Effects of hexanal treatment on the percentage Cumulative weight loss of Apple and Tommy Atkins varieties of Mango 47
Figure 2: Effects of hexanal treatment on the flesh colour of Apple and Tommy Atkins varieties of Mango 49
Figure 3: Effects of hexanal treatment on the peel colour of Apple and Tommy Atkins varieties of Mango 51
Figure 4: Effects of hexanal treatment on the flesh firmness of Apple and Tommy Atkins varieties of Mango 53
Figure 5: Effects of hexanal treatment on the peel firmness of Apple and Tommy Atkins varieties of Mango 55
Figure 6: Effects of hexanal treatment on the respiration rate of Apple and Tommy Atkins varieties of Mango 57
Figure 7: Effects of hexanal treatment on the ethylene rate of Apple and Tommy Atkins varieties of Mango 59
Figure 8: Effects of hexanal treatment on the Total Soluble Solids of Apple and Tommy Atkins varieties of Mango 70
Figure 9: Effects of hexanal treatment on the Ascorbic Acid Content of Apple and Tommy Atkins varieties of Mango 72
Figure 10: Effects of hexanal treatment on the Total Titratable Acidity of Apple and Tommy Atkins varieties of Mango 74
Figure 11: Effects of hexanal treatment on the Beta Carotene Content of Apple and Tommy Atkins varieties of Mango 76
Figure 12: Effects of hexanal treatment on the Glucose Content of Apple and Tommy Atkins varieties of Mango 78
Figure 13: Effects of hexanal treatment on the Fructose Content of Apple and Tommy Atkins varieties of Mango 80
Figure 14: Effects of hexanal treatment on the Sucrose Content of Apple and Tommy Atkins varieties of Mango 82
LIST OF ABBREVIATIONS
ACC – Amino cyclopropane carboxylic acid AEZ – Agro ecological zone
ANOVA – Analysis of variance
EFF – Enhanced Freshness Formulation GDP- Gross domestic product
GRAS- Generally recognized as safe HCD- Horticultural crops directorate
HPLC – High performance liquid chromatograph LSD – Least significant difference
MAP – Modified atmosphere packaging MCP – Methyl cyclopropene
MOA – Ministry of Agriculture RID – Refractive index detector SSC – Soluble solids content
TTA – Total titratable acidity
APPENDICES
Appendix 1: Anova for cumulative weight loss for mango fruits treated with hexanal Appendix 2: Anova for flesh colour for mango fruits treated with hexanal
Appendix 3: Anova for peel colour for mango fruits treated with hexanal
Appendix 4: Anova for flesh firmness for mango fruits treated with hexanal
Appendix 5: Anova for peel firmness for mango fruits treated with hexanal
Appendix 6: Anova for respiration rate for mango fruits treated with hexanal
Appendix 7: Anova for ethylene rate for mango fruits treated with hexanal
Appendix 8: Anova for total soluble solids for mango fruits treated with hexanal
Appendix 9: Anova for Ascorbic acid for mango fruits treated with hexanal
Appendix 10: Anova for Titratable acidity for mango fruits treated with hexanal
Appendix 11: Anova for Beta carotene for mango fruits treated with hexanal
Appendix 12: Anova for glucose content for mango fruits treated with hexanal
Appendix 13: Anova for fructose content for mango fruits treated with hexanal
Appendix 14: Anova for sucrose content for mango fruits treated with hexanal
Appendix 15: Colour wheel
CHAPTER ONE
Introduction
1. Introduction
1.1 Background information
The Agriculture sector contributes 30% of the Gross Domestic Product (HCD, 2018) and is among the major economic activities in the country. It contributes 60% of total export earnings (HCD, 2013) and is ranked the second main foreign exchange earner to the country. Agriculture is important in alleviating hunger and poverty to the poor communities in the society (FAO, 2012). The horticulture sub-sector is an essential source of income, employment for farmers, traders and investors, government revenue as well as foreign exchange earnings (FAO, 2014).
Horticulture has established itself over time as a main sub-sector in the agriculture sector. It has recorded an annual growth rate of 19% and has contributed 33% of the agricultural GDP (HCD, 2018). The most common fruits produced in Kenya in order of value are; bananas (36%), pineapple (21%), mangoes (18%), avocados (5%), pawpaw (5%), passion fruit (3%) oranges (2%), water melon (2%) and tangerines (2%) (HCD, 2018).
Mango (Mangifera indica L.) is among the most valued fruits in the subtropics as well as the tropics. Mango is produced commercially in over 90 countries in the world and is consumed in different forms. Mangoes can either be consumed fresh or in processed form (Mathooko et al., 2013; Mujuka et al., 2020). Additionally, the mango fruit has been placed in a valuable position as an income earner for farmers, international market and traders by its high nutritional attributes and its attractive flavour (Rodriguez et al., 2012; Bundi et al., 2020).
It is estimated that the world produces about 21.5% metric tonnes of mango fruits annually and it increases at an estimated rate of 2.6% annually (Okoth et al., 2014). Asia leads in the production of Mango fruits worldwide with 76.8% of total production, while America comes in second with 13.37%. Africa produces 9% while Europe and the Oceanic countries produce 1% (Jahurul et al., 2015). Globally, the mango value chain has gained popularity following its ability to offer jobs and its immense contribution to rural economies. This has been a response to the increase in demand for the fruit due to its ability to be value added to make jam, chutneys, pickles, jelly and natural juices (Korir et al., 2013; Chappalwar et al., 2020).
Processing of mango fruits into these products is considered as an improvement of shelf life or enhancing the value of unprocessed mangoes thus minimizing postharvest losses.
Kenya is one of the major producers of mango in Africa (Galán, 2010). Additionally, mango is ranked second after banana in terms of quantity produced as well as total area of production (FAOSTAT, 2015). Statistically, mango production contributes about 5% of the agricultural GDP in Kenya and approximately 2% of the national GDP and employs a significant number of the seasonal work force (Ministry of Agriculture, Livestock and Fisheries, 2018). In 2015, the total area under mango cultivation was 46,363 hectares (ha) and the harvest was about 806,574 metric tonnes (MT), while in 2016 the area under mango production rose to 49,097 ha while the output dropped to 779,146 MT (HCD, 2016). In 2018, the area under mangoes decreased by 4% from 50,550ha in 2017 to 48,541ha (HCD, 2018). However, the value and volume in 2018 increased by 5.8% and 9.7%, respectively, compared to 2017. The leading counties in mango production as ranked by value were Makueni, Machakos, Kilifi, and Kwale, whose contribution to the total value was 24.9, 17.7, 14.6, and 4.7 percent respectively (HCD, 2018). Data from the HCD shows that the volumes of mango fruits exported in the year 2020 reduced by up to 2.2 million kilograms.
In 2019, Kenya exported approximately 9.3 million kilograms of mangoes to different destinations valued at KSh.1. 4 billion compared to 7.1 million kilograms exported in the year 2020 valued at KSh.1.1 billion. The most common local varieties grown in Kenya include; Dodo, Kasukari, Ndoto, Sikio la punda, Katili, Kitui, Mombasa, while exotic varieties include; Apple, Batawi, sabine, Sensation, Tommy Atkins, Haden, Keitt, Kent, Ngowe, Nimrod, Maya and Van dyke (Toili et al., 2013). The fruit is considered a great source of antioxidants, phenolic compounds, ascorbic acid, carotenoids as well phenolic compounds (Talcott et al., 2005; Djioua, 2008).
1.1.1 Challenges in mango production
It is a fact that Mango production is a promising and profitable enterprise. However, this high potential is threatened by various challenges with the major one being high postharvest losses which are estimated at 40% (FAO, 2012). The great potential of the mango value chain for expansion and growth remains unexploited. This has been caused by constraints experienced at various stages of the value chain. The main stages in the value chain include; farm level, the marketing stage, the processing stage and the export stage (MOA, 2010). The main constraints faced at the farm level include: low yielding seedlings; poor quality of planting materials, low technological knowledge; lack of proper crop management practices, expensive inputs, oversupply at harvest time which leads to high postharvest losses and bad prices (FAO, 2013). At the marketing stage, farmers face constraints such as: inadequate market information, poor infrastructure and lack of financing to support their activities (MOA, 2010). At this marketing stage, lack of adequate knowledge on the uses and applications of postharvest technologies is in itself a big challenge. In Kenya, only about 7% of the mangoes harvested end up in processing (Marc-Peter, 2015). This is attributed to the low demand locally for dried mangoes and other processed products as well as high competition of mango puree. These challenges have been addressed in the Vision 2030 strategy, second medium term plan (2013 – 2017) which addresses issues surrounding agricultural market access and value addition aimed at enhancing agricultural product development and marketing systems.
Mango fruits are known to be highly perishable and ripen quickly once harvested or being transported. The storage life of mango fruits varies based on varieties and storage environment (Abbasi et al., 2009). Mango shelf life usually takes approximately 2 to3 weeks in cold storage and approximately 4 to 8 days at room temperature. (Herianus et al., 2003). Postharvest losses in mangoes can however be reduced by coming up with other ways and measures to enhance the fruits storage life.
1.2 Problem statement
The mango fruit being a living tissue and a climacteric fruit is vulnerable to constant changes during ripening until it totally deteriorates. Postharvest losses in mango in Kenya are estimated at more than 40% (FAO, 2012). Postharvest technologies therefore need to be developed and applied in the mango value chain to reduce these losses. Over time, various post-harvest technologies have been studied and developed and their use successfully tested in several climacteric fruits such as banana, mango and papaya. Examples of the postharvest technologies that have been developed and tested in mango include Modified Atmosphere Packaging (Githiga et al., 2014), low temperature storage (Ambuko et al., 2008), 1- Methylcyclopropene (Ricardo et al., 2004; Ambuko et al., 2013), hot water treatments (Mirshekari et al., 2015) among others. However, the adoption rate of these technologies especially by small scale farmers is quite low due to high costs, application difficulties and non-availability (Lorevice et al., 2014). While storage in low temperatures is considered one of the most effective methods for extending the shelf life of most perishable commodities after harvest, majority of the small-scale farmers cannot afford the cold storage facilities. The application of 1-Methylcyclopropene (1-MCP) which is a known inhibitor of the action of ethylene, has been used to prolong the storage life of several fruits especially climacteric fruits. Some of these fruits are banana (Boonyaritthongchai et al., 2010, Baez- Sanudo et al., 2009), mango (Hofman et al., 2001, Ambuko et al., 2013), pawpaw (Ahmad et al., 2013), avocado (Meyer and Terry, 2010), strawberry (Ku et al., 1999), oranges (Porat et al., 1999), and apples (Watkins et al., 2006). According to Sisler and Serek (1996), the mode of action of 1-MCP is by irreversibly and permanently binding to ethylene receptors which are present in the particular plant tissue. This in turn leads to slow ripening and softening of fruits, thus enabling distribution and prolonging shelf life while maintaining high quality of the fruits for longer (Blankenship and Dole, 2003; Adkins et al., 2005). However, some undesirable effects of 1-MCP such as abnormal fruit color, uneven softening and inhibited production of essential volatiles and esters have been reported in some fruits (Fan and Matthesis, 1999).
Modified atmosphere and controlled atmosphere storage have been reported to be effective in enhancing fruit shelf life (Scetar et al., 2010). Controlled atmosphere storage however, requires precise control of gases making it expensive and out of reach for majority of the small- scale farmers. On the other hand, Modified Atmosphere Packaging (MAP) is a simple technology that uses bags made of polythene to keep the fruits fresh for longer. In Kenya, however, the technology is not yet commercialized and has been affected by the country's ban on the use of polythene bags (Ministry of environment and natural resources, 2017). Several types of dip treatments have been tested and adopted in some countries for different fruits.
Various chemicals, such as combined solutions of ascorbic acid, calcium chloride and cysteine (Bico et al., 2009), soy lecithin along with natural lysophospholipid (Ahmed and Palta, 2016), phenylurea [CPPU] and gibberellins [GA3] (Huang et al., 2014), salicylic acid (Srivastava and Dwivedi, 2000), potassium permanganate (KMnO4) (Hassan, 2000), 1- MCP (Blankenship, 2001), oxalic acid (Huang et al., 2013) and nitrous oxide (N2O) (Palomer et al., 2005) were reported to be effective in reducing the postharvest losses of fruits during harvesting, transport and storage. In most cases, the chemicals have been found to act as inhibitors of ethylene production thus enhancing the storage life of the fruits. Regardless of the number of technologies and chemicals available for fruit preservation, their adoption is very minimal due to prohibitive costs, application difficulties and non-availability. Limitations of the applicable technologies described above calls for further research in other commercially viable and affordable technologies and innovations to prolong the storage life of mango fruits while maintaining its quality.
1.3 Justification
This study bridges the existing postharvest technologies gap by introducing a naturally occurring organic compound extracted from plants to help in overcoming the constraints that come with fast ripening and senescence in mangoes.
In the recent years, hexanal, which is a naturally occurring six carbon aldehyde resulting from the lipoxygenase pathway following tissue damage (Hildebrand, 1989), has been revealed to improve the quality and storage life of various temperate fruits, such as peaches, cherries, strawberries and nectarines (Sharma et al., 2010) and some tropical fruits such as tomato (Cheema et al., 2014), banana (Yumbya et al., 2020), mango (Anusuya et al., 2016), papaya (Hutchinson et al., 2018) and limequats (Debysingh et al., 2018). Hexanal works by hindering the activity of the phospholipase D enzyme which catalyzes membrane phospholipids hydrolysis and causes deterioration of membranes and thus initiates fruit softening (Paliyath et al., 2008). Treatment by Hexanal has been reported to result in keeping cell membranes stable and intact, enabling fruits to remain fresh looking and firm for longer periods of time. The mechanism of hexanal is achieved by hindering the work of the enzyme phospholipase D which catalyzes the membrane phospholipids hydrolysis and triggers break down of membranes causing fruit softening (Paliyath et al., 2008).
Quantitative PCR focusing on genes associated with ethylene biosynthesis and softening indicated that treating banana fruits with hexanal delayed the manifestation of four genes coding for different cell wall degrading enzymes which are xyloglucan endotransglucosylase, Pectin Methylesterase, Pectin Lyase and Polygalacturonase (Yumbya et al., 2020).
Hexanal has been approved by FDA in the US as a general food additive (US Patent 6,514,914;7,198,81) for use in processed plant-based foods. It is not retained in the treated tissues beyond 48hours of treatment (http:/www.accessdata.fda.gov/). In the human body, hexanal is readily oxidized to hexanoic acid. Like all other alcohols, hexanoic acid is further converted to carbon dioxide and water by the tricarboxylic acid cycle(TCA) during the process of respiration (Kruse et al., 2016) Enhanced Freshness Formulation(EFF) is a biochemical formulation of an artificially synthesized version of hexanal. It is known to slow down the process of ripening in temperate fruits (Sharma et al., 2010). There have been successful studies on the use of Hexanal treatment in tomato (Cheema et al., 2014), papaya (Hutchinson et al., 2018) and Banana (Yumbya et al., 2020). Additionally, there has been studies on the efficacy of hexanal on enhancing the storage life of mango as a pre harvest spray in India (Anusuya et al., 2016). A previous study by Cheema et al. (2014) on tomatoes, indicated that hexanal effectiveness is dependent on several components such as physiological maturity, concentration, application duration, method of application and nature of the commodity. Therefore, its critical to establish the effective dosing range for various commodities grown in differing agro-ecological conditions, varietal differences, and mode of action among other factors. Kenya being a major producer of mango, there is a gap in information on the postharvest application of EFF as a dip, the best concentration of the EFF to give optimal results as well as the interaction of hexanal treatments with different varieties and agro- ecological zones of production of mangoes in Kenya. This study therefore focusses on the use of the EFF as a postharvest dip in mangoes cv. Apple and Tommy Atkins grown at two different agro ecological zones (AEZ II and AEZ IV) in Kenya aimed at prolonging shelf life. Hexanal is easy to use and farmers can start using it with minimal training. It also does not require specialized equipment for application and is used in small quantities making the technology easily applicable to small scale farmers. The adoption and commercialization of hexanal application as a post- harvest technology will reduce losses and increase income to the farmers as well as all the players in the mango value chain.
1.4 Objectives
1.4.1 General objective
The broad objective of this study is to reduce the postharvest losses of mango fruits in Kenya by extension of shelf life through treatment with Hexanal.
1.4.2 Specific objectives
The specific objectives of this study include:
1. To determine the efficacy of hexanal, applied at different concentrations as a post- harvest dip, in improving the shelf life of mango fruits of different varieties harvested from two agro ecological zones in Kenya.
2. To determine the effects of Hexanal treatment on the physical and biochemical attributes of Mango fruits of different varieties grown in two different agro- ecological zones in Kenya.
1.5 Hypotheses
1. Hexanal has zero effect on the storage life of mango fruits of diverse varieties grown in contrasting climatic zones in Kenya.
2. Hexanal treatment has zero effect on the physical and biochemical attributes of diverse varieties grown in contrasting climatic zones in Kenya.
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