EFFECTIVENESS OF SELECTED POSTHARVEST HANDLING PRACTICES AND TECHNOLOGIES TO PRESERVE THE POSTHARVEST QUALITY OF MANGO FRUIT

Mango (Mangifera Indica L.) is one of the major fruits for the domestic market. Production of mango is dominated by the smallholder farmers, majority of whom depend on it for their livelihoods. Mango fruit is a highly perishable climacteric fruit whose shelf life is limited after maturity, resulting in high post-harvest losses. Postharvest deterioration and subsequent losses are as a result of various metabolic processes including respiration and transpiration whose rate depends on temperature management. Cold chain management which entails handling perishable produce at cool (safe) temperature from harvest until the produce reaches the end-user is critical for the preservation of quality. The aim of this study was to evaluate the effectiveness of selected postharvest handling practices and simple technologies to achieve cold chain, extend shelf life and preserve quality of mango fruit. This was achieved through two related on-farm and laboratory experiments.

In the first experiment, four mango varieties namely ‘Apple’, ‘Ngowe’, ‘Kent’ and ‘Tommy Atkins’ harvested at the mature green stage from the farmers’ orchards were used in an on- farm study. To demonstrate proper cold chain management, fruits were harvested early in the morning (before 8 am) and transported in crates which were lined with dampened newspapers to cool the fruits during transit. Upon arrival at the experimental site (Karurumo Aggregation Center), the fruits were precooled using evaporative coolers to remove field heat then stored in the Coolbot™ cold room (10±2oC). The described proper cold chain practices were compared with the common practices among farmers (poor cold chain practices). In this case, the fruits were harvested at midday (noon), transported to the aggregation centre in open crates and then stored at ambient room conditions (Temperatures of 25±7oC, Relative Humidity of 55±15%). The air and fruit pulp temperatures from harvest and subsequent handling and storage at the various conditions were monitored regularly using HUATO® data loggers. During storage, a random sample of 3 fruits (per variety) was taken from each of the storage options after every 3 days to evaluate ripening-related changes including physiological weight loss, colour, firmness and total soluble solids.

In the second experiment, a homogenous sample of mature green ‘Apple’ and ‘Kent’ mango fruits were divided into 10 batches of 60 fruits each to evaluate the effectiveness of four different low-cost storage technologies to preserve quality and extend the shelf life of mango fruits. The technologies evaluated include Coolbot™ cold room (10±2oC, 75±20%RH), Evaporative charcoal cooler (20±5oC, 95±5%RH), Zero energy brick cooler (20±5oC, 90±10%RH) and Wakati™ tent (25±5oC, 95±5%RH). The different technologies were compared with storage at ambient room conditions (25±oC, 55±15%RH). For each storage option, the fruits were divided into two batches where one batch was packaged using Activebag® modified atmosphere packaging (MAP) and the second batch left open (unpackaged). The experiment was laid out as a completely randomized design with a factorial arrangement of treatments. Three fruits per treatment were sampled after every 3 days to evaluate ripening and quality-related changes including physiological weight loss, colour, firmness, and total soluble solids, titratable acidity, B-carotene, sugars, and vitamin C.

Results showed that harvesting time significantly affected fruit pulp temperatures at harvest with fruits harvested before 8 am recording lower pulp temperatures (average 16.4 oC) compared to the fruits harvested at noon (average 31.4 oC). Proper cold chain management delayed ripening as evidenced by slower softening and increase in percentage TSS. Flesh firmness of ‘Apple’ mango reduced by 37% and 91% under the proper cold chain and poor cold chain management respectively by day 12 of storage while TSS increased by 17% and 63% respectively. Proper cold chain management extended shelf life by at least 18 days compared to poor cold chain management. In the second experiment, cold storage significantly extended mango shelf life for ‘Apple’ and ‘Kent’ mango fruits compared to storage at ambient room conditions. This was evidenced by lower respiration rate, slower rate of softening and colour changes compared to ambient room conditions. Fruits under cold storage combined with MAP had a longer shelf life (up to 9 days more) and retained better quality attributes at the end of storage. At the end of storage, unpackaged ‘Apple’ mango retained 50%, 49%, 47%, 46%, and 45% of the initial vitamin C for CoolbotTM cold room, ECC, ZEBC, WakatiTM tent and ambient conditions respectively. On the other hand, the same fruits under cold storage combined with MAP retained 53 %, 52%, 51%, 51%, and 46% of the initial Vitamin C under Coolbot™ cold room, ECC, ZEBC, Wakati™ tent, and ambient conditions storage respectively.

The results of this study show that proper harvest and postharvest handling practices coupled with simple cold storage technologies can be used by smallholder farmers to attain desirable cold chain and preserve the postharvest quality of perishable fruits such as mango. Harvesting mango fruits during the cooler times of the day is recommended as this minimizes the negative effect of high heat load on harvested fruits. The CoolbotTM cold room can be promoted for adoption by farmer groups that have access to electricity (on-grid) while the evaporative coolers can be promoted for farmers and farmer groups without access to electricity (off-grid).

 

 

 

Table 2.1: Production of Mangoes in selected counties, 2016-2017 (Source: HCD, 2017)      9

 

Figure 4.4: Overall shelf life (days in storage) of ‘Apple’ (A) and ‘Kent’ (B) harvested at mature green maturity stages and stored under different storage options with or without Activebag® modified atmosphere packaging. Top Bars represent S.E of means (P≤0.05).   97

 

Appendix 16: Analysis of Variance (ANOVA) table for effect of storage option and modified atmospheric packaging on TTA for ‘Apple’ and ‘Kent’ mango varieties under storage. 138 

 

Horticultural sub-sector in Kenya which comprises fruits, flowers and vegetables has great importance to the economy, ranked 3rd after dairy and tea sub sectors (HCD, 2017). In 2016, the subsector contributed 1.45% to the Gross National Product (GNP). Horticulture is one of the leading foreign exchange earners in the country with a total domestic value of Ksh.248.47 billion and a total production of 6.696 MT, of which Ksh.63.8 billion is contributed by fruits leaving the rest to flowers, vegetables and medicinal plants. The main fruits grown arranged by significance are; bananas, mangoes, pineapples, avocado, water melon and pawpaw (HCD, 2017).

Mango being one of the key horticultural commodities in Kenya has significant domestic and export market. Its value has been ranked 2nd after Avocado in the export market (HCD, 2017). Mango production in Kenya is dominated by the small and medium holder farmers who contribute to up to 80% of the total producers registered by the Fresh Produce Exporters Association of Kenya (FPEAK).

Despite the growth of this subsector in the country and region, its potential has not been fully exploited. This has been linked to the various challenges in the horticultural value chains. Some of these challenges facing practitioners in the mango value chain include costly farm inputs, low quality planting materials, pests/diseases, edaphic factors, climatic limitations among others on the production side. After harvest, the key challenges include poor market access, poor infrastructure, lack of access to affordable technologies to preserve quality, all of which contribute to high postharvest losses.

Post-harvest losses along the mango value chain estimated at 40% (Gor et al., 2012) happen at every stage. The critical stages where these losses occur include at harvesting, transportation, storage and at the retail stage. Mango is prone to post-harvest losses due to its inherent perishability which is aggravated by seasonality. Mango fruiting in Kenya is seasonal with a glut during the peak season between November and February where the highest losses are reported (Maloba et al., 2017).

Post-harvest losses at the harvest stage are attributed to inability to determine fruit maturity which often results in harvesting of immature fruits (Ingle et al., 2000). Other drivers of losses at this stage include, harvesting when the environment is not cool (Samtani and Kushad, 2015: Kader and Rolle, 2004), improper harvesting methods and inappropriate handling that leads to bruising and mechanical injuries. Mechanical injuries provide entry point to pathogens, release wound ethylene and increase deterioration by increasing metabolic reactions (Kader, 2002).

During transportation, post-harvest losses occur due to improper packaging that results to suffocation and mechanical injury (Kader and Rolle, 2004), poor infrastructure causing delays (Rolle, 2006), mixing with high ethylene producing fruits thus accelerating ripening and deterioration (Kader and Rolle, 2004) and transporting in non-refrigerated trucks that require high energy levels to lower temperatures (Kader, 2002).

At the storage stage, losses are mainly due to poor storage conditions which lead to deterioration of the fruits due to various environmental and commodity factors. Losses can also be as a result of mixing fruits with different ethylene sensitivity and overloading in the stores (Pathak et al., 2017). For majority of smallholders involved in mango production, appropriate storage including cold storage facilities is expensive and out of reach. In addition, the scale of production does not justify individual farmer’s investment in cold storage facilities.

Cold chain management is important in horticultural/perishable produce to slow deterioration process by reducing respiration, transpiration, ethylene production and action, and decreases the activities of microorganisms thus slowing ripening and senescence (Ambuko et al., 2018a; Kitinoja, 2013). Maintaining internal (pulp) and the temperature around the stored fruit at a low (safe) temperature is critical for preservation of postharvest quality. Low temperature slows down the metabolic processes such as respiration, transpiration and softening which lead to deterioration perishable produce (Aung and Chang, 2014).

Various post-harvest technologies have been used to address the factors that contribute to deterioration and spoilage of the perishable horticultural produce such as mango fruit. However, there is low adoption of applicable postharvest technologies and practices among smallholder farmers. Studies conducted on projects focusing on postharvest technologies in horticultural value chains between 1996 and 2012 showed that about 83% of the projects were successful but the adoption thereafter was low (Kitinoja, 2010). The low adoption rates are due to; high cost of initial investment, sophisticated postharvest infrastructure, lack of awareness, different group dynamics and limited market access of the products (Kitinoja, 2010).

 

High postharvest losses estimated at 40% are reported in the mango value chain in Kenya (Gor et al., 2012). One of the major causes of increased post-harvest losses among perishable commodities such as mango is poor cold chain management (Kitinoja, 2002). The high postharvest losses reported in mango are attributed to seasonality which results to excess/glut during the high season; high perishability leading to short shelf life once harvested, improper post-harvest handling, poor infrastructure and limited market access (Yahaya and Mardiyya, 2019). Proper cold chain management is the continuous handling of the product within cool/low temperature environment from harvest, collection, packing, processing, storage, transport and marketing until it reaches the final consumer (Kitinoja, 2013). The time of harvest and subsequent handling temperatures determine longevity of the harvested produce. Simple practices such as harvesting produce early in the morning, pre-cooling under a tree, transportation during cooler times of the day followed by cold storage have been reported to contribute to postharvest quality preservation (Ambuko et al., 2018a). Harvesting of fruits and vegetables during cool hours of the day minimizes excessive field heat generation (Arah et al., 2015). Simple storage technologies including evaporative cooling technologies (zero energy brick cooler and evaporative charcoal cooler); Coolbot™ cold storage; Wakati™ are examples of affordable cold storage technologies which have recently been introduced in Kenya (Ambuko et al., 2018a). Previous studies have shown effectiveness of the evaporative cooling technologies (Ambuko et al., 2016; Manyonzo et. al., 2018) and the Coolbot™ cold room (Ambuko et al. 2018b and Karithi, 2016). Previous studies have also shown that effectiveness cold storage technologies to preserve quality of harvested produce is enhanced through modified atmosphere packaging (Karithi 2016; Githiga et al., 2014). Despite their proven effectiveness to preserve quality and extend the shelf life of perishable produce, the adoption of these technologies in Kenya is very low. The low adoption is partly attributed to lack of evaluation of some of the practices and technologies as well as lack of awareness among the potential users of these technologies. Therefore, there is need to evaluate the effectiveness of the selected postharvest technologies and practices and create awareness to enhance adoption.

Cold chain management is critical for postharvest quality preservation and post-harvest loss reduction in the mango value chain. Application of low-cost cold storage technologies and simple cold chain management practices to preserve quality of harvested produce is necessary to reduce postharvest losses and extend the marketing period of highly perishable produce such as mango fruit.

 

The proposed technologies are not only simple and affordable but can be fabricated from locally available materials, making them appropriate for local contexts. Therefore, the study evaluated different simple and affordable but effective practices and technologies that can be utilized to achieve required cold chain for perishable commodities such as mango for shelf-life extension and quality preservation without one having to invest in expensive and sophisticated conventional cold rooms and that proper cold chain management can be achieved in areas without and/or with unstable electricity supply.

To reduce postharvest losses in the mango value chain through application of proper cold chain

management practices.