Effectiveness of Selected Postharvest Handling Practices and Technologies to Preserve the Postharvest Quality of Mango Fruit

Abstract

Mango (Mangifera Indica L.) is one of the major fruits produced in Kenya mainly 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). Application of these practices and technologies can extend the fruits’ shelf life and marketing period thereby minimize postharvest losses in the mango value chain