EFFECT OF STAGE OF MATURITY ON THE EFFICACY OF 1-MCP IN TOMMY ATKINS MANGO FRUITS
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Abstract

Mango is a fruit of high economic and nutritional importance in Kenya. It is currently the second most important export fruit after avocado and a source of livelihoods for many smallholder farmers and other stakeholders involved in its value chain. Although production volumes in Kenya have significantly increased over the years, a high proportion of the fruits (up to 50%) are lost along the value chain. The high losses are attributed to high perishability of the fruits and seasonality. Poor postharvest handling practices and lack of appropriate postharvest technologies further aggravate this situation.  Mango is a climacteric fruit whose ripening is accompanied by a surge in ethylene evolution, which in turn triggers other metabolic processes that hasten ripening. The ripening process can be slowed down by inhibiting perception and action of the ripening hormone, ethylene. 1-methylcyclopropene (1-MCP) is a novel postharvest technology, known to prolong the postharvest shelf life of perishable commodities by inhibiting ethylene production and action. Efficacy of 1-MCP is reported to be affected several factors including, species, variety and stage of maturity.  The objective of this study was to determine the effect of stage of maturity on the efficacy of 1-MCP in mango fruits, variety Tommy Atkins. The fruits were harvested at two stages of maturity based on shoulder elevation also referred to as the fullness of cheeks. The stages were verified in the laboratory from flesh color and respiratory activity. Stage 1 fruits were those at early maturity (mature green), prior to rising of the shoulder,where the flesh was mostly white in color, slightly turning yellow near the seed. Stage 2 fruits were those at advanced maturity when the shoulders had fully risen and with a sunken stem end and theflesh had changed color to yellow-orange. The fruits at the two stages were selected for uniformity and separated into two batches for administration of the various treatments. For each maturity stage, one batch was treated with 1-MCP at 1 ppm for 24 hours while the other batch was left untreated. The treated and untreated fruits were then allowed to undergo normal ripening at ambient room conditions.A random set of five fruits were sampled every two days from each treatment combination for evaluation of various physiological and physicochemical parameters associated with mango ripening. The parameters evaluated include respiration rate, ethylene evolution, cumulative weight loss, flesh hue angle and firmness, 0brix, titratable acidity, beta-carotene, ascorbic acid and soluble sugars (sucrose, fructose and glucose). The experimental design used was a completely randomized design with a factorial arrangement.

                                                                   

Efficacy of 1-MCP was significantly affected by the stage of maturity with stage 1 being more responsive compared to stage 2. For fruits harvested at stage 1, significant treatment effect (p ≤ 0.05) was observed in most of the parameters evaluated. 1-MCP treated fruits retained higher flesh firmness and hue angle compared to untreated control throughout the storage period.  Lower respiration rate was observed in 1-MCP treated fruits compared to untreated fruits throughout the storage period and the respiratory climacteric delayed by 3 – 4 days. Ethylene evolution was erratic in both the treated and untreated fruits, showing no clear trend.  The accumulation of total soluble solids (0brix) and soluble sugars (sucrose, fructose and glucose) progressed faster in untreated fruits, in which titratable acidity also decreased faster compared to 1-MCP treated fruits. At the end of the storage period, 1-MCP treated fruits retained relatively higher ascorbic acid and beta-carotene levels compared to untreated control. The results of this study show that 1-MCP can be used to effectively delay ripening changes in ‘Tommy atkins’ mangos thereby prolonging the shelf life and extending the marketing period. However, the timing of 1-MCP application is critical in realizing the desired effect.