Quality criteria for mango export in Ghana

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Field and laboratory studies were conducted to determine and establish quality criteria for harvesting export mango fruits from Ghana. Methods studied were mainly of physicochemical properties such as age control, visual aids, physical and chemical analyses. Early, mid and late harvest days after fruit-set were established for the four varieties. All determinations were made in relation to the age control criterion because of its precision in measuring or determining harvest maturity stage. Visual aids such as changes in fruit peel/skin colour, changes in colour on the flesh around the stone/seed, fruit shape/indentation, development of a purplish–red blush colour of the pedicel, starch iodine test and the leathery fruit peel that were noticed at maturity in all the varieties were very subjective. Fruits of all the varieties maintained a constant weight, length, width, volume, density and indentation at maturity. Palmer did not show indentation at maturity; rather, this is represented by the intensity of ridges/grooves around the stylar scar/end of its fruit. For latex content, an index value was assigned for the minimal acceptable harvest maturity for Haden, Kent, Palmer and Keitt varieties as 0.075ml, 0.150ml, 0.425ml and 0.116ml, respectively since these results tallied with the other harvest maturity index values. Thus, in fixing maturity indices for mango fruits, days from anthesis to harvest and morphological changes may be taken as criteria. The pattern of chemical changes was strikingly similar in all the varieties. Thus, the increase in total soluble solids (TSS) and TSS/acid ratio and the decreasing trend in titratable acidity (TA) could be used as another criterion for fixing the maturity standard of mango. While TSS and pH values showed an increasing trend, ascorbic acid and TA showed a decreasing trend as maturation/ripening progressed. Also selection of TSS, dry matter and starch as harvesting indices is appropriate since starch is the source of sugar production at the mature stage. Thus, four quality criteria or technical methods (age control, visual, physical and chemical) have been determined and established for harvesting mango fruits for export. Chemical, physical and age control methods necessitated determination and establishment of appropriate harvest maturity indices quite objectively whereas the visual method was subjective, though required no sophisticated equipment, and was easy to operate. Fruits intended for distant markets should be harvested around 112days, 126days, 133days and 140days after fruit set for Haden, Kent, Palmer and Keitt, respectively, i.e., early harvest if they are to be transported by sea, and can be harvested at the early stages of ripening, i.e., mid or late harvest if the fruit is to be transported by air. Fruit skin colour break, pale yellow pulp colour close to the seed, fruit indentation/depression around the peduncle, purplish–red blush colour of the pedicel and leathery fruit peel should be conspicuous at physiological maturity. Fruits should maintain a constant weight, length, width, volume, density and indentation at maturity. TSS, TSS/acid ratio, pH, ascorbic acid and dry matter contents increase to a peak while TA and moisture contents reduce at harvest maturity. A combination of several methods of assessing maturity is therefore recommended in order to establish appropriate quality criteria for export since a single harvest maturity index figure would not always reflect the harvest index in all giving situations. Other methods outside this study such as sinks and floats, growth of seed hairs, development of lenticels, development of abscission layer and others should be investigated under the same conditions to complement the study to make better decisions. Future research should consider easy–to–apply harvest indices and non–destructive methods that correlate positively to enable a computerised system of checking fruit maturity.
A Thesis submitted to the Department of Horticulture, Kwame Nkrumah University of Science and Technology in partial fulfilment of the requirements for the degree of Doctor of Philosophy on Postharvest Physiology, 2010