The Mangosteen, a highly regarded fruit of tropical Asia, is readily accepted by Europeans.
Limited consignments of mangosteen fruit at various stages of maturity and ripeness were received from Kamerunga Horticultural Research Station during November 1985.
Eight individual fruit were selected, one in each of the following ripeness categories:
1. Mid-green, no purple colour.
2. Mid-green, tinge of pink-purple speckling.
3. Mid-green, ¼ tinge pink-purple colour.
4. Uniform light pink-purple colour.
5. Uniform pink-purple colour.
6. Uniform reddish-purple colour.
7. Uniform dark red-purple colour.
8. Uniform dark purple colour.
Each fruit was assessed for visual, physical, sensory and chemical attributes.
36 fruit were selected, 12 in each of three ripeness categories 1, 3 and 4 as outlined in experiment 1.
Four fruit of each category were selected as untreated control fruit. Four fruit of each category were shrink-wrapped in Cryovac MD multiply polyolefin film (19 μ). Four fruit of each category were shrink-wrapped in Cryovac XDR, single wound, polyolefin film (15 μ).
Two fruits were then randomly selected from each of the three treatments in each ripeness category for storage at 20°C for approximately 1 week and at 5°C for approximately 3 weeks. Individual fruit were examined daily and assessed for percent weight loss and appearance.
Two fruit were selected at each of three ripeness categories 1, 2 and 3 as outlined in experiment 1.
One fruit of each category was selected as an untreated control fruit. These fruit were stored in air at 20°C.
One fruit of each category was controlled ripened at 20°C in 100 ppm ethylene gas. Each fruit was examined daily and assessed for changes in fruit appearance.
When each fruit reached a fully-ripe, purple-skin stage, the skin was rated for latex and rind colour, and the aril assessed for eating quality and analysed for percent soluble solids and pH.
Results and Discussion
Experiment 1: quality assessments were carried out on mangosteen fruit of eight ripeness categories, such as amount of latex exuded, discolouration, rind colour, flavour and texture. Mature fruit from fully green to half-colour had a substantial amount of latex exudation from the cut surface of the rind. The aril (edible pulp) of fruit in these categories are discoloured and immature. Fruit firmness, measured objectively by Instron machine (newtons) decreased significantly from mature green to full purple colour, although this softening process was not easily detectable by manual finger pressure. Eating quality was acceptable at a uniform pink skin colour (hedonic scale ratings > 5) and was optimum at category 7, dark red-purple skin colour.
A larger sample of fruit would be required to determine whether consistent changes occur with ripeness category in soluble solids, pH and titratable acidity.
The main observations of the changes in various quality parameters with storage time of 3 ripeness categories and 3 plastic film packaging treatments stored at 20°C and 5°C, were as follows:
(i) During 1 week's storage at 20°C, percent weight loss was effectively controlled by both shrink-wrapped plastic films (< 1. 0%) compared with the unwrapped control fruit which lost approximately 10% of the fresh weight. Calyx and skin discolouration were reduced and fresh fruit appearance maintained by use of the plastic films, without loss of aril eating quality.
(ii) At 5°C, percent weight loss of unwrapped control fruit after 3 weeks was approximately 3. 5%, whereas weight loss of fruit shrink-wrapped in the plastic films was 0.2%. The calyx in all fruit became discoloured during storage, but skin discolouration was again less on film-wrapped fruit. Therefore, the use of shrink-wrap plastic films was an effective means of maintaining fresh-fruit appearance and eating quality at room temperature and under cool storage.
The visual changes which occurred on mature green mangosteen fruit stored at 20°C in air and under ethylene, are summarised:
Purple skin colour developed more rapidly under ethylene than in air. Whether this was the result of ethylene promoting a climacteric pattern of ripening remains to be determined in future trials. Calyx discolouration was reduced on the ethylene-ripened fruit, which also had higher ratings for general appearance as a consequence of more rapid development of uniform purple skin colour. At eating ripe, no differences were found in eating quality of air-ripened and ethylene-ripened fruit.
Because of limited and variable fruit supplies, only preliminary observations could be made from these experiments. However when fruit supplies increase, further postharvest trials should be carried out on fruit maturity, ripeness, controlled ripening, packaging and storage.
DATE: September 1991
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