Effect of various treatments on banana ripening.

Farid, Huda Ahmed Ridda

Huda Ahmed Ridda Farid (School of Pharmacy Ahfad University for Women, Omdurman, Sudan.)

Physiological changes were measured during the ripening and storage of bananas. Mature green banana fruit subjected for different periods at temperatures of 9.5, 11.5, 13.5, 20, 30, 34, 38 and 42[degrees]C to find out the effect of different temperatures on the physiology of banana ripening

Fruit held at each of the temperatures softened and sweetened as determined by changes in pulp rupture, force and pulp soluble solid content. Although no significant differences were observed, fruit softened slightly faster at higher temperatures than at lower ones. A similar trend for changes in the pulp soluble solids was observed with increasing temperatures Exposure to high temperature before storage, accelerated the rate of ethylene production as well as the degree of degreening. The fruit developed a golden yellow peel colour when fully ripened, compared with those kept at chilling temperature which acquired a dull yellow peel colour. Despite these differences in the extent of degreening, other assessed parameters indicated that the fruit treated at different heat and chilling temperatures had all softened to the same extent by day 5.

From the experimental results, it was concluded that pre-ripening heat treatment at the range between 20 and 34[degrees]C had no deteriorative effect on the quality of the fruit.

Introduction

The banana is a remarkable fruit. Not only because, to this day, it is the only tropical fruit ever to have sealed the ratified heights of the total consumer recognition, but also because its cultivation and marketing are so totally different from those of any other fruit (1-2). The most obvious difference is that the harvesting of bananas goes on all year round and is not confined to a particular season.

Bananas are a perishable commodity. Fruit grown for export is harvested much earlier compared with those intended for the local Wade because of the possibility of some ripening fruit to produce sufficient ethylene to induce ripening within the rest of the consignment. As fruit begins to soften, it is much more prone to mechanical damage, which reach the consumer in poor condition. Therefore, control over the ripening process is required to ensure predictable ripening and good quality ripe fruit (3).

Temperature is one of the major environmental constraints governing the quality of many tropical and sub-tropical fruits, which exhibit a physiological dysfunction when exposed to temperatures, which are either too high or too low (4-8). Thus, the choice of temperatures will be greatly affected by various practical considerations and limitations.

Therefore, there will be a need to initially establish the subtle physiological effects at the borderline chilling temperatures and during potential high temperature treatment. The present study involved investigations on the response of bananas to elevated temperatures in comparison to chilling temperatures and the relationship between changes during ripening.

Methodology

i. Plant Material

Pre-climacteric bananas from Honduras (Dole and Hoya) and Ecuador (Fyffes) were obtained from a commercial source (Fyffes Ltd, Dartford, UK.). they belong to the Cavendish Subgroup. The fruit used were of the normal commercial maturity of three quarter grade to full three quarter grade, which means they were almost fully grown.

Only undamaged green fruit were selected for the experiments and the cut crown of each fruit was dipped for 10 seconds in a 50ppm fungicide, benomyl (benlate wetable powder) to control crown rot. The bananas were then air-dried before any further treatment. Before exposing to ethylene, all fingers were weighed and assessed for peel colour, using a colorimeter, after which two set experiments were carried out in duplicate to determine the effect of temperature on the physiology of ripened bananas.

ii. Heat Treatment

Eighteen fruits were held for 45 hours at each of the five temperatures via 20 (as control), 30, 34, 38 and 42[degrees]C. After this the fruit was ventilated and exposed to ethylene for 24 hours to stimulate ripening

iii. Cold Treatment

Eighteen fruits were held for one week at each of the four temperatures 8.5, 11.5, 13.5 and 20[degrees]C. The latter used as control. During this period, peel colour was assessed every two days. Ripening of the fruits was then initiated

iv. Parameters Measured

A. Peel colour score:

A.1. Visually

Colour of banana peel was determined visually and classified according to a banana ripening guide described by Van Losseck (1949).

A.2. Colorimeter

Colour of banana peel was ascertained by Minotla Chroma Meter II: Reflectance (Minotle UK Ltd.) employing a 8ram viewing aperture.

B. Pulp Rupture Force:

This was determined using a salter 0-10kg. electronic force gauge.

C. Pulp to Peel Ratio:

The peel and pulp were separated, weighed individually and expressed as pulp to peel ratio.

D. Total Soluble Solids Content of the Pulp:

This was determined using Abbe Bench Repactometer (Bellingham and Stambey Ltd.).

E. Weight loss:

The weight loss, on removal from a ripening temperature, was calculated as a percentage of initial weight.

F. Ethylene Determination:

This was determined employing a Photorac (10s) Portable Photoionzation Gas chromatography. The instrument was calibrated with 3.4 [micro]l/l of ethylene in nitrogen.

Data obtained were analysed by an analysis of variance.

Results and Discussion

Changes observed in ripening bananas include the visual appearance such as skin colour and shape, which occur simultaneously with other physiological parameters, particularly increase in pulp weight relative to peel weight, pulp soluble solids content and ethylene production.

The colour index changed during ripening in all the treatments and there were no measurable variations within treatments. It was observed that exposing the bananas to high temperature before storage at 20[degrees]C enhanced the rate of ripening. The skin developed on attractive golden yellow colour. By day 7, the fruit developed many dark brown flecks and spot (senescence spotting) on the peel illustrating that it was fully ripened.

There were no significant differences between measurements at low temperatures compared to the control at 20[degrees]C. Four days after initiation of ripening, bananas that had been stored at 9.5 and 11.5[degrees]C developed a dull greenish-yellow colour, which became dull yellow when the fingers are fully ripened.

In heat treatment, it was observed that the pulp rupture force of fruit decreased as the fruit ripened from 2.65 to 0.16 kg And 1.01 to 0.13 kg at 20[degrees]C and 42[degrees]C respectively. The increase in temperature from 20 to 42[degrees]C accelerated the rate and determined the degree of softening of the pulp over the seven days storage period. By day 5, the pulp of all fruits had softened to the same extent. After 7 days, the pulp of the fruit stored at 20[degrees]C 2 after exposure to 42[degrees]C had developed a watery texture, whereas the pulp of fruit held at 20, 30, 34 and 38[degrees]C had a normal appearance of ripe fruit by day 7. Concerning cold treatment, measurement of the pulp rupture force showed that after 2 days the pulp softened more rapidly except for those at 20[degrees]C which showed a steadily softening fill day 5. The variation of pulp firmness with temperature reflects how the various enzymatic process involved in these changes varied in their sensitivity to temperature.

For heat treatment, values obtained indicate that the pulp to peel ratio increased with increase in temperature.

Increase in ratio of pulp to peel tissues occur mainly due to high moisture loss from the latter. Values obtained for cold treatment showed a steadily change in ratio, which means that the cold temperature does not appear to affect this aspect of ripening.

Temperatures between 42 and 30[degrees]C were found to exhibit a significant higher soluble solids content compared with the control 20[degrees]C on day 2. The development of soluble solids on day 4 was similar for the control and the other heat treatments (30-42[degrees]C) which implies that there was a sudden change in the initial ripening response between different temperatures. On the other hand, from the values obtained at lower temperatures, it is noteworthy that the increase in soluble solids content was comparatively much higher between 0 to 4 days than between 4 to 7 days.

The rate of ethylene production was increased with increase in temperature with maximum production at 34[degrees]C. On the contrary, the low values obtained indicate that chilling temperature seemed to delay its evolution.

Conclusion and Recommendations

From these experimental results, there would appear to be no significant difference in the pulp rapture forces and development of soluble solids content during ripening in which case, suggested the possibility that more of these temperature treatments causes abnormal rates of softening or sugar production. However, one should consider the inherent variation in banana maturity. Regarding ethylene production, unlike heat treatment, 'chilling temperatures seemed to delay the rate of its production.

The primary index of maturity used when banana fruit become edible is the peel colour. It is observed that colour changed during ripening in all treatments. The degree of brightness varied. A dull yellow colour was developed in some of the fingers exposed to temperatures below 11.5[degrees]C. On the other hand, exposure of fruit to high temperature for 45 hours prior to storage gave reproducible results. The fruit developed a golden yellow colour. This reveals that pre-storage conditioning could be a practical treatment to prolong the storage life of chilling sensitive crops.

With increased shipments of commodities from tropical and subtropical countries, and with the increase use of mechanical refrigeration in tropical countries, these would remarkably contribute to the growing importance of chilling injury. Therefore, this area of study, pre-storage conditioning in bananas, certainly merits further work.

Table (1): Peel Colour Change (Heat Treatment)

Treatment Period of Colour Score
Temperature Storage
([degrees]C) (Days) L. value A. value B. value

20 0 62.4 -17.2 36.4
 2 61.6 -18.4 38.5
 4 73.0 -6.2 50.6
 5 74.9 -4.4 51.9
 7 75.9 -3.2 51.2

30 0 57.9 -18.6 38.7
 2 65.7 -14.4 41.9
 4 73.9 -6.2 50.0
 5 75.5 -4.2 52.3
 7 73.0 -1.8 53.1

34 0 61.7 -16.2 39.6
 2 59.0 -16.7 40.3
 4 69.9 -10.1 48.6
 5 69.7 -3.0 48.9
 7 72.0 -0.9 49.9

38 0 61.5 -16.5 38.2
 2 65.7 -15.8 42.0
 4 71.2 -7.8 49.1
 5 68.1 -4.4 50.3
 7 65.8 0.5 45.5

42 0 61.2 -18.1 41.0
 2 63.2 -15.7 43.1
 4 57.4 -5.7 34.6
 5 67.1 -3.3 49.1
 7 67.3 -1.1 47.7

Table (2): Peel Colour Change (Cold Treatment)

Treatment Period of Colour Score
Temperature Storage
([degrees]C) (Days) L. value A. value B. value

20 0 62.4 -17.2 36.4
 2 61.6 -18.4 38.5
 4 73.0 -6.2 50.6
 5 74.9 -4.4 51.9
 7 75.9 -3.2 51.2

9.5 0 57.3 -12.3 33.8
 2 56.9 -9.8 33.3
 4 65.6 -3.0 40.9
 5 66.1 -1.6 41.6
 7 73.2 -1.7 51.5

11.5 0 58.9 -9.3 34.2
 2 59.1 -7.6 34.3
 4 61.7 -1.0 35.0
 5 62.2 -0.7 38.1
 7 65.1 -0.2 34.0

13.5 0 69.0 -6.5 47.1
 2 69.9 -2.4 48.7
 4 69.7 -1.2 48.1
 5 71.6 -1.6 48.6
 7 67.3 -0.2 46.4

References:

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