POST-HARVEST QUALITY IMPROVEMENT OF BANANA
I Ramma, SP Beni Madhu and P Peerthum
Agricultural Research and Extension Unit
ABSTRACT
Studies
carried out from 1996 to 1998 revealed that the best maturity index for determining
the harvest time of banana is a combination of bunch age and finger
diameter. However, the bunch age and
finger diameter ranges for indicating optimum harvest maturity stage have to be
worked out for each of the economically important banana varieties.
In a survey
of local markets, crown rot was identified as the major postharvest
disease. Fungicide trial showed that
thiabendazole at the rate of 500 and 1000 ppm and benomyl at the rate of 250
and 500 ppm used as post harvest dip successfully controlled the disease with a
more persistent control with the higher dosages. Industrially ripened fruits
had the longest shelf life of 8 days when stored at 18°C as compared to 7 days when stored
at ambient room conditions and 4 days when stored under simulated warm market
conditions.
Keywords: bananas, Musa spp., shelf life, maturity index, finger diameter, bunch age, post harvest
diseases, harvest, storage, fruit quality.
INTRODUCTION
Banana, one of
major fruits in Mauritius, has now moved from backyard to commercial
production, with an annual production of 9,000 tonnes for the local market.
However, banana being a delicate and highly perishable fruit, the local
production is subjected to serious post harvest losses, mainly due to harvesting
at improper maturity stage, poor handling and storage practices and post
harvest diseases. Research was undertaken within a project, partially funded by
the Mauritius Research Council, to address these issues so as to improve the
post harvest quality of banana. This paper outlines activities undertaken
within the project from 1996 to 1998 related to determination of optimum
harvest maturity index, the disease status of banana on the local market and
the effects of different storage conditions on fruit quality.
MATERIALS
AND METHODS
Details of
activities conducted are described hereunder.
Determination
of an optimum harvest maturity index
Trial Sites
Trials were laid
out in already existing orchards of Wooton Experiment Station and on the premises
of Médine and Britannia Sugar Estates.
At Médine S. E, a trial was conducted on banana cultivar Dwarf Cavendish
over 2 seasons (winter and summer (1997/1998), while at Médine and Britannia
Sugar Estates, trials were carried out on the banana cultivar Williams during
the period of February/March 1997 to July/August 1997.
For all sites,
banana bunches were tagged at the time of flower emergence (shooting) and the
date of flower emergence of each plant was recorded so as to calculate the physiological
age of the bunch at the time of harvest.
Five randomly selected banana bunches of each of the different
physiological ages studied were harvested at the same time, dehanded and the
following parameters were measured:
Mean fruit weight = ((Weight of
bunch - weight of stalk) / total no. of fingers)
Length of finger (external curvature) using banana finger gauge
Diameter of a predetermined finger using vernier caliper (the middle
outermost finger of the second hand from the proximal end of the bunch)
Pulp : peel ratio (calculated as
the mean (weight of peel / weight of pulp) of 10 individual fingers were taken
randomly from each bunch
Effect of
bunch harvest age on shelf life and quality of banana
Five randomly
selected bunches at 4 harvest ages (12, 14, 16 and 18 weeks old) were harvested
from already existing banana c.v.Williams plantation at Anna, Flic-en
Flac. Each bunch was dehanded and
diameter of predetermined finger was recorded. Clusters of 6 fruits each from the 2nd and 3rd hands from the
proximal end were selected from each bunch.
5 clusters from each harvest age were subjected to industrial ripening
and then stored at ambient conditions. Each treatment was replicated 4 times. The fruits were scored for their peel colour
daily and 5 randomly selected fruits (1 from each cluster) were assessed for
the pulp bricks at colour score 6. The
shelf life of the fruits was determined by calculating the number of days between the commencement of ripening
determined by first sign of change in fruit peel colour and end of saleable
life (corresponding to colour score 7).
Appraisal,
identification and control of major post-harvest diseases on banana
A survey of 8
pre-identified markets situated in different localities were conducted on 8
different occasions over the period of June
- October 1996 and April - August 1997 to identify the major post
harvest diseases and their causal organisms.
The markets were visited at monthly intervals and at each sale point a
random sample of 4 hands was collected and kept in polyethylene bags at the
Plant Pathology Laboratory for isolation of pathogen(s) and identification.
The banana hands
were kept in the laboratory and observations and isolations were made at
regular intervals from the advancing margins of the diseases on the crown and
the fruits. Diseased tissues were
plated on standard potato dextrose agar and the micro organisms were allowed to
grow at room temperature for three to five days. Identification of fungi was carried out in the laboratory using a
light microscope.
Following the
survey on disease status of banana, a fungicide evaluation trial was conducted
to control the major disease (crown rot) on banana c.v. Dwarf Cavendish. Fruits were harvested at uniform maturity
and were treated by dipping for 2 minutes in the following solutions:
thiabendazole (Mertect 20S TBZ) @ 500 and 1000
ppm,
benomyl (Benlate 250) @ 250 and
500 ppm,
chlorothalonil (Bravo 500) @ 500 and 1000 ppm
and
prochloraz (Sportak 40) @ 500 and 1000 ppm
control (dip in water only)
A randomised
complete block design with four
replicates was used and each replicate consisted of one hand of unbruised,
healthy banana with 12 to 18 fruits.
The fruit samples were subjected to the above treatments and then air
dried prior to artificial ripening with
ethylene gas under temperature controlled conditions (16 - 18°C) for 4
days.
After the
ripening treatment, the fruits were removed and allowed to ripen at ambient laboratory
conditions and were assessed for crown rot (on the 5th, 7th and 9th days after
harvest) until the fruits attained optimal ripeness( colour score 6). The severity of infection was measured in
terms of a disease index based on a slightly modified scale of (0 - 5) developed by Frossard and Laville,
1973,
where
0= Apparently
healthy fruits
1= slight infection
2= 25 % of crown
infected
3= 50 % of crown
infected
4= 100 % of crown
infected
5= Entire crown
infected and infection progressing towards the pedicels
Extension of
shelf life of fruits after industrially ripening
A trial was
conducted to determine the best storage condition for marketing ripened bananas
as to extend its shelf life and maintain the post-harvest quality. Banana c.v. Dwarf Cavendish was harvested at
full ¾ angularity (finger diameter 32 – 33 mm), bunches dehanded and from each
bunch 4 clusters of 6 fruits of the
second and third hands were selected.
The fruits were industrially ripened for a period of 4 days and after
which they were removed and scored for peel colour and then stored at different
storage conditions namely:
cool (18°C),
ambient (mean 22.5°C)
and
simulated warm market conditions (26 °C)
The fruits were
assessed daily for weight loss, peel colour and shelf life.
RESULTS
AND DISCUSSION
Determination
of a harvest maturity index
Results for
determination of a harvest maturity index are shown in Tables 1, 2 and 3.
Table 1 Maturity indices of
banana variety Williams of different harvest ages grown at Britannia S. E.
(1997)
|
Harvest
age |
Mean finger |
Pulp / peel
Ratio |
||||||
|
Weight |
Length |
Diameter |
||||||
|
weeks |
g |
S.E ± |
cm |
S.E ± |
mm |
S.E ± |
Ratio |
S.E ± |
|
12 |
110.41 |
1.96 |
19.50a |
0.45 |
30.70a |
0.03 |
0.97a |
0.01 |
|
13 |
116.83 |
2.01 |
19.59a |
0.17 |
31.14a |
0.05 |
0.99a |
0.01 |
|
14 |
123.79 |
2.62 |
19.75b |
0.27 |
32.32b |
0.04 |
1.15b |
0.03 |
|
15 |
124.31 |
3.86 |
20.17c |
0.24 |
32.53b |
0.44 |
1.24c |
0.02 |
At Britannia
Sugar Estates correlation coefficient between harvest age and other parameters
varied between 0.867 and 0.964 and the highest correlation was observed between
mean finger diameter and harvest age.
Furthermore, regression analysis showed a high regression coefficient
(0.928) between pulp / peel ratio and mean finger diameter (0.928), suggestive
that finger diameter (caliper grade) can be used as a good index of harvest
maturity. Measurement of finger
diameter on a pre-determined finger on each bunch is relatively easy to be
carried out in the field and is a non-destructive method of determining
maturity of bananas. It gives a good indication of the angularity of the fruit
(degree of fillness)
The pulp/peel
ratio of 1:1 and above (corresponding to finger diameter greater or equal to 32
mm and harvest age greater or equal to 14 weeks for banana c.v, Williams, grown
at Britannia) is considered to be a very good indicator of banana harvest
maturity (of minimum acceptable level of maturity for ripening and ensuring an
acceptable eating quality of bananas, Dalal et al (1970)). However, being a destructive method of
analysis, it is of limited practical commercial application.
The pulp / peel
ratio of less than 1:1 recorded on 12 and 13 weeks old bunches showed that these
had not attained the harvest maturity to ensure minimum acceptable eating
quality.
High variations
in mean fruit weight made it an unreliable index, and this can be explained by
the fact that all bunches did not have equal number of fingers. From Table 2, it is evident that bunches
harvested at the same age had a lower mean fruit weight at Wooton S.E as
compared to Britannia S.E.
Table 2 Maturity indices of banana
variety Williams of different harvest ages at Wooton ES. (1997)
|
Harvest age |
Mean fruit
weight |
Mean finger
length |
Mean finger
diameter |
Pulp / peel |
|
weeks |
g |
cm |
mm |
ratio |
|
13 |
93.6 |
17.50 |
29.30 |
0.94 |
|
14 |
92.0 |
17.50 |
30.12 |
0.98 |
|
15 |
97.7 |
17.75 |
31.81 |
1.01 |
|
16 |
103.2 |
17.72 |
31.85 |
1.01 |
|
17 |
112.0 |
18.21 |
33.62 |
1.14 |
|
18 |
116.6 |
18.29 |
32.72 |
1.16 |
|
19 |
125.0 |
18.85 |
33.91 |
1.22 |
The mean pulp /
peel ratio of 15 week old banana bunches harvested at Britannia (1.15) corresponded
to that of bunches harvested 17 weeks or later at Wooton. This shows the bunch
growth rate varies with the locality.
It may be due to differences in climatic conditions and management
practices. Thus, harvest age alone cannot be used to assess harvest maturity of
a particular banana variety on a wider geographical basis.
Data obtained at
Médine on the banana cultivar Dwarf Cavendish revealed that bunches developing
in winter had a lower mean fruit weight that those recorded in summer when harvested
at the same age. This difference in
growth rate may be attributed to variations in sum of mean daily temperatures
obtained during the bunch growth cycle as has been reported by Ganry et al,
1978. This seasonal variation implies harvesting of winter developing bunches
will require the adoption of a more extended flower emergence to harvest period
as compared to those developing in the hot summer months. Hence, the use of bunch age control alone
for harvesting of a specific banana variety even in one specific site does not
provide adequate guarantee that the fruits will be of uniform maturity.
Previous
research (Montoyo et al, 1984) has shown that it is impossible to set finger
diameter or bunch age limit alone for
universal application since the growth rate varied substantially according to
fruit growing conditions. However, both
bunch age and finger diameter should be
used together as indices of harvest maturity.
They can be performed relatively easy by banana growers in the field by
use of simple equipment known as a vernier calliper or by tagging the bunch
with a coloured ribbon as soon as it emerges. Special banana calliper to assess
banana maturity exists in banana exporting countries. Consequently, introduction of this simple equipment among our
banana growers can prove useful.
Table 3 Maturity indices
of banana variety Dwarf Cavendish at different harvest ages at Médine S. E
(1997/1998)
|
Bearing period |
Harvest Age |
Fruit weight g |
Finger length cm |
Finger diameter
mm |
Pulp / peel
ratio |
|||||||||||
|
weeks |
Mean |
S.E ± |
Mean |
S.E ± |
Mean |
S.E ± |
Mean |
S.E ± |
||||||||
|
Summer |
Temperature range 21-30°C |
12 |
99.8 |
2.24 |
17.4 |
0.17 |
29.6 |
0.02 |
0.93 |
0.02 |
||||||
|
13 |
106.6 |
5.56 |
17.2 |
0.51 |
29.8 |
0.13 |
1.04 |
0.05 |
||||||||
|
14 |
114.5 |
9.02 |
17.4 |
0.73 |
29.5 |
0.17 |
1.08 |
0.04 |
||||||||
|
15 |
108.2 |
3.78 |
17.4 |
0.18 |
29.9 |
0.07 |
1.08 |
0.06 |
||||||||
|
16 |
112.3 |
4.78 |
18.6 |
0.40 |
31.6 |
0.03 |
1.10 |
0.05 |
||||||||
|
Winter |
Temperature
range 19-28°C |
13 |
86.6 |
0.89 |
17.3 |
0.10 |
28.0 |
0.03 |
0.93 |
0.02 |
||||||
|
14 |
88.2 |
1.63 |
17.5 |
0.50 |
28.6 |
0.06 |
0.95 |
0.02 |
||||||||
|
15 |
91.4 |
2.52 |
18.2 |
0.12 |
29.2 |
0.02 |
0.97 |
0.03 |
||||||||
|
16 |
93.6 |
2.69 |
19.3 |
0.25 |
31.4 |
0.07 |
1.01 |
0.01 |
||||||||
|
17 |
91.0 |
1.16 |
19.1 |
0.12 |
30.8 |
0.08 |
1.07 |
0.05 |
||||||||
|
18 |
106.9 |
1.65 |
19.6 |
0.10 |
31.3 |
0.08 |
1.21 |
0.01 |
||||||||
Effect of
bunch harvest age on the quality and shelf life of banana
From results
shown in Table 4, 12 week old
harvested bunches had a mean shelf life of 8 days as compared to 7 days for
bunches of 14, 16 and 18 weeks old. It
clearly indicated that 14 to 18 weeks old bunches could be harvested together
since they gave a uniform ripening when ripened industrially.
Table 4 Effect of harvest
age on the post harvest quality of industrially ripened bananas c.v. Williams
at Anna, Médine stored at ambient conditions
|
Bunch Harvest
age Weeks |
Mean shelf life days |
Mean brix at
c.s 6 |
|
12 |
8 |
14.53 |
|
14 |
7 |
15.08 |
|
16 |
7 |
15.03 |
|
18 |
7 |
15.15 |
c.s – colour score
Mean values of
the pulp brix measured when the fruit reaches colour score 6 showed that fruits
of 14 to 18 weeks old bunches were slightly higher than value recorded on
fruits of the 12 weeks old bunches. The fact that sweetness is an important
characteristic Determining quality of banana, the mean brix values clearly
demonstrate that bunches harvested too early (12 weeks old or less) is of an
inferior quality than those harvested a more advanced stage.
Appraisal, identification and control of major post-harvest diseases on
banana
Crown rot
disease was the major post-harvest disease identified on ripening bananas in
Mauritius followed by anthracnose and blossom end rot (Table 5).
Crown rot was
found to be due to a complex of fungal pathogens, namely Fusarium sp., Colletotrichum
sp., Verticilium sp and Cladosporium sp. It was found to develop rapidly during fruit
ripening thereby reducing the quality and marketability of fruits.
In evaluation of
fungicides, all four fungicides provided a good control of the crown rot disease
as compared to the control (Table 6). In the
latter case, crown rot development was evident 5 days after ripening treatment
and the infection progressed rapidly as the fruit ripened over time
resulting in severe rotting of the crowns 4 days later (ripening index 5 to
6). This resulted in a decrease in the
shelf life as well as the marketability of the fruits.
Table
5 Diseases and disorders
recorded on ripening banana in market surveys, 1997/1998
|
Disease / Disorders |
Frequency
of occurrence |
Micro-organisms
isolated |
|
Crown rot |
86 |
Fusarium
sp. Collectotrichum sp., Cladosporium sp., Verticillium sp. |
|
Peel injury ,Bruising and
Anthracnose |
60 |
Colletotrichum
sp., Fusarium sp. |
|
Anthracnose |
9 |
Colletotrichum
sp. |
|
Anthracnose (latent) |
8 |
Colletotrichum
sp. |
|
Blossom end rot |
8 |
Colletotrichum
sp., Fusarium sp. |
|
Ripe rot |
5 |
Fusarium
sp. |
|
Uneven ripening |
3 |
|
Benomyl
and thiabendazole were found to be superior as compared to chlorothalonil and
prochloraz probably due to their persistence.
Eating quality of fruits assessed through an informal taste panel showed
that prochloraz treated fruits developed off taste. No phytotoxicity was noted in any of the treatments.
Table 6 : Control of
crown rot disease on banana, (1997/1998)
|
Fungicide |
Conc ppm |
Days after harvest |
||
|
5 |
7 |
9 |
||
|
Mean Crown rot |
||||
|
Thiabendazole |
500 |
0 |
0.1 |
0.3 |
|
1000 |
0 |
0 |
0 |
|
|
Benomyl |
250 |
0 |
0.1 |
0.3 |
|
500 |
0 |
0 |
0 |
|
|
Chlorothalonil |
500 |
0.4 |
1.2 |
1.3 |
|
1000 |
0.1 |
0.2 |
0.9 |
|
|
Prochloraz |
500 |
0.3 |
0.3 |
0.3 |
|
1000 |
0.3 |
0.3 |
0.3 |
|
|
Control (water) |
|
2 |
3.2 |
4.1 |
Thiabendazole (@
500, 1000 ppm) and benomyl (@ 250, 500 ppm) gave better control of the
disease. Moreover, it was noted that
the higher dosage gave better control over time compared to the lower dosage
where minor symptoms of crown rot development on some hands were recorded 7 and
9 days after treatment.
Extension of shelf life of fruits after industrial ripening
The temperature
at which industrially ripened banana fruits is stored has a definite significant
effect on its subsequent shelf life. Industrially ripened fruits showed a shelf
life from 8 to 7 and only 4 days when stored at 18°C, ambient room temperature (mean
22.5 °C) and simulated warm market
conditions (26 °C) respectively (Table 7).
Table 7 Mean colour score of
industrially ripened fruits stored at different storage temperatures
|
Days after harvest |
0 |
4 |
5 |
6 |
7 |
8 |
9 |
12 |
13 |
Mean % weight loss / fruit when fruit attain eating
quality (c.s 6) |
|
Ambient, industrial ripening |
1.0 |
2.0 |
2.9 |
3.6 |
4.3 |
5.2 |
6.4 |
7.0 |
|
13.3 |
|
18°C, industrial ripening |
1.0 |
2.0 |
2.4 |
3.0 |
4.0 |
5.0 |
6.0 |
6.6 |
7.0 |
7.8 |
|
26 °C, industrial ripening |
1.0 |
2.0 |
2.4 |
3.4* |
3.5** |
|
|
|
|
9.1 |
Presence of Brown Flecks: *
mild ** severe
Bananas stored under the simulated warm market conditions (26 °C) fail to completely degreen, resulting in
“green-ripe” fruits which are ripe in for every other aspects than peel colour.
After 3 days storage at 26°C, the fruits showed a mean peel
colour score of 3.42 accompanied with
the apparition of brown flecks. The
pulp softened rapidly into slimy texture with a strong unpleasant ester
smell. This storage condition also
favoured the development of fungal infection particularly anthracnose which
developed as brown patches on the peel and caused the pedicel
disintegration. This is a common
problem often reported by banana growers and handlers particularly in the
summer. It may be due to overheating as
a result of poor ventilation during ripening or storage. In the tropics, it has been reported that
bananas of the Cavendish group fail to degreen when ripened at high
temperatures (> 24°C)( Blackbourn et al 1990).
CONCLUSION
From studies
carried out, finger diameter (caliper grade) in combination with bunch age was found to be a reliable index to
determine time of harvest. Pulp / peel
ratio alone was found to be a reliable index too but not practical, being a
destructive method. Mean fruit weight was found to be a non-reliable parameter
due to the fact that bunches did not have equal number of fingers.
Crown rot was
the major post-harvest disease identified on ripening bananas. Thiabendazole at
the rate of 500 and 1000 ppm and benomyl at the rate of 250 and 500 ppm
provided good control of the disease when used as a post harvest dip
immediately after harvest. However,
with the higher dosages control over a longer period of time was obtained.
Industrially
ripened bananas was found to have the longest shelf life when stored at 18 °C for up to 8 days as compared 7 days for
ambient conditions and 4 days at simulated warm market condition. The extension
in shelf life of ripened banana obtained at 18 °C represents an improvement in the
marketability of bananas.
ACKNOWLEDGEMENTS
I wish to
express my thanks to : Mr S.P.Beni Madhu, Principal Research Scientist of the
Plant Pathology Division of AREU for reviewing the manuscript and Mr
R.K.Ramnauth, Biometrician for the statistical
advice and guidance
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