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Carriage of Bananas Musa spp in Refrigerated Ships and

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Carriage of Bananas Musa spp in Refrigerated Ships and Powered By Docstoc
					Carriage of Bananas (Musa spp.) in Refrigerated Ships and Containers:
Preshipment and Shipboard Factors Influencing Cargo Out-Turn
Condition
A.L. Snowdon
Wolfson College
University of Cambridge
Barton Road
Cambridge, CB3 9BB
United Kingdom

Keywords: chilling, diseases, ethylene, leaf-spot, losses, Musa, postharvest, ripening,
  ‘yellow pulp’

Abstract
        Information on the cargo condition of bananas (Musa spp.) is obtained during
out-turn surveys at destination (on behalf of cargo receivers, underwriters, ship
owners or charterers) or during the study of claims documentation submitted by
lawyers acting for one or other of the above parties. There may also be occasion to
visit the producer country. Preshipment factors influencing cargo quality and out-
turn condition include the weather, crop husbandry in relation to leaf-spot diseases,
harvesting and handling techniques, postharvest treatments, method of packaging,
schedule of loading, and carriage instructions written by the shipper/exporter.
Shipboard factors include design and function of the refrigeration and ventilation
equipment, method of stowage, interpretation of carriage instructions, and duration
of voyage. For container shipments it is the shipper’s responsibility to ‘stuff’ the
container in an appropriate manner; the container operator accepts the closed box
and undertakes to supply refrigeration/ventilation in accordance with the shipper’s
carriage instructions. Deterioration (such as premature ripening) is often the result
of a combination of adverse factors. Particular problems include the difficulty of
achieving uniform air circulation through a palletised stow, and the challenge of
shipping additional commodities (which may produce ethylene) in the same vessel.
Accurate diagnosis of the causes of deterioration can assist in prompt settlement of
claims and reduction of losses in the future.

INTRODUCTION
        Banana (Musa spp.) is the most important perishable commodity in international
trade. Cargoes of bananas are carried either in the holds of reefer (refrigerated) vessels or
in refrigerated shipping containers, and a voyage may take a few days or several weeks.
        The period between harvesting of bananas and initiation of normal ripening, i.e.,
the duration of the pre-climacteric phase, is sometimes called ‘green-life’ (Ramírez et al.,
2008). The international banana trade is based on the harvesting and transportation of
hard, green, unripe fruit, which is later ripened in the country of consumption. The aim of
refrigerated carriage of bananas is to deliver fruit that is still in the preclimacteric state, so
that the climacteric may subsequently be artificially induced, in a uniform and controlled
manner, by injection of a measured quantity of manufactured ethylene into the
commercial ripening room. In this way it is feasible, within limits, to release ripened fruit
on to the market according to demand (Stover and Simmonds, 1987).
        Currently, the bananas most usually grown for export are those in the ‘Cavendish’
(AAA genome) group of cultivars, although there is now much emphasis on the need for
new disease-resistant bananas. The lowest temperature at which ‘Cavendish’ may safely
be shipped is in the region of 13.3°C, and this is optimal for extending postharvest life. At
temperatures below this critical value there is a risk of chilling injury. In contrast to most
other fruit commodities, bananas are usually presented to the carrier at ambient
temperature, and it is the task of the ship or container to cool them safely to carriage

Proc. IC on Banana & Plantain in Africa                                                      375
Eds.: T. Dubois et al.
Acta Hort. 879, ISHS 2010
temperature. Most cargoes arrive in good condition, but occasionally some of the fruit
ripens prematurely aboard ship, or suffers chilling injury, resulting in substantial losses
and protracted litigation (Snowdon, 1988).

MATERIALS AND METHODS
         Information is obtained during out-turn surveys at destination (on behalf of cargo
receivers, underwriters, ship owners or charterers) or during the study of claims
documents submitted by lawyers acting for one or other of the above parties. There may
also be occasion to visit the producer country and observe practices in the plantation,
packing house and load-port. The most important pieces of survey equipment include a
camera, a sharp knife, an electronic spear thermometer that is regularly calibrated in
melting ice, calipers to measure ‘grade’, and an aide-mémoire in which to record essential
details.
         Numerous factors determine the quality and condition of a banana cargo on
discharge. Pre-shipment factors are the responsibility of the grower and shipper, while
shipboard factors are the responsibility of the ship owner, charterer or container operator.

PRESHIPMENT FACTORS

Crop Husbandry in Relation to Weather and Diseases
         Fruit characteristics may be influenced by temperature, rainfall, cloud cover and
so forth. These factors also determine the likelihood of disease. There are several diseases
that originate in the plantation and may have important effects after harvest.
         Anthracnose, caused by Colletotrichum spp., is one of the commonest diseases of
bananas and is known in all banana-producing countries. Two types of symptom result
from different modes of infection (De Lapeyre De Bellaire et al., 2008). Anthracnose
lesions on green fruit are generally dark brown to black with a pale margin, have a lens-
or diamond-shape, are slightly sunken and have dimensions of several centimeters. On
ripening fruits the typical symptoms are small, dark, circular spots, which enlarge,
coalesce and become sunken. The lenticular lesions may also be present in ripening fruit.
On both types of lesion, salmon-pink spore masses are eventually produced. The circular
spots are the result of infections initiated in uninjured, immature fruit whilst it is still on
the plant, but which remain quiescent until the onset of ripening. The large lesions are the
result of infection following physical injury, the fungus gaining entry via wounds
sustained during harvest and handling; besides causing an unsightly blemish, both the
injured tissue and the fungus itself emit ethylene, which can induce premature ripening
(Snowdon, 1990).
         Sigatoka disease has resulted in epidemics in Australia, Asia, Africa, Central and
South America and the Caribbean. The potential impact of this disease is substantial.
Mycosphaerella musicola causes ordinary sigatoka, while a more virulent species, M.
fijiensis, has gradually spread and become the dominant species; it causes black leaf-
streak or black sigatoka, which is even more costly to control. The disease is different
from others in that the causal organism is not itself present in the fruit but yet has
profound effects on fruit development. This can have repercussions on the selection of
bananas for distant markets. It is essentially a leaf-spotting disease, which at its worst, can
cause premature death of large areas of the plant’s leaf surface. Photosynthesis is thereby
drastically reduced, sometimes to the extent that fruit does not mature at all. In less severe
outbreaks the effects are insidious, especially if younger leaves are involved. Such
infection causes advancement in physiological age of the fruit. The size of bunches and
individual fingers is reduced, with the result that fruit may be significantly more advanced
than is indicated by its size and appearance. Bananas from infected plants therefore tend
to ripen prematurely. Furthermore, ripening is often uneven, in that single fingers of a
hand or cluster are markedly in advance of, or behind, their neighbors in ‘turning’. In
badly affected fruit (from plants with few healthy leaves), the pulp is buff-salmon in
color, has an astringent taste, and emits an abnormally strong aroma. In less seriously


376
affected fruit (from plants retaining most of their leaves) the pulp may be only slightly
discolored, chiefly along the central line. This disorder, called ‘yellow pulp’, can also be
caused by factors other than black sigatoka. Depending on the severity of attack and
control measures taken, the effects of sigatoka may be manifest as premature ripening on
the plant, in the packing station, on the wharf, or during the voyage, this last showing up
as an increase in the percentage of cartons with ‘ripe and turning’ fruit noted on discharge
of the cargo. If this percentage becomes excessive, it is appropriate to reduce the risk by
harvesting the fruit earlier, i.e., at a younger age or a lower grade (see below). Black
sigatoka management mostly involves spraying the plantation at appropriate intervals
with protective oil and/or fungicide, together with regular removal of diseased leaves. In
most localities such measures are a major component of successful export banana
production (Gowen, 1995).

Maturity of Fruit at Harvest
         Developing banana fruits have an angular cross-section, which gradually becomes
more rounded as the fruit fills out and increases in girth. The diameter of the middle
outside finger of a particular hand defines the ‘grade’, which is expressed in millimeters
or, as is common in Central and South America, in thirty-seconds of an inch. Sometimes
it is expressed as the number of thirty-seconds of an inch beyond one inch, so that a grade
of 12 means a diameter of 44 thirty-seconds of an inch, or l 12/32 inches.
         Bananas must be cut at a maturity that will allow them, under normal transport
conditions, to arrive at their destination (i.e., in the ripening room) before ripening has
commenced. The appropriate maturity stage for cutting depends partly on the cultivar of
banana and partly on the duration of the proposed journey. Fruit intended for distant
destinations must be cut while relatively thin, whereas fruit destined for a short voyage
can develop to a slightly fuller grade before being harvested.
         Fruits of the same grade are not necessarily of the same chronological age (the age
being the number of days from the time when the fruit stem emerges). If fruit is cut by
grade alone, it will be of mixed maturity, such that two hands in the same carton may
differ substantially in age. This increases the risk of premature ripening (Stover and
Simmonds, 1987). For greater uniformity, therefore, maturity is assessed by using both
criteria (age and grade), and in commercial plantations a system of color-coded ribbons is
used to mark the plants at the time of shoot emergence or, rather, at the time when the
developing bunch is ready to be enclosed in a protective polyethylene sleeve or bag. The
principle behind an age-grade control system is that rapidly developing bunches are
harvested when the bananas reach a certain caliper grade (i.e., before they get too big),
and bunches that develop slowly are harvested when they reach a certain chronological
age (i.e., before they get too old). Given the variability in a population of bananas, this
system is an attempt to harvest fruit of similar maturity, and has the important advantage
of permitting the maximization of yield, while at the same time minimizing the risk of
losses caused by premature ripening of ‘forward’ fruit.
         In plantations, all newly-emerging bunches are bagged and tagged, the color of the
ribbon denoting the specific week in which this is done. The majority of the harvesting of
fruit with a particular ribbon color will take place over a three week period. This can be
illustrated by an example of a three-ribbon sequence, which might be appropriate for a
particular cultivar of banana grown in a particular area at a particular time of year, and cut
for a particular length of voyage. Suppose fruit bagged in week 30 receives a blue ribbon,
fruit bagged in week 31 receives a pink ribbon, and fruit bagged in week 32 receives a
silver ribbon. In week 43 silver-ribbon fruit will be only 11 weeks old (77 day fruit), so is
harvested only if it has reached a certain desirable grade. In week 43 pink-ribbon fruit
will be 12 weeks old (84 day fruit) and is likewise harvested (as it was the previous week)
by reference to its grade. In week 43 blue-ribbon fruit will be 13 weeks old (91 day fruit)
and, because of this, all remaining blue-ribbon fruit is ‘swept’, i.e., harvested even if it
has not yet reached the most desirable grade. For each ribbon color, therefore, the system
uses grade as the harvest criterion in the first two weeks of the sequence, and age as the


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criterion in the third or ‘sweep’ week. Beyond this, it is also necessary to monitor the
development of fruit of the subsequent ribbon color(s), since a small proportion of this
will also reach desirable grade and require early harvesting.
        The success of an age-grade control system is founded upon trial and experience,
and depends on the prior accumulation of year-round data relating age and grade at
harvest with quality and condition on out-turn. The factors to be determined are the
critical age and the maximum grade, beyond which there would be an unacceptable
percentage of ‘ripe and turning’ bananas on discharge. The critical age and the maximum
safe grade vary with the season of the year (according to normal or indeed abnormal
weather patterns) and with the incidence of leaf-spot, and it is therefore a matter of
expertise to adjust the harvest criteria according to circumstances (Stover and Simmonds,
1987). The absolute minimum grade, below which bananas are discarded, is determined
solely by the requirements of the market.

Postharvest Handling, Treatment and Packing
        It is essential to handle fruit carefully in order to minimize damage (cuts and
bruises), the effects of which will be manifest when the fruit ripens. Injury results in
increased rates of respiration, and also predisposes the fruit to fungal attack, such as
anthracnose. Cutting the ‘crown’ of the hand is of course unavoidable, and special
precautions are taken to disinfect this vulnerable fresh wound, by dipping or spraying
with a fungicide such as thiabendazole (TBZ). This is to avoid crown rot, a disease
complex caused by several fungi, sometimes in association with bacteria; different
organisms predominate according to locality, time of year and other factors (Snowdon,
1990). Crown rot tends to be most severe in consignments that are in transit for longer
than fourteen days. White, grey or pink mould may form on the surface of the cut crown.
Infected tissue turns black and the rot may advance into the finger stalks, causing the
fingers to drop off when handled. Finger-stalk rot may occur directly, in the absence of
crown rot, if the stalks are injured through flexing of the fingers. Severe infection induces
premature ripening.
        The current method of packaging for bananas consists of a polyethylene bag
within a sturdy, ventilated, cardboard carton. The clusters (part hands) of bananas are
carefully placed in four rows, the two upper and the two lower rows separated by a
flexible cardboard pad designed to prevent fruit-on-fruit injury. The pad is outside the
bag, but projects between the rows via a fold in the bag. Thin polyfilm (0.013 mm or
0.0005 inches or 0.5 mils or 50 gauge) is used in the standard ‘Polypack’ and, besides
reducing abrasion, minimizes fruit moisture loss. Moisture loss is undesirable because of
the concomitant weight loss, and also because water-stressed fruit tends to ripen
prematurely. Thicker polyfilm (0.04 mm or 0.0015 inches or 1.5 mils or 150 gauge) can
be used to create a modified atmosphere (MA) around the fruit. Respiratory gases take
longer to permeate through the thick film, and the resultant low oxygen/high carbon
dioxide atmosphere reduces the fruit’s sensitivity to its own ethylene, thereby prolonging
postharvest life. In the ‘Banavac’ system, the polyethylene bag is partially evacuated
before being tightly sealed at the neck. This procedure permits rapid establishment of an
appropriate atmosphere and reduces the risk of over-modification and resultant
suffocation. ‘Polypack’ packaging cannot be relied on for a period greater than about 28
days, while ‘Banavac’ has been known to maintain green-life for as long as 40 or even 50
days, so is advantageous in the event of delay. If, however, premature ripening does take
place, the enhanced carbon dioxide concentration tends to inhibit color change in the peel,
leading to ‘green-ripes’, in which the pulp is soft and ripe but the peel remains green.
While useful as a means of extending storage life, MA packaging carries one
disadvantage: the polyethylene bag must be punctured before arrival in the ripening room
(to facilitate ingress of ethylene gas), and this involves costly labor.
        Superior to MA is controlled atmosphere (CA), in which appropriate
concentrations of oxygen and carbon dioxide are accurately maintained within the hold
space (by special apparatus), rather than approximately maintained within each package


378
(by means of the fruit’s own respiration). For CA carriage, bananas must be packed in
‘Polypack’. The optimal atmosphere is generally given as about 3.5% oxygen and 5%
carbon dioxide, with a carriage temperature of 14.4°C.

Time between Cutting and Cooling
         Bananas should be stowed in refrigerated space preferably within 24 hours,
certainly within 48 hours, of harvest; a common stipulation is that a period of 36 hours
should not be exceeded. If bananas remain at high ambient temperature for longer than
this, their green-life will be curtailed. Factors influencing the initiation of ripening include
cultivar, growing conditions, age and grade at harvest, storage temperature and humidity
after harvest, and the presence or absence of ethylene in the atmosphere. The following
examples illustrate the time scales involved.
         Bananas intended for local consumption can be left on the plant until the fingers
are fully rounded (full grade). If the harvested bunch is hung in a shaded place at ambient
temperature (25 to 30°C), it will ripen within a few days. At lower temperatures, or with
younger or thinner fruit, initiation of ripening will occur later. For example, it was found
that for 120-day cultivar ‘Valery’ (AAA genome, Cavendish subgroup), the time to ripen
at 18.5°C was 14 days, whereas 90-day fruit took 21 days. Applying the rule of thumb
governing speed of biochemical reactions, it can be estimated that at about 28°C (a typical
ambient temperature in the tropics), the ripening times may be 7 and 10 days,
respectively. Adverse growing conditions or significant sigatoka infection may reduce
this period, and in the presence of ethylene (whether endogenous or from an external
source) initiation of ripening could occur much sooner (Marriott, 1980).
         Since the onset of ripening is characterized by an increase in respiration (the
climacteric rise), and since respiration involves the evolution of heat, the first obvious
indication that ripening has begun may well be the increase in pulp temperature of the
fruit. This is the reason for temperature checks at the time of loading; pulp temperatures
above 32°C give cause for concern, and ‘hot fruit’, if detected, will be refused for loading.
If ripening fruit is inadvertently loaded it will complete the ripening process during the
first few days of the voyage, and by the time of discharge, is likely to have become over-
ripe, brown or black, even moldy and collapsed, depending on its initial state coupled
with the environment and duration of the journey.

Carriage Instructions
        Shippers’ carriage instructions must take into account the cultivar, the weather
during the growing season, the maturity of the fruit at harvest, and the expected duration
of the voyage. Most usually, the recommended delivery air temperature (DAT) for
bananas is in the region of 13.3°C. Shippers’ instructions often stipulate a required
relative humidity, which is largely irrelevant as the bananas are packed in sealed
polyethylene bags and it is not feasible to control relative humidity in most ships.
        It is customary to request that the holds be pre-cooled approximately 48 hours
prior to loading. The major purpose is to check that the refrigeration equipment is
working properly. There is some benefit in chilling the hold structure but, once the
hatches are opened for loading, the tropical heat can soon negate the effect. Whilst
loading is in progress, the refrigeration may be left running (with cargo fans at low
speed), although port practices vary and not all stevedores permit cold air to be blown
whilst they are working. During breaks in loading, the hatches can be closed, for greater
refrigeration efficiency. However, the sooner a compartment can be fully loaded and
closed the better. In order to facilitate cargo cooling in the vital early stages, there is a
particular technique (besides closure of the ship’s fresh air vents - see below), which may
be used to advantage, this technique being a two-stage temperature reduction, loosely
termed ‘shock treatment’. The term is unfortunate; the aim is emphatically not to give the
bananas a shock, but merely to use the refrigeration machinery to best advantage without
injuring the cargo. The procedure is as follows, based on a requested carriage temperature
(i.e., eventual delivery air temperature) of 13.3°C. At the outset, when the bananas


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themselves are still warm, it is safe to aim for a delivery air temperature of, say, 12°C,
which permits a faster extraction of heat. As soon as the return air temperature is down to
about 15°C, or after about 12 hours (whichever is the sooner), the delivery air temperature
is raised to 13.3°C and held there for the remainder of the voyage. There is an important
precaution against chilling injury, which could occur if the temperature of the bananas
were to fall below 13.3°C. If a deck is loaded in two stages (e.g., on two successive days
or at two different ports), the partially loaded deck can be given ‘shock treatment’ but it
would not be appropriate to repeat this regime on completion, lest the first loaded cargo
(now cool) suffer chilling injury. On completion of loading the deck, therefore, the
delivery air temperature is simply reduced to 13.3°C. Similarly, it would be inappropriate
to request shock treatment for pre-cooled fruit (in one or two exporting countries, bananas
are pre-cooled in refrigerated containers before being delivered to the vessel’s holds).
        With the important proviso that the delivery air temperature must not be so low as
to risk chilling injury, the essence of successful banana carriage is rapidly cooling. The
reduction period (a measure of the speed of cooling) may be defined as the time taken,
after final closure of a compartment, for the return air temperature (RAT) to fall to within
2.2°C (4 Fahrenheit degrees) of the requested delivery air temperature (DAT). Thus, if the
requested carriage temperature is 13.3°C, the reduction period would relate to a RAT of
15.5°C. This is one convention; some companies work on a temperature differential of
exactly 2°C, making the appropriate RAT 15.3°C. Typical reduction periods might be 24
to 36 h, and it is important to appreciate that, based as it is on return air temperature, the
duration of the reduction period cannot be controlled but only measured.
        It should be noted that a ‘refrigerated compartment’ might be a single independent
deck, or may comprise a pair of interconnected decks in which air is delivered beneath
deck gratings in the lower deck, rises up through the slatted wood floor of the upper deck
(then known as a spar deck) and is withdrawn from the deckhead of the upper deck, to be
re-circulated once more.

SHIPBOARD FACTORS

Refrigerating Power
        The refrigerating plant must cool the warm fruit and also dissipate the heat
produced by continuous respiration of the bananas. The heat output of pre-climacteric
bananas at different temperatures is given in round figures in Table 1. Once bananas have
entered the climacteric phase their respiratory heat output may be three, four or even five
times the quoted figures. The data demonstrate that the greatest need for refrigerating
power is at the beginning, since bananas are normally loaded at ambient temperature
(typically 25 to 30°C), in contrast to other fruit commodities, which are usually fully pre-
cooled before loading. It was because of the magnitude of this task that banana vessels
were specifically designed with high capacity cooling systems.

Air Circulation System
        The first reefer vessels built specifically to carry bananas were generally designed
with a horizontal airflow because at that time bananas were transported ‘on the stem’, and
such an airflow permitted effective air circulation through the bunches. With the advent
of carton-packing in the 1960s, it became more appropriate to have a vertical system, the
usual method being powerful underdeck air delivery and deckhead exhaust to force air
upwards through the cargo.
        The re-circulation rate in a typical banana vessel is about 90 volumes per hour.
This means that every hour the volume of air passing over the fans is equal to 90 times
the cubic capacity of the empty chamber; it is a way of expressing the power of the fans
in relation to the size of the spaces they serve. Each insulated deck (or pair of decks) is
nominally independent of adjacent chambers, though there is likely to be a mingling of
atmospheres during regular inspection of cargo and machinery. This means that a high
concentration of ethylene in one deck, irrespective of source, can cause premature


380
ripening of bananas in a neighboring deck (Snowdon, 1994).

Stowage
        In vessels with a powerful vertical airflow, a ‘solid stow’, without specific air
channels, is essential. Because the resistance of a tightly packed stack of cartons is much
greater than that of the loosely stowed bunches of earlier times, it is important to take care
when constructing a stow of cartons. They should be stowed in register, so that air can
flow through the interstices between the cartons. Cartons should also be stowed as level
as possible, so that airflow will be uniform. Furthermore, it is necessary to leave sufficient
headspace (≥10 cm) above the stow for the passage of the return air. Special care should
be taken in the hatch coaming, where it is recommended that the height of the stow be
limited and that cartons be stowed diagonally at the perimeter, to permit some passage of
air. Finally, there should be no possibility of short-circuiting of air, since this could lead
to the development of ‘warm spots’ and premature ripening.
        If cartons are palletized, it is even more important to take care with stowage, since
air tends to take the line of least resistance through the spaces between the pallet loads
(Amos and Tanner, 2003). Furthermore, the pallet bases form a second plenum above the
deck gratings, and air can escape with ease, unless baffled by the use of ‘pallet-skirts’,
pieces of card inserted at the time of stowing. In vessels that are not specifically designed
to be pallet-friendly, the curved shape of, especially, the for’d hold means that many
spaces may remain at the edges of the stow. If more than 5% of the deck area remains
uncovered, airflow efficiency (and cooling) can be seriously jeopardized (Mohlin and
Oleszko, 1994).

Cooling Policy
        Rapid cooling of bananas is the essence of successful carriage and the prevention
of premature ripening. The aim is to reduce banana cargo temperature as rapidly as
possible; the sole proviso being that the delivery air temperature should never fall below
the minimum value stipulated by the exporter because of the risk of chilling injury. Any
mention of ‘temperature’ when discussing banana carriage should always be qualified,
according to whether it denotes DAT, RAT, hatch temperature or cargo pulp temperature.
        The two components of the cargo heat load are the ‘sensible heat’ or ‘field heat’
extracted during temperature pull-down, and the respiratory heat, which is substantial
whilst the bananas are still warm, and remains significant even after they are cooled to
carriage temperature. It should be noted that, for the carriage of fruit, a refrigerated vessel
controls delivery air temperature, but return air temperature can only be measured, being
a response to delivery air temperature coupled with the state of the cargo in the hold, the
stowage, the air circulation system and so forth. As explained above, the reduction period
can give an indication of the progress of cooling and is calculated and recorded for each
refrigerated compartment.

Fresh Air Ventilation Policy
        The aim of ventilation is to prevent accumulation of ethylene, which is produced
by bananas and which may precipitate premature ripening. Whilst bananas are still
attached to the plant, and for some hours after harvest, they are relatively insensitive.
Subsequently, however, they may respond to very small amounts of ethylene, whether
produced by the fruit itself and allowed to accumulate, or whether emanating from an
external source. Traces (0.1 ppm or less) in the surrounding atmosphere can shorten the
pre-climacteric period, and higher concentrations can induce a rapid initiation of the
climacteric. A concentration of 1 ppm or above can induce the climacteric within 12 to 24
h; lower concentrations must be applied for longer periods.
        It is not easy to measure low concentrations of ethylene, but measurement of
carbon dioxide (produced in substantial quantities during respiration) gives an indication
of the sufficiency or otherwise of fresh air ventilation. In their instructions for the carriage
of bananas, most companies allow a maximum carbon dioxide level of 0.2 or 0.3%. In the


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absence of a carbon dioxide meter, the aim should be to achieve a continuous intake and
exhaust of fresh air in order to provide no more than about one air change per hour. The
important exception to this is the crucial cooling period at the outset when, for optimal
cooling, the fresh air vents should be completely closed, in order to prevent ingress of
warm moist air from outside. Different companies have different policies, perhaps based
on the differing characteristics of bananas from different origins with regard to the
tendency to premature ripening. One might stipulate a maximum period of 24 hours
without ventilation, while another might permit 48 hours. Yet another used to request
fresh air ventilation from the outset, though perhaps without appreciating the
implications. For the rest of the voyage, the most desirable and cost-effective procedure is
to monitor carbon dioxide and ventilate accordingly. It should be understood that carbon
dioxide itself is not necessarily inimical to bananas, indeed in MA packaging or CA
carriage a raised concentration of carbon dioxide serves to extend storage life. In ordinary
banana carriage, carbon dioxide monitoring (a measurement of fruit respiration rate) is
simply used as a rough indicator of the sufficiency of fresh air ventilation, since in
ordinary (non-CA) carriage ethylene must be flushed out.
        The effect of ethylene on bananas is markedly influenced by temperature. For
example, bananas exposed to 100 ppm of ethylene at 18.5–23°C, started to ripen within
16 to 20 h, whereas at 13.5–15.5°C, ripening was not initiated even after 24 h of
exposure. Despite the relative insensitivity of cooled bananas, shippers’ carriage
instructions may stipulate continuous maximal fresh air ventilation after the cooling-down
period, and for the rest of the voyage. The disadvantage of air freshening is the substantial
heat load imposed on the refrigeration unit. The fresh air system in modern reefer ships is
capable of two, three or even four air changes per hour. The implications of such a
massive intake are often not appreciated, but the energy costs (especially in the humid
tropics) must be considerable. Not only is there the sensible heat to be extracted but also
the latent heat as atmospheric moisture condenses on the cooling coils (energy is evolved
during the phase change from water vapor to liquid). In view of this, it can be
advantageous to design the fresh air system to include a heat exchanger between air
exhaust and air intake, so as to save energy.

CONCLUSIONS
        The out-turn condition of any banana cargo is determined by a multitude of
factors, some of which are the responsibility of the growers and shippers, and some of the
carrier. In each case the forensic approach must be to identify patterns of damage, in order
to determine the cause or causes of deterioration. Preshipment unfitness of some of the
cargo may perhaps be demonstrated by detailed recording of box-codes, since each carton
box carries a packing station code permitting complete traceability. On the other hand,
examination of the vessel’s equipment and log-books may indicate a shipboard problem
in a particular deck. If a single factor is acting adversely, the cargo may arrive with little
or no damage, while if several factors are acting adversely the outcome can be
catastrophic. Identification of causal factors can help to reduce losses in the future.

Literature Cited
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De Lapeyre De Bellaire, L., Chillet, M. and Chilin-Charles, Y. 2008. Measurement of
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   anthracnose, crown rot. Fruits 63:303–306.
Gowen, S. 1995. Bananas and Plantains. Chapman and Hall, London.
Marriott, J. 1980. Bananas – physiology and biochemistry of storage and ripening for
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Mohlin, R. and Oleszko, J. 1994. Studies of air distribution in the holds of a refrigerated
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Tables




Table 1. Heat production of pre-climacteric bananas at different temperatures.

 Temperature (oC)                            Heat production (W kg-1)
 12                                                   0.04
 15                                                   0.05
 20                                                   0.09
 25                                                   0.13
 30                                                   0.20




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