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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 Eds.: T. Dubois et al. Acta Hort. 879, ISHS 2010

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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

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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

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(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

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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 Amos, N. and Tanner, D. 2003. Temperature variability during refrigerated vessel

shipment of fresh produce. Proc. 21st International Congress of Refrigeration. Washington DC, USA 17-22, August. p.23–31.

De Lapeyre De Bellaire, L., Chillet, M. and Chilin-Charles, Y. 2008. Measurement of fungicide efficacy on post-harvest diseases: wound anthracnose, quiescent 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

optimum quality. CRC Crit. Rev. Food Sci. Nutr. 13:41–88. Mohlin, R. and Oleszko, J. 1994. Studies of air distribution in the holds of a refrigerated

ship to design the gratingless air circulation concept for pallet reefers. Proc.

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Commission D2/3, International Institute of Refrigeration. Gdansk, Poland 29 September-1 October. p.106–116.

Ramírez, M., Sáenz, M.V., Vargas, A. and Araya, M. 2008. Leaf pruning intensities at flowering of banana (Musa AAA, cv. Grande Naine) did not influence fruit green and yellow life and quality. Sci. Hort. 115:319–322.

Snowdon, A.L. 1988. A review of the nature and causes of postharvest deterioration in fruits and vegetables, with especial reference to those in international trade. Biodeterioration 7:585–602.

Snowdon, A.L. 1990. A Colour Atlas of Post-Harvest Diseases and Disorders, Vol. 1, General Introduction and Fruits. Wolfe Scientific, London.

Snowdon, A.L. 1994. Diagnosing the causes of out-turn problems in imported tropical fruits. p.94–101. In: B.R. Champ, E. Highley and G.I. Johnson (eds.), Postharvest Handling of Tropical Fruits. ACIAR Proceedings No. 50. ACIAR, Canberra.

Stover, R.H. and Simmonds, N.W. 1987. Bananas. 3rd edition. Longman Scientific and Technical, Harlow.

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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