Sea transportation of fruits and vegetables: an update

 

David Tanner* and Nick Smale

Food Science Australia, North Ryde, New South Wales, Australia

 

 

 

Abstract

Purpose of review: This review covers improvements, both engineering and operational, over the past 5-7 years and refers to a number of new technologies that have developed for container shipment; a mode that has grown significantly in the period that the review covers. Containerisation is a growth area due to an increased focus on ‘whole-of-chain’ logistics. Other areas of growth in this period are the linkages between equipment design and operation and produce quality.

Limitations: This review is limited by the number of scientific publications that it draws on. There are very few scientific groups and publications that focus on this area hence the review has drawn on a number of informative press articles. This limitation is not expected to have an implication on innovation in this industry, but may limit the ability of the industry to attract scientifically trained resources in the future.

Directions for future research: Future research needs are dictated by a number of different factors from government policy to the ever increasing demands of growers, exporters, importers, retailers and ultimately consumers. A number of potential research areas that may become the focus of sea transport research in the near future are discussed.

 

Keywords: containerisation; horticultural produce; shipping; operations; design

 

Stewart Postharvest Review 2005, 1:1

Published online 01 June 2005

doi: 10.2212/spr.2005.1.1

 

 

 

This review covers a number of key areas; equipment improvements, the physiological needs of produce, improvements in operation of the equipment and improving performance. It is by no means comprehensive, but does cover innovations and research that have been implemented or undertaken in the past 5-7 years.

Equipment improvements

Refrigerating equipment technology for marine transport of fresh produce has not changed dramatically over the past five years. Carrier and ThermoKing remain the dominant manufacturers of container refrigeration equipment; with Daikin, Mitsubishi and now Maersk Container Industri also producing refrigeration units [3]. Both ThermoKing and Carrier have introduced models equipped with scroll compressors (‘Magnum’ and ‘EliteLine’ respectively) with increased capacities primarily for use in deep frozen applications [4, 5]. Carrier has also   introduced an advanced defrost management      system which adjusts the interval between defrosts automatically [6]. Independent testing of the system has not been reported.

 

‘Coolboxx’, a Dutch partnership, has released a 13.7m refrigerated container which will initially be used for intermodal services between continental Europe and the UK [7]. Testing of these large containers which carry 33 pallets (1.2 × 0.8m) has not been reported.

 

As fruits and vegetables continue to respire during storage and distribution, a form of atmosphere    control is required to avoid the build up of harmful concentrations of CO₂ or ethylene, or depletion of oxygen. Systems for atmosphere control include ventilation with ambient air, modified atmosphere (MA) systems and controlled atmosphere (CA) systems. Heap and Lawton [8] provide a summary of commercial CA systems available in marine transport. They describe the various systems and sensors available along with limitations of the different systems. Garrett [9] also discusses CA systems for refrigerated containers and notes the lack of standards for characterising the performance of CA  systems.

 

Smale et al. [10] and Heap and Marshall [11] both discuss ventilation requirements for fresh produce in refrigerated containers. The inconsistencies of suggested ventilation rates previously published was noted by both authors, with most suggested rates in excess of the calculated rate required. Smale et al. [10] also reported that a survey of measured ventilation rates showed substantial deviation between the ventilation rate marked on the vent and the measured ventilation rate. In the survey, measured rates of ventilation for containers set at 15 m³/h varied from 3–27 m³/h.

 

Over the past 5 years a number of more sophisticated atmosphere control systems for containers have been introduced. ThermoKing has developed advanced fresh air management (AFAM) and AFAM+ systems for improved management of ventilation. AFAM uses a small motor to set the ventilation rate using the electronic controller, while AFAM+ also includes gas sensors to vary the ventilation rate based on a maximum CO₂ concentration. Both systems allow delaying ventilation for a period to reduce the heat load during initial pull-down. ThermoKing [12] has reported improved produce quality out-turn following shipment of broccoli  using AFAM+, however, independent testing of the system has not been reported in scientific literature. Carrier has in turn developed the AutoFresh system which also uses a motor to control the ventilation of the container [13]. Other CA and MA systems   recently released include MaxTend (MA systems by Mitsubishi Australia Ltd [14]), Tectrol (CA and MA systems by TransFresh Corp. [15]) and Cargofresh (CA systems by Cargofresh Technologies [15]).

 

Physiological needs of the produce

The physiological needs of fruits and vegetables are extremely important to consider when transporting via ocean transport. With the international and    domestic trade in fresh fruits, vegetables and other produce exceeding $70G annually [16], and estimates of losses between harvest and consumption ranging between 5–40%, optimising the storage and shipping conditions for produce is vitally important. The past five years have seen the development of tools that assist shippers, transport operators and storage companies alike to choose appropriate conditions for the produce being handled.

 

Morris and Sharp [17] have developed a system that relies on a database of information for over 1,500 products including edible produce and ornamentals. Information includes recommended shipping temperatures, ventilation settings for container transport, humidity recommendations and CA gas concentrations that will give the best produce quality results. The system (called Optimal Fresh) has recently been released on CD-ROM.

 

A number of commercial shipping companies have also invested in providing guidelines and recommendations for environmental factors (such as temperatures, gas concentrations, relative humidity and likely shelf-life) for the shipment for fruits and vegetables. Brecht and Brecht [18] developed a set of such guidelines that outlined the requirements of a large range of fruits and vegetables for use with ThermoKing’s AFAM and AFAM+ technology. Similar guidelines have been produced by other manufacturers, and can often be accessed via the company’s website.

 

Improved operation

Operation of marine transport equipment including equipment settings, stowage protocols and packaging designs can influence the effectiveness of the refrigerating equipment dramatically. Over the past five years a number of investigations of operational parameters have been reported.

 

Lawton [19] described a ‘Splitter Board’ system designed to improve temperature control in refrigerated containers. The system splits the airflow       adjacent to the door into two streams to reduce the influence of heat and air leakages around the door on cargo temperatures. The system was reported to reduce temperature variability within a 6m container from 3.9 to 1.4^oC.

 

Smale et al. [20] reported on relationships between pressure gradients and air flow rates through horticultural packages under vertical flow conditions as experienced in marine transport systems. Packaging and not produce was reported to cause the majority of flow resistance highlighting the importance of package design. Solid trays used for fruit positioning were also reported to negate most of the benefit of vertical ventilation.

 

A number of models for predicting the airflow    patterns in marine transport systems have been   developed in the past 5 years. Lindqvist [21-23] has developed a computational fluid dynamics (CFD) model to investigate the airflow in refrigerated holds. The model was validated against pressure measurements made throughout a full scale model of a section of a hold filled with banana packaging. A number of variations were tested including pallet orientation, incorporation of restriction plates       designed to improve the airflow pattern and a gratingless system of air distribution. Results indicated only slight improvement of airflow with inclusion of the restriction plates and little difference was seen between the gratingless and grated floor systems. Lindqvist also noted the importance of packaging design on air distribution.

 

Kametani et al. [24] also used a CFD model to predict airflow in an empty refrigerated container. Smale [25] used a resistance network model to predict airflow in both refrigerated containers and holds. Predictions were validated against velocity and fruit temperature measurements in full scale shipments in both containers and holds. Defrost management was highlighted as an area for improvement in refrigerated hold operation. Gratingless systems of air distribution were simulated for both types of systems, with significant detrimental effects predicted in holds but only minor effects in containers.

 

Improving performance

A number of options are available for improving the performance of systems ranging from use of multidisciplinary design teams [26] and the use of prediction tools for design [27] to implementation of standards [28].

 

Cleland [26] explained that packaging systems modify the environment to which a food is exposed and can significantly increase the effectiveness of the refrigeration process. This is particularly relevant in transport systems used for fruits and vegetables, as a poorly designed packaging system can have a detrimental effect on produce quality. Cleland [26] outlines the need to include specialists from marketing, quality assurance, engineering, logistics and distribution in a multidisciplinary team in order to ensure that the packaging system interacts positively in the supply chain.

 

The development and application of predictive models in horticultural packaging and transport systems has increased markedly in the past few years [29-33]. By applying appropriate mathematical tools to the packaging and storage environment design process, quantitative prediction of important variables such as the effect of design changes on performance or produce quality can be made. The former will be       discussed here, while applications of models for  improved produce quality will be discussed in a later section.

 

Jolly et al. [27] developed and tested a mathematical model describing the refrigeration system in a shipping container. The model was validated against measurements made during a series of cooling    capacity tests on a 12m container, with sufficient agreement shown. Han and Gan [34] reported calculated energy savings associated with variable speed scroll compressors under part load operation. The authors calculated that energy savings of approximately 26% were possible for a shipment between the USA and China.

 

World Cargo News [28] announced in June 2004 the development of a new set of industry standards, which provide a means of assessing the reliability, quality and proficiency of companies involved in the transport, handling and storage of perishables and temperature-sensitive produce. These standards (known as Cool Chain Quality Indicators) have been developed by Germanischer Lloyd Certification and the Cool Chain Association for industry and provide a process for continuous improvement and performance measurement.

Linking operation to quality

Over the past 10 years, researchers from New      Zealand and Australia have undertaken intensive studies of air and fruit temperatures within transport systems carrying perishable produce; predominantly fruit from Australasian ports to Asian and European destinations. In most of these cases, the focus of the studies have been on the influence of variability in transport systems on product quality.

 

Many studies have been carried out on container shipment of fruits with the majority of published work being for 6m containers bulk-stowed with produce [35-39]. Amos and Sharp [36, 37] examined the use of 12m refrigerated shipping containers for in-transit cold disinfestation of citrus. Their work examined the container performance factors that required measurement prior to shipping of citrus to ensure that the container would meet the highly stringent temperature requirements demanded by importing countries. The results indicated that age was not a good predictor of suitability, but that container construction had a large influence on its ability to perform the task.

 

To lower freight costs and to gain benefit from    improved logistics, fruit exporters have moved away from bulk-stowed 6m containers to palletised stows in 12m high cube containers. Amos [38] and Tanner and Amos [39] investigated temperature variability in shipments of apples, durian and kiwifruit and found that the in-package temperature range in the container was 5–6^oC (Figure 1). From postharvest laboratory studies, it has been interpolated that this range of temperature would lead to a large spatial variability in out-turn produce quality.

 

Amos and Tanner [40] investigated the temperature variability in reefer vessel shipment of kiwifruit from New Zealand to Japan. In this study, 307     pallets of fruit were selected for intensive temperature monitoring in a single deck. This work showed that the range of in-pallet temperatures during steady-state periods were roughly half of that measured within containers. Further, during periods when the vessel was passing through the tropics, little effect of the high ambient temperature or     humidity was found.

 

As previously explained, there has been increased use of mathematical prediction to assess the influence of operational criteria on produce quality. Such tools allow the impacts of design or operational changes on out-turn quality to be screened prior to any experimental testing, reducing the need to perform “trial and error” testing which is both time consuming and can be expensive. Quality models for fruits and vegetables can add value to measured or predicted environmental data during transport [41]; however, the models are difficult to develop and prove accurate due to inherent variability in produce as a result of differences in growing region, climate and variety. Examples of value addition through model predictions (if the model is well tested, and proven accurate) include allowing commercial marketing decisions to be made and answering what if scenarios in the event of logistics changes.

The work of Tanner and Amos in 2003 [42] quantified the effects of measured temperature differences on kiwifruit firmness throughout a container and applied a produce quality model to measured temperature data in order to assess the effects of spatial variability in temperature throughout a 12m refrigerated container. This study showed a strong and   significant link between changes in fruit firmness in response to temperature history, with fruit consistently exposed to temperature differences of 2^oC having significantly different final fruit firmnesses over a typical container shipment journey from New Zealand to Europe. It should be noted that the temperature variability will result from a combination of environmental factors, including packaging design, loading configuration, container design and operation, and pre-loading temperature control. This study also showed that mathematical modelling, as a tool to assess final fruit quality as a result of temperature variability, could be used to assess the influence of changes in the supply chain, such as packaging design and shipping system operation.

 

Verdijck et al. [43] discussed a model-based produce quality controller that tracks produce quality by means of respiration and fermentation. Through implementing the approach described, energy efficiencies are reportedly possible by permitting fluctuations in the air temperature; given that fruit temperatures will react to the fluctuating temperatures on a much slower time scale. In a full scale trial with       20 tonnes of Elstar apples transported at 5^oC over 33 days, energy consumption was reduced by over 50% with no significant differences in quality between the transported apples and a reference batch held at 5^oC/90% RH. Variability within the load was not discussed by the authors.

Conclusions and future directions

At face value, it would appear to many that there has been little innovation in the shipment of fruits and vegetable via marine transport in the past 5-7 years. However, closer inspection shows that there have been a number of technological improvements in equipment, and a greater appreciation and understanding of the operational factors that influence produce quality over this period. From improvements in container systems, greater energy efficiency and reliability, to improved understanding of the environmental factors that influence storage and shelf-life of produce, innovation in the marine transport area exists. If the current trends in investment,     research and innovation continue, the sector will remain competitive, and there is the opportunity for a lowering of the wastage levels (earlier stated to be between 5 and 40%) that currently exist globally.

 

Future research needs are dictated by a number of different factors, from government policy to the ever increasing demands of growers, exporters, importers, retailers and ultimately consumers. The International Institute of Refrigeration, a neutral inter-governmental organisation, has recently released a list of research priorities for refrigeration research [44]. In this list, those that relate to sea transportation, and that of fruits and vegetables, include:

 

· Application of new insulating materials and blowing agents in refrigerated and frozen transport

· Developing systems and methodologies for energy conservation and energy efficiency

· Characterising environmental performance factors in refrigerated transport applications, including airflow, humidity and temperature

· Cold Chain Logistics research and monitoring, traceability of the transported foods

· Reliability of refrigerating systems for sea transport

· CA utilization in refrigerated transport

· Communication systems for monitoring and controlling of produce temperature and quality during transport

· Reduction of noise emission from the refrigerating units in the refrigerated transport.

 

 

 

References

 

Papers of interest have been highlighted as:

* Marginal importance

** Essential reading

 

1 World Cargo News. Reefer market stays hot. Press Release 2004: 27 – 30.

2 Heap R. International refrigerated transport by sea and air. Proceedings of the 21^st International Congress of Refrigeration: 17-22 August 2003; Washington DC, United States: Short Course.

3 World Cargo News. A cool star is born. Press Release 2004: 60.

4 ThermoKing Corporation. The reefer machine of the future. Press Release 2002.

5 Carrier Transicold. Carrier’s Eliteline™ refrigeration unit is industry’s greenest. Press release 2001.

6 Carrier Transicold. Protect valuable cargoes with Carrier’s auto defrost feature. Press release 2004.

7 World Cargo News. Coolboxx reefers in service. Press Release 2004: 17.

8 Heap RD and Lawton AR. Controlled atmospheres in marine transport: achievements and future needs. Proceedings of the 20^th International Congress of Refrigeration: 19-24 September 1999; Sydney, Australia: Paper 447.

9 Garrett ME. The technology of controlled atmospheres in temperature controlled transportation. Proceedings of the 20^th International Congress of Refrigeration: 19-24 September 1999; Sydney, Australia: Paper 710.

10 Smale NJ, Tanner DJ, Amos ND and Legg A. Container leakage and air exchange rates: a simple measurement method and survey results. Proceedings of the 21^st International Congress of Refrigeration:17-22 August 2003; Washington DC, United States: Paper 245.

**The survey presented in this paper highlights a significant issue in container operation; where marked ventilation settings did not correspond to actual ventilation rates measured in the range required by most horticultural products. A disparity between theoretically required ventilation rates and suggested rates was also noted.

 

11 Heap R and Marshall R. Ventilation effects and requirements in containerized refrigerated transport. Proceedings of the 21^st International Congress of Refrigeration: 17-22 August 2003; Washington DC, United States: Paper 472.

**This short, yet useful, paper outlines a simple methodology for calculating the needs of fruits and vegetables with respect to fresh-air ventilation rates in refrigerated shipping containers. Highlighted in the conclusions is the fact that ventilation rates differ widely depending on the source and that a single, central database for this operational factor is required.

 

12 ThermoKing Corporation. One hot commodity. Press Release 2001.

13 World Cargo News. Go man-go down under. Press Release 2002: 19.

14 Carrier Transicold. Autofresh™ option provides fresh air exchange reliably, accurately. Press release 2001.

15 World Cargo News. CA gaining ground. Press Release 2004: 50 – 51

16 Food and Agriculture Organisation of the United Nations. Summary of Food and Agriculture Statistics. Rome, Italy 2003.

17 Morris SC and Sharp AK. ‘Optimal Fresh’: An expert system giving conditions for the storage and transport of fruit, vegetables and ornamentals. Proceedings of the 20^th International Congress of Refrigeration: 19-24 September 1999; Sydney, Australia: Paper 543.

18 Brecht PE and Brecht JK. VFD AFAM/AFAM+ Setting Guide. Minneapolis, USA: ThermoKing Corporation, Ingersoll-Rand Company 2001.

19 Lawton AR. The splitter board system for improving temperature distribution in ISO containers. Proceedings of the 20^th International Congress of Refrigeration: 19-24 September 1999; Sydney, Australia: Paper 446.

** The splitter board system presented in this paper provides an intervention available to improve the performance of refrigerted containers.

 

20 Smale NJ, Amos ND, Tanner DJ and Cleland DJ. Air flow characteristics of vented horticultural packaging. Proceedings of the 21^st International Congress of Refrigeration: 17-22 August 2003; Washington DC, United States: Paper 244.

**This paper presented quantitative data for air flows through vented horticultural packaging. The causes of flow resistances were investigated and the importance of vent design was highlighted.

21 Lindqvist R. Air distribution in reefer holds [Dissertation]. Norwegian University of Science and Technology, Norway 2000. v

**This thesis presented a mathematical model of airflow for refrigerated holds. The implementation of a gratingless air distribution system was investigated along with a number of interventions to improve air distribution. Pallet and packaging design was highlighted by the author as an important factor in the performance of the system.

22 Lindqvist R. Air distribution design for controlled atmosphere in reefer cargo holds. Proceedings of the 20^th International Congress of Refrigeration: 19-24 September 1999; Sydney, Australia: Paper 346.

23 Lindqvist R. Reefer hold air distribution. Refrig. Sci. & Technol. 1998;2: 121-129.

24 Kametani S, Tamura K and Takano R. Study on the optimum air current distribution of a refrigerated container using two dimensions numerical simulation model. Proceedings of the 21^st International Congress of Refrigeration: 17-22 August 2003; Washington DC, United States: Paper 437.

25  Smale NJ. Mathematical modelling of airflow in refrigerated shipping systems: Model development and testing [PhD Dissertation]. Massey University, Palmerston North, New Zealand; 2004.

** This thesis presented a mathematical model of airflow for refrigerated holds and containers. Observations of airflows and temperatures in both systems were reported. Packaging design and operational factors were highlighted by the author as key areas for improvement of system performance.

26 Cleland AC. Package design for refrigerated food: The need for multi-disciplinary project teams. Trends in Food Science and Technology 1996;7: 269 – 271.

27 Jolly PG, Tso CP, Wong YW and Ng SM. Simulation and measurement on the full-load performance of a refrigeration system in a shipping container. International Journal of Refrigeration 2003;23: 112-126.

 **These authors presented a mathematical model they developed for a refrigeration system in a shipping container. The significance of this is that such a system allows full-load simulation of the thermal performance of the system. Of greatest importance was that the model had been validated and was reported to be ± 10%.

28 World Cargo News. New standard for perishable cargoes. Press Release 2004: 30–31.

29 Meffert HFTH. Modelling product temperature in refrigerated holds. Refrig. Sci. & Technol. 1998;2: 70-83.

30 Tanner DJ, Cleland AC, Opara LU and Robertson TR. A generalised mathematical modelling methodology for design of horticultural food packages exposed to refrigerated conditions: Part 1, Formulation. International Journal of Refrigeration 2002; 25: 33-42.

31 Tanner DJ, Cleland AC and Opara LU. A generalised mathematical modelling methodology for design of horticultural food packages exposed to refrigerated conditions: Part 2, Heat transfer modelling and testing. International Journal of Refrigeration 2002;25: 43-53.

32 Tanner DJ, Cleland AC, and Robertson TR. A generalised mathematical modelling methodology for design of horticultural food packages exposed to refrigerated conditions: Part 3, Mass transfer modelling and testing. International Journal of Refrigeration 2002;25: 54-65.

33 Tso CP, Yu SCM, Poh HJ and Jolly PG. Experimental study on the heat and mass transfer characteristics in a refrigerated truck. International Journal of Refrigeration 2002;25: 340 - 350.

34 Han H and Gan W. Energy conservation of ocean-going refrigerated container transportation. Proceedings of the 21^st International Congress of Refrigeration: 17-22 August 2003; Washington DC, United States: Paper 75.

35 Billing DP, McDonald B. and Hayes AJ. Temperature characteristics within 20-foot reefer containers during export of New Zealand produce. Refrig. Sci. & Technol. 1998;2: 139-147.

36 Amos ND and Sharp AK. Shipping trial of in-transit disinfestation of citrus. Refrig. Sci. & Technol. 1998;2: 148 – 155.

37 Amos ND and Sharp AK. Assessment of 20-foot refrigerated containers for in-transit cold-disinfestation of citrus fruit. Proceedings of the 20^th International Congress of Refrigeration: 19-24 September 1999; Sydney, Australia: Paper 084.

38 Amos ND. Factors affecting fruit temperature maintenance within refrigerated containers. Proc. IRHACE Annual Conf. 2001;1: 7–10.

**This paper presented an outline of factors that influence the temperature uniformity in refrigerated shipping containers. This work drew on data from shipments of apples and durian and made links between operational factors such as fresh-air exchange and evaporator defrost frequency and temperature variability.

39 Tanner DJ. and Amos ND. Temperature variability during shipment of fresh produce. Acta Horticulturae 2003;599: 193 – 203.

**These authors presented a significant addition to the literature; a comprehensive survey of temperatures throughout a stow in a 40’ refrigerated container. This paper acknowledged that there are a number of factors that contribute to the variability reported, including operational, design and product-related (including packaging) influences.

40 Amos ND and Tanner DJ. Temperature variability during refrigerated vessel shipment of fresh produce. Proceedings of the 21^st International Congress of Refrigeration: 17-22 August 2003; Washington DC, United States: Paper 250.

41 Morris SC, Jobling JJ, Tanner DJ and Forbes-Smith M. Prediction of Storage or Shelf Life for Fresh Produce Transported by Refrigerated Containers. Acta Horticulturae 2003;604(1): 305-311.

42 Tanner, D.J. and Amos, N.D. Modelling product quality changes as a result of temperature variability in shipping systems. Proceedings of the 21^st International Congress of Refrigeration: 17-22 August 2003; Washington DC, United States: Paper.

43 **This paper linked the temperature variability inevitably present in transport of horticultural products with the different rates of change in quality attributes. This work focused on firmness of kiwifruit as a result of a 45 day journey from New Zealand to Europe.

44 Verdijck GJC, Preisig HA and van Straten G. Direct product quality control for energy efficient climate controlled transport of agro-material. J. Process Contr. 2005: 15: 235-246.

45 Research Priorities for the International Institute of Refrigeration, 2005. See http://www.iifiir.org/