Fruit and Vegetable Transport

Large-scale production and export of fruits and vegetables, European food safety policy and associated legal regulations, lengthening transport routes, and growing consumer requirements are changing the approach to quality management. These factors necessitate the implementation of new technologies and strict adherence to principles at every stage of production and processing of these articles. Transport is a key element of this chain. Transport, especially over longer distances, must unequivocally be refrigerated transport. Due to the perishability of raw materials, particularly fresh fruits and vegetables, their susceptibility to damage, and the high risk of quality loss, carriers are obligated to maintain the cold chain, i.e., ensure a constant, regulation-specified temperature of once-cooled products from their production (harvest) to purchase by the final consumer. For this purpose, technical measures are employed, such as: controlled atmosphere cold stores, airlocks at entrances and exits of warehouses, shops, and processing plants; refrigerated vehicles with continuous temperature measurement, packaging protecting against mechanical damage, and logistical measures, such as: shortening transport routes, limiting handling operations, appropriate load distribution, selection and combining of loads based on their biological properties and mutual interaction, as well as control and maintenance of hygienic conditions of means of transport and premises. In fruits and vegetables, both during the vegetation period and during their storage and transport, physiological processes (respiration, ripening, and transpiration) occur, which can be significantly slowed down through the use of various technical treatments. Metabolic processes occurring in fruits and vegetables lead to product quality loss. The intensity of these changes depends on temperature, humidity, and atmospheric composition, primarily oxygen, carbon dioxide, and ethylene content, while the final effect is a function of time. Below we discuss the basic parameters of fresh fruit and vegetable transport. TEMPERATURE Temperature has a fundamental influence on the respiration processes and moisture loss occurring in transported fruits and vegetables. The respiration intensity of these products determines the course of metabolic processes taking place within them. The slower these processes occur, the slower the reactions accelerating ripening, ageing, and cell death proceed. The easiest way to reduce respiration intensity is to lower the temperature. However, care must be taken to ensure that the temperature drop does not lead to local freezing of the products; it is therefore advisable to familiarise oneself with the minimum safe transport temperature values, the so-called freezing point of cell sap. Different fruits and vegetables require different conditions; hence, the use of published optimal storage and transport temperature values is essential (table).

HUMIDITY Moisture content in the atmosphere has a very significant impact on the quality and appearance of stored products. Their storage and transport conditions should not promote excessive water loss (see table). Relative humidity below the optimal level causes wilting and shrivelling of most products and loss of their mass, while increased water vapour concentration has an inhibitory effect on transpiration and prevents moisture loss. For the transport of most perishable products, a relative humidity of 85–95% is recommended. An increase above these values promotes water vapour condensation. The probability of pathogen development (especially fungal) also increases, which consequently threatens product spoilage. ATMOSPHERE The gaseous composition of the atmosphere of stored fruits and vegetables affects the course of physiological processes occurring in plant cells. Lowering oxygen concentration and raising carbon dioxide concentration in the atmosphere leads to a reduction in respiration intensity, and thereby to a slowing of the ageing rate of these products, i.e., an extension of their shelf life. Controlled atmosphere technologies used for many years aim to alter the percentage shares of its components and control parameters around the cooled products. The optimal atmospheric composition for storage and transport of fruits and vegetables, as well as refrigeration conditions, are determined individually, taking into account their species, variety, sensitivity to carbon dioxide concentration or oxygen deficiency, degree of ripeness, temperature and duration of transport and storage. Maintaining appropriate concentration levels is extremely important, because, for example, lowering oxygen content below recommended values can result in significant losses resulting from anaerobic respiration. This process leads to tissue necrosis and the formation of substances altering the taste and smell of products (undesirably), and also creates conditions conducive to the development of anaerobic microorganisms, which produce compounds harmful to human health. Excess carbon dioxide, in turn, causes external and internal damage to stored products. Discussing the influence of atmosphere on stored products, the role of ethylene cannot be overlooked. This compound belongs to the group of unsaturated hydrocarbons. It is also a natural hormone participating in the regulation of plant growth and development processes. Its effect on plants is noticeable even at low concentrations. Ethylene can cause premature ripening with its negative consequences, as well as damage to certain products sensitive to its presence (including chlorophyll degradation). The main source of ethylene is climacteric fruits and vegetables (apples, pears, tomatoes, and melons). When planning the transport and storage of fruits and vegetables, one must therefore remember not to combine ethylene-emitting products with those sensitive to its presence. There are several ways to limit the negative impact of ethylene. First and foremost, these are maintaining the cargo batch at a constant, low temperature, lowering oxygen concentration and raising carbon dioxide concentration, as well as joint storage of products characterised by a similar degree of ripeness and undamaged mechanically (during vegetation and improper harvest). AIR MOVEMENT (CIRCULATION) Air circulation allows for maintaining a relatively uniform gas concentration and temperature throughout the entire cargo space and enables the removal of heat generated as a result of physiological processes occurring in stored products, as well as heat gains from the surroundings. With a properly designed air circuit, it is possible to maintain a deviation from the set temperature within 0.5°C. In this regard, proper load arrangement must be remembered, including maintaining uniform gaps between pallets, the ceiling, and chamber walls. Errors in this respect cause air movement disturbances resulting in non-uniform temperature distribution. For control, temperature measurements in the cargo chamber are necessary, at least of the supply air and return air temperature, which is one of the key requirements for transport monitoring.

MSc Eng. Leszek Bednarczyk,

MSc Eng. Dorota Niedojadło,

MSc Eng. Bogdan Szczepański