Finding the cause of impairments in fruit is sometimes difficult. Special attention needs to be paid to the distinction between transport-related and post-harvest damage as outlined below.
In contrast to the natural ripening of climacteric fruit, other physiological changes after harvesting have to be assumed to be decay/spoilage. New growth in roots and tubers is a normal process but represents a reduction in quality and value when the goods are sold.
In addition to normal post-harvest changes there are also abnormal changes caused by, for example, low temperatures, which change the sequence of biochemical processes and cause irreversible damage. In general, plant tissue that has suffered physical damage is predisposed to spoilage.
Physical changes are the main reason for post-harvest spoilage. Before, during and after harvesting, skin injuries of various kinds including bruises can occur, e.g. due to weather, insects, birds or agricultural equipment such as harvesters or automatic packaging machines. Skin injuries lead to increased respiration, loss of moisture and/or increased ethylene production. Healed skin injuries represent a visual defect. Physical damage is significant in that it facilitates the invasion of harmful organisms, resulting in spoilage.
Adverse effects may be caused by insecticides, fungicides, herbicides, growth regulators or fertilisers, but post-harvest treatment may also cause damage. An example would be the bleaching of grapes exposed to elevated levels of sulphur-oxide concentrations (SO2 pads).
Spoilage due to pathogens
Infections with harmful organisms can occur during the growth phase and harvest time, as well as during processing, storage, transport, sale or even after purchase.
The development can be divided into two phases: the infection and the manifestation of symptoms – either immediately or after some time. Harmful organisms gain access through natural openings such as lenticels or skin injuries. However, some fungal species can penetrate undamaged skin areas as well.
The development of spoilage leads to increased respiration, heat generation and increased ethylene production. Some moulds also produce ethylene in the process. This makes healthy tissue susceptible to infection.
Such circumstances are significantly affected by external factors such as temperature, humidity and composition of the atmosphere. These factors determine whether, when and how the harmful symptoms occur. Accordingly, careful attention must be paid to transport and storage conditions.