Fresh fruit and vegetables

How do you ensure that fruit and vegetables are well preserved, given that they need to breathe?

coupe de fruits frais

Unlike most foods, fresh fruit and vegetables continue to ‘breathe’ after they have been harvested.

This process consumes oxygen and produces carbon dioxide and water vapour.

The key to keeping these packaged products ‘fresh’ is to reduce the rate of breathability without affecting the quality of the product (its taste, texture and appearance).

RISKS OF SPOILAGE OF FRUIT AND VEGETABLES

In general, the rate of spoilage can be reduced by maintaining a low temperature, or by creating a low level of oxygen and a high level of carbon dioxide in the protective atmosphere. However, things aren’t quite so simple…

When the amount of oxygen in the packaging atmosphere is too low, a process called anaerobic respiration occurs. This process produces undesirable aromas and odours in the product and leads to food spoilage. In addition, too much carbon dioxide can damage certain types of product or alter their taste by increasing acidity.

In addition to these considerations, the high water content of this type of food, combined with the fact that fruit is intrinsically acidic, can lead to decomposition, with the appearance of mould and the development of yeast.

The flesh can also be softened by the attack of enzymes and microbes which, over time, cause putrefaction.

Ethylene is a fruit messenger that triggers the cellular ageing process and activates neighbouring fruits to begin the process of ripening and destruction. The ethylene production process can be blocked by blocking the fruit’s metabolism through oxygen enrichment. At 80% oxygen, the fruit’s metabolism is blocked. Simply return to a normal atmosphere and enrich the atmosphere with ethylene to restart the process. This technique is used just before display. On a larger scale, the ripening rooms are equipped with air-conditioning systems.

Ethylene starts to affect fruit at 400 ppm.

WHAT PACKAGING MATERIALS AND TECHNIQUES ARE RECOMMENDED FOR FRUIT AND VEGETABLES?

The packaging material used for fruit and vegetables is particularly important, as is its permeability and breathability.

If produce is enclosed in a hermetically sealed container, oxygen will be lacking and there is a risk that it will develop undesirable anaerobic conditions.

On the other hand, if the material is open, the protective atmosphere escapes and no benefits are obtained.

The aim is to achieve a state of equilibrium to produce a balanced protective atmosphere or EMA.

Example: In certain applications such as endives, micro-perforated films are used to obtain a defined exchange threshold between the atmosphere inside and outside the sachet, and thus avoid colour changes and deterioration of the film.

PACKAGING IN A PROTECTIVE ATMOSPHERE

Here, oxygen and carbon dioxide can pass from inside to outside the container and vice versa, so that oxygen consumed inside the container is replaced by oxygen from outside; the carbon dioxide level is maintained in the same way.

Another advantage of the protective atmosphere is that it reduces the fruit or vegetable’s natural production of a gas called ethylene, which speeds up the ripening process.

In a mixed salad container, for example, a typical EMA could be made up of 5% oxygen, 15% carbon dioxide and 80% nitrogen.

This can extend the shelf life of the product by up to eight days, whereas if it were exposed to air, the shelf life would be limited to just four or five days.

A protective atmosphere can have a powerful effect on the brown pigmentation of cut fruit and vegetables, potatoes and apples, resulting from oxidation produced by enzymes released when the flesh is damaged. In these cases, a mixture of carbon dioxide and nitrogen in the packaging can prevent brown pigmentation for several days, rather than a few minutes or hours without protection.

Recommended equipment for quality control of fruit and vegetable packaging

Thanks to its ability to analyse gas and leakage in the same sample, the EXOS is well suited to a particularly technical field that combines several types of packaging for fresh produce. The EXOS’s ability to give a leakage value is perfectly suited to measuring the breathability of micro-perforated films, as demonstrated by the APEF.