Modified atmosphere technology in cherry postharvest

By: Francisca Barros B, Jessica Rodríguez F, Militza Ivelic K/ Trío Kimün.

Modified atmosphere technology (MAP) has been a postharvest tool that has contributed to preserving the useful life of this fruit and allowing it to successfully reach distant markets such as the Chinese market.

MAP consists of altering the composition of the internal atmosphere of gases (oxygen and carbon dioxide) inside the container, either actively (by incorporating gases) or passively through the product’s own breathing.

The atmosphere generated inside the container will depend on the characteristics of the film used, the packaged product and the environmental conditions to which it is subjected. In the case of cherries, the use of this technology has made it possible to prolong the useful life of the fruit, which has resulted in greener and fresher pedicels (mainly due to the higher humidity levels inside the bag), maintenance of the characteristics organoleptic qualities and the reduction of the risks of rotting.

When deciding which MAP container to use, it should be considered that the cherry is a non-climacteric fruit with a moderate respiratory rate (10-20 ml CO2/kgh at 5°C). The films used for this fruit must be designed based on this information, as well as its permeability to O2, CO2 and water vapor, it must be such that the thermal fluctuation to which the fruit may be subjected is considered, especially at destination, where it is still There are no optimal conditions for managing the cold chain. At this point it is essential to maintain the aerobic condition of the fruit to avoid fermentation problems. The gas concentrations that are sought to be obtained taking into account the aforementioned reality are 10-15% O2 and 5-8% CO2.

When using this technology, several aspects must be taken into consideration to achieve the desired objective, among these key points the following stand out:

  • The quality and state of maturity of the fruit.
  • Management of the cold chain from the packaging to the destination of the fruit, with critical points being the temperature of the pulp at the time of sealing the bag (up to 8°C is used to avoid condensation) and the temperature of loading into the container ( not greater than 0.5ºC since the temperature in the container is only maintained).
  • Sealing of the bag to ensure the creation of the atmosphere.
  • Configuration of the temperature and the opening of the lamp of the container. In this last point, the need for ventilation of the container must be considered to ensure the entry of oxygen and the exit of CO2, otherwise strange odors and flavors may be generated due to alteration of the atmosphere. MAP bags were developed to function in an environment with normal air concentrations.

In our country we have national suppliers that have developed and innovated in the supply of packaging as well as foreign companies that have local representatives. In the last two decades, the main containers used with this technology in cherries are 5 kg bags (the most used container) and 2.5 kg bags.

The main considerations that must be taken into account when choosing the bag to be used are the following:

  • Bag Dimensions:

The length, width and height of the bag will depend on the box in which the fruit will be packed as well as the sealing system to be used (automatic or manual sealing). From a practical point of view, the bag must cover all the internal spaces of the box; gusseted bags are generally used to comply with this condition (Figure 1). To facilitate the packing and filling of the fruit in the boxes, especially in the case of cherries, where boxes are automatically filled, it is important that the bag can be folded outwards to carry out this work.

  • Bag thickness:

The thickness of the bag has an impact on its sealing and on the resistance to tearing and puncture. The bag must allow it to be used and manipulated in all types of boxes (regardless of its composition) without running the risk of it breaking or being damaged. On the other hand, the Chinese receiver prefers thicker bags (over 40 microns).

  • Optical properties of the bag (gloss and transparency):

The bag must allow the fruit to be displayed, this being particularly important in the case of cherries, which are considered a gift and an expensive product.

Also related to the optics of the bag, when checking a box of cherries, the receiver checks whether or not the bag is condensed and then touches the fruit through it to see if it is soft or firm.

For 5-6 years some exporters together with the providers of this technology have developed other MAP containers whose results have been variable at a commercial level. With the objective of automating the packaging process, MAP thermoformed containers were developed through thermomolding technology for the 5kg container, but its commercial result was not as expected despite its impact on productivity, managing to reduce the personnel assigned to packaging and preparation of materials.

On the other hand, in order to avoid having to repackage at destination, and thus avoid food safety problems and facilitate online sales (e-commerce), heat-sealed containers have been developed that consist of rigid containers with a lid. or upper film sheet through which the permeability of the container is adjusted, these formats have been worked from 500g to 2kg. The sheets that cover the containers can even be resealable (¨reclose¨). In this case, the other component of the container is a transparent clamshell treated with an anti-condensation additive and without ventilation. This type of packaging has been used for specific programs for supermarkets and its main limitation has been its productivity.

A challenge in the development of this technology has been the search for a system to prevent toxicity problems due to high CO2 levels and low O2 levels in the event of temperature changes. For this, various tests have been carried out where “smart” membranes have been tested that they would have the ability to adapt to the reality of our supply chain by modifying its permeability. Unfortunately to date there is no commercial solution that meets these objectives.

Surely in the coming years we will continue to see more innovations in packaging, packaging and post-harvest technologies that will allow us to improve our cherry offer.

Figura 4. Equipo para sellado de clamshells         

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