Improving the Conservation and Ripening of Fruits Using CO2 Monitoring

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The first bite of a plump, ripe juicy strawberry for many, signals the start of Summer. At its optimum ripeness, the signature characteristics of the strawberry are a bright red sheen, with a soft, sweet aroma and a firm texture. However, within just a day or two, this delightful fruit treat can turn into a mushy, flavorless mess. What’s more, strawberries when spoiled can also turn into a home to mold.

There is such a stark difference in eating well-ripened fruits vs either under or over-ripe specimens, that perceived ripeness has an extremely strong influence on consumer buying behavior and the probability of purchase.1 There may be a significant time period between when the fruit is picked and when it arrives onto the supermarket shelf. Therefore, it is essential to control the ripening process for fruits to ensure they can be sold in their prime.2

Mechanisms of Ripening

Ripening is a natural part of the maturation of fruits, helping them obtain their optimal flavor, quality and textural properties. The ripening process involves a host of changes in the fruit’s composition (including the transformation of starch into sugar) that are a result of a cascade of chemical and biochemical reactions in the fruit.3

The involvement and production of chemicals during the ripening process implies that ripening can be controlled by altering the atmospheric composition around the fruit. Ethylene is one of the most widely used chemicals that can speed up the ripening process. In fact, it is so effective at speeding up the process that it is known as ‘the ripening hormone’.4

During the ripening of fruits, Ethylene is naturally produced, and it can also trigger biochemical cascades and physiological responses – such as the aging and shedding of petals or additional growth in some cells. Bananas, for instance, produce vast quantities of ethylene. This can have a detrimental effect on the lifetimes of fruit stored alongside them.

Carbon Dioxide and Ripening

It is important to note that Ethylene is not the only chemical that can determine the lifecycle of fruits. In fact, Carbon dioxide (CO2) is another by-product that is created during the ripening process. Thus, controlling CO2 concentrations can be done to adjust the rate of the ripening process. Controlling CO2 can also help finetune some of the properties and characteristics of the fruit.5

For instance, in the case of kaki fruit, the under-ripened fruit can taste quite astringent and unpleasant, but its firmer texture is better suited for transportation purposes, with less risk of damage to the fruit’s flesh. However, ripening the kaki within an atmosphere of carbon dioxide can improve the flavor of the ripe fruit, while also maintaining the solidity of the unripe fruit.

Controlling the CO2 atmospheric concentrations is a process also adopted for oranges and many citrus fruits, since this helps in altering the color of the fruit – transforming it from an unappetizing green to a healthy orange, without impacting the flavor in the slightest.

In addition to ripening, the careful control of CO2 and oxygen (O2) levels can aid in maintaining the fruit’s preservation and freshness. Atmospheric conditions can change with time, as fruits continue to ‘breathe’ and produce various gases. For instance, the use of controlled CO2/O­2 atmospheres for apples can ensure a stable fruit flavor and quality for as long as nine months following harvest.6

Sensing Solutions

The maintenance of optimal CO2 concentrations is a complex task, requiring highly sensitive online monitoring with feedback loops to ensure optimization. To achieve this, Edinburgh Sensors – the market leaders with 40+ years of experience – are developing highly sensitive, rapid response near-infrared sensors to detect hydrocarbon gases and CO2.

Edinburgh Sensors offers a range of CO2 sensors to match every application need – including the Gascard NG7, Guardian NG8, the IRgaskiT9, and the Gascheck.10 Among these, the Gascard NG provides a large amount of flexibility in terms of set-up, monitoring options, and integration into connected systems.

The Gascard NG is available in two versions – either as the stand-alone card or as the Boxed Gascard11. The latter comes with the Gascard NG card inside a pre-built housing to minimize installation and set-up time. The sensor’s high sensitivity and accuracy features are essential for this application, especially considering the low concentrations of CO2 and O2 that are often optimal for controlled atmospheric preservation of fruits (for apples, between 2 – 6 % of CO2 and 2 – 3 % of O2).

Gascard NG

Gascard NG

The Gascard, for example, can detect CO2 concentrations in the range of 0 – 5000 ppm. It can also work under realistic temperature and humidity conditions, with the capability of providing accurate readings over humidity conditions spanning 0 – 95 %. The Gascard’s other powerful feature is that, by using RS232 communications, the Gascard can be integrated with other control or data logging devices easily.

In addition, there is also the option for onboard LAN support where required. As a result, it is relatively straightforward to set up feedback systems to constantly monitor, log, and adjust the atmospheric conditions surrounding the fruit, thus ensuring the produce is always at its best.

Thus, with its ability to reduce waste (by protecting unripe surrounding fruit from overripe fruit), optimize ripening at the time of sale, and improve product quality, the instruments from Edinburgh Sensors offer cost-efficient and high-quality devices for online monitoring of CO2 levels.

References and Further Reading

  1. Bruhn, C. et al. (1991) “Consumer Perception of Quality.” Journal of Food Quality, 14: 184–95
  2. How old are the ‘fresh’ fruit and vegetables we eat, https://www.theguardian.com/lifeandstyle/2003/jul/13/foodanddrink.features18, (accessed May 2019)
  3. Giovannoni, J J,. (2001) Molecular Biology of Fruit Maturation and Ripening. Annu. Rev. Plant Mol. Biol. 52: 725–749.
  4. Barry, C.S. et al.. (2007) Ethylene and Fruit Ripening Journal of Plant Growth Regulation 26: 143–59. https://doi.org/10.1002/9781118223086.ch11.
  5. Burg, Stanley P., et al.. (1969) Interaction of Ethylene, Oxygen and Carbon Dioxide in the Control of Fruit Ripening. Qualitas Plantarum et Materiae Vegetabiles 19 1–3: 185–200. https://doi.org/10.1007/BF01101152.
  6. Streif, J. et al. (2016). Production of Volatile Aroma Substances by ‘Golden Delicious’ Apple Fruits after Storage for Various Times in Different CO2 and O2 Concentrations Journal of Horticultural Science 63 (2): 193–99. https://doi.org/10.1080/14620316.1988.11515847.
  7. Gascard NG, https://edinburghsensors.com/products/oem/gascard-ng/, (accessed May 2019)
  8. Guardian NG, https://edinburghsensors.com/products/gas-monitors/guardian-ng/, (accessed May 2019)
  9. IRgaskiT, https://edinburghsensors.com/products/oem/irgaskit/, (accessed May 2019)
  10. Gascheck, https://edinburghsensors.com/products/oem/gascheck/, (accessed May 2019)
  11. Boxed Gascard, https://edinburghsensors.com/products/oem/boxed-gascard/, (accessed February 2019)

This information has been sourced, reviewed and adapted from materials provided by Edinburgh Sensors.

For more information on this source, please visit Edinburgh Sensors.

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