Measuring CO2 to Optimise the Bulk Storage of Food

Date Announced: 24 Jul 2017

Meeting the food requirements of a growing global population is becoming increasingly difficult. Despite the need for additional food, it is estimated that 50-60% of grain is lost after harvesting, at a cost of about $1 trillion per year.¹

One of the major reasons for lost grain is spoilage due to mould or insect infestation during storage.² To provide a constant supply of grain year-round, after grains are harvested they are often kept in long term storage. Maintaining the quality of stored grain is crucial, both to ensure the quality of the final food products, and to prevent economic losses for farmers.

Insects and moulds can grow in stored grain, and their ability to flourish depends on the temperature and moisture of the stored grain. Moulds are the most common cause of grain spoilage and can cause changes in the appearance and quality of stored grains. Some moulds can release toxic chemicals called mycotoxins which can suppress the immune system, reduce nutrient absorption, cause cancer, and even be lethal in high doses. It is therefore crucially important to prevent the presence of mycotoxins in food products.²

Monitoring Stored Grain

Farmers are advised to check their stored grain weekly for signs of spoilage.³ Traditionally, grains are checked visually and by odour. Grain sampling can allow earlier detection of insects and moulds, but these methods can be tedious and time-consuming. Rapid, simple methods are needed for early detection of spoilage and to prevent grain losses.²

When moulds and insects grow, and respire, they produce CO₂, moisture and heat. Temperature sensors detect increases in temperature caused by mould growth or insect infestation, therefore indicating the presence of grain spoilage. However, they are not able to detect temperature increases caused by infestation unless the infestation is within a few meters of the sensors. CO₂ sensors can detect the CO₂ produced by moulds and insects during respiration. As the CO₂ gas moves with air currents, CO₂ sensors can detect infestations that are located further away from the sensor than temperature sensors. CO₂ measurements are therefore an important part of the toolkit needed to monitor stored grain quality.²

Using CO₂ Measurements to Detect Spoilage

CO₂ monitoring can be used for early detection of spoilage in stored grains, and to monitor the quality of stored grains. Safe grain storage usually results in CO₂ concentrations below 600 ppm, while concentrations of 600-1500 ppm indicate the onset of mould growth. CO₂ concentrations above 1500 ppm indicate severe infestations and could represent the presence of mycotoxins.⁴

CO₂ measurements can be taken easily, quickly and can detect infestations 3-5 weeks earlier than temperature monitoring. Once spoilage is detected, the manager of the storage facility can address the problem by aerating, turning, or selling the grain. Furthermore, CO₂ measurements can aid in deciding which storage structure should be unloaded first.²

Research published by Purdue University and Kansas State University have confirmed that high CO₂ levels detected by stationary and portable devices are associated with high levels of spoilage and the presence of mycotoxins.^4,5 Furthermore, they compared the ability of temperature sensors and CO2 sensors in a storage unit filled with grain to detect the presence of a simulated ‘hot spot’ created using a water drip to encourage mould growth.

The CO₂ concentration in the headspace of the storage unit showed a strong correlation with the temperature at the core of the hot spot, and the CO₂ sensors were, therefore, able to detect biological activity. The temperature sensors were not able to detect the mould growth, despite being placed within 0.3-1 m of the hotspot.⁶

To enable efficient monitoring of grain spoilage accurate, reliable and simple to use CO₂ detectors are required. Gascard NG Gas Detector from Edinburgh Sensors provide accurate CO₂ measurements along with atmospheric data, enabling grain storage managers to make decisions with confidence.⁷

The Gascard NG Gas Detector uses a proprietary dual wavelength infrared sensor to enable the long term, reliable measurement of CO₂ over a wide range of concentrations and in temperatures ranging from 0-45 °C. Measurements are unaffected by humidity (0-95% relative humidity) and the onboard pressure and temperature sensors provide real-time environmental compensation, resulting in the most accurate CO2 concentration readings.

Conclusion

Easy, fast, and accurate CO₂ concentration monitoring during grain storage can provide early detection of grain spoilage, resulting in reduced grain losses, higher quality stored grain, and lower mycotoxin levels. CO₂ monitoring could save millions of dollars annually in the grain production industry.⁴

References

1. Kumar D, Kalita P, Reducing Postharvest Losses during Storage of Grain Crops to Strengthen Food Security in Developing Countries. Foods 6(1):8, 2017.
2. http://www.world-grain.com/Departments/Grain-Operations/2016/7/Monitoring-CO2-in-stored-grain.aspx?cck=1 Accessed May 25th, 2017.
3. HGCA Grain storage guide for cereals and oilseeds, third edition, available from: https://cereals.ahdb.org.uk/media/490264/g52-grain-storage-guide-3rd-edition.pdf Accessed May 25th, 2017.
4. Maier DE, Channaiah LH, Martinez-Kawas, A, Lawrence JS, Chaves EV, Coradi PC, Fromme GA, Monitoring carbon dioxide concentration for early detection of spoilage in stored grain. Proceedings of the 10th International Working Conference on Stored Product Protection, 425, 2010.
5. Maier DE, Hulasare R, Qian B, Armstrong P, Monitoring carbon dioxide levels for early detection of spoilage and pests in stored grain. Proceedings of the 9th International Working Conference on Stored Product Protection PS10-6160, 2006.
6. Ileleji KE, Maier DE, Bhat C, Woloshuk CP, Detection of a Developing Hot Spot in Stored Corn with a CO2 Sensor. Applied Engineering in Agriculture 22(2):275-289, 2006.
7. https://edinburghsensors.com/products/oem/gascard-ng/ Accessed May 25th, 2017.

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