Modified and Controlled Atmosphere: Today’s Technologies
This is our second post on modified atmosphere systems. Lost? Catch up here.
When it comes to freshness in the produce supply chain, keeping a close eye on atmospheric conditions is just as critical as monitoring temperature. Recently developed technologies known as modified atmosphere (MA) and controlled atmosphere (CA) systems regulate this aspect of quality during transport. MA/CA systems expose fresh produce (fruits, vegetables, and flowers) to a higher concentration of carbon dioxide (CO2) and lower concentration of oxygen (O2) than is normally present in the air. Controlling the gases responsible for the natural senescence of fresh produce can help maintain quality for a longer period of time and extend postharvest life.
Modified atmosphere (MA) systems measure and control of gas levels at a broad level. Gas levels are allowed to fluctuate over time in the natural course of produce interaction.
Controlled atmosphere (CA) systems strictly measure and control atmospheric gas levels within the refrigerated space. The gas levels are mechanically maintained at the desired limits for the entire trip period.
MA/CA technologies can be applied on a large scale within a pallet or whole container, or within smaller refrigerated spaces down to individual packs.
Modified atmosphere (MA) systems
1. Polyethylene pallet covers
This technology is often used for shipping non-climacteric fruit such as strawberries, cherries and raspberries, which tolerate high CO2 levels. High CO2 concentrations greater than (15%) create an antibacterial effect. Individual pallets are covered with a polyethylene cover/shroud and sealed at the base using tape or heat seals. The desired gas mixture is then injected into the cover.
2. Polyethylene liners/bags for boxes
Polyethylene liners (bags) create an MA environment within a carton/box of produce during transit. This technique is often used in-transit for produce such as cherries or bananas. For example, transporting bananas using polyethylene liners, also known as a Banavac system, increased the postharvest life of the fruit by up to 50-60 days.
3. Modified atmosphere packaging (MAP)
MA systems are also used within individual packages. Packaging material which allows some gas permeability is used to keep gas levels relatively steady over time. The desired gas ratio can be achieved actively by inserting a gaseous mixture into the package, or passively as a result of the produce’s respiration, which involves O2 consumption and CO2 production.
4. eAutoFresh™ by Carrier Transicold
This eAutoFresh ventilation system uses a CO2 software-controlled sensor to precisely control the fresh air exchange rate within a shipment. The ventilation units are transferable between container units equipped with a ML2i or ML3 controller. This system is an energy-saving alternative to systems which continuously vent refrigerated containers.
Controlled atmosphere (CA) systems
1. EverFRESH® system by Carrier Transicold
EverFRESH® uses fresh air and nitrogen (N2) to maintain desired O2 and CO2 levels within a container. The system is fitted with a N2 generator membrane, which separates N2 from the outside atmosphere and injects it into the container. If O2 drops below the desired level, air vents automatically open to let fresh air in. A CO2 bottle can also be added, if the levels of CO2 required are higher than what the produce can naturally generate.
2. XtendFRESH™ system by Carrier Transicold
The XtendFRESH™ system is fitted with O2 and CO2 sensors, as well as a carbon scrubber which controls CO2 and ethylene (C2H4). It also uses a door curtain to create a tight seal within the container. The XtendFRESH is a modular system which can be installed on container refrigeration units with Micro-Link® 3 controllers, and can maintain levels of 3-21% O2 and 0-19% CO2. Higher CO2 levels are possible with the addition of an optional CO2 bottle. If O2 levels drop below the desired level, air vents automatically open to let fresh air in.
MA and CA technologies are becoming increasingly popular for the transport of fresh produce all over the world. They can be as simple as a packaging method that regulates gas levels more effectively, or as complex as the CA ventilation systems seen above. Whatever path you choose, MA/CA systems can help you take control of an essential factor in produce freshness.
Fig 1: Recommended CA / MA conditions for some common fresh fruit and vegetables. Data compiled from Kader, et al., 1989; Kader, et al., 2002; Danish Technological Institute, 2008; Baroni, et al., 2009; ICCT, 2014.
Sensitech combines strong food industry expertise and cold chain best practices with state-of-the-art monitoring technology and analytics to help food producers, shippers and buyers ensure the quality and freshness of their food products worldwide. Contact our Professional Services team to learn more about how our CO2 studies and how Sensitech ColdStream® Services can help drive process improvements and improve your bottom line.
Did you miss part one? – Are Modified Atmosphere Systems Right for You?