How to Extend the Shelf Life of Fresh Produce: Innovations in Gas Monitoring and Controlled Atmospheres

• Extend the shelf life of fresh produce: Oxygen, carbon dioxide, and ethylene are monitored in all postharvest stages, including controlled atmosphere storage and transport facilities and modified atmosphere packaging.
• Ethylene is monitored to manage and maintain fresh produce quality, ripeness, and shelf life by detecting ethylene accumulation hotspots.
• Oxygen and carbon dioxide estimation helps to maintain individual gas at prescribed concentrations to slow respiration, ripening, senescence, decay, and microbial spoilage, thereby helping to extend the shelf life of fresh produce.

Ambient conditions in the fresh produce supply chain determine freshness and quality and extend the shelf life of produce by influencing several internal physiological processes. Measuring the gases with small portable devices suitable for all spaces and environments in the supply chain can help detect and manage these processes to reduce wastage and improve ROI. Find out more on how gas analyzers can help your business.

Ambient Gas Parameters

The internal physiological processes the supply chain seeks to control through gas analysis are respiration, ripening, spoilage because of microbes, injury, and damage, see Figure 1.

The ambient conditions are important for climacteric fruits, which have not completed their fruit development and will undergo ripening postharvest in the supply chain.

The important ambient conditions for fresh produce in the supply chain are temperature, relative humidity, and three leading gases- ethylene, oxygen, and carbon oxide.

Sensing quality through gas measurements to extend shelf life requires a thorough understanding of gas responses to create the ideal combination for the supply chain. Discussed below are some common responses to the three gases.

Ethylene

Ethylene is a phytohormone produced by fruits to trigger ripening. The gas is measured to indicate the ripening stage and to predict shelf-life.

Ethylene gas volumes of less than 1 part per million (ppm) are enough to start the climacteric fruit ripening process. Non-climacteric fruits’ ripening is not started by ethylene. Still, several are susceptible to other effects of ethylene, such as degreening due to loss of chlorophyll, accumulation of bitter compounds in parsnips and carrots, and fruit softening in fruits like watermelons.

Ethylene is used for artificial ripening and degreening; however, its production at unscheduled stages in the supply chain can reduce shelf life by setting off ripening and other processes that end in senescence and decay. Therefore, ethylene is measured during storage and transport.

Ethylene levels can be controlled by ventilation or by using scrubbers.

The gas analyzers must be sensitive enough to measure quantities less than 1 ppm. Since other organic substances are also present, the device should be able to detect gas in the atmosphere, among several others.

Figure 1. “Postharvest refrigerated supply chain of fruits and vegetables,” Onwude et al. 2020. (Image credits: https://doi.org/10.3390/pr8111431)

Oxygen and Carbon Dioxide

Fresh produce continues to respire after harvest, using oxygen (O2) in the ambient air to produce carbon dioxide (CO2). An increased respiration rate, which can occur under high temperatures, triggers ethylene production in climacteric fresh produce. As respiration rates rise, the shelf life of fresh produce reduces.

Maintaining low O2 and high CO2 levels can keep respiration and ethylene levels down. The range of concentrations for O2 and CO2 for each commodity is fixed, and a higher or lower deviation from this range can result in stress, which again produces ethylene and causes decay. Fresh produce shows that O2 and CO2 levels also influence ethylene sensitivity.

Moreover, an increase in CO2 in ambient air, if not removed by ventilation or scrubbers, can lead to anaerobic respiration and decay. The shift from aerobic to anaerobic respiration depends on fruit maturity, temperatures, and O2 levels.

Maintaining optimum gas levels can reduce food waste and increase ROI. Therefore, gas analysis is integral, especially for global fresh produce supply chains directed to developed countries, where controlled and modified atmospheres are standard for extending postharvest life and withstanding long transport distances.

Grading Facilities

Though fresh produce quality parameters are commonly monitored to sort and grade fresh produce, ethylene levels are also controlled in grading facilities’ sorting belts. It was found that even in areas where fresh produce is not stationary for long, ethylene concentrations can reach 500 ppb for apples. So, these facilities should be well-ventilated to prevent the accumulation of the phytohormone that exogenous sources like machines can produce. The F-900 Portable Ethylene Analyzer, highly sensitive to the phytohormone, can monitor ethylene levels.

Controlled Atmosphere Storage Facilities

Controlled atmosphere (CA) storage facilities alter O2 and CO2 levels to suit requirements for different commodities, along with temperature and relative humidity. CA storage rooms have sealed joints between roofs, walls, floors, and air-tight doors to control gas compositions. They require constant gas concentration monitoring. CA facilities maintain quality, extend availability year-round, and reduce waste.

Controlled atmosphere facilities alter the proportion of O2 and CO2 gases to lower respiration rates and ethylene production, controlling ripening and maintaining nutritional value, firmness, and color. For example, apples were firmer in CA store rooms than when air-stored. Still, apple ethylene levels can be around 10 ppb with an ethylene scrubber.

The advantages of helping CO2 high are preventing chilling injury and preventing microbial and pest growth. For instance, 10-15% CO2 inhibits botrytis rot in strawberries and cherries. While < 1 %O2 and 40-60% CO2 control insects in vegetables and fresh and dry fruits.

Deviations from ambient air can have detrimental effects, such as bruising, skin browning, irregular ripening, and the development of off-odors. So, real-time monitoring of O2 and CO2 is necessary for CA storage. Tools like the handheld Felix F-940 Store It! Gas Analyzer can be used for spot checks of the three gases. The  F-901 AccuRipe & AccuStore is suitable for continuously monitoring and controlling gases, temperature, and relative humidity.

The benefits of CA storage are considerable for pears, apples, and cabbages, so they are kept in CA facilities.

Transport

Fresh produce can be exposed to extreme temperatures during transport, especially warmth in tropical countries, and transported in open exposed lorries. In addition, vibrations and shock can cause stress in fresh produce and increase ethylene levels.

CA conditions can buffer produce from temperature and, to some extent, vibrations during transport and distribution, along with gas monitoring. CA facilities could be used for long-distance transport of avocados, bananas, kakis, onions, kiwifruit, and strawberries. More straightforward solutions include edible coatings or polymeric films that can create the optimum atmospheric conditions within and around commodities during transport.

Gas analyzers such as the portable  F-920 Check It! Gas Analyzer helps monitor gases in transit.

Ripening Rooms

Ripening rooms have to measure ethylene, the standard agent for artificial ripening of fruits and degreening citrus. It can be done with a portable F-960 Ripen It! Gas Analyzer or the fixed F-901 AccuRipe & AccuStore for continuous monitoring and control.

Fruit ripening programs are specific for each fruit and are designed to get the desired color and flavor to meet consumer satisfaction.

In addition to the phytohormone, the concentrations of the other two gases, CO2 and O2, are also monitored as they can influence the ripening rate. Optimum levels of O2 ensure proper ripening. CO2 produced by respiration should not be more than 0.5 to 1% as it can slow the ripening process.

Besides the three gases, monitoring temperature is necessary, as it hastens ripening. Fresh produce can be ripened in batches in required quantities before being sent to wholesale distribution centers.

Packaging

Modified atmosphere packaging (MAP)  is another way to extend shelf life by providing commodities with precise environments favorable for their quality retention. MAP also extends fresh produce availability year-round and reduces waste.

As in CA facilities, O2 and CO2 concentrations are altered from ambient levels to slow respiration, ripening, and senescence. Most of the time, low O2 and high CO2 slow down respiration and other metabolic activities and create conditions unsuitable for spoilage microbes. Most MAPs also improve moisture retention of fresh produce to maintain freshness and quality. Packaging also acts as a barrier to contaminants and microbes.

Since lower O2 levels can lead to fermentation and off-odors, high O2 and high CO2 are used nowadays. The range of the two gases is specific for each commodity. Other gases like nitrogen or a mixture can be used.

The concentrations of gases must be measured while packaging to ensure the desired environment and later during distribution and retailing for quality control. Active MAP uses respiration in its model to achieve the target environment after some days, while passive MAP has the targetted atmosphere from the start.

MAP aims to avoid ethylene production to keep commodities from decaying, so this gas must also be monitored.

Portable gas analyzers for headspace and MAP like the Felix Instruments’ F-920 Check it! Gas Analyzer and the F-900 Portable Ethylene Analyzer measure all three gases without damaging the MAP.

Retailing and Labelling

Retailers check gases in packages for quality control, gas leaks in packages, and labeling. Checking MAP headspace environments with gas analyzers and the quality of fresh produce with Near-infrared spectroscopy can help retailers fix the correct “use by” date and extend marketing time for fresh produce to increase ROI.

Save Food and Extend the Shelf Life of Fresh Produce

Using gas analyzers helps the fresh produce supply chain stakeholders maintain necessary conditions from farm gate to consumer. Any deviation, even for a few hours at any point of the chain, can spoil the perishable products, so using standard tools like the Felix Instruments’ user-friendly and small tools for accurate measurements in real-time can save food, increase profits, and reduce waste.

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