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In situ, continuous and real-time monitoring of respiration (R) and respiratory quotient (RQ) are crucial for identifying the optimal conditions for the long-term storage of fresh produce. This study reports the application of a gas sensor (RMS88) and a modular respirometer for in situ real-time monitoring of gas concentrations and respiration rates of strawberries during storage in a lab-scale controlled atmosphere chamber (190 L) and of Pinova apples in a commercial storage facility (170 t). The RMS88 consisted of wireless O2 (0% to 25%) and CO2 sensors (0% to 0.5% and 0% to 5%). The modular respirometer (3.3 L for strawberries and 7.4 L for apples) consisted of a leak-proof arrangement with a water-containing base plate and a glass jar on top. Gas concentrations were continuously recorded by the RMS88 at regular intervals of 1 min for strawberries and 5 min for apples and, in real-time, transferred to a terminal program to calculate respiration rates ( R O 2 and R CO 2 ) and RQ. Respiration measurement was done in cycles of flushing and measurement period. A respiration measurement cycle with a measurement period of 2 h up to 3 h was shown to be useful for strawberries under air at 10 °C. The start of anaerobic respiration of strawberries due to low O2 concentration (1%) could be recorded in real-time. R O 2 and R CO 2 of Pinova apples were recorded every 5 min during storage and mean values of 1.6 and 2.7 mL kg−1 h−1, respectively, were obtained when controlled atmosphere (CA) conditions (2% O2, 1.3% CO2 and 2 °C) were established. The modular respirometer was found to be useful for in situ real-time monitoring of respiration rate during storage of fresh produce and offers great potential to be incorporated into RQ-based dynamic CA storage system.

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Adjusting beneficial gas concentrations in real time in response to changing storage conditions is important for fresh produce, especially throughout the supply chain when temperature abuse occurs frequently. In this study, a controlled-ventilated box for bulk transportation of fresh produce was demonstrated and tested under variable temperatures. The presented system comprised a rigid container with a miniature blower installed in the opening of its wall for facilitating the gas exchange and an additional wall opening with a metal tube protruding into the inner container’s space. The in-package atmosphere was formed by the balance between the respiratory activity of the produce and the influx of fresh air through the wall openings, regulated by switching the blower ON or OFF. The mass transfer coefficient for metal tubes of different dimensions was measured under modified atmosphere featuring 15% CO2 and 5% O2 at 10 °C. The addition of an air blower increased the mass transfer coefficient by at least 100 times. A further storage trial with cherries was successfully performed at 10 °C and 20 °C. The demonstrated trial featured some significant inputs to increase the knowledge about better storage of fresh produce throughout the supply chain and storage.

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The storage of fruit at minimum oxygen condition is crucial for optimal fruit quality maintenance. However, the optimal oxygen partial pressure of fruit varies according to several factors such as species, cultivar, harvest maturity, temperature, growing season and storage period. Based on these factors, storage technologies were developed that allow for the detection of the lower oxygen limit (LOL) and the storage of fruit under the lowest optimal oxygen partial pressure. One emerging technology is known as dynamic controlled atmosphere (DCA). Commercially, there are four DCA systems used: [1] DCA based on ethanol production and accumulation (DCA-Eth); [2] DCA based on chlorophyll fluorescence (DCA-CF); DCA based on the respiratory quotient (DCA-RQ) and [4] DCA based solely on CO2 production (DCA-CD). This reviews the recent developments of these DCA systems and their effect on fruit quality. Generally, the storage of fruit under DCA has a positive effect on the overall fruit quality, with regards to reduced physiological disorders and higher flesh firmness maintenance, when compared to controlled atmosphere (CA). Evidence also shows that storing fruit under DCA-RQ and DCA-CD allowed higher volatile compound emission and concentration, which can contribute positively to fruit flavor. The DCA systems are “green storage technologies” because the system enables the increase of storage temperature and thereby saving electrical energy. Storage of apples under DCA maintains an overall fruit quality similar to CA combined with the ripening inhibitor 1-Methylcyclopropen (1-MCP), which is an interesting option for organic fruit storage. Dynamic controlled atmosphere is a recently developed storage technique and is in constant improvement. The latest developed DCA techniques (DCA-RQ and DCA-CD), in contrast to DCA-CF, allow the use of extremely low oxygen levels. In the future, new and multi-sensor DCA systems are under development, which might not just control O2 partial pressure but also temperature and other parameters to allow for more energy efficient but high quality fruit storage systems.