A NEW INTERACTIVE STORAGE CONCEPT: DYNAMIC CONTROL OF RESPIRATION

Last decade, several dynamic storage systems were developed aiming at storage just above oxygen levels where fermentation occurs (<1%). Dynamic control is based on stress response of the fruits, which can be defined as ethanol production (DCS and ILOS) or increased chlorophyll fluorescence status (DCA). Important advantages of these systems are disorder prevention and firmness retention. In The Netherlands, a complete new system is being developed: Dynamic Control of Respiration (DCR). CO₂ production as well as oxygen uptake are measured to determine the respiratory quotient (RQ). RQ-values were calculated by dividing accumulation of CO₂ by uptake of oxygen. The DCR system adjusts O₂ levels in the storage room based on RQ-values. Important questions around the RQ measurement: is the respiration quotient a reliable marker to determine the lowest tolerable oxygen concentration for the fruits and is it possible to use in commercial rooms? Apples of ‘Elstar’ were exposed to extremely low, dynamic oxygen levels. Apples stored for 5 months in 1.2 kPa O₂ combined with 2% CO₂ in 1.8°C were placed in cuvettes. RQ and ethanol measurements started at 1.2% O₂ and subsequent continued in 0.6, 0.3, 0.2, 0.1 and 0.05% O₂ executed with the same fruits, continuously after 6 days adaptation. At 0.3% O₂ RQ increased gradually followed by increased ethanol production proving that RQ seems to be a reliable marker for fermentation. The DCR system has been applied in 6 commercial ULO rooms, and 2 16-t semi-practice rooms. RQs were determined by shutting down all conditioning of a ULO room while monitoring O₂ and CO₂ evolution. In all commercial rooms the final oxygen conditions were set by the measurement of RQ indicating that the DCR system is a promising interactive storage system. DCR also reduced respiratory heat production up to a factor 2 compared to standard ULO, resulting in significant energy savings.