A comparative study between different sensors used to detect the lower oxygen level during dynamic controlled storage of 'Conference' pears

To guarantee the availability of high quality pears throughout the year, the new trend in storage is to reduce the oxygen levels within a chamber and continuously monitor the lower oxygen level (LOL) tolerated by the fruit prior to anaerobiosis (referred to dynamic controlled atmosphere (DCA)). LOL monitoring includes measurements of chlorophyll fluorescence (CF), respiratory quotient (RQ) and/or ethanol accumulation (EtOH), all of them well implemented in apples but not in pears. The objectives of this study were to explore the suitability of DCA to store ‘Conference’ pears, to reveal the best method to determine the LOL based on the fruit physiology and to check possible key volatiles emitted by the fruit into the storage atmosphere as markers of LOL. To do so, we used ‘Conference’ pears harvested at the optimal commercial maturity and stored them in a semi-commercial chamber at 0°C for up to 8 months under DCA conditions. The O₂ and CO₂ levels within the storage atmosphere were controlled by an advanced control respiration (ACR) system which decreased O₂ levels until a consistent LOL signal (depicted by either RQ, CF or EtOH) was clearly observed. Changes in the volatiles concentration within the storage atmosphere were also recorded. In general, DCA storage allowed preservation of ‘Conference’ pears at optimum quality. Our data showed a correlation between CF and RQ measurements during the first 6 weeks of the cold storage, having a CF peak when RQ values were higher than 1. However, this correlation was lost as the storage period increased, observing exclusively CF peaks that did not match either higher RQ values or ethanol levels. Overall, both RQ and CF signals were only useful during the period of acclimatization of the fruit to the cold or when moving from relatively high (ca. 2%) to low O₂ levels. Further variables such as the emitted fruit volatiles can be used to monitor the LOL levels tolerated by the fruit.