Abstract
A non-destructive monitoring system that assesses low-oxygen stress of chlorophyll-containing fruit (HarvestWatch; Satlantic Inc., Halifax, N.S., Canada) was applied during storage. It allows for the changing of the atmospheric composition in the CA-room dynamically to the actual physiological state of the fruit (DCA), in contrast to the usually static conditions of CA storage. A decrease of the oxygen concentration to the lowest levels tolerated by the fruit should optimize the greatest benefits of ultra low oxygen (ULO) storage without risking losses caused by anaerobic conditions. The monitoring system is based on the measurement of chlorophyll fluorescence by means of FIRM (fluorescence interactive response monitor, Satlantic Inc.) sensors on samples of six apples. Below the fruit specific oxygen-threshold, the theoretical estimate of F 0 at zero irradiance, F α increases. The oxygen concentration of the controlled atmosphere was set slightly above the tolerance level of the fruit as determined by the rise of F α. The effects of DCA on the control of superficial scald and on quality preservation of apple fruit cv. 'Granny Smith' were compared with those of 1-MCP and diphenylamine (DPA) postharvest treatments. Optimal recommended CA conditions were used as a reference. The delay of quality loss was determined by means of internal quality, taste panel preference and incidence of physiological disorders, such as superficial scald, core flush and anaerobic breakdown. Results of the scaling to commercial dimensions in a 150 t room are also given. According to the fruit's fluorescence response to low oxygen stress, O 2 was set at 0.4 kPa plus 1.3 kPa CO 2. After 6 months of storage followed by 7 or 14 days of ripening at 20°C, the occurrence of superficial scald was completely absent and no signs of low oxygen disorders could be seen on 23 different batches of fruit. Moreover taste was not influenced by off-flavors. Firmness was maintained at levels comparable to 1-MCP treatment. However the efficacy of 1-MCP in totally controlling scald, reducing core flush and delaying ripening could be confirmed even during shelf life conditions.