More than 350,000 tonnes of apples are now stored worldwide using new technology, patented in Canada by Prof Robert Prange’s group, with further development at the Agricultural Research Institute Laimburg, Italy. UK fruit growers recently benefited from Prof Prange explaining the science behind the system at a seminar organised by UK agents for Isolcell, UKCA and fruit advisors FAST.
When chlorophyll, present in fruit skins, is exposed to light it becomes ‘energised’, but the cell is not fast enough or ready to chemically convert the energy to sugar. Instead, light is re-emitted, as fluorescence. Whilst researching stress effects on chlorophyll fluorescence, the potential to monitor low oxygen stress of fruit in controlled atmosphere storage was investigated.
The fluorescence of apples remains relatively stable as oxygen in the atmosphere is reduced to 0.8% but as it is reduced to 0.2%, the fluorescence dramatically and rapidly increases indicating the fruit has started anaerobic respiration and is stressed. Increasing oxygen sees the fluorescence rapidly return to normal. The system uses a specialised flourometer housed in a “kennel” box with a sample of fruit to measure these changes.
The technique can also be used to detect other storage stresses such as low temperature, increased carbon dioxide and refrigerant leaks into store – even the lights going on in store registers on the system with a spike of fluorescence. The Italian research showed attributes of product quality such as flavour can also be monitored.
Prof Prange said that any produce including vegetables could be monitored in storage in a similar way. Indeed, he had seen cabbage, peppers and lettuce show a fluorescence response to low oxygen in storage. Other researchers reported monitoring of asparagus, broccoli and spinach in addition to cabbage, peppers and lettuce in both CA and non-CA store. He said the technique could have a place in monitoring quality in fresh produce such as vegetables.