Acid test explores that ripe moment

2019-03-08 08:15:05

By Mick Hamer FRUIT farmers will soon be able to tell exactly when their crops are ripe for picking, thanks to a small, cheap probe developed by researchers at the University of Southampton. The probe, which measures acidity and sugar levels, has just been tested on fields of tomatoes in California by a ketchup manufacturer. The probe is made by printing six tiny electrodes on a substrate of aluminium oxide 600 micrometres thick, says John Atkinson, who heads the research team. It measures about 2.5 centimetres by 5 centimetres. Similar probes have been used to test water quality and to detect gas. To test for ripeness, the researchers cut open a tomato and insert a capillary that sucks up juice into the probe. Three of the electrodes measure the pH and the others the concentration of sugar in the juice. “The test takes seconds,” says Atkinson. The great advantage of the probe, says Atkinson, “is its price, size and ruggedness”. The university made 15 000 probes for the Californian trials at a cost of just 50 p each. “It’s virtually a throwaway sensor,” says Atkinson. If the Californian trials prove successful, the researchers intend to develop a portable data processor that can give farm workers an instant print-out as they walk around their fields. Currently, data from the probe are fed into an office computer for analysis. “It certainly sounds like a useful bit of equipment,” says Kate Evans of Horticultural Research International, which is based in Kent. She points out, however, that there are other ways of testing for ripeness in the field. HRI, for example,