A NONDESTRUCTIVE METHOD FOR MEASURING THE WATER POTENTIAL OF FRUIT AND VEGETABLES

Water potentials of fruit and vegetables are usually measured with eit her pressure chambers or thermocouple psychrometers. Both methods dema nd considerable expertise and experience. The main disadvantage of the pressure chamber is the unknown influence of pressurization on tissue . Psychrometers suffer the problem that only pieces of tissue can be u sed. To overcome this problem we have devised a non-destructive measur e of water potential. The proposed method is based on relative weight change of a series of salt solutions placed close to the epidermis. Th ese solutions are contained inside patches which are made with one sid e of microporous polyethylene, allowing the exchange of water vapour b etween the tissue and the patch. Patches, each containing different co ncentrations of salt solution, are taped to the epidermis. The fruit o r vegetable, with patches attached, is then wrapped in cling wrap and left to equilibrate overnight at constant temperature. The basis of th e method is the assumption that the water potential of the salt soluti on in the patch which neither gains nor loses weight is equal to the w ater potential of the fruit or vegetable. This method has been tested in two ways: one using microporous bags containing solutions with know n water potentials, and the other with carrots. Changes in water poten tial, osmotic potential, total soluble solids and relative water conte nt of carrots stored for 3 days at 20 degrees C and ambient relative h umidity were monitored, The method accurately measured the water poten tial of salt solutions contained inside microporous bags and was able to measure a significant difference between fresh and stored carrots. This method could prove useful for use in storage or ripening experime nts where the changes in water potential at the surface of intact comm odities could be followed over time.