Effect of osmotic adjustment on the rheology of potato tissue. The use of discriminant analysis for interpretation

The cell turgor pressure of potato tissue was adjusted by hyper- and hypotonic solutions of mannitol. Tubers of cv. Maris Piper were stored for 12 weeks. Rectangular beams of tissue were subjected to threepoint bend tests and Young¿s modulus was calculated. Variability in mechanical properties was less when cells were fully turgid. Dimensional parameters suggested that potato tissue is anisotropic. The results indicated the importance of water content when analysing Young¿s modulus of potato tissue from rectangular beams. Young¿s modulus proved an adequate mechanical parameter, which, along with dimensional parameters, is suitable for classifying samples of potato in different stages of turgor on the basis of the osmotic adjustment performed. There was evidence of incipient plasmolysis after osmotic adjustment to a concentration of 0.6 M mannitol as supported either by Young¿s modulus values or by discriminant analysis. Young¿s modulus measured on rectangular beams was not an adequate mechanical property to detect the effects of storage time over a 12-week period.M.D. Alvarez wishes to thank the Spanish Department of Education & Culture for an FPI fellowship, and project ALI98–1055.Peer Reviewe