EVALUATION OF RHEOLOGICAL PROPERTIES CONTRIBUTING TO FRUIT TEXTURE

Abstract

Transgenic tomato isolines wild-type, antisense-PG, antisense-PME, rin and rin[(E8/PG)/(E8/PG)] have been created having reduced or enhanced levels of single pectin degrading enzymes, with the purpose of altering fruit texture. However, because of limitations in current methods of fruit textural analysis, it has been difficult to identify and characterize the often subtle effects of altered pectin chemistry on fruit texture. Stress relaxation measurements provided additional insights beyond that which could be achieved by conventional textural analysis. The methodology permits the acquisition of time-dependent as well as non-time-dependent parameters. We found, using stress-relaxation analysis, that important texture differences between transgenic genotypes could be identified. Antisense-PG fruit were significantly more resistant to initial load stress than wild-type isolines, but relaxation of tissue following stress application in antisense-PG fruit was not significantly altered. In contrast, antisense-PME fruit showed no alteration in resistance to initial load stress, but the time required for relaxation of tissue following stress was significantly lower in antisense-PME fruit than in wild-type isolines. In rin[(E8/PG)/(E8/PG)] fruit, resistance to initial load was lower and time of relaxation was longer than in wild-type fruit. In transformed rin fruit, the pericarp was softer but nevertheless the analysis suggested the development ofa higher tissue viscosity.