European journal of horticultural science vol:69 issue:6 pages:250-257
Texture is an important quality parameter in fresh horticultural products. However, its complexity and variability entails that instrumental analyses describe it only partial whereas various properties are involved. For example, product water status, cell wall physical properties and tissue structure interdependently determine compressive and tensile strength, and elastic properties, which all together characterise texture. Furthermore, short-term effects on texture under unfavourable conditions during shelf five may be functionally different from those occurring during long-term storage. During recent years, new methods such as the acoustic impulse-response technique have become available to non-destructively analyse the elastic texture components. In addition, water potential, osmotic potential and turgor can be non-destructively assessed with the pressure bomb in combination with pressure volume analyses in many products. An experiment was designed to comprehensively study the effects of water status on different tissue elastic parameters. Water potential (Psi), fresh mass, apparent elastic modulus (E, quasi-static compression test), and stiffness factor (S, acoustic impulse-response test) were repeatedly determined on radish tubers during desiccation by free transpiration. E showed a two-phased linear relationship with Psi. At water potentials beyond the turgor-loss-region, the slope of this relationship largely declined. In turgescent tubers a considerable part of the variation of E could be explained by water potential. S showed a less clear two-phased relation and wilting seems to exhibit only minor effects on stiffness. Both E and S increased linearly with pressure potential but S showed a weaker correlation with turgor. While the decline in acoustic stiffness with increasing relative water deficit seemed to follow an exponential model, the correlation between E and RWD could be best described by a power function. E and S increased with increasing volumetric modulus of elasticity (epsilon) in a curvilinear manner. When E and S were compared directly, a curvilinear correlation was found. These results show that S is a good indicator for changes in produce water content. Both parameters are useful to indicate postharvest texture changes. However, the results point toward the possibility, that S is less related to short-term changes of product rigidity than E.