Viscoelastic behavior of melon tissue as influenced by blanching and osmotic dehydration

Viscoelastic properties of melon tissue exposed to steam blanching and osmotic dehydration (atmospheric or under vacuum) in glucose aqueous solutions were analyzed in a dynamic rheometer using oscillatory shear and creep tests. The storage modulus (G') greatly exceeded the viscous modulus (G") for raw and treated melon tissues, but the elastic component was partially lost because of processing. Blanching caused less than a 1-fold decrease in G', whereas osmotic dehydration resulted in approximately a 3-fold decrease in G' relative to the untreated melon. Both moduli showed a weak dependence on frequency, with greater slope of the G' frequency lines for treated samples. A mechanical model, consisting of a spring in series with 2 Voigt elements and a dashpot element, properly predicted the creep compliance response for all melon samples. In general, overall compliance significantly increased by the treatments. The instantaneous elastic compliance and the viscoelastic compliances were the most sensitive viscoelastic parameters for distinguishing the differences in cell wall structure among osmotically dehydrated sample at atmospheric pressure and the tissues exposed to the other osmotic treatments. In contrast, G' modulus did not show an ability to evidence these structural differences because there were no significant differences in the G' values of osmotically dehydrated tissues at atmospheric pressure or in vacuum, with or without calcium addition.