Viscoelastic and Histological Properties of Grape Skins

Comparisons were made between the viscoelastic properties and the histology of the skins of two varieties of Muscadine grapes ( Vitis rotundifolia ) and of Thompson Seedless grapes ( Vitis vinifera ). Uniaxial tensile tests and puncture tests were performed using the Universal Testing Machine (Instron Model 1130) at three different, constant deformation rates. The grapes were prepared for sectioning by embedding in the low viscosity epoxy resin, Spurr. 1–2μ thick sections were taken and the average area of the cells of the skins calculated. The failure stress in puncture tests correlated well with average cell area (r = 0.99). The thickness of the skin was positively correlated with relaxation time determined from uniaxial tensile tests (r = 0.97).