Planar potato crisps were prepared from potato tubers of four varieties (Agria, Javor, Nicola and Panda). The effect of slice blanching in water and solutions of Na‐, Ca‐, and Mg‐chlorides prior to frying, as well as the effect of storage time of the tubers prior to test were also studied. The deformation curves from a three point bending test were evaluated and Young's modulus (EM), maximum relative deflection (MRD), maximum tensile stress (MTS) and surface energy (SE) were determined. The MRD and MTS correspond to rupture point values of deflection and stress, respectively. The obtained results show that almost all test parameters (MTS is an exception) depend mainly on the blanching solution and the ratio of monovalent (K and Na) to divalent ions (Ca and Mg) in the crisps. Variety dependence was observed mainly in MRD and EM. An increase in the ratio monovalent over divalent cation concentrations led to lower MRD‐ and SE‐values and at the same conditions to higher Young's moduli. EM‐values of 320–340 MPa were obtained for the two varieties with higher content of starch (Javor and Panda) while for the two varieties with lower starch content (Agria and Nicola) values of 230–250 MPa were observed. The MRD was of 0.057–0.061 for Javor and Panda and 0.075–0.080 for Agria and Nicola. The starch content could not explain the observed variety differences for maximum tensile stress and surface energy.

Cherries of three varieties were compressed between two plates in the loudingunloading test to determine the energy dissipated during the test. After compression, the bruise volume of the deformed fruit was determined. Bruise resistance coeficient (BRC) and bruise sensitivity (BS) were evaluated in a similar way as for apples. It is shown that, contrary to the results for apples, the BRC and BS values depend on the compression ratio in a more complicated way for cherries than for apples. The principal differences in bruise sensitivity were observed for diTerent cherry varieties. n e s e differences cannot be explained by the macroscopic mechanical properties of the fruits only.

Gold Delicious and Spartan apples were compressed between two plates and the bruise‐spot volume was subsequently inspected. Fruits were loaded and unloaded at a strain of about 8%. Tests were performed from harvest to the end of storage under: normal conditions (cold storage at 2C for Spartan and OC for Golden Delicious) and modified conditions (the same temperatures but the Biofresh solution was applied to the fruits before being cooled in storage). The contact Hertz theory can be used to describe the compression curve up to the bioyield point. The parameter BMR (bioyield stress to apparent modulus of elasticity ratio) was used for classification of the whole storage period; it was divided into three parts: softening Ia, weakening Ib, ripened II. There was a linear relation between bruise volume and the absorbed energy for fruits tested at all storage times. But over Ib and II the bruise volume was a relatively stable exponential function of the absorbed energy only. The lowest value of the energy absorbed by a fruit without any bruising decreased in Ia and was relatively stable in other parts. The effect of the Biofresh solution on the mechanical parameters was very limited, affecting only the hysteresis losses in Golden Delicious apples.