Low-level bruising of stored apples due to quasi-static loading up to constant compression strain

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 0C 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 fraction 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.