LOW-LEVEL BRUISING OF STORED APPLES DUE TO QUASI-STATIC LOADING UP TOCONSTANT COMPRESSION STRAIN

Gold Delicious and Spartan apples were compressed between two plates a nd the bruise-spot volume was subsequently inspected. Fruits were load ed and unloaded at a strain of about 8%. Tests were performed from har vest to the end of storage under: normal conditions (cold storage at 2 C for Spartan and 0C for Golden Delicious) and modified conditions (th e same temperatures but the Biofresh solution was applied to the fruit s before being cooled in storage). The contact Hertz theory can be use d to describe the compression curve up to the bioyield point. The para meter BMR (bioyield stress to apparent modulus of elasticity ratio) wa s 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 frui ts tested at all storage times. But over Ib and II the bruise volume w as a relatively stable exponential fraction of the absorbed energy onl y. The lowest value of the energy absorbed by a fruit without any brui sing decreased in Ia and was relatively stable in other parts. The eff ect of the Biofresh solution on the mechanical parameters was very lim ited, affecting only the hysteresis losses in Golden Delicious apples.