Dropping bruise fragilities and bruise boundaries of ‘Gala’ apples

The major mechanical damages of fruit are usually not direct split but local bruise caused by dropping impact during harvesting, sorting, packaging, and transportation. It is necessary to develop engineering approaches to control the fruit’s local bruise volume and bruise ratio. As an extension of traditional product fragility and damage boundary, the concept of dropping bruise fragility and bruise boundary was developed and the definition of them was presented in this paper. In view of the limitations for traditional testing methods, the method and procedure for determining dropping bruise fragility and bruise boundary were also established by adopting free-fall dropping tests. The free-fall dropping impact tests with a series of drop heights were conducted on fresh ‘Gala’ apples. The dropping bruise fragilities and bruise boundaries of ‘Gala’ apples at different bruise ratios were determined by means of test results and theoretical analysis. The results showed that there were obvious differences between dropping bruise boundary and traditional damage boundary of products. Even if the velocity approached zero, the ‘Gala’ apple could be bruised as long as acceleration of it exceeds a certain value. Moreover, a series of dropping bruise fragilities and dropping bruise boundaries of the ‘Gala’ apple were established corresponding to its bruise ratios.