Determining the resistance to mechanical damage of apples under impact loads

The most destructive impacts on biological materials are impact loads, which cause tissue damage under surface peel. For apples, tissue damage increases due to the contact stresses resulting from the round shape of the fruit. Measurements of surface and volume of bruised apples expressed as a function of drop height have been measured, and a method has been developed to determine the resistance and the threshold to bruising for 'Idared', 'Golden Delicious' and 'Jonagold' apples. This method determines the resistance to bruises based on average surface pressures used as a load parameter in relation to the volume of damaged tissue. The relationship between the bruise surface and the volume was determined and confirmed as a power curve with a R2 determination factor of 0.97. A Bruise Resistance Index (BRI), defined as ratio of the average pressures to the bruised surface, was calculated as the ratio of surface pressure to measured bruise volume depending on the drop height. Comparison of both indicators showed that proposed BRIb power models precisely represent real BRI power curves. The bruise threshold as well as the bruise resistance for apples is an effective and rapid tool for assessment of damage degree.