Evaluation of bruise resistance of pears to impact load

• Bruise resistance can be efficiently described by surface pressure.
• Drop height of 30–46 mm is bruise threshold for pears.
• Contact plane is stabilized after 3–4 impacts.
• Multiple impact causes loss of pressure in the middle bruise.
• The increase of the bruise volume does not increase pressures significantly.

The main cause of bruises resulting in loss for fruit growers are dynamic and impact type loads to which fruit is exposed during harvesting, loading and transport. Due to the characteristic shape of the contact plane of the fruit during the impact with the hard surface of e.g., a box or another fruit, there appears a problem of pressure force concentrated in a small area, leading to local exceeding of allowable limits. The authors focused on experimental procedure aimed at quantitative assessment of damage to the ‘Clapp’s Favorite’ pear fruit depending on the changes in surface pressures that occur during impact loads. The study analyzed the influence of impact loads on the bruise resistance by measuring the surface pressures at varying drop heights and a specified number of impacts. The Tekscan® system was applied to determine force impulse values and contact plane areas, which enabled the calculation of surface pressure distribution. A computer analysis of the images of damaged tissue was carried out in order to determine the bruise volume, and a method for evaluating bruise resistance in pears was proposed based on the obtained BRI indicators (bruise resistance index—relationship between contact pressure and bruise volume). Both the analysis of the instantaneous force values, contact planes and surface pressures, as well as verifying analysis of the volume images enabled to determine bruise resistance in the case of the investigated ‘Clapp’s Favorite’ pears at level of 8%. Also the pear bruise threshold was estimated at 46 mm with force impulses of up to 100 N. The presented method allows for the determination of the bruise resistance of fruits with high water content by measuring the surface pressure, accounting for the shape of the fruit’s surface, mechanical properties of the flesh, and compression force.