Methods to evidence mechanical injuries on 'Packham's Triumph' pears

Mechanical injuries are responsible for most of the postharvest fresh produce losses. Changes in plant tissues resulting from mechanical damages might remain unnoticed for some time. Some slight lesions are not detectable by hasty visual inspections but can contribute to speed up postharvest deterioration. Therefore, the objective of the present study was to evaluate the efficacy of different methods to evidence mechanical injuries on 'Packham's Triumph' pears. Pears of different sizes were packed into plastic boxes and placed in an orbital shaker to inflict mechanical damages by friction at up to 210 revolutions min^-1 (rpm) for 20 min. Mechanical injuries were determined after a) bagging the pears in low density polyethylene for 24 h, b) immersion in a 0.1% (w/v) 2,3,5-triphenyl tetrazolium chloride solution for 20 h or c) exposure for 2 h to 3 mL L^-1 (v/v) sulfur dioxide (SO₂). After these periods the pears were visually evaluated and ranked for occurrence of mechanical damages based on a scale ranging from zero (no injury) to five (severe damages). The highest rotations resulted in the most severe lesions. Presence of cuts was considered the most severe level of damage. 2,3,5-triphenyl tetrazolium evidenced lesions inflicted on the pears at 70 rpm and even on the control fruit. At 140 and 210 rpm all detection methods did signal the inflicted lesions. 2,3,5-triphenyl tetrazolium solutions are capable to stain more indelible damages which may occur at harvest and postharvest procedures of 'Packham's Triumph' pears.