Mechanical Injury of Fresh Produce 89
cultivar significantly affected all of the tissue failure properties except shock wave
speed.
4.6 STORAGE
Mechanically stressed fruit exhibits visible degeneration of mesocarp and endocarp
during storage. Storage polyamines in fruit have been reported to be involved in alle-
viating a number of stress conditions associated with fruit storage. Putrescine, for
example, tends to accumulate in plant organs exposed to chilling stress.^79 Polyamine
accumulation also occurs in response to external mechanical bruising of mandarin
cultivars.^80 The role of polyamines in extending shelf life and the reduction of mechan-
ical damage in plums (Prunus salicina Lindl.) was demonstrated by Pérez-Vicente et
al.^81 Activation of the polyamine biosynthesis pathway during storage indicated accu-
mulation of cell wall putrescine and spermidine, which are possibly responsible for the
greater firmness of putrescine-treated plums. It was suggested that the increase in free
spermidine levels could act as a physiological marker of mechanical damage.
Apricots (Prunus armeniaca cv. Mauricio) infiltrated with exogenous putrescine
(at 1 mM) before storage (5 days at 10°C) and then mechanically damaged showed
higher firmness and a delayed color change than the controls.82,83 The treatment was
effective in reducing the damaged area and volume after compression. Endogenous
spermidine was at similar levels in treated fruits, both damaged and undamaged.
The most significant effect was observed in damaged apricots, in which an increase
in spermidine levels was observed in response to mechanical damage, whereas
undamaged apricots had the lowest concentrations of this polyamine during storage.
Lemon fruit under postharvest putrescine and calcium treatments also maintained
higher firmness values and more resistance to peel rupture than control fruit during
storage.^84 Treated lemons showed less deformation when the compression force (50 N)
to induce mechanical damage was applied. Treated and damaged fruits showed a
decline in polyamine content while ABA and color changed in parallel with matu-
ration during storage, unlike in control fruits in which increases in spermine and
ABA levels occurred as a consequence of mechanical damage.
Mechanical damage considerably increases alpha-solanine glycoalkaloids in
potato tubers. Storage of mechanically damaged tubers further increased glycoalka-
loids in the first 5 months of storage but decreased to initial values in the subsequent
3 months.^85 Steroid glycoalkaloid content decreased during cold storage and
increased significantly under shop conditions in damaged tubers. Peeling and
removal of bruises reduced the content to an acceptable level of < 40 mg/kg.^86 In a
study by Rataj and Dzupin^87 to determine the relationship between the effect of
storage of potatoes on the density of tubers, the shape coefficient, and the air force
necessary for penetrating part of a tuber at quasistasis, it was concluded that the
density and axial compression tests showed no significant changes throughout the
duration of storage. Moderate changes observed in the dimensions and in the shape
coefficient were slight increases.
Storage properties of fruit may vary depending on cultivar and packaging mate-
rial used. At the time of harvest, Tsu Li and Ya Li pears resisted mechanical damage