84 Produce Degradation: Reaction Pathways and their Prevention
Damage inflicted on the fruit 100 to 150 days postharvest led to greater spoilage
rate and flesh-browning than damage occurring at harvest time.^38 The pH of bruised
apple tissue was significantly higher and °Brix significantly lower than the pH and
°Brix of undamaged tissue regardless of the source.^39
Apricots as well other stone fruit such as peaches and nectarines are dense, with
a low volume of intercellular air space, and are susceptible to deep bruising. In
peaches the bruise symptoms inside the flesh are cone-shaped with radial frac-
tures.5,40,41 Fruit impact, under the low to moderate impact energies used, often has
negligible effects on fruit respiration and ethylene production in peaches. Bruise
incidence increases with volume and drop height, especially with advancing stage
of ripeness. Maness et al.^5 suggested that the severity of peach fruit bruise could be
determined by either bruise incidence or bruise volume of mesocarp tissue. An
assessment of the effects of mechanical handling on peaches using cultivars of Big
Top, Caldesi 2000, Centry, and Rich Lady peaches subjected to impacts represen-
tative of the conditions observed at the critical points in packing lines by means of
a simple drop-test device revealed that at the highest impact level (180 g, 2.20 m/sec)
damaged fruit did not exceed 18% and the average dimension of the flesh did not
exceed 10 mm in diameter (Big Top) and 6 mm (Centry) in depth. In general, repeated
drops did not seem to cause substantial additional damage.^42 Degree of ripeness has
a significant effect on quality and shelf life of strawberries. Picking berries when
they are partially ripe can reduce mechanical damage during postharvest transport
and extend shelf life compared with picking fully ripened berries. However, this
needs to be balanced with the reduced sensory and nutritional quality obtained with
partially ripened berries.^43
Tissue damage appears to increase with increased freezing stress. The severity
of damage to each of the tissues varied seasonally. Chlorophyll fluorescence emis-
sions were lower with higher freezing stress (except during November and Decem-
ber, when test temperatures were not low enough to significantly damage the seed-
lings) and showed a strong relationship with morphological assessments of freezing
stress. The bulky nature and high moisture content of yam tubers make them vul-
nerable to mechanical damage during production, handling, and storage operations.
Mechanical damage susceptibility is also influenced by the modulus of deformability,
bio-yield strength, rupture strength, and density of yam tubers.^44 Harvested cassava
roots undergo a rapid postharvest deterioration that is associated with mechanical
damage and incipient wound healing. Physiological and biochemical changes that
take place following harvesting mainly include activation of preexisting enzymes,
degradation of membrane lipids, gene expression, and signal transmission from the
sites of wounding.^45 Wound responses in cassava do not remain localized at wound
surfaces in roots when they are held at low storage relative humidity but spread
through the roots, causing discoloration of the vascular tissue and storage paren-
chyma.^46 Roots stored at high relative humidity show a more typical wound response
with localized production of phenols and periderm formation. Mechanical damage
during harvesting and transport produces injuries leading to internal discoloration
and rotting decay associated with microbial infections, especially at a high temper-
ature and relative humidity of storage. Deterioration can be delayed by root “curing”
(wound healing) by storage at 25 to 35°C and 80 to 50% relative humidity. Chemical