88 Produce Degradation: Reaction Pathways and their Prevention
harvesting methods had no effects on these parameters.^74 Flexible curved fingers of
predetermined curvature and stiffness used for harvesting Valencia oranges removed
about 90% of mature oranges; 64.1 to 77.6% showed no mechanical damage, 2.0
to 3.9% had severe mechanical damage (damage evaluation 3 weeks after harvest),
and 0.3 to 2.7% showed decay 7 weeks after harvest (storage at 4.4°C).^75 Cushion
materials installed on mechanical harvesters in the 1960s through the 1970s to
prevent splitting and bruising of fruit have been replaced by smooth, hard surfaces.
In a study to determine the effect of cushion and hard surfaces on mechanical
damage, drop tests were used to evaluate cherries’ firmness sensitivity and identified
cushion materials that can reduce firmness loss during mechanical harvesting. Firm-
ness loss averaged 28% for a 0.9-m (3-foot) drop onto a hard surface compared to
6 to 10% for four cushion materials.^76 Cherries dropped 4 m (13 feet) onto a tightly
stretched tarp without cushion material resulted in a loss of firmness of 35%, but
only 14 to 28% showed loss of firmness with cushion material. To minimize mechan-
ical damage and maintain firmness, hard harvester surfaces that cherries impact
should be covered with adequate cushioning.
Mechanical stress received during harvest of cucumbers (Cucumis sativus L.)
was demonstrated to affect physiological degeneration of the placental tissues and
their suitability for use in some pickled products. In experiments to compare rolling
and dropping of cucumbers, rolling had a greater effect on refreshed delayed light
emission (RDLE) from chlorophyll than did dropping. After 48 hours, RDLE sup-
pression persisted and starch granules were no longer evident in chloroplasts from
mechanically stressed fruit, but very electron-dense inclusions had developed in the
chloroplasts.^76 The quality of concord grapes is affected by mechanical harvesting
and handling. Grapes with brush (vascular bundle) intact had less damage for a given
number of drops than did grapes with brush removed. Weight loss occurred in
Concord grapes and increased with severity of mechanical damage, increased storage
temperature, and time. Bulk density increased with severity of mechanical damage
and appears to have the best potential as a means of rapidly determining the degree
of damage.^77 Translucence or water soaking of the flesh is a problem in pineapples
(Ananas comosus L.) marketed fresh. Affected fruit is more prone to postharvest
mechanical damage and the flavor is poor. Fruit translucency and preharvest condi-
tions that predispose fruit to translucency were studied by Paull^78 who developed a
model to show the best relationship between preharvest weather and translucency.
A period of 2 to 3 months before harvest was found to be crucial in the development
of fruit translucency at harvest and crown growth. Translucency was more severe
and had a higher incidence when maximum and minimum temperatures 3 months
before harvest were low (15 to 23°C), relative to that at high temperatures (20 to
29°C). Fruit with larger crowns had a lower incidence and severity of translucency.
Effect of harvesting and subsequent handling on mechanical damage of pairs
was tested using cylindrical tissue samples of two pear cultivars (D’Anjou and Bosc)
in two sizes.^79 Using dynamic axial compression at four strain rates, it was deter-
mined that strain rate significantly affected the failure stress, failure strain, and the
secant elastic modulus, while it had no effect on the shock wave speed or tissue
toughness. Larger pears had higher failure stresses and lower failure strains, and