Mechanical Injury of Fresh Produce 91
Mechanically damaged vegetables should be separated in the field, particularly
from batches intended for longer storage. Studies on damaged vegetables revealed
that losses due to molds were 5 to 11 times higher in carrots, 1.5 to 1.8 times higher
in white cabbage, and 2 to 4 times higher in onions than in corresponding undamaged
vegetables.^96 Carrot slices obtained from freshly harvested roots are also more
sensitive to mechanical damage and short-term storage than those prepared from
roots previously stored. Carrot root slices stored for 4 days at 20°C reacted with a
strong accumulation of total phenols, especially chlorogenic acid. Synthesis of
phenols was accompanied by an increase in phenylalanine ammonia lyase activity,
wound-induced respiration, and ethylene production.^97
4.7 DETECTION
The variability in factors that affect tissue damage within a population of produce
has led to efforts to determine damage susceptibility. A number of sampling tech-
niques have been described to quantify the scope of the problem for specific indus-
tries.98,99 Bollen et al.^62 used a logistic function to describe the relationship between
impact energy and the likelihood of a certain bruise size occurring. The approach
takes into account the natural variability of bruising within any given population.
The slope of the logit was shown to be a characteristic of variety, with the logit
offset describing season and maturity variation for apples. The method also provided
a good prediction technique for the susceptibility of varieties of nectarines and
potatoes.^100
Using measurements of visible infrared light passing through the longitudinal
midsection of whole cucumber fruit, Miller et al.^101 quantified on a unitless sigmoid
scale from 1 to 10 the effect of mechanical injury on fruit quality. Unbruised
cucumbers exhibited transmission values between 2 and 3, regardless of cultivar.
Mechanical-stress treatment that simulated bruising incurred during harvesting and
handling of cucumbers caused a decline in the internal quality of the fruit and was
associated with an increase to a value of 6 in light transmission compared to that
of unstressed fruit. Light transmission increased as the severity of stress applied to
the fruit increased. Fruits exhibiting high transmission values were judged by human
sensory evaluations to be of lower quality than those exhibiting low transmission
values.
Bruises may take place beneath the peel and may be difficult to detect by visual
or automatic color sorting, especially for fruits such as dark-colored apples. X-ray
imaging,102,103 magnetic resonance imaging (MRI)^104 , and near-infrared (NIR)
reflectance105,106 are among the successful techniques used for defect grading. Near-
infrared imaging was used by Upchurch et al.^107 to characterize the influence of
time, bruise type, and severity on the NIR reflectance from bruised and unbruised
regions on Delicious and Golden Delicious apples. Within 24 h after inducing
damage, a maximum contrast in NIR reflectance occurred for both impact and
compression types of bruises. The contrast decreased until it equaled the contrast for
an unbruised region, and changes in contrast after 1 day were more gradual for impact-
type bruises than for bruises created by compression. Surfaces of mechanically injured