100 Produce Degradation: Reaction Pathways and their Prevention
Golden Delicious and Granny Smith apples exhibited formation of wall thickenings
extending four to six cell layers from the wound. Cell walls near healed wounds
stained positive for phenolic substances, tannins, lignins, and callose after 38 days
at 5°C or 14 days at 20°C. These compounds have been associated with wound
healing in many plants and have been implicated in resistance to infection and
colonization in many host/pathogen systems.^210 Spotts et al.^211 reported that wounded
pear tissue rapidly accumulated callose and tannins as well as gums, but tests for
lignin were negative. It was suggested that this could possibly result from the test’s
not allowing sufficient time for lignin to accumulate in the wound tissue or that
lignin was lost during fixation of the tissue in formalin-acetic acid-ethanol. Ligni-
fication of cells in the injured area increases resistance to infection of injured peel
in oranges and lemons.^212 Oleocellosis is a physiological rind disorder of citrus fruit
commonly caused by mechanical damage and the consequent rupture of the epider-
mis above oil glands. It is an unattractive surface blemish caused by phytotoxic
effects of released rind oils. The blemish is characterized by rind collapse and
darkening and is attributed to cellular damage. Released surface oil appears to
infiltrate the rind via the ruptured epidermis, resulting in rapid degeneration of
cortical, but not epidermal, cell contents.^213 Wounding also increases lignin formation
in the cell walls of peaches.^179
Bland et al.^100 compared the healing of potato cv. Russet Burbank tuber cores
with that of cuts and bruises on whole tubers. Water loss from cut surfaces on whole
tubers decreased more rapidly than that from cores of tissue. Bruises made on whole
tubers also healed more slowly than cut surfaces on tubers.
4.11 TEMPERATURE EFFECT
Good management of temperature can reduce the physiological response of the tissue
to bruising and control the appearance of bruising symptoms. Temperature greatly
affects tissue response to mechanical damage. Baritelle and Hyde^214 have shown that
an increase in handling temperature of both potatoes and pears increased the failure
strain of the tissue, while in apples no effect was observed. Moreover, temperature
can influence tissue resistance to bruising by affecting cell turgor. An increase in
relative turgor reduces strain failure of tissue.^214 Contradictory results have, however,
been obtained in relation to fruit temperature and mechanical damage. For example,
the resistance of sweet cherries to compression damage decreased linearly with
increasing temperature, but the incidence of impact-induced surface pitting increased
linearly as fruit temperature decreased.^215 Impact bruising damage was greatest in
several varieties of sweet cherries at low temperatures, while vibration damage was
not influenced by fruit temperature.^216 In blueberries, the loss of major quality
attributes increased with increasing damage levels and increasing storage tempera-
ture.^217 The mechanical strength of frozen potato tissue decreases with an increase
in the number of temperature fluctuations and in most cases is lower in packed
samples. Moisture loss was greatest in the –18 to –6°C range for prepacked samples.
Changes in the maximum compression force, a measure of mechanical damage,
occur with storage temperature.^218