Mechanical and Temperature Effects on Shelf Life Stability of Fruits and Vegetables - Food Shelf Life Stability: Chemical, Biochemical, and Microbiological Changes - page 51

senescence and decay. Pathogens enter at the site where the fruit or vegetable is
severed. An example is stem-end rot caused by Diploidia matalensis occurring in
citrus fruits, papayas, and mangos, and by Botrytis cinerea or Penicilium expansum
among fleshy-stemmed varieties of apples and pears. 50 Additional openings like cuts,
cracks, and abrasions also act as points of entry of the pathogens. The presence of
moisture on the wound surface is ideal for fungal spore germination given the right
atmosphere. Even for pathogens that can penetrate the skin of the produce, the
presence of wounds or cuts accelerates their penetration and infection. In stone fruits,
the conidia of Monolinia fructicola gain access through fresh wounds, providing the
needed moisture and nutrients for their growth. 51
Mechanical harvesting, which is more injurious than manual harvesting, causes
more bruises and excessive pressure that stimulates latent infections without neces-
sarily rupturing the rind. According to Rippon, 52 blue mold in apples and soft rot in
potatoes, which are both initiated within the lenticels, result from crushing of cells
around the lenticels due to excessive pressure. Cuts, skinnings, wounds, and cracks
are avenues of water loss in potato tubers causing shrinkage and weight loss. Storage
of potato tubers that are mechanically damaged is not advisable. Sorting of severely
damaged tubers has to be carried out before storage, and curing will take care of
healing the rest of the tubers with minor injuries like cuts and abrasion.
Sommer 51 outlined the following events after the inflection of mechanical injury:
Cells ruptured by the cut are killed and cellular contents are mixed and exposed in
the wound area. Enzymes, such as polyphenol oxidases, which are compartmentalized
when the cell is alive, are mixed with the polyphenols in the cell sap. Browning in
the wound results from enzymatic oxidation of phenolic compounds. Living cells near
the injury are stimulated to become very active metabolically even though they do
not themselves show signs of major injury. Repair is set in motion by these stressed
but unbroken cells. Polyphenol synthesis may lead to the accumulation of greater
quantities of those already present. New compounds, often similar to those that appear
following infection, may appear in the wound area.
Klein 53 reported in the case of apples that both aerobic and anaerobic respiration
rates do not increase after impact and compression loading. Even then, it was
observed that carbon dioxide production increased. It was explained that this phe-
nomenon results from enzymatic reactions following the destruction of apple tissue
and the release of the contents of the ruptured cells. Monitoring CO 2 production,
when compared with controls, is one way of detecting the level of mechanical injury
in the commodity.
The development of “spongy tissue” in mangos, characterized by soft pulp, pale
color, with acidic and off-flavors, is a direct effect of mechanical damage according
to Salunkhe and Desai. 54 “Wound pathogens” can gain entry through injuries inflicted
during harvesting and handling. Stem-end rot in mangos results from an injury
created by severing the fruit from the tree. Friction discoloration is common among
pears. Enzymatic browning, which is catalyzed by polyphenol oxidase, 55 appears
when injury exposes the cellular contents to oxygen. 39 According to Meheriuk and
McPhee, 56 immature fruits or fruits of advanced maturity are more susceptible to