Agriculture Reference
In-Depth Information
for up to 2 weeks. Decay can be avoided by ensuring that
cladodes are not damaged when cut from the plant.
Fungicide dips reduce post-harvest decay of cladodes, but
are not used commercially.
In the case of the fruit, harvest damage to the peel and
stem end of cactus fruit will lead to attack by numerous
pathogens and result in fruit decay. Common post-harvest
pathogens on cactus fruit are mostly fungi and include
Fusarium
spp.,
Alternaria
spp. and
Penicillium
spp., but
yeasts and bacteria also cause decay. Hot water dips at 53°C
to 55°C for 5 minutes and fungicide-containing waxes may
reduce surface decay, but are not effective when there is
damage to the stem ends. Pre-harvest calcium sprays result
in less post-harvest decay (Schirra
et al
. 1999).
percentage of pulp, low seed content of seeds, a peel that is
easy to remove, high sugar content (12-17%), low acidity
(0.03-0.12%) and freedom from defects.
Good-quality cladodes (nopalitos) are thin, fresh-looking
and turgid and have a brilliant green colour. In the early
stages of growth, vestigial true leaves, usually subtended
by spines, are present on the stems, but the leaves often
abscise by the time cladodes reach commercial size.
However, an indication of freshness is when true leaves
remain on the stem and are green. The popularity of
O. atropes
has increased recently in Mexico because of its
texture and pleasant smell (Vigueras & Portillo, 2001).
O. leucotricha
(duraznillo) and
O. robusta
yield high-quality
cladodes because the pericarp can easily removed, do not
fall apart during boiling and do not release mucilage.
INSECT PESTS
Among the natural enemies of prickly pear cladodes are
Cactoblastis coctorum
and
Dactilopius opuntia
, and both
are used in Australia and South Africa to control the expan-
sion of the plant.
Cactophagus spinolae Gyll
,
Chelinidea
tabulata Burm
,
Hesperolabops gelastops Kyrkaley
,
Olyacella nephelepsa Dyar
,
Lanífera cyclades Druce
,
Dactylopies indicus Green
,
Seriocatrips opuntia Hood
and
Moneilema variolaris
feed on cladodes internal tissue,
decrease the production and in some cases cause the death
of the plant.
Diabrotica sp
. and
Phyllophaga spp
. attack
the roots of cactus and generate severe injuries (Granados &
Castañeda 1996).
Maturity and harvesting indices
Stage of maturity or ripeness at harvest is very important
for fruit quality. As discussed above, being a CAM plant
the acid content of cladodes may fluctuate greatly during
the day and affect their flavour (Rodríguez-Felix &
Cantwell 1988). Therefore, because of diurnal acidity
changes it is recommended that stems be harvested 2 to 3 h
after sunrise to be best used as a vegetable (Mizrahi
et al
.
1997). Small cladodes, however, are not CAM-active.
Cladodes are harvested based on size and can be small
(< 10 cm long) or medium (< 20 cm long). In Mexico, clad-
odes are harvested when they are 15 to 20 cm long (weight
90-100 g), by cutting at the articulation with the 'mother
cladode'. Over-mature cladodes are thick with spongy
white tissue, are acidic in flavour, and are not commonly
consumed. Cladodes should be harvested when young and
tender and not early in the morning to avoid a high acid
content (Table 13.2). Acid content will not only depend on
time of harvest, but also on the species and post-harvest
conditions. Low temperature storage at 5°C maintains acid
levels, while warmer storage conditions of 15°C to 20°C
result in decreased acid content (Cantwell
et al
. 1992).
Cladodes harvested before reaching a length of 10 cm are
usually CAM inactive and virtually lack spines.
Prickly pear fruit takes about 4 months from fruit set to
reach harvest maturity (Alvarado 1978). Fruit maturity
indices include fruit size and fullness, changes in peel col-
our, abscission of the small spines or glochids, fruit firm-
ness and flattening of the floral cavity or receptacle. Peel
colour is the single most important index for commercial
harvest. Soluble solids content have been reported to cor-
relate well with colour for some types of prickly pear fruit,
but not by others (Lakshminarayana
et al
. 1979). Different
“white” prickly pear fruit maturity can be described as
PHYSICAL DAMAGE
Physical damage is an important problem that limits the
post-harvest life of prickly pear fruit. Fruit can be bruised
easily during harvest, but damage to the stem end is by far
the most serious because it leads to attack by pathogens
and fruit decay. Damage at the stem end of the fruit can be
eliminated by careful harvesting, twisting fruit from the
stem or cutting fruit with a small piece of stem attached.
Fruit harvested with a small piece of the stem attached may
be packed that way or cured at moderate temperatures of
15°C to 20°C with airflow so the stem dries and falls off
before fruit are packed. However, in some
Opuntia
species
large subtending spines makes this technique difficult.
High-gloss fruit waxes are often used to improve visual
appearance and reduce dehydration, especially when fruit
are dry-brushed to remove small tufts of spines or glochids.
QUALITY CHARACTERISTICS AND CRITERIA
Prickly pear fruit consist of a thick fleshy skin surrounding
a juicy pulp, of different colours and flavours depending on
species. High-quality fruit are characterized by a high
