Agriculture Reference
In-Depth Information
Quality issues
Physiological disorders resulting from chilling or the use
of modified atmospheres are among the most common
post-harvest quality problems. Chilled fruits may show
abnormal ripening, skin browning or other discolouration,
and prompt decay when the fruits return to ambient tem-
peratures. Also important are desiccation and mechanical
damage (Paull & Chen 2002a). Modified atmospheres may
cause skin blackening and off-flavours (Ali & Lazan 1997).
Pre-harvest use of herbicides or pesticides may lead to
phytotoxic effects, with red or brown blotches on the skin.
Sun scorch leads to premature ripening and infection which
can be combated by wrapping fruits in brown paper bags.
Post-harvest diseases mainly arise from pre-harvest
infection, and so treatment and care in the field can
markedly reduce the incidence of post-harvest problems.
Anthracnose is the most important disease of guava, caused
by
Glomerella cingulata
(Stonem.) Spauld. & v. Schrenk
(Snowdon 1990). Symptoms include brown or black spots,
leading to sunken patches becoming more apparent as the
fruit matures. Other important pathogens are
Botryodiplodia
theobromae
Pat. that causes a soft, watery rot and
Pestalotiopsis psidii
(Pat.) Mordue, the cause of canker or
stylar end spot. Species of
Mucor, Aspergillus, Rhizopus
and
Phomopsis
may occur, particularly on injured fruits
(Paull & Chen 2002a). Post-harvest control is by fungicide
dipping, refrigeration or irradiation at 0.15 to 0.45 kGy.
The use of antagonistic fungi and bacteria has also been
suggested (Pandey
et al
. 1993).
Post-harvest pests also usually arise from pre-harvest
infestations, with eggs laid on mature fruit that hatch during
storage. Fruit flies are the major concern here, from the
genera
Dacus
,
Anastrepha
and
Bactrocera
, particularly for
concerns related to quarantine. As well as feeding damage
by larvae, puncture wounds allow entry of pathogenic fungi
and bacteria. Control is by bagging fruits, spraying, phero-
mone or bait trapping or deployment of parasitoids and other
bio-agents. Mealy bugs can also be a problem, leading to
misshapen fruits and secondary infections. Promising post-
harvest control of pests has been achieved by coatings and
modified atmospheres. Use of hot-water dips is generally
considered not applicable because the thin skin of guavas
provides little protection from heat damage (Yusof &
Hashim 1992) but hot water has been used as a quarantine
treatment against fruit flies (Gould & Sharp 1992).
purple passion fruit or purple grenadilla,
P. edulis
Sims
forma
edulis
, and the yellow passion fruit,
P. edulis
Sims
forma
flavicarpa
Deg (Chan 1980). The purple form is
grown extensively in Brazil, East Africa, Sri Lanka,
Australia and India, whereas the yellow type is mainly
exploited in the Caribbean, Hawaii and the South Pacific.
Mature purple passion fruits are round or egg-shaped,
4-9 cm long and 3.5 to 7 cm in diameter, and they weigh
25-50 g. The skin is moderately thick and hard, containing
a yellow to orange pulp. Yellow types have slightly larger
fruits, are 50-150 g and have a hard skin, again with yellow
to orange flesh but more aromatic and juicy (Chan 1980;
Paull & Chen 2002b).
Passion fruit may be consumed fresh but most are
processed into juice or purée in jams, jellies and marmalade
(Morton 1987).
Harvesting
Passion fruit takes about 72 days to mature after flowering.
The fruits should be completely mature at harvest with
fully developed skin colour. Fruits with a green rind exhibit
off-flavours despite being internally mature (Bora &
Narain 1997). Size, shape, acidity, skin colour and soluble
solids are the main criteria used to evaluate quality. In
yellow passion fruit the SSC ranges from 10 to 18%, with
a range of 10-20% in purple types. Yellow passion fruit
have higher acidity (Paull & Chen 2002b).
Fruit is harvested when more than 75% of the skin has
turned yellow or purple (Chan 1980). Purple fruit should
be 5 to 8 cm in diameter, yellow should be 6 to 8 cm, with a
fully developed skin colour (Paull & Chen 2002b). Mature
fruits for processing are usually collected, allowed to
abscise and picked up from the ground every two to seven
days. Fruits for sale as fresh product are picked directly
from the vines to preserve good appearance and keeping
quality (Bora & Narain 1997).
Passion fruit are transported in boxes and placed in room
or forced-air cold storage if they are to be immediately
processed. Recommended storage conditions for yellow
passion fruit are 7-10°C at 90-95% relative humidity,
which gives a storage period of two weeks (Arjona
et al
.
1992). Storage below 6.5°C causes chill injury, with
discolouration, off-flavours, pitting, water-soaking and
ripening uneven or absent (Bora & Narain 1997; Paull &
Chen 2002b). Purple fruit is chill tolerant and can be stored
at 3-5°C for three to five weeks (Paull & Chen 2002b).
Loss of water is the main storage problem, leading to
weight loss, shrivelling and wilting, though pulp quality is
not significantly affected (Paull & Chen 2002b). Thus ripe
fruits kept at ambient temperature and humidity (27 + 2°C
PASSION FRUIT
Passiflora
is a perennial woody vine native to the Americas.
About 50 or 60 of the 450 species bear edible fruits
(Mabberley 1997). The main commercial species are the
