Agriculture Reference
In-Depth Information
few or many small seeds in the centre, and sclereid stone
cells that may give the flesh a gritty texture. Flesh colour
varies from white to salmon pink, with a sweet musky
scent. Common guava fruits are eaten fresh or processed
into jellies, cheese, ketchup, purée and juice. The cattleya
or strawberry guava (
P. cattleianum
Sabine) is smaller
than the common variety and less valuable for commercial
purposes, though it may be preferred for its sweet,
strawberry flavour by cooks (Wilson 1980). Guava can be
consumed at the mature green stage, with a sweet apple
taste and white flesh, or fully ripe when the flesh is white
to bright red and the skin is yellow (Paull & Chen 2002a).
End use of the fruits affects the choice of cultivar. Thus,
cultivars for fresh consumption produce slightly acid,
sweet and less gritty fruits, whereas those for processing
give fruits of high acidity with deep pink or salmon red
flesh (Ali & Lazan 1997). Guavas are usually consumed
whole, but slices of mature green fruits are eaten in
southeast Asia. Ripe fruit is also sliced, with seeds and skin
removed. Both types are sold from trays with an over-wrap
(Paull & Chen 2002a).
chilling and shelf lives vary with the type of cultivar. Thus,
cv. Beaumont takes about five days to ripen and has a shelf
life of 1-2 weeks, whereas cv. Kampuchea ripens after 24
days and has a shelf life of 3-4 weeks (Lazan & Ali 1997).
Guavas are sensitive to sunlight and so transport is best
done at night (Wilson 1980). In the United States, guavas
are usually shipped in 4.5 kg boxes in single layers, with
foam wrapping to limit damage (Paull & Chen 2002a).
Cooling
After harvest guavas should be cooled to about 10°C,
using room-, forced air- or hydro-cooling. Fruit maturity
influences keeping qualities. Thus mature green guavas
can be kept at 8-10°C for two to three weeks, whereas
ripe fruit keeps for up to one week at 5-8°C. Both types
should be maintained at 90-95% relative humidity
(Snowdon 1990; Kader 1999). Shelf life at 20°C is also
about a week (Paull & Chen 2002a).
In-store treatments
Given that guava has a short shelf life of 2-3 days at room
temperature (Carvalho 1994), efforts to prolong keeping
times using various sprays have been tested, but different
cultivars respond differently. Spraying with 1% calcium
nitrate, alone or together with 0.2% zinc chloride reduced
respiration and weight loss, maintained firmness and
extended shelf life (Ali & Lazan 1997). Coatings of
5% carnauba- or cellulose-based (2-4% hydroxypropyl
cellulose) emulsions delayed colour changes and limited
increases in total soluble solids and softening, but led to skin
blackening in some cultivars (McGuire & Hallman 1995).
Sprays of 1-MCP at 300 nl l
−1
for 6 h, or 900 nl l
−1
for 3 h,
delayed ripening for up to nine days (Bassetto
et al
. 2005).
Harvesting
Firm, mature and undamaged fruits are harvested by hand
two or three times a week and collected in baskets. Skin
colour is usually used to assess maturity, depending on
whether firm or fully ripe flesh is required (Paull & Chen
2002a). The harvest period is eight to ten weeks. The
recommended optimum time for harvesting is two to
three weeks before the fruits are fully mature, because of
deleterious physiological changes associated with ripen-
ing, such as yellowing and decrease in flesh firmness
(Ali & Lazan 1997). Soluble solids content at maturity
varies from 3% in green fruit to >10% in fully ripe fruit.
Titratable acidity ranges from 0.2% to 1.5%, depending on
the cultivar. Seasonal variation in acidity occurs in some
cultivars (Paull & Chen 2002a).
Mature guavas decline rapidly in quality and so they
are usually processed without delay. Carriage is in wooden
crates that protect the delicate fruit from mechanical
damage, with the fruits preferably upright (Siddiqui
et al
. 1991) and wrapped individually in newspaper or
similar impregnated with 0.5 g per pack biphenyl and/or
3 g l
−1
potassium permanganate (to absorb ethylene).
Refrigeration during transport is advisable; at 5°C to 10°C
and 85% to 90% relative humidity, storage life is up to
three (Snowdon 1990) or five weeks (Wilson 1980). In the
United States, guavas are pre-cooled immediately after
harvest (Campbell 1994) but care must be taken to avoid
chilling injury to which they are susceptible. Responses to
Modified and controlled atmosphere storage
Guavas are climacteric fruit and respond well to modified
atmosphere storage. Storage in low-density polyethylene
films retards ripening by slowing down the processes
of softening and increasing soluble solids, acidity and
ascorbic acid (Lazan & Ali 1997). Treatment with 10% O
2
and 5% CO
2
for 24 h, prior to storage in air for two weeks
at 4°C, delayed colour development and reduced damage
from chilling (Bautista & Silver 1997). Controlled atmos-
phere storage with elevated carbon dioxide also delays
ripening but may damage the fruit at levels of 10% CO
2
.
For fruit at room temperature, continuous flushing with
saturated air extends shelf life, as does removal of ethylene.
Vacuum infiltration with 10% CaCl
2
at ambient tempera-
ture has been shown to delay softening and suppress rises
in pectin and titratable acidity, but with no effect on the
incidence of disease (Lazan & Ali 1997).