Grapefruit

Infobox on Grapefruit
Example of Grapefruit
Freshness facts
Optimum carrying temperature	Generally 10°C to 15°C, dependent upon variety
Highest freezing point	-1,1°C
Acceptable product temp. at loading into containers	Max. 5°C above carrying temperature
Optimum humidity	90%
Ventilation setting for containers	50 m³/hr
Storage life	1-2 months, dependent upon variety
Climacteric / non-climacteric	Non-Climacteric
Ethylene production	Very Low
Ethylene sensitivity	Moderate
Modified / controlled atmosphere	5%-10% CO2; 3%-10% O2
Potential benefits	Although some benefit of increased firmness and delayed senescence can be gained from controlled atmosphere storage, commercial use of controlled atmosphere storage for grapefruit is very limited or non-existent.
Availability
Australia/New Zealand South Africa South America USA	May - October April - September October - June

Grapefruit

Harvesting and handling

The grapefruit is a large, yellow-peeled, round citrus fruit weighing approximately 250 - 700 g. Its pulp is very juicy and has a refreshing, aromatic taste. The bitter taste is caused by the glycoside naringin; the amount of this bitter substance present varies according to variety and place of origin. Grapefruit from the tropics generally have a sweeter, less sharp flavour than those from cooler regions of cultivation. The "Ruby" and "Ruby red" varieties, for example, are red-fleshed, seedless fruits with a reddish tinge to the peel in parts (russeting) and a milder, sweeter flavour than other varieties. In international trade, they are two of the most important varieties.

The degree of ripeness of citrus fruit is determined on the basis of three criteria:

• by the ripeness index: this is determined by the Brix value, which is a measure of the sugar/acid ratio of the fruit.
• by cutting at purchase: freshness is determined by cutting the fruit in half from the stem-end to the opposite end. If the fruit is withered at the stem-end, it must not be shipped.
• by peel colour: the colour of the peel is not necessarily a reliable indicator of ripeness, but its surface gloss is.

Fruit harvested early in the season may be 'degreened' by means of manufactured ethylene released into the room. The appropriate regime is dictated by cultivar and growing conditions. Ethylene treatment carries with it the disadvantage of hastening the death of green 'button' tissue, thereby predisposing the fruit to invasion by stem-end rot fungi.

Fungicides are diphenyl, orthophenylphenol (OPP) and thiabendazole (TBZ). Diphenyl can be recognised from its naphthalene-like odour. The fungicides primarily prevent blue and green moulds, but they do impair flavour and indication of their use is mandatory. Waxing to prevent loss of aroma and weight is required because the washing process removes the natural wax layer. The film of wax sprayed onto the peel only partially seals the pores so that the fruits are still able to respire.

Grapefruit are mainly eaten fresh as a very popular breakfast fruit, but they are also used in the production of juices, marmalades, salads etc. Because of its impact- and pressure-sensitivity, the fruit has to be handled with appropriate care. A high quality fresh-market grapefruit will have a turgid, smooth peel and be relatively blemish-free. The fruit should be elliptical and firm, and bitterness should be at a minimum.

Cooling and storage

The selection of a proper temperature for storing grapefruit should be based on pre-harvest factors - including weather during growth, tree condition, and orchard treatments - as well as ripeness of the fruit, postharvest handling, and length of proposed storage.

Storage and transport temperatures differ considerably in their specific details according to variety and country of origin and are stated as different in the literature. For this reason, it is imperative that the specific travel temperature be indicated in writing by the consignor. The cargo should be pre-cooled prior to loading. California and Arizona grapefruits store best (4-6 weeks) at 14° to 15°C and Florida/Texas grapefruit at 10°C. Israeli and South African grapefruit are to be kept at 10°C to 12°C, at which they have a PSL of 10-16 weeks.

Coating grapefruit with high shine water waxes reduces the incidence of chilling injury and may permit slightly lower carrying temperatures (approx. 8°C) to reduce fruit respiration and minimise postharvest pitting which is a peel disorder that affects waxed grapefruit stored at higher temperatures. Pitting associated with postharvest pitting is targeted to areas of the peel surrounding the oil glands, whereas pitting associated with chilling injury is not targeted to oil glands.

Chilling damage is manifested in citrus fruits in particular by spots on the peel (brown dots on the peel), accompanied by a bitter taste and unpleasant odour, rot and cell wall collapse. The glossiness of the peel is lost and the albedo layer (inner layer of the peel), which is normally white, turns a dark colour. When the fruit is divided up, the segments, which have a low juice content, break up and the whole fruit is glassy and soft. The severity of the chilling damage is determined not only by the extent to which the temperature has fallen beneath the limit, but also by the length of exposure to this temperature. In grapefruit there is a risk of chilling damage at temperatures below 6°C.

Excessively rapid warming of refrigerated fruit results in condensation and spoilage, and excessively high temperatures render the grapefruit highly impact-sensitive and susceptible to mould. The addition of fresh air is extremely important as citrus fruit can start to ferment within a few hours due to anaerobic respiration (resulting in total loss of the fruit). If ventilation is inadequate, storage damage may occur, taking the form of a bitter flavour and peel scab.

Mixed loads

Grapefruits can be shipped in mixed loads but they are chilling sensitive and so should (generally) not be kept below 10°C for long shipments.

Cautions

O₂ below 3% can cause off-flavours. CO₂ greater than 10% may cause off-flavours and areas of scald like damage on the rind. Grapefruits are chilling sensitive and their sensitivity may vary with variety, growing area and maturity.

Storage disorders

Alternaria rot, Anthracnose, Aspergillus rot, Black mould rot, Black pit, Black spot, Blue mould, Brown rot, Canker, Chilling injury, Cottonry rot, Degreening, Fusarium, Green mould rot, Grey mould rot, Insect damage, Melanose, Rind discoloration, Scab, Scald, Senescent breakdown, Sooty blotch, Sooty mould, Stem end rot.