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 kind of berry with a leathery rind that is divided into segments. Each segment contains hundreds of individual juice vesicles that comprise the majority of the edible portion of the fruit. White and red pigmented cultivars are grown. Marsh is the predominant white cultivar. Ruby Red, Star Ruby, Henderson, Ray Ruby, and Flame are the most popular red pigmented varieties.

A high quality fresh-market grapefruit will have a turgid, smooth peel and be relatively blemish-free. The fruit should be elliptical and firm. An appropriate balance of SSC:TA within the edible portion should be achieved, and bitterness should be at a minimum.

Marketable fresh grapefruit generally range from size 23 (23 fruit/carton) through 56 (56 fruit/carton). Grade standards for fresh grapefruit rely on color-break, texture, peel blemishes, shape and firmness. In markets that emphasize processing, grapefruit must achieve a minimum juice content and SSC/TA ratio before harvest. Grapefruit are commonly packed, stored and shipped in 4/5 bushel cardboard cartons.

Grapefruit is a non-climacteric fruit and does not exhibit a classic ripening pattern of increased respiration and ethylene production.

Degreening is necessary for marketing early-season fresh grapefruit in areas where night temperatures remain high. High RH of approx. 90% must be maintained to avoid softening and accentuation of existing peel injuries or blemishes.

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. Hence, it is imperative that the specific carrying 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.