The name grapefruit is probably derived from the fact that the fruits commonly occur in small clusters, rather singly. The original significance of the name of this important fruit is obscure. The fruit is borne in bunches and therefore, it has been named grapefruit. It should be distinguished from Chakotra which is much bigger in size and can be distinguished easily from the peel. The street hawkers called it Grapefruit and sometimes Chakotra. The Chakotra is a different fruit and is also known as Shadock. To distinguish the English name, the grapefruit is called Pomelo and Chakotra is called Pummelo. The Latin name is Citrus paradisi and other old name is citrus maxima, Chakotra is botanically known as Citrus grandis.
Pigment Contents of Grapefruit (In micrograms per 100 grams)
It is presumed that the grapefruit was originated in the West Indies as limb variant of chakotra. So pomelo is derived from pummelo is certain, but whether by somatic mutation or natural hybridization is not know. Most probably it is a natural hybrid. The first known use of the term grapefruit occurred in 1814 in Jamaica, in which it was referred to as special and smaller kind of shaddock whose flavor somewhat resembled that of the grape. According to Ziegler and Wolfe (1961) the introduction of this fruit in Florida was made by Count Odette Phillippe, a Frenchman, who settled near Safety Harbor on Tampa Bay in 1823 and brought with him seeds or seedlings of the grapefruit and other citrus fruits from the Bahma Islands. This excellent fruit flourished in the State of Florida in USA In fact, except Red blush (Ruby), all the Grapefruit varieties of commercial importance have originated in Florida. However, a new variety named as Shamber originated in California and introduced in Pakistan in 1945. The United States is the largest producer of this fruit followed by Israel, Jamica, Cuba (West Indies), South Africa and Argentina.
The grapefruit tree is vigorous and largest citrus trees requiring more space. The grapefruit tree reaches 15 to 20 ft (4.5-6 m) or even 45 ft (13.7 m) with age, has a rounded top of spreading branches; the trunk may exceed 6 inches (15 cm) in diameter; that of a very old tree actually attained nearly 8 ft (2.4 m) in circumference. The twigs normally bear short, supple thorns. The evergreen leaves are ovate, 3 to 6 in (7.5-15 cm) long, and 1.75 to 3 inches (4.5-7.5 cm) wide; dark-green above, lighter beneath, with minute, rounded teeth on the margins, and dotted with tiny oil glands; the petiole has broad, oblanceolate or obovate wings. The white, 4-petalled flowers, are 1.75 to 2 inches (4.5-5 cm) across and borne singly or in clusters in the leaf axils. The fruit is nearly round or oblate to slightly pear-shaped, 4 to 6 inches (10-15 cm) wide with smooth, finely dotted peel, up to 3/8 in (1 cm) thick, pale-lemon, sometimes blushed with pink, and aromatic outwardly; white, spongy and bitter inside. The center may be solid or semi-hollow. The pale-yellow, nearly whitish, or pink, or even deep-red pulp is in 11 to 14 segments with thin, membranous, somewhat bitter walls; very juicy, acid to sweet-acid in flavor when fully ripe. While some fruits are seedless or nearly so, there may be up to 90 white, elliptical, pointed seeds about 1/2 in (1.25 cm) in length. Unlike those of the pummelo, grapefruit seeds are usually polyembryonic. The number of fruits in a cluster varies greatly; a dozen is unusual but there have been as many as 20. It is heat resistant and as cold tolerant as sweet orange (malta). It is a very hard tree. The climate of central and Southern Punjab and Northern Sindh is ideally suited for the cultivation of grapefruit.
The grapefruit prospers in a warm subtropical climate. Temperature differences affect the length of time from flowering to fruit maturity. At Riverside, California the period is 13 months; at warmer Brawley in the Imperial Valley of southern California, only 7 to 8 months. The fruit is lower in acidity in the Indian River region and areas of southern Florida, the lower Rio Grande Valley of Texas, and in the tropics than in cooler situations. Humidity contributes to thinness of peel, while in arid climates the peel is thicker and rough and, as might be expected, the juice content is lower. Low winter temperatures also result in thicker peel the following year and even affect the fruit shape. Ideal rainfall for grapefruit is 36 to 44 in (91.4-111.7 cm) rather evenly distributed the year around. Under subtropical conditions, the flavor of grapefruit becomes more sprightly. Because of its refreshing flavor and mild bitterness contributed by the glucoside Naringin, the fresh grapefruit is unexcelled as a breakfast fruit served either in halves or as juice.
The grapefruit is grown on a range of soil types. In the main growing area of Florida, the soil is mildly acid sand and applications of lime may be beneficial. On the east coast there are coquina shell deposits and, in the extreme southern part of the peninsula, there is little soil mixed with the prevailing oolitic limestone. Where the grapefruit is grown in California, Arizona and Texas, the soils are largely alkaline and frequent irrigation causes undesirable alkaline salts to rise to the surface. In Surinam, grapefruit is grown on clay. Successful grapefruit culture depends mainly on the choice of rootstock best adapted to each type of soil. Salinity of the soil and in irrigation water retards water uptake by the root system and reduces yields.
In the early years of grapefruit-growing, the customary citrus rootstocks were utilized: sour orange on heavy hammock and flatwoods soils, rough lemon on sand, though trees grafted on this stock were short-lived. In the early 1950’s, sweet orange was being preferred over sour orange. In 1946, the United States Department of Agriculture, Texas A & M University, and Rio Farms, Inc., of Monte Alto, Texas, launched a cooperative program of testing grapefruit on different rootstocks. Of 13 different rootstocks utilized, ’Swingle citrumelo’, ’Morton’ and ’Troyer’ citranges gave the best yield of large fruits. Rough lemon and ’Christian’ trifoliate orange reduced acidity. ’Swingle citrumelo’ was never used extensively as a rootstock until 1974 when it was released to nurserymen and growers because of its tolerance of exocortis, xyloporosis, and tristeza and resistance to foot-rot and citrus nematode, and low uptake of salts, together with its ability to support heavy crops. It is now in third place after ’Troyer’ citrange and sour orange.
In the past, ’Marsh’ and ’Hooghart’, the commercial grapefruits of Surinam, have been grown there on sour orange rootstock, but fear of tristeza inspired a rootstock testing program. Among the stocks tried, ’King’ and ’Sunki’ resulted in high yield and excellent quality in contrast to rough lemon and Rangpur lime. The two latter also showed susceptibility to Phytophthora root rot. ’Cleopatra’ lowered the yield, and trifoliate orange proved unsatisfactory in such a humid climate. In the Lower Rio Grande Valley of Texas, grapefruit trees on ’Swingle citrumelo’ have grown very poorly on heavy clay as compared to those on sour orange.
In general, culture of grapefruit is similar to that of the orange, except that wider spacing is necessary. Nutritional experiments with grapefruit have shown that excessive nitrogen results in malformed fruit, coarser texture and less juice. Lack of certain minor elements is evident in symptoms often mistaken for disease. The condition called exanthema is caused by copper deficiency; mottle leaf results from zinc deficiency. Several products are prepared from this fruit such as single-strength canned juice, canned sections, essential oil and pectin are the principal by product obtained from the rind. The grapefruit falls into two natural groups. The common (white) and pigmented. The most important white varieties are Duncan, Marsh seedless and Walters. These varieties have been tried in Pakistan and have given excellent performance.
Promising Grapefruit Varieties
Duncan: This cultivar apparently originated as a seedling from the original grapefruit tree introduced into Florida by Phillippe (Cooper and Chapot 1977). This variety was imported from Florida. It is the biggest size variety and contains 40 to 50 seeds. It gives maximum juice. The scientists at U.S.A. have produced a seedless Duncan fruit, it is the oldest variety and its performance has been very satisfactory in Pakistan. It has excellent flavor.
Marsh seedless:According to Webber (1943), Marsh apparently originated a chance seedling planted about 1860 on a farm near Lakeland, Florida. It is smaller in size than Duncan but its surface is smooth and shining. There are only 3-4 seeds and it is, therefore, called seedless. This is the most common variety and has maximum uses in the U.S.A. It is being cultivated in the most of the countries out side the United States and in Pakistan as well.
Foster: It has originated as a Limb sport on a tree of the Walters which is a white seedy type. This is the first pigmented grapefruit variety has a red blush on its skin. It is commonly grown in Pakistan and usually one sees it on the fruit vendors. People enjoy its juice. The variety is quite seedy having up 50 Seeds / Fruit.
Thompson: It is also originated as a Limb sport on a Marsh tree and discovered in 1913. The pink colour in Thompson is limited to the pulp. It shows no colour on the rind. There is absence of colour in the membrane and mesocarp. It is nearly seedless and not very commonly grown in Pakistan but one sees it in Fruit Exhibitions.
Ruby: It was found in 1929 as a budsport on Thompson in McAllen, Texas. It has a deep flesh colour with a red blush on the peel. It has occurred as Limb sport on a Thompson tree. Its performance has been good in Pakistan but has not become so popular as Foster. It contains only 3 to 4 seeds is an excellent variety of Texas.
Shamber: This is almost a seedless variety and its juice is deep pink colour like Ruby. It has been introduced by the Department of Agriculture and is becoming popular. Some of the growers have exclusively planted this variety and is available in the market on the stalls and fruit vendors. It has great future. All the other varieties were introduced in Pakistan from Florida but this particular variety from California. It is a bud sport of Marsh seedless.
In 1973, several new varieties of grapefruit were introduced in Punjab and their performance is being studied.
Dietetic and other therapeutic qualities
Composition of Marsh seedless Grapefruit
Citric acid: 0.89 %
Sucrose: 01.34 %
Acidity Degress Brix: 6.95 %
Total sugar: 4.78 %
Water: 93.05 %
Ash: 00.218 %
Reducing sugar: 3.44 %
Average weight of fruit: 466.2 gm
Vitamin C and the bitter principal Naringin (C27 H32 O14.2H2O) distinguish it from other citrus fruits. It contains vitamin C 35 mg per 100 ml juice. The requirement of an adult is 75 mg per day. The local Hakeems recommend grapefruit as a heart tonic on imperical basis. According to Sinclair, Naringin distinguishes it from other citrus species. It is very bitter. It is related to the hesperides in sweet orange and lemon but differs in structural formulas. It is abundant in the mesocarp and albedo. Naringin occurs in low concentrations in the juice of mature grapefruit but at higher concentrations in segment membrane, core and peel.
Naringin may be considered as the pro-vitamin P as Carotene is to pro-vitamin A is considered as an essential vitamin. Probably it consists of unsaturated fatty acids which act as antioxidants and slow down the process of degradation of glucose so that the energy is released to the human organs slowly.
The common belief among ignorant people is that the consumption of acid fruits results in producing acidity in the system. Contrary to this belief, it was shown that citrus juices (the juice of fruits like lemon, orange and grapefruit) act as alkali.
The acid juice will produce a considerable amount of oxygen which will convert uric acid into urea and perhaps carbonic acid and thus eliminate excess of ureates from the blood. Later researches have also shown that the citric acid, in the citrus fruit juice forms alkaline salts of sodium. Potassium etc, present in the blood thus rendering the blood stream alkaline.
Pests and Diseases
The grapefruit is subject to most of the same pests that attack the orange, including Caribbean and Mediterranean fruit flies. Exposure of early-season fruit to 60 and 90 krad causes scald and rind breakdown after 28 days of storage, and mainly pitting in midseason and late fruits. Minimal injury results from exposure to 7.5, 15, and 30 krad.
The tree is highly susceptible to citrus canker and several viruses: crinkly leaf virus, psorosis, tristeza, xyloporosis, and infectious variegation. Mesophyll collapse is caused by extreme drought and dehydrating wind.
Harvesting and Handling
In Pakistan all commercial cultivars reach legal maturity in September or October if sprayed after blooming with lead arsenate to reduce acidity. Even after legal maturity the grapefruit can be “stored” on the tree for months, merely increasing in size, and extending the marketing season. The fruits can be harvested until near the end of May when they begin to fall and seeds start sprouting in the fruit. The only adverse effect of late harvesting is a corresponding reduction in the following year’s crop. It has been found that spot-picking of the largest fruits partially counteracts this effect of late harvest. Fruit drop can be retarded by spraying with a combination of gibberellic acid and 2,4-D. Either of these agents or both together will reduce the germination of seeds. Germination may be inhibited for periods up to 11 weeks by cool storage at 50º F (10º C).
Grapefruits were formerly harvested by climbing the trees or using picking hooks which frequently damaged the fruit. Today, the fruits on low branches are picked by hand from the ground; higher fruits are usually harvested by workers on ladders who snap the stems or clip the fruits as required. California began utilizing a modified olive limb-shaker for harvesting grapefruit in 1972. The machines work in pairs to harvest opposite sides of each tree and the trees must be pruned to remove deadwood and to give access to 3-5 main limbs for shaking. Lower branches must be lopped off to leave a clear 2 1/2 ft (75 cm) space for the catching frame. Mechanical harvesting causes some superficial injury. A team of 3 workers with one machine can harvest 150 to 188 field boxes 50 lbs (22.7 kg) when filled per hour, as compared with 45 boxes per hour for 3 manual pickers. Stems are removed from the fruits before packing to avoid stem-damage.
Early in the season, when the fruits are mature but not fully colored, they are often degreened by exposure to ethylene gas. The grapefruit is remarkable for its durability, but modern practices of applying fungicide to the harvested fruit are given credit for the great reduction in marketing losses. The cull rate in New York wholesale warehouses in 1983 was found to be 1.4% (mostly fungal), as compared with 13 % estimated in 1960. Retail losses in 1983 were 3.5%, and only a small proportion were the result of physical injury.
The grapefruit keeps well at 65º F (18.33º C) or higher for a week or more and for 2 or 3 weeks in the fruit/vegetable compartment of the home refrigerator. The first sign of breakdown is dehydration and collapse of the stem-end. To retard moisture loss, fruits for marketing are washed and waxed as soon as possible after harvest. When kept in prolonged storage, the grapefruit is subject to chilling injury (peel pitting) at temperatures below 50º F (10º C). The degree of injury depends on several factors: the fruits on the outside of the tree are more susceptible than the fruits that have been sheltered by foliage. The use of preharvest growth regulators tends to reduce susceptibility, as does 100% relative humidity during storage. Preconditioning at 60.8º F (16º C) for 7 days before storing at 33.8º F (1º C) prevents injury. Lowering the temperature gradually after preconditioning is also beneficial, as is sealing the fruit in polyethylene shrink-film before refrigerating.
The banning of ethylene dibromide fumigation except for export has made it necessary to resort to cold treatment as an alternative measure against fruit fly infestation for shipment to Texas, Arizona and California. The United States Department of Agriculture now requires that imported citrus fruits be kept at 32º F (0º C) for 10 days or at 36º F (2.2º C) for 16 days after the fruit has been cooled down to the specified temperature. In Israel, investigators have found that waxing with a coating containing fungicide, and holding the packed fruit for 6 days at 62.6º F (17º C) before the cold treatment, gives good protection from chilling injury and decay in storage. Cold treatment costs 5 times as much as fumigation with ethylene dibromide. Methyl bromide has been tested and proposed as an effective fumigant.
Cooper, W.C. and Chapot, H. 1977. Fruit production- With special emphasis on fruit for processing. In Citrus Science and Technology, Vol. 2. S. Nagy. P. E. Shaw, and M. K. Veldhuis (Editors). AVI Publishing Co., Westport, CT.
Ziegler, L. W., and H. S. Wolfe. 1961. Citrus growing in Florida. Univ. Fla. Press, Gainesville. 248 pp.
Webber, H. J. 1943. Cultivated varieties of citrus. In: Webber, h. J., and L.D. Batchelor (eds.). The citrus industry. I: 475-668. Univ. Calif. Press, Berkeley and Los Angeles. Agriculture Hunt.
By: M. Azher Nawaz*, Dr. Waqar Ahmed** and M. Mithal Jiskani***
* Agriculture Officer, Dhanote, District Lodhran
**Institute of Horticultural Sciences, University of Agriculture, Faisalabad
*** Assistant Professor, Sindh Agriculture University, Tando Jam, Sindh