Caballero B. (ed.) Encyclopaedia of Food Science, Food Technology and Nutrition. Ten-Volume Set

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sunburn and possibly freeze damage. The Eureka

tree, however, is less thorny than the Lisbon and

thus easier to pick. The Eureka tree also appears to

be more susceptible to cold damage, making it most

suitable for the coastal areas of California and Aus-

tralia, where freezes seldom occur. The two fruits,

however, are very similar, and processors in particular

have difficulty in differentiating the two.

0008 The Mesero lemon, of Spanish origin but grown

more commonly in Italy, is considered one of the best

processing lemons; it has a smooth, thin, somewhat

pale rind, but contains a large amount of juice. Con-

versely, the Interdonato is primarily a fresh cultivar,

with a lower juice content and a smooth, thin rind. The

fruit itself is large, and the flesh contains few seeds.

0009 Winter is the main harvest for Verna fruit grown in

Spain, Algeria, and Morocco. However, in Spain,

where Verna is the primary cultivar, a significant

supply of fruit is kept available for harvest through-

out much of the summer, a peak season for lemon

demand. The Femminello, a name for an everbearing

group of cultivars grown in the Mediterranean coun-

tries, has its main crop reaching maturing in the late

winter and early spring but is also marketed through-

out the year. Interestingly, in Italy, each particular

lemon crop has its own name, and is marketed

according to season instead of by the varietal name.

Thus, the Primofiore is from the September through

November harvest, the Limoni is from December to

May, the Bianchetti is from the April to June harvest,

and the Verdelli is from the June to September har-

vest. Collectively, this group accounts for about 75%

of the lemons grown in Italy. Most (over 90%) of the

lemons grown in Italy are produced in the coastal

area of Sicily, a warm, dry climate that is highly

favorable for lemon production The Interdonoto, an-

other Mediterranean cultivar, is harvested in the fall

and early winter. This cultivar is a significant portion

of Turkey’s lemon crop.

0010 The Genova is grown principally in South America

and is the leading variety in Chile. The fruit has a

good internal quality (high acid, flavor, and juice

yield), similar to Eureka, and a characteristic spher-

ical shape. The origin of Genova is Italy, and it is

actually considered a strain of Eureka in California,

where it was first imported from Italy in the late

nineteenth century.

0011 Compared to other citrus, the projected production

growth of lemons is forecast to be only modest, with

an estimated rate of 1.5% per annum into 2005. This

is about half the growth of the previous decade. The

geographic production will also shift, with the

strongest production growth forecast for Italy and

Argentina, and with possible crop reductions in

California.

Fruit Structure and Chemistry

0012The structure of the lemon fruit is similar to other

citrus and consists of the peel and the interior edible

portion (endocarp or pulp). The peel is composed of

two distinct layers; the outside layer is termed

the flavedo (epicarp), and the interior of the peel

(the white spongy part) is the albedo (mesocarp).

The many chemical constituents of the lemon fruit

are distributed among the various tissues, usually in

differing concentrations. The flavedo is composed of

mainly carotenoid pigments, vitamins, and essential

oils. The green appearance of immature lemon fla-

vedo is due to the predominance of chlorophyl over

the carotenoid pigments prior to complete ripening.

The albedo contains celluloses and soluble carbohy-

drates, pectin and protopectin, flavonoids, amino

acids, and vitamins. The oil glands, containing the

valuable essential oil, are embedded primarily in

the flavedo, although larger oil glands may also

extend through to the upper part of the albedo.

0013The pulp of the lemon fruit, like other citrus, is

divided into segments called carpels. Each segment

is composed of up to several hundred units called

juice sacs or vesicles. These vesicles are the compart-

ments, which contain the actual lemon juice. The

walls of the vesicles are composed of celluloses, hemi-

celluloses, pectin, protopectin, sugars, flavonoids,

and other minor components such as amino acids

and vitamin C. When intact, the vesicles effectively

contain the juice and limit microbial and enzymatic

degradation of the juice.

0014Comparisons of California fruit (navel and Valen-

cia oranges, and lemons) show that, in relation to the

oranges, lemons have a somewhat lower protein con-

tent, a substantially lower sugar content, and a much

higher acid content. These biochemical measure-

ments of the fruit, confirmed by obvious taste charac-

teristics, lead to the categorization of citrus by

horticulturalists as either low-acid (oranges, manda-

rins and grapefruit) or high-acid (lemons and limes)

fruit. Lemon juice contains about 4.3–4.8 g citric acid

per 100 ml, as compared to around 0.8–1.0 g per

100 ml for mandarin, orange, or grapefruit juices.

0015Fresh lemon juice has approximately the following

vitamin levels per 100 g: b-carotene, 12 mg; thiamin,

0.3 mg; riboflavin, 0.01 mg; vitamin B

, 0.05 mg;

folate, 13 mg; and vitamin C, 36 mg. These figures

vary depending on the source of the fruit and process-

ing and storage conditions.

0016The peel and seeds of all citrus are relatively rich in

phenolic compounds such as flavonoids and phenolic

acids. Phenolic compounds are known, potent anti-

oxidants. Citrus flavonoids include polymethoxy-

lated flavones and glycosylated flavanones; both are

1356 CITRUS FRUITS/Lemons

unique to citrus and are thought to have bioactive

properties such as anticancer, antiinflammatory, and

antiviral effects, among others. Methanol extracts of

lemon seeds are rich in eriocitrin and hesperidin,

while peel extracts contain significant amounts of

neoeriocitrin, naringin, and neohesperidin. There

are many ongoing research programs investigating

the functional properties of these flavonoids, and

other bioactive compounds in all citrus, including

lemon.

0017 All fruits and fruit products contain a range of

volatile, low-molecular-weight (< 250) compounds

that are important in producing the characteristic

flavor and aroma of the specific fruit. The predomin-

ant compounds responsible for lemon aroma number

are relatively few (two to five) compared to other

citrus. The most important component is citral, an

aldehyde that is a cis–trans mixture of the isomers

neral and geranial. Table 3 summarizes some volatile

compounds found in commercial lemon oils and

essences.

Postharvest Handling and Fruit for the

Fresh Market

0018 In the past, the USA, Italy, and Spain dominated total

lemon production, and, as noted in Table 1, Argen-

tina has become a major producer. For fresh fruit

markets, Spain has the major and profitable role in

supplying fresh lemon fruit to Western Europe and

other markets; the USA, Argentina, and Italy con-

tinue to process about half of their fruit and market

the other half as fresh fruit.

0019 Two terms must be understood in order to discuss

citrus fruit quality, markets, and economics: grade

and maturity. The grade refers to external character-

istics such as size, presence of blemishes, and appear-

ance, while maturity refers to mostly internal

characteristics such as juice content, taste, total sol-

uble solids (TSS), acid content (titratable acidity; TA)

and the ratio of TSS to TA. As with most produce

destined for the fresh market, appearance is the pri-

mary attribute of quality for fresh market lemons,

and grading is critical and standardized in a given

country or region. Consumers may make repurchas-

ing decisions based upon internal quality, but gener-

ally will not choose a fruit initially if it presents

exterior faults. Areas with hot, dry summers and

cool, wet winters (Mediterranean climate) typically

produce citrus fruit with brighter, thicker peel than

areas with more humid growing seasons and warmer

winter nights. The Mediterranean climate is also as-

sociated with generally better exterior fruit appear-

ance (at the same level of inputs such as fertilizer and

pesticides) than fruit grown in a humid climate and is

yet another reason for the predominance of fresh

market lemon production in the Mediterranean-type

climate. Quality indices include color intensity and

uniformity; size (larger lemons are preferred), visually

pleasing shape and smoothness; freedom from obvi-

ous decay and damage; and freedom from exterior

blemishes, splotches, and rind discoloration. Fresh-

fruit pricing in most lemon-producing countries is

based on these factors, along with market supply

and demand.

0020Lemons for both the fresh and processed markets

are harvested manually. Pickers use bags, ladders,

clippers, and gauges to judge the size of the fruit.

Fruit picked early in each variety’s particular growing

season may be quite green, even though they may be

deemed physiologically mature. Lemons picked while

still green will generally have a longer postharvest

shelf-life than the fully yellow lemons that need to

be handled gently and marketed more rapidly. Young

lemons can be degreened at the packing house, if

necessary. Degreening is accomplished by exposing

the lemons to 1–10 p.p.m. ethylene for 1–3 days at

relatively high temperatures (20–25



C). Ethylene is

a natural product of plant metabolism and acts as a

plant hormone by regulating many aspects of growth,

development, and senescence of the fruit.

0021At the packing house, the lemons are unloaded,

washed, and graded, degreened as described above,

if necessary, sized, waxed, and packed in cartons or

other shipping containers. Each packing house may

be set up slightly differently, but the major unit oper-

ations in packing fresh lemons are the same as for

other citrus fruit.

0022Citrus fruits, lemons included, are nonclimacteric,

and their respiration and ethylene production rates

are low. Postharvest changes are therefore low in

relation to commodities that are climacteric, such as

avocados, bananas, and berries. Most lemon cultivars

can be, and are, stored for a moderate amount of

time; this requires no special controlled atmosphere

(as with apples) if the environmental conditions of

humidity and temperature are carefully controlled,

and the fruit has been properly handled. The

tbl0003 Table 3 Volatile compounds identified in lemon oils and

essences

Acetone Myrcene

3-Buten-2-ol Neral

Ethanol Octanal

Geranial Octanol

Geranyl acetate b-Pinene

Limonene Terpinene-4-ol

Linalool a-Terpineol

Methanol

CITRUS FRUITS/Lemons 1357

optimum temperature range for lemon storage is

12–14



C, depending on cultivar, maturity stage at

harvest, and intended distribution and transport

time. The relative optimum humidity for storage is

90–95%.

0023 An interesting and specific example of long-

term lemon storage is the traditional practice of

harvesting lemons (primarily in the coastal California

area) in mid- to late winter, and storing them until the

summer marketing season. These lemons, when

picked, are green, thick-skinned, and not very juicy

but after storage (termed curing) are yellow, juicy, and

thin-skinned. The thinning of the peel is due to water

transpiration loss, while the increase in juice yield is

probably due to physiological changes in which the

water in the juice vesicles is released into the vesicles

from its gel-bound form at the membrane.

0024 As noted, lemon fruit for fresh markets must be

attractive and wholesome in appearance; physio-

logical disorders, defined as the breakdown of

fruit tissue not caused by microbes or mechanical

damage, must be prevented or minimized. Adverse

preharvest or postharvest conditions, or nutritional

deficiencies during growth and development, can

cause physiological disorders in lemons. Fresh citrus

fruit are more prone than pome fruits (apples, pears)

to a particular type of physiological disorder, termed

chilling disorder. In lemons, storage at suboptimal

temperatures can lead to symptoms such as pitting

of the flavedo, membrane browning, and red

blotches. Lemons should not be stored at tempera-

tures below 10



Major Processed Products and

Byproducts

0025 Lemon juice is a commonly used ingredient in both

commercial and home kitchens, as well as a compon-

ent of many processed food and beverage formulas.

The following discussion focuses on the commercial

production of lemon juice and concentrate.

0026 After the fruit has been delivered to the processing

plant, it is unloaded, washed, and graded. The juice is

extracted in the same manner as other citrus fruit;

Brown and FMC extractors are the most commonly

used in the western hemisphere, although there are

other citrus juice extractors available. Either prior to

(Brown system) or during (FMC system) extraction,

the lemon oil in the peel is recovered by washing with

water to form an emulsion that is used to produce

cold-pressed (CP) lemon oil (see below). After extrac-

tion, the juice is separated from the rag, seeds, and

ruptured juice sacs in a process known as finishing.

The juice sacs, along with a small amount of juice,

may be stabilized and packaged to produce a product

termed pulpy juice, which can be added to juices,

beverages, and other food products. Juice that

requires even more depulping can be centrifuged to

reduce the insoluble solids level even further.

0027Most lemon juice is then heat-stabilized and con-

centrated in special evaporators developed for the

citrus industry. These evaporators operate under a

moderate vacuum and thus lower temperatures to

minimize undesirable thermal effects. While all citrus

juices are particularly susceptible to thermal abuse

during processing, lemon juice is especially prone to

reactions such as browning and acid hydrolysis,

which are accelerated by the very high TA of the

juice. Most fruit and vegetable juices are concentrated

to a standard



Brix level (



Brix is a measure of sol-

uble solids, which is correlated to sugar content or

sucrose equivalent). Since the major soluble solid in

high-acid fruit (lemons and limes) is citric acid, not

sugar, lemon and lime concentrates are produced and

sold on the basis of grams of equivalent citric acid

per liter of solution (GPL). Lemon concentrate of

400 + 5 GPL is most commonly produced. The con-

centrate is then either stored at low temperature in

large stainless steel tanks or packed in drums or pails

and frozen.

0028Single-strength lemon juice can be bottled or other-

wise packaged for consumer, food service, or indus-

trial use. Most often, the juice is reconstituted to a

standardized GPL from lemon concentrate and puri-

fied water. Approved preservatives, such as sodium

benzoate at very specific levels, are often added. Some

not-from-concentrate (NFC) lemon juice is produced

and packaged, but its initially higher quality suffers

unless the product is quickly pasteurized, packaged,

and then frozen (10 to 20



C) throughout ware-

housing, distribution, and marketing.

0029Lemon juice and concentrate are most often used

throughout the world not as pure juice but as an

ingredient in juice beverages. In many parts of the

world, a sweetened, diluted lemon drink, known as

lemonade, is the most popular citrus drink. Lemon-

ade is specifically defined in the USA under the Code

of Federal Regulations and must have the requisite

GPL of citric acid from the lemon juice (not added) to

be marketed under that name. Elsewhere, standards

may differ, although almost all lemonade is composed

of lemon concentrate, water, and sweetener(s), and

possibly added flavors and colors, in slightly differing

proportions.

0030Lemon oil is a valuable byproduct and, along with

lime oil, has the greatest economic value of all of the

CP citrus oils. It has been made for centuries in Sicily

by traditional processes, and the methods and oil

characterization have been described in the classical

essential oil literature. This discussion focuses on

1358 CITRUS FRUITS/Lemons

current recovery methods in commercial use in lemon

processing facilities.

0031 As the water–oil emulsion is produced just before

or during the juice extraction step, it enters the oil-

recovery process. The emulsion may contain small

particles of peel and other insoluble solids, and may

be sent to a finisher for their removal. In both the

Brown and FMC systems, the emulsion, containing

about 0.5–3.0% oil goes through a two-step centrifu-

gation process. The first centrifuge, known as the

desludger, concentrates the mixture to about

50–60% oil, removing water and insoluble solids.

The second step, known as polishing, removes the

remainder of the water, along with any remaining

solids. Depending on the specifications of the oil

that is being produced, the lemon oil may be

dewaxed. This process is known as winterization

and refers to the removal of natural waxes from the

peel, by exposing the oil to low temperatures and

letting the wax solidify and settle out. The oil is then

packaged in containers that are inert and that exclude

air.

0032 The typical yield of oil from lemon peel is some-

what less than the total amount available (60–70%)

and is dependent on the efficiencies of the operations,

fruit condition, and even economic incentives. Lemon

oil recovery processes usually try to recover as much

oil as possible, due to the value of CP lemon oil.

Recovery of lemon oil from Californian lemons

ranges from about 4 to 10 kg of oil per tonne of fruit.

0033 Lemon oil quality is related to the aldehyde

content, specifically citral, which ranges from about

2.0 to 5.5%, depending on horticultural factors.

d-Limonene, the major constituent (> 95%) of orange

and grapefruit CP oils, is significantly less in lemon oil

but still the major volatile component of CP lemon

oil. The largely flavorless, but oxidatively unstable,

d-limonene may be removed through various concen-

tration techniques to produce a folded lemon oil that

is more stable and more highly concentrated in desir-

able flavor compounds.

0034 The albedo portion of spent lemon peel is an im-

portant source of raw material for commercial pectin

production and contains about 35–40% pectin on a

dry-weight basis. Pectin is a functional ingredient in

many processed food products, where it is used ex-

tensively as a gelling agent and mouth-feel enhancer.

Pectin exists primarily a polymer of galacturonic acid

units, some of which are esterified with methanol,

and has a molecular weight of between 100 000 and

300 000. As most pectin is sold as a dry powder, there

is a complex recovery scheme to obtain the pectin

from the spent peel and process it into a commercially

useful product. Figure 1 is a flow diagram outlining

the major processing steps in refining citrus pectin,

which is extracted from the peel through an acid

treatment, then recovered by precipitation with alco-

hol. Lemon, grapefruit, and lime albedo have a higher

level of pectins than that of orange or tangerine,

neither of which is typically used for commercial

pectin production.

See also: Citrus Fruits: Types on the Market; Controlled-

atmosphere Storage: Effects on Fruit and Vegetables;

Essential Oils: Properties and Uses; Flavor (Flavour)

Compounds: Structures and Characteristics; Production

Methods; Packaging: Packaging of Liquids; Pectin:

Properties and Determination

Further Reading

Braddock RJ (1999) Handbook of Citrus By-products and

Processing Technology. New York: John Wiley.

Carter BA (1993) Lemon and lime juices. In: Nagy S, Chen

CS and Shaw PE (eds) Fruit Juice Processing Technology.

Auburndale, FL: AgScience.

Guenther E (1949) Individual essential oils of the plant

Families Rutaceae and Labiatae. In: The Essential Oils,

vols. 1 and 3. Van Nostrand: New York.

Kimball D (1996) Grapefruit, lemons, and limes. In: Somo-

gyi LP, Barrett DM and Hui YH (eds) Processing Fruits:

Science and Technology, vol. 2, pp. 305–336. Lancaster,

PA: Technomic.

Saunt J (2000) Citrus Varieties of the World. Norwich, UK:

Sinclair International Limited.

Sinclair WB (1984) The Biochemistry and Physiology of the

Lemon. Oakland, CA: University of California.

Shredded peel

Acid extraction

Solids removal

Solution concentration

Alcohol precipitation

Drying

Size reduction

Pectin

fig0001Figure 1 Commercial citrus pectin production.

CITRUS FRUITS/Lemons 1359

Grapefruits

J Forsyth, Citrus Consultant, Sydney, NSW, Australia

Background

0001 Grapefruits, with 6% of world production, are the

fourth most important commercial group within

the edible Citrus species. They consist of a small

number of cultivars that vary in importance due

to market requirements, growing conditions, and

climatic zones. Stable production over the last 20

years is now being influenced by new cultivars with

lower acid levels and red-pigmented flesh. These

factors are creating renewed interest by growers, mar-

keters, and consumers for fruit or processed products.

0002 They are mainly consumed as fresh fruit because of

their refreshing, but distinctive, flavor, and they are

desirable as a chilled breakfast fruit served in halves

or as a juice. The 1970s ‘grapefruit diet’ created con-

siderable interest in this fruit. There are several health

benefits associated with fresh citrus consumption,

such as the low levels of energy (calories), fat, and

sodium and good sources of vitamin C, dietary fiber,

folate, and potassium.

Origin

0003 As with other Citrus species, the origin and signifi-

cance of the grapefruit name remain obscure. It is

considered unique as it is the only citrus species

known to have originated in the New World and not

Asia. Almost certainly, the grapefruit originated in the

West Indies/Caribbean region during the seventeenth

and eighteenth centuries, before being introduced to

Florida in the USA early in the nineteenth century

(Figure 1).

Classification

0004The taxonomic classification of the Citrus species is

complex and diverse, and not universally agreed

upon, in this article grapefruit will be classified by

C. paradisi (Macfadyen). Citrus as a social and cul-

tural fruit crop, also has local names throughout the

world, often for an identical group, e.g., Pample-

mousse in French, Pompelmo in Italian, or Pomelo

in Spanish. Note that Pomelo (C. grandis (L). Osbeck)

is also known as shaddock or pomelo/pummelo and,

while similar in many characteristics (like shape and

rind color, but larger fruits), horticulturally, the pum-

melos and grapefruit comprise separate classes.

Grapefruit Groups

0005The grapefruit group and related hybrids group of

cultivars is limited, with important commercial but

very diverse cultivars that are classified into two

groups: common (or white fleshed) and pigmented.

The fruit is medium to large in size and more sea-

sonal, with each cultivar maturing and suitable for

harvesting over a relatively short period of time. Dif-

ferent cultivars are available that can supply fresh

fruit from very early to very late maturity.

fig0001 Figure 1 (see color plate 34) Grapefruit are often borne in clusters, like a small bunch of grapes and this has been suggested as the

origin of the fruits name.

1360 CITRUS FRUITS/Grapefruits

Common or White-fleshed

0006 Marsh is the main cultivar with a number of other,

now minor, seedy types including Duncan, Davis, and

Wheeny.

0007 Marsh (seedless) This originated as a chance seed-

ling in Florida, selected and commercially propagated

in 1886, as the first seedless grapefruit. The cultivar

spread throughout the world to become the most

important grapefruit grown. In more recent times,

planting has declined in favor of the new red-fleshed

cultivars.

0008 The fruit is medium in size with few or no seeds.

The rind color is pale to light yellow at marurity,

medium thin, and very smooth. The flesh is buff-

colored, tender, and juicy, with a good flavor. Because

of the high heat requirements, successful Marsh

production is restricted commercially to very hot

climates (Figure 2).

0009 White hybrids A breeding program by the Univer-

sity of California in 1958 crossed an acidless pum-

melo with a white seedy grapefruit, resulting in the

selection and release of two new patented low-acid

seedless grapefruit hybrids: Oroblanco and Melo-

gold. The classification is as for grapefruit C. para-

disi. They have many similar characteristics (thick

rinds) but some differences.

0010 Oroblanco This was released in 1980, with major

plantings limited to California and Israel. The fruit

shape is similar to that of Marsh, but it is larger and

slightly flatter. The rind remains greener far longer

(even when internally mature) and is thicker. The

flesh is paler with an open core. Oroblanco matures

about 6 weeks before Marsh, and the flavor is sweeter

due to higher total soluble solids (TSS) and lower

acid. This internal quality, together with the lack of

bitterness, when Marsh is grown in cooler areas,

created early interest when it was first released to

industry. Initial plantings on vigorous rootstocks

like rough lemon and C. volkamerianna adversely

affected the fruit quality – thick rinds, reduced juice

content, and poorer flavor. Oroblanco is considered

by growers to be slightly better than Melogold, partly

because of the better TSS: acid ratio and smaller fruit

(Figure 3).

0011Melogold This was released in 1985. The fruit

shape is similar to that of other grapefruit except for

a slightly tapering neck (sheepnose), and the fruit

often initially produces significantly larger fruit, but

as the trees become older, the average fruit size is

reduced. The rind color is more normal than the

greener Oroblanco and the taste inferior, although

Melogold has a thinner skin and smoother texture,

and matures slightly later in the season. The fruit does

not peel easily, and the segments do not separate as

with traditional breakfast grapefruit or pummelo.

Initially, growers in California preferred Melogold,

but this is now being replaced.

Pigmented

0012While the older cultivars were considered ‘pink’-

fleshed with Thompson and Redblush the main culti-

vars; newer selections are classified as ‘red’-fleshed,

due to the deeper pigmentation in the rind and flesh

while also being seedless. From this group, Star Ruby,

Flame, and Rio Red are becoming more important on

world markets, with a consumer trend away from the

older white-fleshed cultivars.

0013Pink-fleshed Foster originated as a limb sport and

the first recognized pink-fleshed cultivar located in

Florida (1907). The pink or red rind and flesh pig-

ments in grapefruit are lycopene and carotene, and

are not due to anthocyanins, as in blood oranges.

Thompson (Pink Marsh) was found as a limb sport

on a Marsh tree in 1913 and replaced Foster as a

commercial cultivar.

0014Redblush (Ruby, Ruby Red) This originated as a

limb sport of Thompson in Texas in 1931, while

Ruby is thought to have originated from the same

source but in a different locality in 1929. Both are so

similar as to be indistinguishable for all practical

purposes and are considered identical. The fruit is

similar to Thompson (which it generally replaced),

except for a much deeper pigmentation in the flesh

and albedo (but not the juice) and a crimson blush on

the rind, especially at the points of contact between

fig0002 Figure 2 Marsh is one of the oldest, most important and widely

grown cultivars.

CITRUS FRUITS/Grapefruits 1361

fruits. This was the first pink grapefruit that could be

recognized externally without having to cut the fruit,

due to a rind blush. Having been replaced in some

localities by the newer red-fleshed cultivars, Redblush

remains an important cultivar in Florida, California,

and South Africa (Figure 4).

0015 Red-fleshed The following cultivars are relative

new to the industry, originating from more recent

natural mutations or seedlings, breeding, or irradi-

ation programs in the USA from the 1970s:

0016 Star Ruby This was selected as a seedling from a

Texas seed irradiation program in 1959 and released

to industry in 1970. The fruit has a yellow, smooth,

fine, and thin rind, with red blushes. The flesh is

redder than that of Redblush, with a later maturity,

higher TSS and acid but few seeds (rarely more than

two). The juice content is high and as sweet as,

or sweeter than, Marsh and other new pigmented

cultivars.

0017 The tree shows herbicide, nematicide, heat, and

cold sensitivity. These deleterious effects have been

widely recorded, as Star Ruby appears the most diffi-

cult of the new grapefruits to grow successfully. It is

also more susceptible to Phytophthora diseases and to

Alternaria brown spot. These problems lead to erratic

bearing, small fruit size, low tree vigour, and short

longevity.

fig0004Figure 4 Redblush was the first cultivar to have a deeper red

flesh and some rind pigmentation.

fig0003 Figure 3 (see color plate 35) Oroblanco is a new low acid white-fleshed hybrid grapefruit.

1362 CITRUS FRUITS/Grapefruits

0018 Subsequent nucellar clones from the original Star

Ruby, now available in Israel, Southern Africa, and

Australia, produce high-quality fruit with less of the

above-mentioned cultural problems (Figure 5).

0019 Flame This is now thought to have originated from

a natural mutation of Ruby Red grapefruit seed

collected in Texas (1973) and, after selection and

evaluation, was released in 1987. During the last

decade, more has become known about Flame’s per-

formance, especially from Florida and Argentina.

0020 Trees are vigorous and not as cold- or herbicide-

sensitive as Star Ruby. The larger round fruit has an

attractive appearance with a very smooth thin rind;

an external blush is slightly less than Rio Red or Star

Ruby. The background rind color tends to be light

bronze (similar to Star Ruby) rather than yellow like

Rio Red. Internally, the color is of a uniform intensity,

similar to Rio Red, and uniform across the segments.

Fruit hangs on the tree, with a maturity similar to that

of Star Ruby, but earlier than Rio Red. Flame is now

widely planted in Florida and is expected to perform

well in similar climates.

0021Rio Red This originated in Texas from irradiated

budwood sourced from a Ruby Red tree, which, in

1976, produced a natural bud mutation that was then

evaluated before release in 1988. The fruit shape is

generally good but tends to be slightly sheepnose

when grown under semiarid and drier conditions.

0022The Rio Red fruit is the latest maturing of the new

cultivars, and a deep blush develops where adjacent

fruits touch. The flesh color may be patchy, especially

early and late in the season, but for much of the

marketing period is only slightly lighter than Star

Ruby. The thicker rind is compensated for by a softer

flesh and higher juice content.

0023Henderson and Ray Ruby These are two other new

red-fleshed varieties from Texas that have attracted

only a minor growing or marketing interest. All these

new red cultivars have been available for a relatively

short period. Little comparative information is avail-

able for the red-fleshed cultivars, on the effect of

different climatic growing conditions in many citrus-

growing regions of the world, i.e. the effect on tree

longevity, yield, fruit quality and pigmentation.

Table 1 summarizes several important fruit quality

parameters.

Growing Regions and Conditions

0024Grapefruit, with a range of total heat requirements, is

grown in varying climatic conditions and regions,

including the humid tropics, arid subtropics, and

intermediate climates. Commercial production tends

to be located in two narrow belts of the subtropics

and between 20 and 40



latitude north and south of

the equator.

0025Resistance to heat is outstanding and in cold toler-

ance is similar to that of sweet oranges. Their very

high heat requirement for the production of good-

quality fruit restricts successful commercial culture

to hotter climates. The sweetest, juiciest, and most

bitter-free fruit is grown in semitropical summer rain-

fall areas such as Florida, Texas, and areas of South-

ern Africa. This makes grapefruit almost equally well

adapted to hot desert and humid semitropical or

tropical climates. In the cooler drier Mediterranean

climates, there is a tendency for the fruit to have a

thicker rind, lower sugar, high acid levels, and some

bitterness.

0026Under desert growing conditions, the color is

brighter and deeper with a rich flavor more pro-

nounced than in humid climates, where smaller fruit

sizes, a less oblate shape, and a lower juice content

fig0005 Figure 5 (see color plate 36) Star Ruby is a newer grapefruit

cultivar with a deep red pigmented flesh.

CITRUS FRUITS/Grapefruits 1363

may occur. For example, Florida leads the world in

grapefruit production, with a warm to hot and humid

climate, resulting in a grapefruit of excellent internal

quality, with a thin peel and attractive shape.

0027 For the newer red-fleshed cultivars, the trees are

resistant to heat but sensitive to cold. They can be

grown under a range of climatic conditions, but very

hot and warm night temperatures are necessary to

produce high-quality fruit. The newer low acid culti-

vars like Oroblanco may be harvested and marketed

before the full yellow rind color develops, with green

or only pale colored rinds, although the fruit is

mature to eat with a TSS: acid ratio of 8:1 and less

than 1% acid.

0028 Site selection and soil management will be influ-

enced by climate, while some cultural practices

may modify harmful effects, including cold protec-

tion, irrigation, and windbreaks. However, they

cannot completely overcome major unfavorable cli-

matic effects on tree growth or fruit quality. Some of

these effects include regular severe frosts, poor rind

color/pigment development, variable maturity, high

acidity or naringin levels, poor fruit form, or pest

and disease incidence.

0029 Although susceptible to the normal range of citrus

pests and diseases, they are particularly susceptible to

grapefruit stem pitting caused by certain strains of

Citrus Tristeza Virus (CTV). The disease will cause

sudden or ‘quick tree decline,’ pits in the tree and

small, lopsided or malformed fruits. CTV is spread

in infected budwood and the brown citrus aphid Tox-

optera citricida. This disease is endemic in many

countries, but the planting of tolerant rootstocks

like Troyer and Carrizo citrange, together with only

propagating nursery trees with budwood that has

been preimmunized and carries a mild strain cross-

protection, will limit losses.

Production Statistics

0030Although grapefruit is a relatively new citrus fruit,

having been marketed for just over 100 years, grape-

fruit is now the fourth most important citrus with 6%

of total production in 1998–99, after oranges (with

66%), mandarins (17%), lemons, and limes (11%).

0031The world’s grapefruit production has been almost

stable from the 10-year average of 4640 10

tin

1980/81 to 1988/89, to only slightly larger average

total crops (allowing for annual variations) in the

four 1995/96–1998/99 seasons of 4851 10

t, as

shown in Table 2. About 20% of this production is

estimated to be pummelo fruit.

0032Although production is forecast to increase slightly

to 4930 10

t by 2005, this is still below the slightly

tbl0001 Table 1 Some internal and external grapefruit quality parameters

Variety Percentage juice

Percentage acid

TSS:acidratio

Number of seeds

Rind Flesh

Oroblanco 47 0.6 15.9 0 Nil Nil

Melogold 40 0.8 14.5 6 Nil Nil

Marsh 39 1.5 7.5 2 Nil Nil

Thompson na na na 3 Nil 1

Redblush 40 1.3 6.6 2 2 2

Henderson 36 1.9 5.8 1 4 3

Ray Ruby 35 1.8 5.8 2 4 3

Rio Red 43 1.3 7.1 4 4 4

Flame 41 1.3 7.7 3 4 4

Star Ruby 46 1.4 8.1 2 5 5

University of California sampling date December (various years for comparison) and rind or flesh pigmentation 1 pale/poor to 5 deepest.

na, not available.

tbl0002 Table 2 World grapefruit production trends

Year Totalproduction (10

t) Exported (10

t) Processed (10

1980/81 to 1988/89 average 4640 920 1815

1995/96 5007 1175 1986

1996/97 5056 1177 1919

1997/98 4726 1082 1733

1998/99 4614 1135 1682

Four-year average 4851 (38%) 1142 (24%) 1830 (38%)

From FAO (1999) Citrus Fruit Fresh and Processed, Annual Statistics,Tables 1^10 and 16^20. Rome: Food and Agriculture Organization; USDA (1999) World

fresh citrus situation. In: World Horticultural Trade and US Export Opportunities, Circular Series FHORTH. Foreign Agricultural Service.

1364 CITRUS FRUITS/Grapefruits

higher production recorded in 1995–97 (Table 2).

The latest increases will mostly be in pummelo pro-

duction, especially in Asia, China, the Philippines,

Indonesia, and India. Only small increases in are

grapefruit production are expected in Mexico, Argen-

tina, Cuba, Brazil, and South Africa.

0033 The largest growing regions are in the northern

hemisphere, with 86% (Table 3) of world production,

and include countries like the USA, Israel, Cuba, and

China, while the southern hemisphere, with only

14%, is relatively minor but expanding, mainly in

Argentina and South Africa.

0034 Unlike other citrus types, the Mediterranean region

(apart from Israel) produces only minor quantities of

grapefruit (14% of the world production, Table 3),

mainly due to local climatic conditions. There is,

however, interest in producing new red grapefruit

cultivars, especially in Spain, Cyprus, and Turkey.

0035 In the two largest citrus-producing countries

(Brazil and the USA), grapefruit are relatively minor

with only 4% in Brazil, but due to a wider range of

climatic regions especially in Florida and Texas, a

more significant 19% of USA total production. The

relative importance of grapefruit producing in some

countries is outlined below.

USA

0036Florida is the principal state with about 17% (or

56 630 ha) of citrus plantings devoted to grapefruit,

with Marsh the main cultivar (50% of planting)

because of its use in both fresh and processing

markets. Older, pink-fleshed varieties like Thompson

and Redblush make up 37% and were the industry

standards. Recent development has revolved around

the new ‘seedless’ red-fleshed cultivars. Since 1982,

many new plantings were Flame and Ray Ruby and,

more recently, Rio Red. Some Star Ruby has been

planted, but cultural problems have limited grower

acceptance, despite prices usually being higher than

for other red cultivars.

0037Interest in the newer cultivars is based on current

consumer preference for red-fleshed grapefruit. Be-

cause of the long marketing season, retaining flesh

color is critical. Flame and other deep red-fleshed

fruit begin and end the season with a better color

than that of Redblush. A rind blush also enhances

consumer appeal, and despite perceptions, there are

no substantial quality differences between white and

red-fleshed grapefruit.

0038White grapefruit are easily processed (in the early

1990s, about 70% of the crop), but a relatively

high TSS:acid ratio juice is required while a smaller

part of the red types are processed (30–40%). Fresh

fruit exports are important, e.g., for white seedless

cultivars to Japan, but the French market favors the

red-fleshed seedless.

0039In Texas, before the freezes in the late 1980s, nearly

66% of all citrus plantings were devoted to grape-

fruit, mainly the red-fleshed varieties – Redblush, Rio

Red, Star Ruby, Ray Ruby, and Henderson. Extensive

replanting in the early 1990s indicated that 61% were

grapefruit, with 87% Rio Red (replacing the incon-

sistent bearing and cultural problems of Star Ruby)

and 5% Henderson and Ray.

0040In California and Arizona, grapefruit are less im-

portant (9% of plantings), but Marsh and Redblush

are grown in selected areas. Oroblanco was being

grown (1000 ha planted by 1999) for the Japanese

export market and was preferred by growers over

Melogold, but in recent years, returns have been re-

duced markedly. Problems with low production,

small fruit sizes, and thick rinds are now reported,

and only limited plantings are expected.

Israel

0041In the 1980s, Israel’s grapefruit declined from a 60%

dominance of the European import market to 30%,

tbl0003 Table 3 Fresh grapefruit crop production and utilization (with

respective percentages), and the main producing countries

throughout the world in 1998–99

Region/country Totalproduction

10

t(%)

Exports

10

t(%)

Processed

10

t(%)

Northern hemisphere

USA 2285 425 1200

Mediterranean

region

Italy 2

Spain 28 22 2

Israel 321 123 184

Algeria 1

Morocco 2

Tunisia 50

Cyprus 52 33 16

Turkey 85 63 11

Subtotal

(Mediterranean)

631 (14%) 235 217

Cuba 270 40 155

Mexico 180 35

China 255

Subtotal (northern) 3979 (86%) 950 1607

Southern hemisphere

Argentina 210 30 40

Brazil 62

Australia 17

South Africa 189 145 35

Subtotal (southern) 634 (14%) 186 75

To t a l ( w o r l d ) 4614 (39%) 1135 (25%) 1682 (36%)

From FAO (1999) Citrus Fruit Fresh and Processed, Annual Statistics, Tables

1^10 and 16^20. Rome: Food and Agriculture Organization; USDA (1999)

World fresh citrus situation. In: World Horticultural Trade and US Export

Opportunities, Circular Series FHORTH. Foreign Agricultural Service.

CITRUS FRUITS/Grapefruits 1365