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25% of the whole fruit. The flavedo contains peel oil

in the oil sacs and the albedo most of the pectins.

After juice extraction, rag, pulp, and seeds account

for the rest of the total fruit weight. Most of the fruit

(almost 90%), is water. The rest is mainly formed by

sugars and acids. Minerals, amino acids, aroma com-

pounds, and pectins are present in smaller propor-

tions. These percentages vary greatly in other citrus

fruits, but they also vary within orange fruits,

depending on variety, ripeness, area, and culture prac-

tices. Concentrations, distribution, and methods of

analysis of these constituents will be discussed in

more detail in the following sections.

Sugars and Acids

0009 Soluble solids of citrus juices consist mainly of sugars

and acids. Sugars are more abundant (70–80% of

total solids) in oranges, tangerines, and grapefruits,

whereas citric acid is predominant in ripe lemons and

limes. Soluble solids are usually expressed in degrees

Brix (for easy and rapid evaluation with refractom-

eters), referring to all juice solids as sucrose. Total

acidity is expressed in grams of citric acid per

100 ml of juice, approximately equivalent to percent-

age.

0010The total solids increase with ripeness in all citrus

species. In most cases, this is due to the increase in

sugar content but, in lemons, citric acid increases

with ripeness. Ranges from 9 to 14



Brix and from

1.5 to 0.5% acidity can be considered usual in orange

juices processed in citrus plants. Commercial juices,

prepared by blending juices of different varieties at

different degrees of ripeness, show less variations:

from 11 to 12



Brix and from 0.8 to 0.9% acidity

are normal ranges. (See Ripening of Fruit.)

0011The degrees Brix-to-acidity ratio, also called the

maturity index, is a fundamental measure of quality

of citrus juices. In commercial orange juice it usually

has values from 12 to 14 and no orange juice is con-

sidered of high quality if it shows a ratio lower than

11. The importance of the degrees Brix-to-acidity

ratio as a quality index lies in its relationship with

the equilibrium between sweetness and sourness, one

of the most appreciated sensory characteristics of

citrus fruits. As discussed above, degree Brix value

depends mainly on sugars.

0012Only three sugars are important in citrus fruits,

sucrose, glucose, and fructose, which produce

juice (or fruit) sweetness. Other sugars, such as gal-

actose, heptulose, mannose, rhamnose, xylose, or tre-

halose, have only been detected as traces. (See

Carbohydrates: Classification and Properties; Fruc-

tose; Sucrose: Properties and Determination.)

0013The analysis of citrus sugars has been approached

by many different methods. A classical standard

method is the determination of reducing sugars (fruc-

tose and glucose) by copper reduction, followed by

tbl0001 Table 1 Approximate composition of oranges

Overall composition (%)

Juice 40–50

Flavedo 8–10

Albedo 15–25

Rag, pulp, and seeds Rest

Main constituents (%)

Water 85–90

Sugars 6–9

Acids 0.5–1.5

Pectins 0.5–1.5

Minerals 0.5–0.8

Essential oils 0.2–0.5

Fiber 0.5–1.0

Protein 0.5–0.8

Fat 0.1–0.2

Fruit

Pericarp

Mesocarp

Endocarp

Epicarp

Epidermis

Hypodermis

Flavedo

Outer mesocarp

Peel

Juice

Inner mesocarp

Albedo

Seeds

fig0001 Figure 1 Structure of citrus fruits. Reproduced from Citrus Fruits: Composition and characterization, Encyclopaedia of Food Science,

Food Technology and Nutrition, Macrae R, Robinson RK and Sadler MJ (eds), 1993, Academic Press.

1336 CITRUS FRUITS/Composition and Characterization

the inversion of sucrose to fructose and glucose,

which can then also be determined as reducing sugars.

By this method, the concentrations of the main citrus

sugars (reducing and nonreducing) are determined.

When the sugar composition must be known in

more detail, separative (chromatographic) methods

are used. Numerous analyses of citrus sugars have

been performed by paper chromatography, gas chro-

matography, and high-performance liquid chroma-

tography. Traces of the different minor sugars

mentioned above have been detected by these tech-

niques. The analyses of citrus sugars have shown that

the typical ratios of sucrose to glucose to fructose are

2:1:1 in orange juice, 1:4:4 in lemons and 1:3:3 in

limes. Typical contents of total sugars are 8% of total

weight in orange and grapefruit juices, and 2% in

lemon juice, although these percentages can vary

greatly with variety and ripeness. (See Chromatog-

raphy: Principles; High-performance Liquid Chroma-

tography; Gas Chromatography.)

0014 The major acid in citrus fruits is citric acid. Total

acidity, which is determined by titration, is expressed

as grams of citric acid per 100 ml of juice. Malic acid

is the second most important acid, present in variable

but much lower amounts than citric acid. Other or-

ganic acids, such as succinic, malonic, lactic, oxalic,

phosphoric, tartaric, adipic, isocitric, etc., are present

in even smaller amounts and have been detected by

separative methods, such as gas chromatography of

methyl ester derivatives. (See Acids: Properties and

Determination.)

0015 Acid content, like total solids, varies greatly with

ripeness. Ranges from 0.5 to 1.5% in orange juice,

from 0.8 to 2.5% in grapefruits, and from 4 to 8% in

lemons and limes are usual.

Polysaccharides

0016 Citrus fruits contain cellulose, hemicelluloses, and

pectic substances, mainly in the peel. The juice

contains only small amounts of these compounds, al-

though they play an important role. From the nutri-

tional point of view, they provide dietary fiber.

Concerning quality, pectin acts as a colloidal stabilizer,

protecting juice cloud. Pectins are polymers of galac-

turonic acid and exist in juices at levels of about 0.5%.

In the form of the methyl ester, polygalacturonic acid

maintains juice turbidity. If deesterification occurs, the

colloid degrades and the juice clarifies. The main

reason for thermal treatment of commercial juices is

not only to destroy microorganisms, but to inactivate

the enzyme pectinesterase, which produces pectin deg-

radation. Citrus peel, mainly from lemon, is an im-

portant source of commercial pectins, which is of great

interest in the food industry because of their gelling

power. (See Dietary Fiber: Properties and Sources.)

Nitrogenous Compounds

0017About 0.7% of citrus juices consists of nitrogenous

compounds. Free amino acids are the most important

part of the nitrogenous fraction (70%); the rest

consists of vitamins, proteins (mainly enzymes), and

inorganic compounds. Although not important as

nutrients due to their low concentration, amino

acids are extensively used for characterization pur-

poses and to detect adulteration in fruit juices. Total

nitrogen determination (closely related to total amino

acid content) is a standard method of purity control.

Nevertheless, the nitrogen content can be easily ma-

nipulated by adding inorganic salts. For this reason,

separative techniques allowing the determination of

individual amino acids are of considerable interest.

Gas chromatography of volatile derivatives has often

been used for this purpose, as has ion exchange chro-

matography. Reversed-phase liquid chromatography

is an increasingly accepted technique. Figure 2 shows

chromatograms obtained by this method from the

dansyl derivatives of orange juice amino acids. (See

Time (min)

10 20 30 40

fig0002Figure 2 Liquid chromatogram of orange juice amino acids:

1, aspartic acid; 2, glutamic acid; 3, asparagine; 4, glutamine;

5, serine; 6, threonine; 7, glycine; 8, alanine; 9, arginine; 10,

g-aminobutyric acid; 11, proline; 12, valine; 13, methionine;

14, ornithine; 15, lysine; 16, histidine. Reproduced from Citrus

Fruits: Composition and characterization, Encyclopaedia of Food

Science, Food Technology and Nutrition, Macrae R, Robinson RK

and Sadler MJ (eds), 1993, Academic Press.

CITRUS FRUITS/Composition and Characterization 1337

Amino Acids: Determination; Chromatography:

Thin-layer Chromatography.)

Bitter Compounds

0018 Two main types of bitterness, caused by two different

types of compounds, occur in citrus fruits. Flavanone

neohesperidosides, as naringin in grapefruit and neo-

hesperidin in sour oranges, produce the typical bitter-

ness of fruits and juices from these species. The other

type of bitterness, which constitutes an extremely

negative quality factor in some orange juices, is pro-

duced by limonin, a triterpene derivative of the limo-

noid group. Limonin bitterness is known as ‘delayed

bitterness’ since it is not detected in fresh fruits or

freshly extracted juices, but develops during juice

storage or with heat treatment. The reason is that

fresh fruits do not contain limonin, but a nonbitter

precursor which converts into limonin after juice

preparation. Limonin is detected by taste at concen-

trations of about 6–8mg l

1

in orange juice. Citrus

industries avoid exceeding these concentrations in

commercial juices by using only proper fruits or by

blending different raw materials to obtain the desired

final products. The limonin content of orange juice

depends on variety and ripeness. It is extremely high

in Navel varieties (still about 15 mg l

1

at a degrees

Brix-to-acidity ratio of 12), which makes them very

unsuitable for juice processing. Generally, early var-

ieties produce more bitter juices than late varieties but

country/region of origin can also affect limonin con-

tents. Problems of bitterness are worse in temperate

areas (California, Australia, Spain) than in tropical or

subtropical regions (Brazil, Florida). (See Flavor (Fla-

vour) Compounds: Structures and Characteristics.)

0019 Reduction of bitterness has been attempted by

many means, involving changes in cultivation prac-

tices (rootstock, fertilization) and juice treatments.

Debittering of processed juices seems to be the most

promising approach and some citrus industries are

already equipped with debittering devices.

0020 Limonin analysis is essential in quality control.

Thin-layer chromatography or immunoassay methods

as well as liquid chromatography techniques are used

in its determination.

Minerals

0021 Amounts and proportions of minerals contained in

citrus juices are interesting for nutrition. Total min-

eral content, referred to as ‘ash,’ is about 0.4% of

juice weight. Ash composition varies in relation to the

species, ripeness, growth area, and methods of culti-

vation. Generally, the major inorganic components of

citrus juices are potassium and nitrogen, each ac-

counting for about 40% of the total. Calcium, mag-

nesium, and phosphorus are less abundant (about

5% each). Sodium, iron, sulfur, and chlorine are

also important. About 20 more minerals have been

detected in smaller proportions or only as traces.

Some of these minor constituents have been proposed

for ascertaining the geographic origin of orange juice.

Minerals are very satisfactorily determined by atomic

absorption spectrometry or plasma emission tech-

niques, where available. Refer to individual minerals.

Aromas

0022The typical citrus aroma depends on many minor

constituents. Their individual contribution and rela-

tive proportions, as well as interactions among them,

give the characteristic odor to each species. These

constituents are present in juice vesicles of the endo-

carp and, in larger amounts and different propor-

tions, in the oil sacs of the flavedo. When extracting

the juice, oil sacs break and part of the oil joins the

juice. Peel oil is also obtained as an independent

product in citrus plants. One of its principal uses is

as a flavoring ingredient for soft drinks.

0023Odor compounds constitute a part of the volatile

fraction of citrus juices, which also contain nonodor-

ous compounds. The distinction between both types

of constituents and the evaluation of their relative

importance in juice aromas are important research

objectives in this field. Table 2 shows the main types

of compounds forming the volatile fraction of orange

juice. Several examples of individual constituents,

including some which cause off-flavors, are listed in

the table. Major constituents of the volatile fraction

are ethanol (about 0.5 ml l

1

in juice) and limonene

(0.15 ml l

1

). None of these are important for aroma,

since their concentrations are lower than detection

thresholds. Chromatography, preferably gas chroma-

tography using capillary columns of high resolution

coupled to a mass spectrometer, is the most suitable

method for determining either individual compounds

or quite large groups of volatile compounds in a

single analysis. Due to the low concentrations in the

juice of most volatiles, a concentration step may be

necessary for detailed studies. This step can be per-

formed by solvent extraction of the juice or of a juice

distillate, followed by solvent removal.

0024For rapid determinations, necessary in routine

quality control, the total analysis of recoverable oil

or the specific analysis of some groups of constitu-

ents, such as alcohols, aldehydes, and ketones, or

unsaturated constituents, is also used. (See Alcohol:

Properties and Determination; Essential Oils: Proper-

ties and Uses.)

Other Minor Constituents

0025Juice color in all citrus fruits is due to carotenoids,

with the exception of blood oranges in which

1338 CITRUS FRUITS/Composition and Characterization

anthocyanins, types of flavonoid compounds, are re-

sponsible for their typical color. b-Carotene is present

in orange juice in concentrations of about 0.5 mg l

1

representing a small but significant source of vitamin

A. Color is one of the principal quality attributes of

citrus juices and several methods, either visual or

instrumental, have been used for its evaluation. The

Hunter colorimeter must be mentioned since it was

specifically developed for citrus fruits. Basically it

determines three parameters: L, a, and b, respectively

related to lightness, green-to-red, and blue-to-yellow

preponderance. (See Colorants (Colourants): Proper-

ties and Determination of Natural Pigments.)

0026 Lipids constitute about 0.07% of orange juice and

consist mainly of fatty acids, 90% of them being

palmitic, palmitoleic, oleic, linoleic, and linolenic

acids. The rest of the lipid fraction includes a range

of both polar and nonpolar compounds. Lipids can be

partially responsible for off-flavor development since,

even though they contribute little to flavor, they are

precursors of malodorous compounds. Independ-

ently, lipids are important for taxonomy because

each different species has its own profile of lipid

components. (See Fatty Acids: Analysis.)

0027Fully methoxylated flavones, belonging to the fla-

vonoid group, are considerably more abundant in the

peel than in the juice, where their concentration in-

creases with extracting pressure. Consequently, these

compounds can be considered as a potential index of

extractor performance. Figure 3 shows chromato-

grams obtained by liquid chromatography of fully

methoxylated flavones of orange and tangerine juices.

0028Vitamins are very important minor constituents of

citrus fruits, and will be discussed in the following

section.

Nutritional Value

0029Although citrus fruits cannot be considered as basic

foods, they are excellent complementary foods to

appropriate diets. During the eighteenth century,

citrus fruits were the only known source of vitamin

C able to prevent scurvy on long sea journeys, but this

was a long time ago. Nevertheless, the contribution to

the diet of vitamins, minerals, and dietary fiber from

citrus fruits is still significant. (See Scurvy.)

789101112

Time (min)

13 14 1615

(a) Orange juice

(b) Tangerine juice

fig0003Figure 3 Liquid chromatogram of fully methoxylated flavones

of (a) orange juice and (b) tangerine juice. 1, Isosinensetin;

2, gossypetin; 3, sinensetin; 4, isoscutellarein; 5, quercetagetin;

6, nobiletin; 7, scutellarein; 8, heptamethoxyflavone; 9, tangere-

tin. Reproduced from Sendra JM, Navarro JL, and Izquierdo L

(1988) C

solid-phase isolation and high-performance liquid

chromatography/ultraviolet diode array determination of fully

methoxylated flavones in citrus juices. Journal of Chromato-

graphic Science 26: 443–448.

tbl0002 Table 2 Composition of the volatile fraction of orange juice

Ty p e s o f

compound

Approximate number of

identified constituents

of thetype

Examples

Alcohols 54 Linalool

a-Terpineol

4-Vinylguaiacol

Citronellol

Nerol

Octanol

Geraniol

Methanol

Ethanol

Aldehydes 41 Acetaldehyde

Hexanal

Citronellal

Geranial

Neral

Ketones 16 Carvone

Nootkatone

Acetone

Esters 39 Ethyl butyrate

Methyl butyrate

Ethyl acetate

Linalyl acetate

Hydrocarbons 51 a-Pinene

Terpinolene

Valencene

Myrcene

Limonene

Acids 10 Acetic

Butyric

Others 12 Ethyl butyl ether

Linalool oxides

Some constituents produce off-flavor.

CITRUS FRUITS/Composition and Characterization 1339

0030 Orange juice is an important source of vitamins.

Composition tables show that it contains (per 100 ml)

about 100 mg thiamin, 30 mg riboflavin, 40 mg vitamin

,20mg vitamin E, 300 mg niacin, 200 mg panto-

thenic acid, 300 mg folacin and 50 mg vitamin C.

Thus, a glass of orange juice covers the daily require-

ments of vitamin C, about 25% of those for folacin,

and 5% for vitamin B

. This contribution to dietary

needs increases in interest if the low energy content of

orange juice (about 50 cal per 100 ml) is considered as

this allows higher consumption of orange juice than

of other foods richer in vitamins (but also in energy).

On the other hand, commercial orange juice needs

less heat treatment for microorganism inactivation

than other less acid foods, so vitamin losses are

lower. Refer to individual vitamins.

0031 Lemon juice contains similar amounts of vitamins

C and B

, but less folacin (100 mg per 100 ml),

whereas tangerine juice is poorer in vitamin C

(30 mg per 100 ml), and grapefruit juice has a lower

content of all these three vitamins.

0032 Concerning minerals, citrus juices are rich in

potassium (150–200 mg l

1

) but low in sodium

(1–2mgl

1

), which makes them very suitable for

people receiving treatment with diuretics.

0033 Finally, cellulose, hemicelluloses, and pectins con-

tained in citrus fruits are a source of dietary fiber, but

which will make only a small contribution to daily

intake for most people. (See Dietary Fiber: Properties

and Sources.)

Authentication

0034 Citrus processing is an important world industry and

some products reach high prices, which may make the

idea of adulteration attractive. Although typical adul-

teration of citrus juices (by dilution, addition of sugar,

blends of juices from different species without declar-

ation) is not harmful to health, the consumer is

paying for a substandard product, and unfair compe-

tition against honest producers is always involved.

(See Adulteration of Foods: Detection.)

0035 The methods for detecting adulteration generally

consist of comparing the values of some selected

characteristics (i.e., constituent concentrations) of

suspicious samples with the known ranges of values

in pure products. The effectiveness of the method will

depend mainly on the success in selecting those char-

acteristics which are specific to the pure product, easy

to determine accurately, and difficult to mask. For a

sound knowledge of the characteristics of pure prod-

ucts, sufficient data, representative of the possible

raw materials, must be collected. Data variability is

usually high due to ripeness, area, or fruit variety.

Consequently, values show wide ranges, which

complicates the detection of adulteration. Mean

values and ranges of several characteristics of Spanish

orange juices are presented in Table 3.

0036Detection methods may be based on the determin-

ation of one, few, or many characteristics. Instrumen-

tal analysis, computers, and statistics are useful in all

cases but essential where multiple data must be

obtained and processed from each sample.

0037Several types of adulteration are possible in citrus

products. The most important will be mentioned and

the methods developed for their detection discussed.

0038Since water, sucrose, and citric acid are the main

constituents of juices and can be obtained from

cheaper sources, an easy type of adulteration consists

of their addition to the juice in proportions that keep

the solid content and acidity at normal juice levels. In

this simple method, the adulteration should be easy

to detect, since concentrations of the remaining con-

tbl0003Table 3 Mean values and ranges of some characteristics of

Spanish orange juices (values in mg l

1

, except for absorbances)

Mean Minimum Maximum

Aspartic acid 165.6 26.9 412.8

Glutamic acid 86.5 18.9 205.8

Asparagine 434.0 113.2 933.4

Glutamine 33.3 5.3 132.1

Serine 124.9 33.4 272.4

Threonine 20.9 8.8 50.0

Glycine 26.8 12.4 57.6

Alanine 89.5 49.7 182.6

Arginine 408.0 88.9 953.2

g-Aminobutyric acid 250.7 83.4 470.4

Proline 1549.0 617.8 3973.0

Valine 14.8 3.4 62.4

Methionine 15.3 1.8 42.2

Ornithine 11.9 3.1 96.8

Lysine 32.8 11.1 62.4

Histidine 8.4 3.0 42.5

Acidity 11 000.0 5090.0 18 400.0

Absorbance at 280 nm 1.46 0.44 3.07

Absorbance at 325 nm 0.960 0.295 2.23

Absorbance at 443 nm 0.131 0.015 0.487

Sucrose 36 920.0 17 900.0 46 300.0

Glucose 20 880.0 13 190.0 29 240.0

Fructose 24 620.0 15 000.0 44 160.0

Potassium 1296.0 562.4 1872.0

Magnesium 98.4 74.6 146.7

Calcium 118.8 62.2 212.0

Ash 3165.0 2100.0 4248.0

Isocitric acid 117.1 40.6 207.2

Isosinensetin 0.129 0.02 0.61

Gossypetin 0.059 0.0 0.22

Sinensetin 1.62 0.07 7.15

Isoscutellarein 0.042 0.0 0.39

Quercetagetin 0.359 0.01 1.77

Nobiletin 2.24 0.0 9.12

Scutellarein 0.569 0.1 2.95

Heptamethoxyflavone 1.01 0.15 4.4

Tangeretin 0.321 0.02 2.81

1340 CITRUS FRUITS/Composition and Characterization

stituents decrease with dilution level. However, these

concentrations can also be manipulated. Detection

methods have increased in complexity by successively

determining minerals, individual sugars, total nitro-

gen, nitrogen from amino acids, specific amino acids,

and so on. Masking procedures also increased in their

complexity by successively adding inorganic salts,

blends of sugars, ammonium salts, glycine, amino

acid blends, and so on. The ideal final situation to

prevent adulteration will be achieved when masking

procedures are either more difficult or more expen-

sive than producing pure products.

0039 The methods mentioned above work on the basis

that all artificially added constituents, even from ex-

ternal sources, are normal constituents of juices. So,

only through the modification of the natural propor-

tions between added and nonadded constituents can

fraud be detected. A different approach is to consider

that raw materials from extraneous sources must

show some differences. For example ratios of carbon

(

C) or oxygen (

O) isotopes can be used

to determine if any sugar or water comes from

sources other than the citrus fruit.

0040 Blends of juices from different species can be

detected through the knowledge of the pattern distri-

bution of certain compounds in each species. A

method of detecting the addition of grapefruit juice

to orange juice consists of analyzing the profiles of

flavanone glycoside concentrations.

0041 Finally, ultraviolet absorption is useful for deter-

mining the addition of pulpwash solids to orange juice.

See also: Acids: Properties and Determination;

Adulteration of Foods: Detection; Alcohol: Properties

and Determination; Amino Acids: Determination;

Carbohydrates: Classification and Properties;

Chromatography: Principles; Thin-layer

Chromatography; High-performance Liquid

Chromatography; Gas Chromatography; Colorants

(Colourants): Properties and Determination of Natural

Pigments; Dietary Fiber: Properties and Sources;

Essential Oils: Properties and Uses; Fatty Acids:

Analysis; Flavor (Flavour) Compounds: Structures and

Characteristics; Fructose; Ripening of Fruit; Scurvy;

Sucrose: Properties and Determination

Further Reading

Feinberg M, Favier JC and Ireland-Ripert J (eds) (1991)

pertoire Ge

neral des Aliments. Table de Composition.

Paris: Institut National de la Recherche Agronomique.

Kawaii S, Tomono Y, Katase E et al. (2001) Quantitative

study of fruit flavonoids in citrus hybrids of King

(C. nobilis) and Mukaku Kishu (C. Kinokuni). Journal

of Agricultural Food Chemistry 49(8): 3982–3986.

Lota ML, de Rocca Serra D, Tomi F, Jacquemond C and

Casanova J (2002) Volatile components of peel and leaf

oils of lemon and lime species. Journal of Agricultural

Food Chemistry 50(4): 796–805.

Nagy S and Attaway J (eds) (1980) Citrus Nutrition and

Quality. Washington, DC: American Chemical Society.

Nagy S, Shaw P and Veldhuis M (eds) (1977) Citrus Science

and Technology. Westport: AVI.

Nagy S, Attaway J and Rhodes M (eds) (1988) Adulteration

of Fruit Juice Beverages. New York: Marcel Dekker.

Sendra JM, Navarro JL and Izquierdo L (1988) C

solid-

phase isolation and high-performance liquid chromatog-

raphy/ultraviolet diode array determination of fully

methoxylated flavones in citrus juices. Journal of Chro-

matographic Science 26: 443–448.

Oranges

S Pao, CREC, Lake Alfred, FL, USA

P J Fellers, Winter Haven, FL, USA

Background

0001Of all the various fruits in the world, the sweet orange

(Citrus sinensis Osbeck) is perhaps the most cher-

ished. The refreshing natural flavor of orange flesh

or juice from mature fruit is characterized as uniquely

pleasing, with just the right mix of sweetness and

tartness. Furthermore, the fruit’s bright sunny color

is especially appealing and often complements other

food items on a dining table. Much effort has been

expended in the attempt to imitate orange flavor and

color.

0002The orange is the most widely grown and popular

citrus species worldwide. Its origin is believed to

be the tropical and subtropical regions of Asia. The

mention of oranges in Chinese literature dates to

2200 bc, long before they were introduced to Europe

– about 1400 ad Continental America probably re-

ceived its first oranges in the early-to-mid 1500s with

the arrival of the explorers Bernal Diaz in Mexico and

Ponce de Leon in Florida. Brazil probably received its

first oranges with the coming of the Portuguese in

the mid-1500s. Oranges entered interstate commerce

in the USA in the early 1800s with the shipping

of fruit, usually in barrels, from coastal Florida locals

to northern cities. Today oranges and orange prod-

ucts are shipped all over the world from areas of

production.

Production and Utilization

0003Oranges are cultivated in both tropical and sub-

tropical regions around the world. The quality of a

CITRUS FRUITS/Oranges 1341

specific variety of fruit produced is largely influenced

by rootstock, climate, types of soil, grove practice,

and harvesting time. Commercial propagation of

citrus is usually accomplished by bud-grafting a de-

sired variety on to a suitable rootstock. Major root-

stocks used in Florida for sweet orange varieties are

Carrizo citrange, sour orange, Swingle citrumelo,

Cleopatra mandarin, Volkameriana lemon, rough

lemon, Milam lemon, and Palestine sweet lime.

Orange varieties with different ripening periods are

often cultivated to extend the availability of fruit

from a particular producing region.

0004 World production of oranges in 1998–99 amounted

to 53 10

t, up 17 10

t from 1988–89. Of all

the countries in the world, Brazil and the USA

produce the lion’s share of oranges (Table 1). Some

lesser-producing countries not listed include Algeria,

Cyprus, Israel, Japan, Lebanon, Tunisia, Uruguay,

Former USSR, and Venezuela. About 58% of

the world’s orange production is consumed fresh.

The USA and Brazil process the bulk of their

crops, while countries like China and Egypt process

very little of their crops. Spain is the world’s

largest exporter of fresh oranges, while Brazil is

the largest exporter of processed orange juice. The

leading orange fruit-importing countries in 1998–99

were Germany (467 10

t), The Netherlands

(424 10

t), and France (423 10

t).

Anatomy and Varieties

0005 A citrus fruit is botanically classified as a type of berry

called a hesperidium that has a thick, leathery rind,

with numerous oil glands, and a large flesh portion

composed of several wedge-shaped sections. Unlike

pome fruit, such as the apple, the citrus fruit is de-

rived from a superior ovary, an ovary completely

separate from the calyx. In general, the development

of citrus fruit does not create a cavity at the blossom

end of the fruit at any maturation stage.

0006Oranges are most often round, in contrast to the

various shapes of many other citrus species. Gener-

ally, grapefruit are larger than oranges, while manda-

rins (especially tangerines), lemons, and limes are

smaller. The major structural features of an orange

from the outside to the center of an equatorial section

are as follows: peel composed of the epidermis (outer

layer of cells); flavedo, a layer of tissue containing

plastids which are dark green when immature, and oil

glands dispersed throughout; albedo, a white pulpy

material surrounding the segments which in turn hold

the individual juice vesicles or juice sacs; and seeds

(if any) arranged around the pulpy core. Each seg-

ment is encased by a rather tough segment membrane

or wall which, along with the juice vesicles, is rup-

tured when the fruit is extracted for the juice.

Examples of seedy orange varieties are Pineapple

and Parson Brown, whereas Hamlin, Washington

navel, and Valencia are examples of seedless or nearly

seedless varieties.

0007Oranges may be classified as sweet or bitter (sour),

the latter having generally little commercial import-

ance for the fruit, but great importance for the use as

a rootstock. Sweet orange varieties are further classi-

fied, as follows: (1) common orange, represented by

many important varieties, including Valencia (per-

haps the major variety worldwide), Hamlin (import-

ant in Florida and Brazil), Pera and Natal (both of

importance in Brazil), Pineapple (important in

Florida), Parson Brown, Shamouti (of importance in

Israel and several other Middle Eastern countries); (2)

sugar or acidless orange, possessing a bland flavor;

(3) blood or pigmented orange, important in the

Mediterranean area of Europe, especially Spain; and

(4) navel orange, especially Washington navel

(of great importance in California). In addition, the

Temple orange, a natural tangor, has economic

significance and is being cultivated in quantity in

Florida.

Composition and Nutritional Value

0008An orange is composed of about 88% water. The

chief soluble solids in orange juice are the soluble

carbohydrates or sugars (c. 10%), while citric acid is

the main soluble solid in lemons and limes. The chief

sugars in orange juice – glucose, fructose, and sucrose

– occur in the approximate ratio of 1:1:2. Total sugars

(especially the sucrose fraction) generally increase

tbl0001 Table 1 Major orange-producing countries and amount

(10

t) exported and processed for 1998–99

Country Production Fresh

Fresh export Fruit processed

Brazil 15912 4162 82 11750

USA 8986 1456 245 7530

Mexico 2903 2543 50 360

China 2724 2595 5 129

Spain 2624 2034 1214 590

Egypt 1442 1340 215 102

Italy 1422 961 75 461

South Africa 989 764 500 225

Morocco 867 789 361 78

Greece 801 584 260 217

Turkey 780 722 102 58

Argentina 660 530 75 130

Australia 524 294 125 230

Cuba 450 110 10 340

As calculated from production amount less the amount of fruit processed.

From Food and Agriculture Organization of the United Nations (2000) Citrus

Fruit, Fresh and Processed. Annual Statistics.

1342 CITRUS FRUITS/Oranges

with advancing maturity, and the stylar half of the

fruit possesses more than the stem half.

0009 Fresh oranges and grapefruit contain dietary fiber,

being mostly soluble fibers such as pectic substances.

Fiber aids in digestion and elimination, and when part

of a low-fat diet rich in fruits and vegetables, the fiber

therein may help reduce the risk of some cancers.

Also, low-fat diets rich in fruits and vegetables con-

taining soluble fiber may reduce the risk of heart

disease. Pectin or pectic substances, made up of com-

plex carbohydrate derivatives or polysaccharides, are

important in terms of juice quality for imparting body

or viscosity and the cloudy appearance. Pectic sub-

stances are a major component of primary cell wall

and middle lamella in all fruit. In the orange, up to

30% of the albedo, on a dry-weight basis, may be

pectin, but only 0.01–0.13% occurs in the juice.

Without heat stabilization to inactivate pectinesterase

enzyme, clarification or loss of cloud may occur in

single-strength orange juice due to the settling out of

pectins and other solids, while in concentrate a pectin

gel may form, resulting in a nonpourable product.

The pectinesterase in orange fruit is mainly associated

with fruit peel, rag, and juice sac tissue (pulp). It is

introduced to the juice from the ruptured cell mem-

brane or wall tissue during the extraction process. In

addition to pectinesterase, numerous other enzymes

have been identified, including 18 oxidoreductases,

nine lyases, nine transferases, seven hydrolases, three

isomerases, and three ligases.

0010 The acidity of orange juice is due primarily to the

organic acid, citric acid and, to a much lesser extent,

malic and succinic acids. Orange juice with about

0.5–1.0% acid (pH of about 3.5) is less acidic than

that of grapefruit, and much less acidic than lemon

and lime. Perhaps more so than any other quality

factor, it is the favorable ratio of sugar to acid

(sweetness to tartness), along with the unique

orange flavor, that gives orange juice its universal

high consumer acceptance. Orange flesh and orange

juice are excellent sources of ascorbic acid (vitamin

C). One medium-sized orange (about 154 g) may

provide 120% of required daily vitamin C value.

Vitamin C is an important antioxidant and scien-

tists now believe that antioxidants may counteract

harmful free radicals, which may contribute to the

onset of several major diseases. Folate (folate acid), a

B-vitamin commonly found in orange juice and green

leafy vegetables, has been shown to help in the pro-

duction of mature red blood cells. Recent research

shows that women of child-bearing age can reduce

the risk of having babies with birth defects of the

brain and spine by consuming ample quantities of

fruits and vegetables to maintain adequate levels of

folate.

0011About 70% of the nitrogen in citrus juices occurs in

free amino acids which constitute about 0.1% (w/w)

in oranges. Proline is the major amino acid with less

quantities of asparagine, aspartic acid, arginine, and

gamma-aminobutyric acid.

0012The most abundant mineral in orange juice is po-

tassium, with other minerals of significant quantity

being calcium, iron, magnesium, phosphorus, and

sulfur. Other elements of note are chlorine and nitro-

gen. Orange flesh and orange juice are considered to

be excellent sources of potassium which is necessary

to maintain fluid balance in the body, maintain cell

strength and structure, and aid in nerve transmission.

0013Limonin, a triterpene derivative, because of its

bitter nature, is an important constituent in certain

citrus fruits, such as navel orange and grapefruit.

When the juice of navel oranges is extracted, an

undesirable bitter taste develops in the juice after a

period of time. This is a problem of great significance

in several large citrus-producing areas around the

world, unless a debittering treatment is used. Limonin

exists in the major sweet orange varieties (Hamlin,

Pineapple, and Valencia) but generally in low enough

levels not to produce significant bitterness problems.

0014Most of the lipid content of oranges occurs as fatty

acids, with most being in the seeds. The five major

fatty acids are palmitic, palmitoleic, oleic, linoleic,

and linolenic. Phosphatidylcholine and phosphatidyl-

ethanolamine comprise the bulk of the phospholipid

fraction of Florida and Calfornia orange juice.

Orange essential oils are found primarily in the peel,

with significantly less in the juice vesicles. One study

shows that the amount of oil in fruit ranged from a

low 0.29% in Hamlins to a high of 0.94% in Valen-

cias. Orange oil contains at least 150 volatile essential

oil components. Of these, d-limonene is most abun-

dant, comprising about 95% by weight of orange oil,

but it is the oxygenated aldehydes and esters that are

considered the most important contributors to orange

flavor. Many oxygenated alcohols are present in

orange oil but not ketones. Coumarins and flavonoids

comprise most of the 1% of the nonvolatile constitu-

ents in orange oil. Generall, total yield of orange oil

decreases with increasing maturity.

0015An unusually large number and quantity of flavo-

noids, C

compounds, occur in citrus. Compounds

have been identified in oranges representing the three

major flavonoid types: (1) flavanones (including flava-

nonols) generally occurring as glycosides in oranges,

(2) flavones (including flavonols), and (3) anthocya-

nins, of importance in citrus only as red pigments in

blood oranges.

0016The orange color in peel generally associated with

mature fruit is due primarily to carotenoids, chiefly

b-citraurin, while the green peel color generally

CITRUS FRUITS/Oranges 1343

associated with immature oranges is due to chloro-

phyl. The main pigment in orange juice producing the

orange color is the carotenoid, b-crytoxanthin.

Harvesting and Packinghouse Procedures

0017 Oranges, like most other nonclimacteric fruits, do not

continue to ripen after separation from the trees.

Therefore, the fruit are picked only after they have

reached maturity. In most citrus-producing areas, ma-

turity standards must be met prior to the fruit being

utilized in the fresh or processed markets. In the USA,

the US Department of Agriculture and various state

agencies develop and oversee the maturity standards.

Internal standards generally consider a minimum

ratio of Brix to percentage of acid (below which the

juice will taste too acidic or tart), total soluble solids,

total acid, and juice content. External grade stand-

ards include skin color, texture, discoloration and

blemishes, fruit form, and firmness.

0018 Harvesting is accomplished primarily by hand, and

the fruit is placed in a picking bag or other container.

A considerable effort has been expended on develop-

ing mechanical harvesting methods, especially with

fruit that is destined for processing. In the 1999–2000

season, an estimated 6500 acres of oranges were

mechanically harvested in Florida. The harvesting

systems varied from those which could shake fruit

to the ground from the oldest and tallest trees (*10

trees per hour) to those which could be continuously

shaken with fruit caught on smaller uniformly spaced

and skirted trees (*500 trees per hour). In most of

the heavy citrus-producing areas, oranges harvested

for fresh market are placed in pallet boxes (a standard

pallet box in Florida holds 408.2 kg or 900 lb of

oranges) for transport to the packinghouses. Other-

wise, fruit may be loaded on to semitrailer trucks for

bulk transport to the processing plants.

0019 Most fresh oranges are marketed in the USA in

fiberboard boxes holding 14.5–19.0 kg (32.0–41.9 lb)

net weight of fruit. Preparation of oranges for market

may include degreening, washing, applying fungi-

cides, grading, waxing, and sizing. These procedures

are usually performed in a citrus packinghouse near

the groves. Figure 1 is a common process flowchart

for a citrus packinghouse.

0020 Some early-season oranges such as Hamlins and

Washington navels are mature internally but may

still be greenish or patchy green externally. Consumers

generally believe greenish fruit to be immature, thus it

is desirable to degreen the fruit. Degreening may be

accomplished through use of either ethylene, or color

enhancement utilizing a dye or a combination of

the two treatments. In Florida, degreening with ethyl-

ene gas, a natural plant hormone, is generally at

1–5 p.p.m. in a room maintained for 36 h or less

between 29 and 30



C, 90–96% relative humidity,

and having at least one change of air per hour. Use

of much longer holding periods such as 72 or 96 h is

not uncommon at times. Degreening procedures vary

with citrus growing area, cultivar, fruit condition, etc.

Color enhancement of the peel may be used in certain

cases. In Florida, for example, for degreened (or nat-

urally pale) oranges, temples and tangelos having a

final yellow appearance, these fruit, under govern-

ment supervision, may be flooded in a tank contain-

ing Citrus Red no. 2 for orange color enhancement,

with 2 p.p.m. residue being allowed following

rinsing. California and many other countries do not

allow coloring of citrus.

0021Fruit may be treated with fungicides to control

postharvest decay. Important postharvest fungal

diseases are stem-end rot caused by Diplodia natalen-

sis or Phomopsis citri, green mold caused by Penicil-

lium digitatum, and sour rot caused by Geotrichum

candidum. Fungicides, each with its own mode of

application, used to control decay include sodium

ortho-phenlyphenate (SOPP), thiabendazole (TBZ),

and imazalil. Oranges to be exported from the USA

to other citrus-producing areas are either fumigated

with methyl bromide or subjected to cold treatment at

1.1



C for 17 days to rid the fruit of potentially harm-

ful fruit fly larvae and eggs.

0022In the washing operation, natural waxes are lost

and rind permeability is increased, allowing moisture

loss, and a decrease in sugar content, flavor, texture,

quality, and ascorbic acid. Waxing of fruit tends to

minimize the negative side-effects of washing plus

enhancing the appearance of the rind and, in some

Fruit unloading and destemming

Initial grading and sampling

Waxing and drying

Grading and sizing

Labeling and packing

Storage and shipping

Washing and fungicide application

fig0001Figure 1 Common process flowchart for a citrus packinghouse.

1344 CITRUS FRUITS/Oranges

cases, provides a vehicle for antimicrobial agents.

There are numerous formulations of waxes and wax-

like materials available for application on oranges,

but the most commonly used are water waxes, either

emulsion-based or as a resin solution. During storage,

waxes on fruit may cause the reduction of fruit

internal oxygen levels, and increase internal carbon

dioxide and ethanol levels. Recent studies show that

the shellac-based waxes which give high surface shine

are not the optimal choice for extended cold storage

of oranges due to their relatively poor control of

water loss and their low gas permeability that lead

to off-flavor development within 5–10 weeks of stor-

age. Polyethylene- and carnauba-based waxes, on the

other hand, may provide better weight loss control,

allow sufficient gas exchange, and maintain good in-

ternal quality under the extended storage conditions.

0023 Storing citrus in the refrigerator keeps it better-

tasting, better-looking, and firmer than citrus stored

at room temperature. Cold storage of oranges

at 0–1



C for Florida fruit, and 3–9



C for California

fruit, will generally provide several weeks of

marketability; otherwise, fruit held at room tempera-

ture has a significantly shorter shelf-life. Controlled-

atmosphere storage, using increased carbon dioxide

and decreased oxygen at cool temperature, does not

work for extending the shelf-life of citrus fruit.

Fresh and Minimally Processed Citrus

Products

0024 ‘Fresh’ or ‘fresh-squeezed’ citrus juice is pure juice

obtained from mature citrus fruit and has not been

further pasteurized, frozen, or concentrated after

extraction. It is valued by many consumers for its

superior natural taste and fresh quality. Although

less processing is involved within its production, it is

generally marketed at higher prices than pasteurized

juice. Commercially, fresh orange juice is mechanic-

ally extracted from graded and washed fruit, and is

commonly distributed for the retail market once

packaged and refrigerated. Both chemical and ther-

mal antimicrobial treatments may be applied to fruit

surfaces prior to juice extraction to achieve a desired

decontamination. In the USA, federal regulations also

mandate the application of Hazard Analysis and Crit-

ical Control Point (HACCP) principles for the safe

and sanitary processing of juices. Mechanical juice

extractors that are designed to separate the juice

from the fruit peel, seeds, and large pieces of pulp

simultaneously are commonly utilized in the fresh

juice industry. Small-scale extractors squeeze one

fruit at a time and are often favored by local retailers.

They are portable, simple to clean, and specially

designed to attract the attention of shoppers in store

or roadside operations. At juice-processing plants,

largescale extractors are used. These machines have

the capacity to extract hundreds of fruit per minute.

Many of these extractors are adjustable with different

types of cutters and strainer tubes to accommodate

fruit of various sizes, and allow desired amounts of oil

and pulp to pass into the juice. Good mechanical

extraction of oranges yields about 45–55% juice by

weight. Juice-blending programs are used by some

processors following extraction. The program often

extends the season by mixing juice from two or more

varieties of available fruit to enhance nonblended

juice color and/or taste. After processing, juice is

packed and marketed at 0–4



C. Freshly squeezed

orange juice packed in plastic containers and held at

1to4



C loses somewhat less than 1% ascorbic acid

per day. The loss of ascorbic acid in the juice of whole

oranges during the normal marketing life is expected

to be less than 10%. (See Hazard Analysis Critical

Control Point.)

0025‘Fresh-cut produce’ is an established food category

that incorporates old and new processing techniques

to prepare fresh, convenient, ready-to-eat products.

Although the laborious task of removing citrus peel

for personal consumption has been reduced by peelers

such as modified knives and scoops, a growing seg-

ment of consumers desire no preparation. Thus, pre-

paring citrus fruit to ready-to-eat forms would

encourage fruit consumption at more dining occa-

sions and by greater numbers of consumers. Both

hand and mechanical peeling methods have been

used in commercial preparation of citrus products

for retail and food service outlets. The traditional

peeling processes are often facilitated by steam treat-

ment to loosen the peel and/or chemical digestion

to remove peel remnants. High-temperature treat-

ments and caustic chemicals damage the fruit and

render it unsuitable for the fresh market. The

resulting product is one that is chemically preserved,

canned, or frozen before consumption. Citrus fruit

may also be mechanically peeled with knives without

steam or chemical treatment, but wastage is typically

high and juice vesicle damage is often excessive.

Recent efforts have been focused on minimizing

damage due to peeling to maintain the integrity of

fruit during storage. It has been found that the re-

moval of citrus peel may be facilitated by vacuum or

pressure infusion of an enzyme mixture (consisting of

pectinase and/or pectinase and cellulase) or water

into the peel. The fluids digest or solubilize the

pectin-rich albedo tissue of the peel, and thus, the

peel is loosened from the flesh. The peel may then be

manually or mechanically removed, and the flesh may

be packaged intact or cut into sections for marketing

and consumption.

CITRUS FRUITS/Oranges 1345