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PAPAYAS

J H Moy, University of Hawaii at Manoa, Honolulu,

USA

Introduction

0001 Papaya, a mildly sweet, melon-like tropical fruit

belonging to the family Caricacae, is a native of

tropical America (Central America and the Carib-

bean, including Mexico, Costa Rica, and the Baha-

mas). After the Spaniards took the fruit to Luzon

Island in the Philippines in the mid sixteenth century,

it reached Malacca shortly afterward, and then India.

It has been widely grown throughout tropical and

subtropical regions such as Australia; Hawaii, Flor-

ida, Texas, California, and Puerto Rico in the USA;

Peru; Venezuela; various parts of Central and South

Africa; and Bangladesh, Pakistan, and India. The

Australians call it ‘pawpaw’ while the Venezuelans

call it ‘lechosa.’

0002 Fruit size may vary from less than 0.5 kg to 3 kg. A

climacteric fruit, it is mainly consumed fresh when

ripened after harvest. Ripening is judged by the ap-

proximate percentage of yellowness on its skin, and

more accurately by measuring its total soluble solids

(TSS) contents with a refractometer. Export-grade

papayas grown in Hawaii should have a minimum

of 11.5% TSS. Firmness, as gaged by touch or by a

texture-measuring device, is another way of judging

ripening. The firmness is related to the biochemical

changes in three fractions of pectins in papayas, and is

not a very accurate index of ripeness. Green papayas

can also be consumed as a salad or in soups, both of

which are quite popular in South-east Asia.

0003 Hawaii, part of the USA, is the world’s largest

exporter of papayas, with about 16 000 t in 1999,

valued at US$14.15 million. Most of the outship-

ments are to the US mainland, with about 25%

going to Japan. Brazil is the second largest exporter,

with most papayas going to European countries such

as Germany, France, and the UK. Kenya, the Ivory

Coast, and Malaysia also ship papayas to European

markets. For recent shipment statistics, (See Fruits

of Tropical Climates: Commercial and Dietary Im-

portance.)

Species and Cultivars

0004Papaya belongs to the family Caricaceae – a small,

somewhat anomalous family with four genera and 31

species, of which three are in tropical and subtropical

America and one in Africa. The genera and the

number of included species are: Carica, 22; Facaratia,

6; Farilla,1;andCylicomorpha, 2. The edible fruits

are found only in Carica, of which C. papaya, the

common papaya, is extensively grown. Other species

include: C. chilensis, C. goudotiana, C. monoica, and

C. pubesceus. C. candamarcensis, known as moun-

tain papaya, grows to a height of about 2.5 m, toler-

ates low temperature, and thrives well at an elevation

between 1500 and 2000 m. C. monoica grows in the

Amazon basin.

0005A large number of papaya cultivars are grown in

different parts of the tropical and subtropical regions.

However, none are true cultivars because they do not

reliably transmit the parental characters to all their

progeny. Some of the better known cultivars are listed

below, with their average weight in kg in parentheses:

0006Washington (0.9–1.0)

0007Honey dew (1.1–1.5)

0008Coimbatore 1 (1.2–1.5) – a selection from the

progenies of cv. Ranchi

0009Coimbatore 2 (1.0–1.5) – a high papain-yielding

cultivar

0010Coimbatore 3 (0.9–1.0) – a hybrid between Co. 2

and Sunrise Solo

0011Coimbatore 4 (1.3–1.5) – a cross between Co.

1 and Washington (The coimbatore cultivars

were released from the Tamil Nadu Agricultural

University, Coimbatore.)

0012Pusa Delicious (1.0)

0013Pusa Majesty (0.95)

0014Pusa Giant (1.9)

10.

0015Pusa Dwarf (1.0) (The pusa cultivars were bred

at the India Agricultural Research Institute

Regional Station, Pusa, Bihar.)

11.

0016Sunrise Solo (0.4–1.0) – red-fleshed

12.

0017Sunset Solo (0.4–1.0) – red-fleshed

13.

0018SunUp (0.4–1.0) – a genetically transformed

sunset, red-fleshed

14.

0019Kapoho Solo (0.5–1.4) – yellow-fleshed

PAPAYAS 4345

15.0020 Waimanalo Solo (0.5–1.4) – yellow-fleshed

16.

0021 Rainbow (0.5–1.4) – a transgenic cross between

Kapoho and SunUp, yellow-fleshed (The two

transgenic cultivars have been grown on the

island of Hawaii since 1998)

17.

0022 Pink-Fleshed Sweet (0.85)

18.

0023 Thailand (1.9–2.2)

0024 Other important cultivars are: Guinea Gold, Sun-

nybank, and Hybrid 5 (Australia); Hortus Gold and

Honey Gold (South Africa); Tai Ning No. 2, Panama

red and Solo No. 1 (Taiwan); Red Rock and Cariflora

(Florida, USA); Red Fleshed, (Philippines); Madhu-

bindu, Barwani, Ranchi, and Peradeniya (India).

Botany and Horticulture

0025 Papaya is a herbaceous, unbranched plant. Its stem is

supported by phloem fibers encircling a hollow stem,

which can grow up to 8–10 m high. Its leaves are

large, deeply lobe-shaped with long hollow petioles,

and spirally crown the stem. Flowers, male and

female, can be on the same plant (monoecious) or

on separate plants (dioecious), or as male and female

parts on the same flower (hermaphrodite).

0026 Papaya fruits are mostly round in the female tree

and cylindrical and pear-shaped in the hermaphrodite

tree. Underneath the smooth, thin skin (green when

immature, orange-yellow when ripe) is a thick layer

of deep yellow to orange-red pericarp with an ellip-

tical, central cavity containing many small, round

black seeds coated with jelly-like tissues (Figures

1 and 2).

Planting

0027 The three major environmental factors to consider in

selecting a site to grow papayas are temperature,

moisture (rainfall and soil drainage), and wind. The

hermaphrodite papaya plant preferred for commer-

cial orchards is more sensitive to its growing environ-

ment than the female papaya plant. Selection of a

suitable site is therefore critical. Another condition

to consider is the amount of sunlight the site receives

to support plant growth and fruit production. Insuffi-

cient sunlight results in fruits with inadequate sugar

and low yields, and encourages plant diseases that

affect papaya production.

0028The temperature of the site is the most important

factor. Optimal production is generally limited to

elevation under 160 m within a temperature range of

16–31



C. Temperature below 16



C could cause car-

peloidy, resulting in ‘cat-face’ deformity when floral

stamens develop abnormally into fleshy, carpel-like

structures. High temperature (32–35



C) may induce

female sterility, in which normally hermaphroditic

papaya plants produce male flowers, resulting in

poor fruit set and production.

0029A minimum monthly rainfall of 10 cm and an aver-

age relative humidity of 66% are considered ideal for

papaya growth and production. Drip irrigation can

supplement low rainfall. Good soil drainage is also

essential. When soil drainage is restricted, papaya is

susceptible to fungal root diseases. The plants are

severely affected by waterlogging and can be killed

when subjected to puddled conditions for even a few

hours. The Puna area on the island of Hawaii is well-

suited to commercial papaya production because of

the very porous lava soils.

0030Papaya plants must be protected from wind. Plants

exposed to constant wind develop deformed, crinkled

leaves. When wind stress damage is excessive, the

plant growth, fruit set, fruit quality, and productivity

will be reduced. Wind-blown dust can cause sap

bleeding that harms fruit appearance. In coastal

fig0001 Figure 1 (see color plate 119) Rainbow cultivar growing in

Hawaii, weighing 0.66 kg.

fig0002Figure 2 (see color plate 120) Thailand cultivar growing in

Thailand, weighing 2.50 kg.

4346 PAPAYAS

areas, salt spray carried by wind can desiccate leaves

and kill papaya plants. Winds of 64 km h

1

can

uproot papaya trees growing in mineral soils, espe-

cially when accompanied by heavy rain. Windbreaks

should be established well in advance of planting a

papaya crop. On the other hand, adequate air move-

ment is important in reducing incidence of fungal

diseases such as phytophthora and anthracnose.

These diseases can become severe when there is

excessive free moisture and high humidity around

the plant.

0031 Papaya can either be seeded directly or trans-

planted into a new field. Direct seeding can be prac-

ticed in porous soil. Six-week-old seedlings can be

transplanted into less porous fields. Planting in

‘virgin’ lands or fields in which papaya has not been

grown before is preferred because of low disease and

insect pressure. However, it is becoming increasingly

difficult to find such fields. Other important horticul-

tural aspects of planting papaya are plant sex selec-

tion, thinning, fertilizer applications, leaf trimming,

weed control, pest management, and disease control.

Transgenic Cultivars

0032 For more than four decades, papaya production in the

Hawaiian island chain was severely affected by the

papaya ringspot virus (PRV). In the 1960s, papaya

planting was forced to move from the island of Oahu

to the Puna area of the island of Hawaii. Since 1992,

the introduction and subsequent spread of PRV in

commercial orchards in Puna has resulted in a signifi-

cant decrease in papaya production in the state of

Hawaii.

0033 The only solution seemed to be to produce a trans-

genic cultivar that would be resistant to the virus.

Faced with this extremely challenging task, molecular

biologists from Cornell University, the University of

Hawaii, and the Upjoin Company collaborated from

1987 to 1991 to obtain the first transformed plant

that appeared to have PRV resistance. It took several

more years for plant breeders at the University of

Hawaii to inbreed the resistant plant to produce a

tree-breeding, redfleshed cultivar that was named

UH sunup (also referred to as SunUp). Because the

papaya industry wanted a yellow-fleshed fruit, plant

breeder Richard Manshardt crossed SunUp with

Kapoho to produce a yellow-fleshed F

hybrid that

was named UH Rainbow (also called Rainbow).

0034 SunUp is totally resistant to the virus, but Rain-

bow, in greenhouse studies, has shown susceptibility

to PRV until about 7 weeks of age. This is referred to

as young plant susceptibility. The plants become fully

resistant to PRV after 3 months of age. The hybrid

Rainbow has some differences from the Kapoho: (1) a

lower sex-segregation ratio; (2) plants grown from

seeds of F

hybrids do not breed true; (3) a higher

sensitivity to calcium deficiency; (4) more sensitive to

phythophthora and will require timely application of

fungicides; and (5) ripens faster than Kapoho but

slower than Sunrise fruits.

0035These two lines of transgenic cultivars have been

rigorously reviewed and approved by three US agen-

cies: the US Department of Agriculture (USDA), the

Environmental Protection Agency (EPA), and the

Food and Drug Administration (FDA). The USDA

determined that these new plants would not contam-

inate other existing germ plasma, and they would not

foster a new strain of virus. The USDA concluded,

therefore, that they posed no hazards to agriculture in

the USA. The EPA sets tolerance limits for regulated

chemicals. The coat protein used in the genetic engin-

eering process was considered a pesticide, to be regu-

lated because its function is to eliminate diseases. The

EPA subsequently agreed with University of Hawaii

scientists that there was no tolerance required for coat

protein. The FDA’s job is to protect the public from

unsafe products. The FDA was satisfied that the nu-

trients of the original material (fruit) were retained,

and therefore did not require a toxicity test. All three

agencies declared the two transgenic cultivars safe for

human consumption.

0036Those wishing to purchase seeds of transgenic

papaya cultivars must adhere to a licensing process

as well as sign a sublicense agreement with the Papaya

Administrative Committee in the state of Hawaii.

Nutrient Composition and Fruit Chemistry

Nutrient Composition

0037The papaya fruit is a good source of ascorbic acid

(vitamin C) and carotenoids (provitamin A), two

important nutrients for people in the subtropical

and tropical regions. Table 1 shows the nutrient com-

position of papaya from data published in 1965,

1990, and 1999.

Chemistry and Biochemistry

0038Sugars are the principal carbohydrates in papayas,

with very little starch. Refractometric measurements

of total soluble solids (%TSS) show some differences

in various cultivars. Those grown in Florida have

been reported to range from 5.6 to 7.2%; those in

India vary from 6.5 to 13%, while the Hawaiian

cultivars measure 11.5–13.5%. The sugars in ripe

papayas in which the invertase has been inactivated

were reported to be 48% sucrose, 30% glucose, and

22% fructose.

0039Papaya is a low-acid fruit, with the total titratable

acidity of about 0.1% calculated as citric acid. The

PAPAYAS 4347

pH of the pulp ranges from 5.5 to 5.9, far higher than

the pHs of other tropical fruits at 3.2–4.5, which

explains the low tartness of the papaya fruit. The

organic acids in papayas are mainly equal amounts

of malic and citric acid, with smaller amounts of

ascorbic and a-ketoglutaric acid.

0040 The volatile flavors of papayas were reported to

consist of 124 compounds. Linalool is the major

component with characteristic fresh papaya aroma

and flavor. Benzyl isothiocyanate, another major

component, has a pungent off-aroma. Other off-

aroma, off-flavor compounds in papaya pulp have

been identified as butyric, hexanoic, and octanoic

acids and their corresponding methyl esters. These

components were analyzed with gas chromatography

and mass spectrometry. (See Chromatography: Gas

Chromatography; Flavor (Flavour) Compounds:

Structures and Characteristics; Mass Spectrometry:

Principles and Instrumentation.)

0041 Carotenoids are the pigments of the ripe papaya

flesh, which is deep yellow. Red-fleshed papaya culti-

vars additionally contain lycopene, which gives the

pulp an orange-red color. (See Colorants (Colourants):

Properties and Determination of Natural Pigments.)

0042 In addition to papain being an economically

important enzyme in green papaya, several other

enzymes play a role in the stability and quality of

processed papaya products. Pectinesterase (3.1.1.11),

the enzyme responsible for gel formation in unheated

papaya pure

e, contributes to some increase in acidity

in pure

e as a result of demethoxylation of the carb-

oxyl groups in the pectins. Thioglucosidase (myrosi-

nase) (3.2.3.1) is responsible for generating benzyl

isothiocyanate, a sulfurous, pungent, odiferous com-

pound which contributes to the off-aroma of papaya

products. When fruit tissues are macerated, acid

phosphatase (3.1.3.2) catalyzes the hydrolysis of the

P–O bond of orthophosphoric monoesters, producing

ROH and phosphoric acid, which increases the acid-

ity of the pure

e. Another enzyme, b-fructofuranosi-

dase (invertase) (3.2.1.26), is responsible for the

hydrolysis of sucrose to fructose and glucose.

Harvesting, Handling, and Storage

0043Summer fruits become mature in 22 weeks, while 26

weeks are needed during the winter. Fruits are typic-

ally harvested weekly or twice weekly at color-break

(a tinge of yellowness on a green fruit) by hand, or

with the aid of a cut-off ‘plumber’s helper’ (a rubber

suction cup) attached to a pole for hard-to-reach

fruits. Fruits can also be harvested with a ladder, or

from a large fruit bin mounted on a tractor high-lift.

Careful handling with minimal bruising and abrasion

helps with postharvest sorting, packing, shipping,

and marketing.

0044To control fungal decay of postharvested fruit, a

dip in hot water at 49



C for 20 min was found to be

very effective. Hot-water spray with fungicide or a

wax dip containing fungicide is also effective.

0045Storing papayas at temperatures below 7



C after

harvest can result in chill injury. The recommended

storage temperature is 10



Quarantine Treatment

0046Fruit flies and other insect pests are prevalent in the

tropics and the subtropics. Most soft tropical fruits

are prone to infestation by fruit flies. A quarantine

treatment approved by the plant quarantine authority

of each country must be applied to fruits before they

can be exported to noninfested areas. Up until 1984,

chemical fumigants such as ethylene dibromide (EDB)

were widely used, until tests showed them to be car-

cinogenic to laboratory animals. Since then, quaran-

tine treatment options are thermal or cold treatment,

or irradiation.

0047Papayas grown in Hawaii are infested with four

species of fruit flies: the Oriental fruit fly (Dacus

dorsalis), the Mediterranean fruit fly (Ceratitis capi-

tata), the melon fly (Dacus cucurbitae), and the Ma-

laysian fruit fly (Bactrocera latifrons). After EDB was

banned, a double-dip hot-water treatment (42



C for

tbl0001 Table 1 Nutrient composition of papaya per 100 g of edible pulp

Moisture (%) 86–89

Carbohydrate (g) 9.5–12.2

Protein (N 6.25: g) 0.36–0.5

Fat (g) 0.06–0.1

Fiber (g) 0.5–0.6

Ash (g) 0.5–0.6

Ascorbic acid (mg) 40–84

Vitamin A (mg) 11–32

Thiamin (mg) 0.027–0.04

Riboflavin (mg) 0.043–0.25

Niacin (mg) 0.20–0.33

Calcium (mg) 10–30

Phosphorus (mg) 10–12

Iron (mg) 0.2–4.0

Energy (cal) 40–48

Vitamin A data assuming 12 mgofall-trans b-carotone ¼ 1 mg all-trans

retinol.

Sources of data: Wenkam NS and Miller: CD (1965) Composition of Hawaii

Fruits. Bulletin 135. Honolulus, Hawaii: Hawaii Agricultural Experiment

Station, University of Hawaii at Manoa; Muthukrishnan CR and Irulappan I

(1990) In: Bose TK and Mitra SK (eds) Fruits: Tropical and Subtropical, pp.

303–335. Calcutta: Naya Prokash. Moy JH, Paull RE, Bian X, Chung R and

Wong L (1999) Quality of tropical fruits irradiated as a quarantine

treatment. In: Moy JH and Wong L (eds). Proceedings of the workshop on the

use of Irradiation as a Quarantine Treatment of Food and Agricultural

Commodities pp. 45–53. Honolulu, Hawaii: College of Tropical Agriculture

and Human Resources, University of Hawaii and Dept of Hawaii, State of

Hawaii.

4348 PAPAYAS

30 min, 49



C for 20 min) was used but was aban-

doned after 3 years because a high percentage of

treated fruits became injured by the heat. Subse-

quently, two other thermal treatments were used.

One is a modified vapor heat treatment, and the

other is called a high-temperature forced-air (HTFA)

procedure. Both are very similar. The difference is the

relative humidity of the heated air admitted to the

treatment chambers. The air in the vapor heat treat-

ment has moisture added to the air throughout, with

the relative humidity kept at 90% or above. In the

HTFA method, ambient air is heated and admitted

into the chamber, and only in the last hour of a 4-h

treatment is the relative humidity required to be kept

at 90–100%. Both methods require about 4 h to reach

the endpoint, which is when the center of the fruit

reaches 47.2



C. Fruits are then cooled with a water

spray for about 30 min. Several fruit packers in

Hawaii are using these methods, which work quite

well. However, both are time-consuming and com-

modity-specific. Total uniformity in heating is also

difficult to achieve because of variation in fruit size,

fruit ripeness (affecting thermal conductivity and heat

transfer rates), and physical locations within a cham-

ber. After heat treatment, it is common to find lumpy

texture and lack of flavor in a few percent of the heat-

treated fruits in each batch, caused by enzymes

responsible for ripening being inactivated by heat.

0048 Cold treatment requires that fruits be kept at 1 or



C for 12–14 days to immobilize and inactivate fruit

fly eggs and larvae before the fruits can be taken to

the supermarkets. Not many tropical fruits can toler-

ate this time–temperature regime, papaya being one

of them.

0049 Though somewhat controversial, several decades

of research in Hawaii and in other parts of the

world have proven that irradiation is the most effica-

cious quarantine treatment procedure. The treatment

is efficient (15–20 min in a commercial irradiator)

and effective (all fruits are thoroughly irradiated to

cause the fruit fly eggs and larvae to be sexually

sterilized, regardless of fruit size and ripeness). Irradi-

ated papayas ripen normally or slightly delayed,

and their chemical, physical, nutrient, and sensory

qualities are well retained. Radiation sources can be

gamma-rays (from cobalt-60), an electron beam (with

limited penetration), or X-rays (converted from

e-beam). Fruits irradiated will not become radioactive

because there is a limit on the energy level used. In

April 1995, Hawaii became the first place in the world

to use irradiation as a quarantine treatment of its

papayas and other tropical fruits. The generic quar-

antine dose approved by the USDA is 0.25 kGy.

Starting in 2001, more countries will be using this

technology to treat their fruits for export markets.

Processed Products

Chunks (Refrigerated or Frozen)

0050After being washed, deseeded, and peeled, papayas

can be cut into chunks, then refrigerated or frozen as

a convenient food. It is available in some super-

markets in the salad section. Another niche market

for this type of product is the airlines. A number of

airlines prefer the convenience of serving these pre-

pared fruits to their passengers. The frozen chunks

are more suitable for serving with ice cream or for

further manufacturing into dessert products.

Canned (Mixed with Other Fruits)

0051Papaya can be made into a canned product, or as a

cocktail of several fruits. Chunks or dices of papayas

or mixed fruits can be filled into a can and covered

with hot (75



C), acidified syrup (c.40



Brix with pH

adjusted to 3.6–3.8 with citric acid: 40



Brix ¼40 g of

sugar mixed with 60 g of water at 20



C). After the air

in the head space in the cans (c. 6.3–8.0 mm) has been

exhausted by steam, the cans are sealed and pasteur-

ized with steam, or in a boiling-water bath. (See

Canning: Principles.)

Pure

0052Papaya pure

e is prepared in the form of a free-flowing

paste, without seeds, skin, or unwanted fiber. The

pure

e can be an intermediate product used for manu-

facturing several end products such as juices, nectars,

jams, jellies, syrups, and dried fruit rolls or leathers.

Papaya pure

e and other fruit pure

es in the USA can be

manufactured with a high degree of mechanization.

Several aspects of pure

e manufacturing are important

to produce a quality product.

0053Ripe papaya fruits should be steamed for 2 min to

coagulate the latex in the peel, preventing the latex

from entering into the pure

e. Also, steaming

increases pure

e yield by softening the outer layers

of the fruit, and inactivates enzymes in the peel.

The fruits are spray-cooled to remove the re-

sidual heat.

0054Fruits are sliced, crushed, and dropped into a

centrifugal separator. All the skin and most of

the seeds are separated. The remaining seeds

are separated in a paddle pulper fitted with

rubber paddles and a small screen (c. 0.80–

0.85 mm).

0055The pure

e is acidified with citric acid (a 50%

solution) to a pH of about 3.4–3.6 to inhibit

gelatin of the pure

e. Acidification also helps con-

trol microbial activity and enhances the effect of

subsequent heat pasteurization.

PAPAYAS 4349

4.0056 A smooth pure

e can be obtained by passing the

liquid through a paddle finisher with a 0.50 mm

screen to remove seed specks and undesirable

fiber.

0057 The pure

e is pasteurized in a heat exchanger at



C for 2 min, then cooled to a few degrees

above ambient temperature.

0058 The pure

e can be aseptically packed in suitable

flexible containers, or frozen in bulk at 20



or below.

Beverages

0059 Juice, drinks, nectars, and cordials can be prepared

from papaya pure

e through formulation by adding

appropriate amounts of water, sweeteners, and

acidulants to the pure

e. Commonly used acidulants

include citric acid, malic acid, lemon and lime juice.

These beverages can be pasteurized in bottles or cans

after being acidified to a pH below 4.4.

Dried Products

0060 Several forms of dried products can be prepared from

papaya slices. Since papaya is a soft fruit when fully

ripe, three-quarter ripe fruits are more suitable for

preparing dried slices. Drying can be carried out in

a hot-air drier, a vacuum drier or a freeze drier, with

increasing product quality but correspondingly

higher cost. Solar drying of papaya slices is also a

very practical means of preserving papaya with

good quality. The final moisture content of dried

papaya should be around 5–8% (wet weight basis).

Good packaging is important to retain quality and to

prevent insects from entering the package. University

of Hawaii researchers have designed and built a con-

tinuous solar drier on the island of Kauai in Hawaii,

capable of drying 450 kg of papaya slices within a

24-h period. This drier uses only renewable energy –

solar and biogas.

0061 University of Hawaii researchers have also de-

veloped a vacuum-puff freeze drying process to

make high-quality juice powder, including papaya.

The process involves mixing a papaya pure

e with a

small amount of sucrose, freezing the mixture, and

then placing it into a freeze drier. Initially, the pure

e–

sucrose or juice–sucrose mixture puffs into a foam

when raised to its freezing point. It then refreezes

under a good vacuum. The endpoint is reached

when 1% of moisture is left. The freeze-dried product

is a crystalline powder, and can be rehydrated into

a nectar, similar to freeze-dried coffee. Freeze-dried

powders also retain the color and flavor of the

original pure

e or juice with the right degree of

sweetness.

Papain

Source

0062A milky latex in immature papaya fruit contains an

enzyme called papain. Papain from the dried latex

is in great demand on the international markets,

especially in the UK and the USA.

Properties

0063Papain is a proteolytic enzyme, capable of hydrolyz-

ing or breaking down protein materials.

Applications

0064In the food, pharmaceutical, textile, and tanning

industries, papain is used as a meat tenderizer; for

clearing beer; in the manufacture of cosmetics such

as face creams and dental creams; in degumming

silk and rayon; in the preshrinking of wool; and in

tanning leather.

0065In the medical field, papain can be used to treat

necrotic tissues, dyspepsia and other digestive ail-

ments, ringworm and roundworm infections, skin

lesions and ulcers, eczema, and other skin diseases

and kidney disorders. Papain is used in detecting

stomach and intestinal cancers and also in correcting

diphtheria.

Production

0066The latex of a green papaya drips into a container

after the skin is slit. Papain is the dried latex in

powder form. The collection of latex is very labor-

intensive. Papain production is influenced by several

factors:

0067Fruit size and shape: oblong fruits 36 cm in length

and 28 cm in diameter were found to give the

highest papain yield. In general, papain yield

increases with increasing fruit size.

0068Fruit maturity: unripe but fully grown fruits yield

maximum papain, especially when fruits have

been grown to 75–90 days after fruit set.

0069Season: the flow of latex is low if the temperature

is below 10



0070Cultivars: in India and Sri Lanka, cultivars found

to have high papain yield were Washington,

Philippine, Botanist’s Selection, Peradeniya and

Coimbatore 1.

Yield

0071Papain yield varies from 1.23 to 7.45 g per fruit

among nine cultivars, with the cultivar Washington

recording the highest mean yield of 7.45 g per fruit. In

a papaya tree, the total papain yield can vary from

150 g to 227 g.

4350 PAPAYAS

Role of Papaya in Human Health

0072 The flesh of papaya contains high levels of three car-

otenoids: b-cryptoxanthin, b-carotene, and lycopene.

Different papaya cultivars vary in concentrations and

ratios of these carotenoids. It has been reported that

many individual carotenoids, including b-carotene

and lycopene, have the ability to prevent transform-

ation of cells to cancer phenotypes in a model system in

vitro. No study has considered carotenoid combin-

ations as they occur in fruits, such as papaya, and the

possibility of synergistic effects via multiple inhibitory

mechanisms. Research has been proposed to study the

effectiveness of various combinations of carotenoids

as inhibitors of cancer development in mammalian

systems, and the cellular and molecular mechanisms

if it proves to be effective. The implication is that fruits

rich in carotenoids and lycopene such as papaya and

tomato could be beneficial to human health.

See also: Canning: Principles; Chromatography: Gas

Chromatography; Colorants (Colourants): Properties

and Determination of Natural Pigments; Flavor (Flavour)

Compounds: Structures and Characteristics; Fruits of

Tropical Climates: Commercial and Dietary Importance;

Mass Spectrometry: Principles and Instrumentation

Further Reading

Bose TK and Mitra SK (eds) (1990) Fruits: Tropical and

Subtropical, pp. 303–335. Calcutta: Naya Prokash.

Moy JH, Paull RE, Bian X, Chung R and Wong L (1999)

Quality of tropical fruits irradiated as a quarantine treat-

ment. In: Moy JH and Wong L (eds) Proceedings of the

Workshop on the Use of Irradiation as a Quarantine,

Treatment of Food and Agricultural Commodities, pp.

45–53. Honolulu, Hawaii: College of Tropical Agricul-

ture and Human Resources, University of Hawaii, and

Dept of Hawaii, State of Hawaii.

Nakasone HY and Paull RE (1998) Tropical Fruits, pp.

239–269. Oxford: CAB International.

Nishima M, Zee F, Ebesu R et al. (2000) Papaya Production

in Hawaii, pp. 1–8. Honolulu, Hawaii: College of

Tropical Agriculture and Human Resources, University

of Hawaii at Manoa.

Shaw PE, Chan HT Jr and Nagy S (eds) (1998) Tropical and

Subtropical Fruits, pp. 401–445. Auburndale, FL, USA:

AgScience.

Wenkam NS and Miller CD (1965) Composition of Hawaii

Fruits. Bulletin 135. Honolulu, Hawaii: Hawaii Agri-

cultural Experiment Station, University of Hawaii at

Manoa.

PARASITES

Contents

Occurrence and Detection

Illness and Treatment

Occurrence and Detection

J Melo-Cristino, Faculdade de Medicina de Lisboa,

Lisbon, Portugal

J Botas, formerly of Hospital de Santa Maria, Lisbon,

Portugal

This article is reproduced from Encyclopaedia of Food Science,

Importance of Parasites in Human

Infection

0001 Parasites are a heterogeneous group of invertebrate

animals, including unicellular microrganisms (proto-

zoa) and multicellular organisms with organ systems

(helminths), which can infect a diversity of other

animals, including humans.

0002Human infections are frequently acquired by inges-

tion of contaminated water or food. They are import-

ant all over the world and their prevalence can be very

high, especially in tropical and subtropical regions.

Many parasites have a worldwide distribution, but

others occur in limited endemic areas. However, fre-

quent and rapid travel of people from nonendemic

areas (tourists, scholars, business people, military per-

sonnel, immigrants, etc.) returning from visits to en-

demic areas contributes to infection by such parasites.

0003The spectrum of human disease is extremely wide.

Many parasites are not noticed, and the infection is

asymptomatic, while others are major human patho-

gens and are responsible for high morbidity and mor-

tality. Infections may have an acute onset with intense

symptoms or may require months or years before

becoming clinically evident. Recently, some parasites

PARASITES/Occurrence and Detection 4351

have become more important as they have been rec-

ognized as major pathogens in immunocompromised

hosts, particularly in patients with acquired immune

deficiency syndrome (AIDS). (See HIV Disease and

Nutrition.)

Protozoa Involved in Foodborne and

Waterborne Human Infection

0004 The most significant foodborne and waterborne

protozoa are shown in Table 1. They are class-

ified into phylum Sarcomastigophora (amoebae and

flagellates), phylum Ciliophora (ciliates), phylum

Apicomplexa (coccidia), and phylum Microspora

(microsporidia). Characteristics for differentiation

include motility and stages in life cycles and repli-

cation.

0005 Motility is accomplished by different mechanisms,

namely pseudopodia in amoebae, flagella in flagel-

lates, and movement of rows of cilia in ciliates.

Coccidia and microsporidia are essentially nonmotile

obligate intracellular parasites.

0006 The life cycles of amoebae, flagellates, and ciliates

include two stages, the trophozoite and the cyst.

The trophozoite is the vegetative, motile, feeding

stage usually found in the intestine. The cyst is the

resting, resistant, thick-walled infective stage ex-

creted in feces. Replication is accomplished by binary

fission of trophozoites or by development of several

trophozoites inside mature cysts.

0007 Coccidial life cycles include stages of asexual

development (trophozoite, schizont or meront and

merozoite) and stages of sexual differentiation

(microgamont and macrogamont) that lead to the

production of oocysts, which are shed in feces. The

oocyst, containing sporozoites, which may require a

period of maturation outside the host, is the resistant

and infective stage. Microsporidia multiply by binary

fission or multiple fission, producing spores which are

excreted in urine or in feces. The spore possessing the

infective agent or sporoplasm is the resistant stage.

Helminths Involved in Foodborne and

Waterborne Human Infection

0008The most significant foodborne and waterborne hel-

minths are shown in Table 2. Helminths comprise

the phylum Nematoda (nematodes) and the phylum

Platyhelminthes (trematodes and cestodes).

0009Nematodes or roundworms have cylindrical bodies,

separate sexes and a complete digestive system. Life

cycles can be simple and direct or complex with one

or more intermediate hosts. Hosts are defined as

intermediate hosts when they harbor an asexual

stage of the parasite and definitive hosts when they

harbor the sexual stage.

0010Trematodes or flukes have flattened leaf-shaped

bodies, and most are hermaphroditic with an incom-

plete digestive system. They have complex life cycles,

with snails serving as first intermediate hosts and

other aquatic animals as second intermediate hosts.

Some trematodes may also encyst on aquatic plants.

0011Cestodes or tapeworms have segmented ribbon-

like bodies, are hermaphroditic, and lack a digestive

system. Some have direct life cycles, while others need

one or more intermediate hosts. Infective stages of

helminths include eggs laid by adult worms and asex-

ual stages encysted in animal tissues or on plants.

Occurrence of Parasites in Foods and

Water and Mechanisms of Entry into the

Food Chain

0012Parasites have access to food and water by two

routes. One is by contamination with the feces of

infected humans or animals passing infective resistant

stages such as cysts and oocysts of protozoa and eggs

of helminths. Another route exists when an infective

tbl0001 Table 1 Foodborne and waterborne protozoa causing human infection

Amoebae Flagellates Ciliates Coccidia Microsporidia

Endolimax nana

Chilomastix mesnili

Balantidium coli Cyclospora cayetanensis Encephalitozoon sp.

Entamoeba coli

Dientamoeba fragilis Cryptosporidium spp.

Enterocytozoon sp.

Entamoeba hartmanii

Enteromonas hominis

Isospora belli

Nosema sp.

Entamoeba histolytica/dispar

Giardia intestinalis Toxoplasma gondii

Pleistophora sp.

Iodamoeba b

tschlii

Retortamonas intestinalis

Sarcocystis spp.

Blastocystis hominis

Tr i c h o m o n a s h o m i n i s

Trichomonas tenax

Nonpathogenic for immunocompetent humans.

Infection often serious in immunocompromised patients: most human infections are with C. parvum .

E. histolytica and E. dis par are morphologically identical, but only E. histolytica causes disease.

Inclusion in the amoebae group has recently been proposed by some authors.

4352 PARASITES/Occurrence and Detection

viable stage of the life cycle of a parasite is present in

animal tissues or on plants.

0013 Environmental contamination with human or

animal faeces is correlated with socioeconomic con-

ditions and occurs more frequently in areas with poor

sanitation and poor personal hygiene. However, even

in developed countries, the use of animal or human

feces as a fertilizer may be responsible for the contam-

ination of natural water courses, wells or water sup-

plies. As a consequence, fruits and vegetables may be

contaminated during irrigation. Flies and other

arthropods may also have an important role in pas-

sive transmission.

0014 Prepared food may also be contaminated either by

use of polluted water during preparation or by food

handlers who are carriers. Asymptomatic carriage is

common, and carriers may be reservoirs of the para-

sites and may excrete infective stages, continuously

or intermittently, for long periods of time. Many

excreted stages (cysts, oocysts, and eggs) are very

resistant and may survive in the environment for

weeks or months.

0015 Parasites which may cause human infection trans-

mitted by water or foods contaminated with feces

include all protozoa shown in Table 1 and the

helminths Ascaris lumbricoides, Enterobius vermicu-

laris, Trichuris trichiura, Capillaria hepatica, Hyme-

nolepis nana, H. diminuta, Echinococcus granulosus,

E. multilocularis, and Multiceps multiceps.

0016 Cryptosporidium parvum and Cyclospora cayeta-

nensis, in particular, have been responsible for several

large outbreaks resulting from either contaminated

drinking water or contamination on food (fruits or

vegetables).

0017 Many of them are human intestinal parasites with

no known animal reservoirs, including the amoebae,

Dientamoeba fragilis, Isospora belli, A. lumbricoides,

En. vermicularis,andT. trichiura. Therefore, their

presence implies contamination with human feces.

Furthermore, the presence of human commensal or

nonpathogenic amoebae also implies contamination

with human feces and reflects the possibility of trans-

mission of pathogenic species.

0018The most significant helminths causing human in-

fection by ingestion of foods containing viable asex-

ual infective stages are shown in Table 3. Toxoplasma

gondii and Sarcocystis spp. are protozoa which may

be transmitted to humans by ingestion of infected

meat.

0019Ingestion of raw or improperly cooked meat, as

well as sausages, dried, cured, and smoked meat

from animals serving as intermediate hosts, is a

frequent cause of infection. Examples of parasites

transmitted by beef include To. gondii, Sarcocystis

spp., and Taenia saginata. Pork is implicated in the

transmission of To. gondii, Sarcocystis spp., Taenia

solium,andTrichinella spiralis. Other livestock raw

meat may transmit To. gondii. Crustaceans involved

in transmission of parasites include crabs (Paragoni-

mus westermani, Angiostrongylus spp.), prawns and

shrimps (Anisakis spp., Angiostrongylus spp.). (See

Shellfish: Contamination and Spoilage of Molluscs

and Crustaceans.)

0020Uncooked aquatic vegetables, where infective meta-

cercariae encyst, such as water chestnuts and water-

cress may be responsible for human infection with

the trematodes Fasciolopsis buski and Fasciola

hepatica, respectively.

Fate on Processing/Storage

0021Protozoal cysts or oocysts and helminth eggs

are moderately or highly resistant to chlorination

at concentrations used to disinfect water, e.g.,

Cryptosporidium spp., Giardia intestinalis, A. lum-

bricoides, and T. trichiuria. They are, however, gener-

ally susceptible to heat and to freezing at 20



0022Helminth-encysted metacercariae or infective

larvae in meat, fish, or crustaceans are generally

killed by heating and by prolonged freezing at

20



C. However, they often resist smoking, curing,

or pickling, e.g., Tr. spiralis.

tbl0002 Table 2 Foodborne and waterborne helminths causing human infection

Nematodes Trematodes Cestodes

Angiostrongylus spp. Clonorchis sinensis Diphyllobothrium spp.

Anisakis spp. Fasciola hepatica Dipylidium caninum

Ascaris lumbricoides Fasciolopsis buski Echinococcus granulosus

Bayliascaris procyonis Heterophyes heterophyes Echinococcus multilocularis

Capillaria hepatica Metagonimus yokogawai Hymenolepis diminuta

Capillaria philippinensis Opistorchis spp. Hymenolepis nana

Dracunculus medinensis Paragonimus westermani Multiceps multiceps

Enterobius vermicularis Spirometra spp.

Toxocara spp. Taenia saginata

Trichinella spiralis Taenia solium

Trichuris trichiura

PARASITES/Occurrence and Detection 4353

Detection in Foods and Water

0023 Incrimination of foods and water in the transmission

of parasites is almost always indirect and based on

epidemiological association. Direct isolation of these

parasites from foods or water is very difficult. Water-

filtration techniques for detection of cysts, oocysts, or

eggs may be used, but too often with poor results.

Enrichment culture media are not currently available

in microbiology laboratories. Thus, it is not possible

to recover small numbers of parasites from foods or

water by in-vitro culture methods. Furthermore, the

viability and infectivity of a parasitic stage cannot be

assessed.

0024 Direct incrimination of food in human infection is

obvious when ingestion of an infected food is the only

possible way for the infection to occur. All parasites in

Table 3 belong to this group. Encysted larvae of

Tr. spiralis, Ta. solium, and Ta. saginata may be

detected in raw meat after specific procedures, such

as enzymatic digestion. A similar approach to raw

fish may have little practical value. Other helminths,

e.g., E. granulosus and F. hepatica, may be detected

by the examination of viscera from livestock animals.

Detection in Humans

0025 The diagnosis of a parasitic infection can be made

directly by the finding and identification of the para-

site, or indirectly by immunological methods detecting

specific antibodies. DNA probes, other molecular

techniques, and immunological methods using mono-

clonal antibodies for the detection of specific parasitic

antigens in serum and in body tissues have recently

been described and are promising powerful diagnostic

tools for the future.

0026 Intestinal parasites are currently diagnosed by mor-

phological identification of trophozoites, cysts,

oocysts, eggs, or adult worms in feces, whereas tissue

parasites are generally diagnosed by immunological

methods.

0027Microscopic examination of fecal specimens by

direct wet mount, wet mount after concentration

and/or permanent stains, is the most important

method for the diagnosis of intestinal or biliary para-

sites. As excretion is variable, at least three specimens

should be examined, the specimens being collected at

2- or 3-day intervals.

0028Tissue parasites may occasionally be diagnosed by

direct detection and identification in biopsy material

from lesions. History of traveling into endemic areas

combined with appropriate clinical symptoms and

radiological, ultrasound, or computed tomography

examinations may be very important diagnostic clues.

However, detection of rising titers of specific anti-

bodies is the most useful way to establish the diagnosis.

Current immunological methods include complement

fixation indirect immunofluorescence, indirect hem-

maglutination, enzyme-linked immunosorbent assay,

immunoelectrophoresis, and double-diffusion tests. In

immunocompromised patients, these tests are less

satisfactory for the diagnosis of infection. Recently,

several easy-to-use antigen detection tests have

become available and are of particular value in the

diagnosis of Giardia intestinalis, Cryptosporidium

parvum,andEntamoeba histolytica.(See Immuno-

assays: Principles; Radioimmunoassay and Enzyme

Immunoassay.)

Specific Examples

Cryptosporidium

spp.

0029Cryptosporidium spp. have a worldwide distribution

and are responsible for enteric infection in humans

and many animals, especially cattle and sheep. Infec-

tion is acquired by ingestion of water or food contain-

ing oocysts, which are excreted in an infective form

that does not need maturation outside the gut. Trans-

mission can occur from animals to humans (zoonotic)

as well as from humans to humans (nonzoonotic).

tbl0003 Table 3 Helminths transmitted by foods containing asexual infective stages

Food Nematodes Trematodes Cestodes

Meat Trichinella spiralis Taenia saginata

Taenia solium

Fish Anisakis spp. Clonorchis sinensis Diphyllobothrium latum

Capillaria philippinensis Heterophyes heterophyes Spirometra spp.

Metagonimus yokogawai

Opistorchis viverrini

Paragonimus westermani

Crustaceans Angiostrongylus spp. Paragonimus westermani

Anisakis spp.

Vegetables Fasciola hepatica

Fasciolopsis buski

4354 PARASITES/Occurrence and Detection