What is papaya

The papaya (Carica papaya L.) also called papaw or pawpaw, is a tropical fruit tree, one of the 22 accepted species in the genus Carica of the family Caricaceae ¹⁾. Its origin is in the tropics of the Americas, perhaps from southern Mexico and neighboring Central America.

Commonly and erroneously referred to as a “tree”, the papaya plant is properly a large herb growing at the rate of 6 to 10 ft (1.8-3 m) the first year and reaching 20 or even 30 ft (6-9 m) in height, with a hollow green or deep-purple stem becoming 12 to 16 in (30-40 cm) or more thick at the base and roughened by leaf scars. The leaves emerge directly from the upper part of the stem in a spiral on nearly horizontal petioles 1 to 3 1/2 ft (30-105 cm) long, hollow, succulent, green or more or less dark purple. The blade, deeply divided into 5 to 9 main segments, each irregularly subdivided, varies from 1 to 2 ft (30-60 cm) in width and has prominent yellowish ribs and veins. The life of a leaf is 4 to 6 months. Both the stem and leaves contain copious white milky latex.

Generally, the papaya fruit is melon-like, oval to nearly round, somewhat pyriform, or elongated club-shaped, 6 to 20 in (15-50 cm) long and 4 to 8 in (10-20 cm) thick; weighing up to 20 lbs (9 kg). Semi-wild (naturalized) plants bear miniature fruits 1 to 6 in (2.5-15 cm) long. The skin is waxy and thin but fairly tough. When the fruit is green and hard it is rich in white latex. As it ripens, it becomes light- or deep-yellow externally and the thick wall of succulent flesh becomes aromatic, yellow, orange or various shades of salmon or red. It is then juicy, sweetish and somewhat like a cantaloupe in flavor; in some types quite musky. Attached lightly to the wall by soft, white, fibrous tissue, are usually numerous small, black, ovoid, corrugated, peppery seeds about 3/16 in (5 mm) long, each coated with a transparent, gelatinous aril.

Figure 1. Papaya fruit

How to eat papaya

Ripe papayas are most commonly eaten fresh, merely peeled, seeded, cut in wedges and served with a half or quarter of lime or lemon. Sometimes a few seeds are left attached for those who enjoy their peppery flavor but not many should be eaten. The flesh is often cubed or shaped into balls and served in fruit salad or fruit cup. Firm-ripe papaya may be seasoned and baked for consumption as a vegetable. Ripe flesh is commonly made into sauce for shortcake or ice cream sundaes, or is added to ice cream just before freezing; or is cooked in pie, pickled, or preserved as marmalade or jam. Papaya and pineapple cubes, covered with sugar sirup, may be quick-frozen for later serving as dessert. Half-ripe fruits are sliced and crystallized as a sweetmeat.

Papaya juice and nectar may be prepared from peeled or unpeeled fruit and are sold fresh in bottles or canned. In Hawaii, papayas are reduced to puree with sucrose added to retard gelling and the puree is frozen for later use locally or in mainland USA in fruit juice blending or for making jam.

Unripe papaya is never eaten raw because of its latex content. [Raw green papaya is frequently used in Thai and Vietnamese cooking.] Even for use in salads, it must first be peeled, seeded, and boiled until tender, then chilled. Green papaya is frequently boiled and served as a vegetable. Cubed green papaya is cooked in mixed vegetable soup. Green papaya is commonly canned in sugar sirup in Puerto Rico for local consumption and for export. Green papayas for canning in Queensland must be checked for nitrate levels. High nitrate content causes detinning of ordinary cans, and all papayas with over 30 ppm nitrate must be packed in cans lacquered on the inside. Australian growers are hopeful that the papaya can be bred for low nitrate uptake.

Young leaves are cooked and eaten like spinach in the East Indies. Mature leaves are bitter and must be boiled with a change of water to eliminate much of the bitterness. Papaya leaves contain the bitter alkaloids, carpaine and pseudocarpaine, which act on the heart and respiration like digitalis, but are destroyed by heat. In addition, two previously undiscovered major D1-piperideine alkaloids, dehydrocarpaine I and II, more potent than carpaine, were reported from the University of Hawaii in 1979. Sprays of male flowers are sold in Asian and Indonesian markets and in New Guinea for boiling with several changes of water to remove bitterness and then eating as a vegetable. In Indonesia, the flowers are sometimes candied. Young stems are cooked and served in Africa. Older stems, after peeling, are grated, the bitter juice squeezed out, and the mash mixed with sugar and salt.

In India, papaya seeds are sometimes found as an adulterant of whole black pepper. Collaborating chemists in Italy and Somalia identified 18 amino acids in papaya seeds, principally, in descending order of abundance, glutamic acid, arginine, proline, and aspartic acid in the endosperm; and proline, tyrosine, lysine, aspartic acid, and glutamic acid in the sarcotesta. A yellow to brown, faintly scented oil was extracted from the sundried, powdered seeds of unripe papayas at the Central Food Technological Research Institute, Mysore, India. White seeds yielded 16.1% and black seeds 26.8% and it was suggested that the oil might have edible and industrial uses.

Papaya nutrition facts

Raw papaya pulp contains 88% water, 11% carbohydrates, and negligible fat and protein. In a 100 gram amount, papaya fruit provides 43 kilocalories. The papaya is regarded as a fair source of iron and calcium; a good source of vitamins A, B and G and an excellent source of vitamin C (ascorbic acid) (75% of the Daily Value, DV) and a moderate source of folate (10% DV).

Table 1. Papaya (raw) nutrition facts

Nutrient	Unit	Value per 100 g
Approximates
Water	g	88.06
Energy	kcal	43
Energy	kJ	179
Protein	g	0.47
Total lipid (fat)	g	0.26
Ash	g	0.39
Carbohydrate, by difference	g	10.82
Fiber, total dietary	g	1.7
Sugars, total	g	7.82
Sucrose	g	0
Glucose (dextrose)	g	4.09
Fructose	g	3.73
Lactose	g	0
Maltose	g	0
Galactose	g	0
Starch	g	0
Minerals
Calcium, Ca	mg	20
Iron, Fe	mg	0.25
Magnesium, Mg	mg	21
Phosphorus, P	mg	10
Potassium, K	mg	182
Sodium, Na	mg	8
Zinc, Zn	mg	0.08
Copper, Cu	mg	0.045
Manganese, Mn	mg	0.04
Selenium, Se	µg	0.6
Vitamins
Vitamin C, total ascorbic acid	mg	60.9
Thiamin	mg	0.023
Riboflavin	mg	0.027
Niacin	mg	0.357
Pantothenic acid	mg	0.191
Vitamin B-6	mg	0.038
Folate, total	µg	37
Folic acid	µg	0
Folate, food	µg	37
Folate, DFE	µg	37
Choline, total	mg	6.1
Vitamin B-12	µg	0
Vitamin B-12, added	µg	0
Vitamin A, RAE	µg	47
Retinol	µg	0
Carotene, beta	µg	274
Carotene, alpha	µg	2
Cryptoxanthin, beta	µg	589
Vitamin A, IU	IU	950
Lycopene	µg	1828
Lutein + zeaxanthin	µg	89
Vitamin E (alpha-tocopherol)	mg	0.3
Vitamin E, added	mg	0
Tocopherol, beta	mg	0.02
Tocopherol, gamma	mg	0.09
Tocopherol, delta	mg	0.01
Vitamin D (D2 + D3)	µg	0
Vitamin D	IU	0
Vitamin K (phylloquinone)	µg	2.6
Lipids
Fatty acids, total saturated	g	0.081
04:00:00	g	0
06:00:00	g	0
08:00:00	g	0
10:00:00	g	0
12:00:00	g	0.002
14:00:00	g	0.013
16:00:00	g	0.06
18:00:00	g	0.004
Fatty acids, total monounsaturated	g	0.072
16:1 undifferentiated	g	0.038
18:1 undifferentiated	g	0.034
20:01:00	g	0
22:1 undifferentiated	g	0
Fatty acids, total polyunsaturated	g	0.058
18:2 undifferentiated	g	0.011
18:3 undifferentiated	g	0.047
18:04:00	g	0
20:4 undifferentiated	g	0
20:5 n-3 (EPA)	g	0
22:5 n-3 (DPA)	g	0
22:6 n-3 (DHA)	g	0
Fatty acids, total trans	g	0
Cholesterol	mg	0
Amino Acids
Tryptophan	g	0.008
Threonine	g	0.011
Isoleucine	g	0.008
Leucine	g	0.016
Lysine	g	0.025
Methionine	g	0.002
Phenylalanine	g	0.009
Tyrosine	g	0.005
Valine	g	0.01
Arginine	g	0.01
Histidine	g	0.005
Alanine	g	0.014
Aspartic acid	g	0.049
Glutamic acid	g	0.033
Glycine	g	0.018
Proline	g	0.01
Serine	g	0.015
Other
Alcohol, ethyl	g	0
Caffeine	mg	0
Theobromine	mg	0
Flavones
Apigenin	mg	0
Luteolin	mg	0
Flavonols
Kaempferol	mg	0
Myricetin	mg	0
Quercetin	mg	0
Isoflavones
Daidzein	mg	0
Genistein	mg	0
Total isoflavones	mg	0

[Source ²⁾]

Papaya enzyme

Papain

The latex of the papaya plant and its green fruits contains two proteolytic enzymes, papain and chymopapain ³⁾. The latter is most abundant but papain is twice as potent. In 1933, Ceylon (Sri Lanka) was the leading commercial source of papain but it has been surpassed by East Africa where large-scale production began in 1937.

The latex is obtained by making incisions on the surface of the green fruits early in the morning and repeating every 4 or 5 days until the latex ceases to flow. The tool is of bone, glass, sharp-edged bamboo or stainless steel (knife or raxor blade). Ordinary steel stains the latex. The latex coagulates quickly and for best results, is spread on fabric and oven-dried at a low temperature, then ground to powder and packed in tins. Sun-drying tends to discolor the product. One must tap 1,500 average-size fruits to gain 1 1/2 lbs (0.68 kg) of papain.

The lanced fruits may be allowed to ripen and can be eaten locally, or they can be employed for making dried papaya “leather” or powdered papaya, or may be utilized as a source of pectin.

Because of its papain content, a piece of green papaya can be rubbed on a portion of tough meat to tenderize it. Sometimes a chunk of green papaya is cooked with meat for the same purpose.

One of the best known uses of papain is in commercial products marketed as meat tenderizers, especially for home use. A modern development is the injection of papain into beef cattle a half-hour before slaughtering to tenderize more of the meat than would normally be tender. Papain-treated meat should never be eaten “rare” but should be cooked sufficiently to inactivate the enzyme. The tongue, liver and kidneys of injected animals must be consumed quickly after cooking or utilized immediately in food or feed products, as they are highly perishable.

Papain has many other practical applications. It is used to clarify beer, also to treat wool and silk before dyeing, to de-hair hides before tanning, and it serves as an adjunct in rubber manufacturing. It is applied on tuna liver before extraction of the oil which is thereby made richer in vitamins A and D. Papain is also used in toothpastes, cosmetics and detergents, as well as pharmaceutical preparations to aid digestion.

Papain has been employed to treat ulcers, dissolve membranes in diphtheria, and reduce swelling, fever and adhesions after surgery. With considerable risk, it has been applied on meat impacted in the gullet. Chemopapain is sometimes injected in cases of slipped spinal discs or pinched nerves. Precautions should be taken because some individuals are allergic to papain in any form and even to meat tenderized with papain.

Papaya health benefits

Papaya has high antioxidant activity ⁴⁾ and rich in phytochemicals such as flavonoids – quercetin, followed by myricetin and kaempferol (1264.0 mg/kg) ⁵⁾. Different plant parts such as fruit, leaf, seed, root, bark, and flowers have been used as health treatments in tropical countries where it is grown. The seeds of papaya, however, have contraceptive effect on male fertility as well as manifest antifertility, anti-implantation, and abortifacient activity in female rats ⁶⁾ suggesting a possibility to alter sex hormone levels.

Recent studies have shown papaya beneficial effect as an anti-inflammatory agent ⁷⁾, for its wound healing properties ⁸⁾, antitumour as well as immune-modulatory effects ⁹⁾ and as an antioxidant ¹⁰⁾. A toxicity study (acute, subacute, and chronic toxicity) conducted on Sprague Dawley rats administered with papaya leaves juice of the sekaki variant revealed that it was safe for oral consumption ¹¹⁾.

The papaya leaf extract/concentrate has been scientifically investigated for pharmacological properties such as anti-microbial, anti-parasitic (antimalarial) activity, anti-cancer, anti-inflammatory and membrane stabilization properties ¹²⁾. In Sri Lankan traditional medicine the leaf juice of papaya is claimed as a powerful remedy for modulating the immune system. Thus far several in vitro and in vivo experiments have been carried out to investigate the immuno pharmacological properties of the leaf concentrate of papaya. Dharmarathna et al. ¹³⁾ observed a marked platelet count elevation in non-thrombocytopenic mice following the oral treatment of papaya extract for seven days. Another study conducted using non thrombocytopenic rats reported a marked increment in platelet counts, mean cell haemoglobin (MCH) and mean corpuscular volume (MCV) following the oral treatment with this leaf formulation for 7 days ¹⁴⁾. In addition to animal experimentation, the platelet increasing activity of papaya leaf extract has been validated in thrombocytopenia associated dengue patients. An open labeled randomized controlled trial carried out with 228 patients (Treatment = 111, Control = 117) with dengue fever and dengue haemorrhagic fever revealed a significant increase of platelet counts after 40 and 48 hours of oral administration of papaya leaf juice for 3 consecutive days ¹⁵⁾. A pilot study reported an increase of platelet and WBC (white blood cell) counts of dengue patients after 24 h of administration of papaya leaf juice and patients recovered without hospital admission ¹⁶⁾. A similar effect was also observed in an open labeled randomized controlled trial with 30 dengue patients treated with a tablet (Caripill) prepared from papaya leaf extract ¹⁷⁾; A significant increase of platelet counts was observed following oral treatment with this tablet three times daily for five days and exerted fewer side effects and good tolerability. Increase of both platelets and white blood cells (WBCs) were consistent with previous studies established with non-thrombocytopenic ¹⁸⁾, ¹⁹⁾ as well as thrombocytopenic mice models ²⁰⁾, ²¹⁾. These finding supports the claim that the papaya leaves juice consumption during the course of dengue infection has the potential to induce the rapid production of platelets ²²⁾, which was clearly demonstrated that papaya leaf concentrate may be a potential candidate for further research for treating low blood platelets (thrombocytopenia). However, currently, it is also necessary not to rely entirely on the leaf extract and ignore standard treatment for dengue until the benefits are established. Large scale randomized clinical trials in dengue-confirmed patients is necessary to establish their usefulness ²³⁾.

Several test tube studies ²⁴⁾, ²⁵⁾ have attributed anti-cancer activities to papaya pectins (the branch of arabinogalactan type II (AGII) structure) ²⁶⁾.

The papaya seeds had a high content of lipid (29.16%) and protein (25.63%). The lipid in the papaya seeds is considered economically attractive for industrial extraction, especially when compared to conventional oilseed crops such as corn and soybean ²⁷⁾. Traditionally, papaya seeds were used in parts of Asia and South America as a vermifugal (an anthelmintic medicine) ²⁸⁾ and seed preparations were also used in folk medicine due to its abortive properties to favor a good menstrual flow ²⁹⁾. In recent years, many studies have been conducted to utilize the papaya seeds and extensive research has been carried out on the use of the seeds as a source of oil ³⁰⁾, ³¹⁾, ³²⁾, It was reported that the papaya seed oil had an interesting composition (72% of monounsaturated fatty acids with 71% oleic acid) and hence representing a promising source of oleic oil for various applications ³³⁾. Furthermore, the papaya seed extract has been pronounced with some special functions such as antibacterial ³⁴⁾, anti-fertility ³⁵⁾, ³⁶⁾, antihelminthic and antiamoebic ³⁷⁾ activities. Previous studies have discovered many bioactive compounds existed in papaya seeds ³⁸⁾, including substantial amounts of carotenoid pigments, isothiocyanate and phenolic compounds ³⁹⁾.

In tropical folk medicine, the fresh latex is smeared on boils, warts and freckles and given as a vermifuge (an anthelmintic medicine). In India, it is applied on the uterus as an irritant to cause abortion. The unripe fruit is sometimes hazardously ingested to achieve abortion. Seeds, too, may bring on abortion. They are often taken as an emmenagogue and given as a vermifuge. The root is ground to a paste with salt, diluted with water and given as an enema to induce abortion. A root decoction is claimed to expel roundworms. Roots are also used to make salt.

Crushed leaves wrapped around tough meat will tenderize it overnight. The leaf also functions as a vermifuge and as a primitive soap substitute in laundering. Dried leaves have been smoked to relieve asthma or as a tobacco substitute. Packages of dried, pulverized leaves are sold by “health food” stores for making tea, despite the fact that the leaf decoction is administered as a purgative for horses in Ghana and in the Ivory Coast it is a treatment for genito-urinary ailments. The dried leaf infusion is taken for stomach troubles in Ghana and they say it is purgative and may cause abortion.

Papaya Allergy

Report has already been made of skin irritation in papaya harvesters because of the action of fresh papaya latex and of the possible hazard of consuming undercooked meat tenderized with papain. It must be added that the pollen of papaya flowers has induced severe respiratory reactions in sensitive individuals. Thereafter, such people react to contact with any part of the plant and to eating ripe papaya or any food containing papaya, or meat tenderized with papain.