Papaya

Introduction


The papaya is the fruit of
Carica papaya which belongs to the genus Carica. The papaya is one of native plants of Central America; however, it has been planted widely in most of tropical and subtropical countries.

Generally, the name of Carica papaya is various in different countries, for instance, papaya in Malaysia and Thailand, papaw / paw paw in Australia; in Europe, papaya is also named “tree melon” etc (Morton, 2006; Papaya, 2008).

Recent years, attention of papaya is given due to the nutritional and medical issue of papaya, and most studies are concentrated on two ways, roughly: papaya fruit and papaya latex. Papaya fruit is a good source of carbohydrate, as well as high levels of vitamins (Vc and Va)and minerals (copper and magnesium) (Wall, 2006).

Papaya latex is released from laticifers in both female and hermaphrodite plants. Papaya latex contains at least four cysteine endopeptidases and other constituents including hydrolase inhibitors and lipase, which has been widely applied for food industries, pharmacy, and a direct treatment of paediatric burns in some poorest African countries, such as Gambia (Azarkan, Dibiani, Goormaghtigh, Raussens, & Baeyens-Volant, 2006; Chen & Tsai, 2005; Maria, Sinisterra, Tsai, & Alcantara, 2006; Morcelle, Barberis, Priolo, Caffini, & Clapes, 2006; Nitsawang, Hatti-Kaul, & Kanasawud, 2006; Starley, Mohammed, Schneider, & Bickler, 1999)
.


Description


Papaya is a tree-like, short-lived, unbranched plant with a hollow green or deep-purple stem (30-40 c
Koeh-029.jpg
Papay tree and fruit, from Wikipedia
m in diameter), which can grow up to 1.8-3 m each year. The leaves are emerged from the upper part of stem, and can reach 105 cm in length, with green or more or less dark purple.

The quantity of papaya latex is gender-dependent of the five-petalled flowers and the age-dependent of the plant. Generally, male trees and older trees yield less papaya latex than female and hermaphrodite trees. In addition to milky latex, papaya is also a plant for the ripe fruit which is rich in carbohydrate, vitamins (A and C) and minerals (magnesium).

Papaya fruit also contains papain which is a major component of papaya latex and widely applied for meat tenderisation. Some physical behavious (such as color and size) of papaya fruit are various due to various cultivars.

To date, at least 40 cultivars of papaya are well-known and widely distributed in the world. The behaviors are based on local climate and soil conditions, such as Kamiya, Mexican Red, Mexican Yellow, Solo, Sunrise, Sunset, Vista Solo and Waimanalo. For example, the fruit of Sunset cultivar is a small to medium-sized, pear-shaped, orange or red fruit, which is more popular in Hawaii (California Rare Fruits Growers, n.d.; Duke, 1996; Mortan, 2006; Papaya; 2008).


Chemical components


A green papaya fruit has been reported by Duke (1996), which (per 100 g) provides 26 calories, 92.1 g H2O, 1.0 g protein, 0.1 g fat, 6.2 g total carbohydrate, 0.9 g fiber and 0.6 g ash. USDA National Nutrient database recorded an orange-freshed papaya (per 100 g) contained 39 calories, 88.8 g H2O, 0.61 g protein, 0.14 g fat, 9.81 g total carbohydrate, 1.8 g fiber, 0.61 g ash (Table.1). Additionally, Oyoyede (2005) tested the chemical profile of unripe pulp of carica papaya and reported papaya fruit was very rich in carbohydrate (42.28% starch, 15.15% sugar) but low levels of fat. Papaya fruit also contains high levels of vitamin C (51.2 mg/100g), vitamin A precursors including β-carotene (232.3 μg/100g), and β-cryptoxanthin (594.3 μg/100g), as well as magnesium (19.2-32.7 mg/100g), which has been reported by Wall (2006).

The papaya seeds contain balance-nutrients which consists of protein (24.3%), fatty oil (25.3%) and total carbohydrate (32.5%). Although it contains significantly high level of unsaturated fatty acids, papaya seeds seem not to be good oil seeds.

In some tropical countries, papaya leaves are used as food sources, which can be cooked by stir-fry. The papaya leaves (per 100 g), were reported by Duke (1996), contains 74 calories, 77.5 g H2O, 7.0 g. protein, 2.0g fat, 11.3 g total carbohydrate, 1. 8 g fiber, 2.2 g ash, 344 mg Ca, 142 mg P, 0.8 mg Fe, 16 mg Na, 652 mg K, 11,565 ug β-carotene equivalent, 0.09 mg thiamine, 0.48 mg riboflavin, 2.1 mg niacin, and 140 mg ascorbic acid, as well 136 mg vitamin E.

Recent years, papaya latex and its commercial products have been widely applied in baking and beverage industries, pharmacy and new chemicals synthesis. There are four major components including papain (EC. 3.4.22.2), chymopapain (EC. 3.4.22.6), caricain (EC. 3.4.22.30), glycyl endopeptidase (EC. 3.4.22.25), and papaya lipase (EC. 3.1.1.3).

Table.1. Chemical components of per 100 g oranged-freshed papaya fruit (the data from USDA Nutrient
database)

Nutrient
Units
Value per 100 grams
Proximates


Water
g
88.83
Energy
kcal
39
Energy
kj
163
Protein
g
0.61
Total lipid (fat)
g
0.14
Ash
g
0.61
Carbohydrate, by difference
g
9.81
Fiber, total dietary
g
1.8
Sugars, total
g
5.90
Minerals


Calcium, Ca
mg
24
Magnesium, Mg
mg
10
Potassium, K
mg
257
Sodium, Na
mg
3
Zinc, Zn
mg
0.07
Vitamins


Vitamin C, total ascorbic acid
mg
61.8
Niacin
mg
0.338
Pantothenic acid
mg
0.218
Folate, total
mcg
38
Folate, food
mcg
38
Folate, DFE
mcg_DFE
38
Choline, total
mg
6.1
Vitamin A,IU
IU
1094
Vitamin A, RAE
mcg_RAE
55
Virtamin E (alpha-tocopherol)
mg
0.73
Vitamin K
mcg
2.6
Lipids


Fatty acids, toital saturated
g
0.043
Fatty acids, total monosaturated
g
0.038
Fatty acids, total polysaturated
g
0.031
Other


Carotene, beta
mcg
276
Cryptoxanthin, beta
mcg
761
Lutein+Zeaxanthin
mcg
75

Benefits
529px-Carica_papaya_-_papaya_-_var-tropical_dwarf_papaya_-_desc-fruit.jpg
Papaya trunk with immature frui, from Wikipedia

Nutritional value


Papaya fruit is rich in carbohydrates (42.28% starch and 15.15% sugar in pulp), but is deficiency of protein and fat (Bari et al., 2006; Oyoyede, 2005). Per 100 g of the fruit can provide 39 kcal (163 kj) energy. Hereby papaya is a very important food source in some developing countries.

Vitamin C, vitamin A and certain minerals are rich in papaya fruit. For example, orange freshed papaya fruit contains 61.8 mg vitamin C, 1094 IU vitamin A, 38.0 mcg folate and 257 mg potassium, which provide 103% DV (Percent Daily Values) for vitamin C, 22% DV for vitamin A, 10% DV for folate and 7% DV for potassium (per 100g). Additionally, Wall (2006) stated that papaya fruits of Hawaii cultivar (100 g) contained 9% of DRI (daietary reference intake) for Cu, and 6-8% of the DRI for Magnesium.

Papaya leaves are used to cook in some tropical countries, which contain higher calories than papaya fruit. Moreover, the leaves also have high levels of protein (7.0 g), calcium (334 mg), phosphorus (142 mg), sodium (16 mg), vitamin B and vitamin E (136 mg) (Duke, 1996).


Antioxidative property


Oxidative damage is related to high incidents of some degenerative diseases including cancer, arthritis, arteriosclerosis, inflammation, aging and brain dysfunction. Antioxidants are the substances that can prevent or retard the oxidation of easily oxidisable materials such as fat, the functions of which are generally based on their abilities to scavenge reactive free radicals in food (MacDonald-Wicks, Wood, & Garg, 2006).

Vitamin B, vitamin C, vitamin E, carotenoids and phenolic compounds are the most abundant antioxidants present in plant foods (Hernadez, Lobo, & Gonzalez, 2006; Lim, Lim, & Tee, 2007). Most studies reported that papaya fruits and its leaves had high antioxidant capacity due to their high contents of vitamin B (in leaves), vitamin C, E (in fruits), and carotenoids (Bari et al., 2006; Lim et al., 2007; Setiawan, Sulaeman, Giraud, & Driskell, 2001; Wall, 2006).

Almost all studies reported papaya fruits contained low total phenolic compounds content. However, some studies stated that papaya fruits had low antioxidant capacity (Patthamakanokporn, Puwastien, Nitithamyong, & Sirichakwal, 2008), which might be caused by various antioxidant activity methods and various papaya cultivars.

Medical benefits


Besides antioxidative property, papaya plant was proven to be an important medical plant due to its specific enzymes. Papain is found in both papaya fruits and latex, which has been utilised for meat tenderization for one thousand years in Central America.

Recent years, papain and other endopeptidases have been proven to have several medical benefits, such as defibrinating wounds and treatment of edemas (Nitsawang et al., 2006). In some poor African countries, such as Gambia, tropical papaya is used to treat paediatric burns due to its proteolytic enzymes. Exception of papain, other endopeptidases, such as leukopapain and chymopapain, is also able to facilitate wound cleaning, promoting growth and improving the quality of the scar.

Papaya contains some specific antimicrobial substrates including carpaine and aglycones (Starley et al., 1999). Oyoyede (2005) also reported the extractions of fruits and seeds had antibacterial activity against Staphylococcus aureus, Bacillus cereus, Esherischia coli, Pseudomanas, aeruginosa and Shigella flexneri. Additionally, papaya fruits have several other applications, such as the relief of nervous pains and elephantoid growth, etc.

Biocatalytic function


Papaya lipase (EC. 3.1.1.3) is an important component of papaya latex that is produced by papaya plants. Papaya lipase has many advantages over the lipase produced by animals and other organisms, such as microorganisms. Papaya lipase is a naturally immobilized biocatalyst that is tightly bound to water-insoluble matrix. Recent years, papaya lipase has been widely applied for fat and oils modification, esterification and inter-esterification reactions in organic media, enantioselective hydrolysis of (R, S)-naproxen 2,2,2-trifluoroethyl ester and production of non-steroidal anti-inflammatory drug (S)-naproxen (NSAIDs) (Chen & Tsai, 2005; Maria et al., 2006).

Papain_cartoon.png
Papain, from Wikipedia


Toxicology and allergy


Besides these benefits, consumption of papaya was also reported to cause adverse reactions including toxicology and allergy. Some persons are allergic to the flower powder, and fruit and the latex that may also result in irritation due to papain and chymopapain. However, clinic reports about allergy induced by papaya are very rare. De clerck, Ebo, Bridts and Stevens (2003) stated papaya-borne allergy belonged to IgE-mediated immnune system disorder, which can result in oropharyngeal itching, angioedema, wheal, flare reaction and rhino-conjunctivitis.

The toxicity of carpaine presents in papaya fruits, seeds, latex and leaves is dose-dependent. Cyangenic glucosides present in the leaves and roots, which can form cyanide which can subsequently introduce undesirable effects on human health. Tannin is also rich in the papaya fruits and leaves, which is a major antinutrient in plants. Additionally, papaya fruit contains high level of carotenoids. There were many reports have been suggested that excessive consumption of papaya might cause carotenemia, a harmless yellowing of the palms and soles (Carica papaya, 2001; Duke, 1996; Papaya 2008).


References


Written by Feng Shi
M.Sc. student
Food and Wine Science group, Lincoln University NZ