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|Latin Name||Cucumis melo spp.|
|Common Name||Melon, Common melon, Muskmelon, Armenian cucumber|
|Categories||Fruits, Food Of Plant Origin|
A food, which may result in allergy symptoms in sensitised individuals.
Melons are probably native to Asia, though they have been in cultivation for so long that their original habitat is obscure.
Melons are warm-season vine plants belonging to the gourd family. Melon has been developed into many cultivars, including smooth-skinned varieties with fruit (gourd-like, but with sweet, very watery flesh) of many shapes, sizes and colours, e.g. honeydew melon, muskmelon, winter melon, and various ‘netted’ cultivars known as cantaloupe.
Among Cucurbitaceae, C. melo includes very important cultivars. They are grown primarily for their fruit, which generally has a sweet, aromatic flavour; they have great diversity of size (50 g to 15 kg), of flesh colour (orange, green, white, and pink), of rind colour (green, yellow, white, orange, red, and gray), of form (round, flat, and elongated), and of dimension (4 to 200 cm). C. melo can be broken down into 7 distinct types, based on these variations in the species. The melon fruits may be either climacteric or non-climacteric, i.e. the fruit may adhere to the stem, or have an abscission layer and fall from the plant naturally at maturity. (1)
Melon is an accessory fruit of a type that botanists call an epigynous berry. It is produced by an annual climbing or trailing herb with a fibrous root and grey-green, angular stems that have stiff, bristly, spreading hairs, mainly on the ridges. The fruit is ellipsoid in shape and is attached by a stout 8-11 mm-long stalk.
Melons are generally a dessert fruit, eaten raw in slices or cubes, or as an ingredient in cold desserts such as sorbet. Their delicate flavour and high water content make them poor candidates for cooking and preserving. Their availability tends to be seasonal, but more-sophisticated transport is changing this in many locales.
An edible oil is obtained from the seed, but since the oil is difficult to extract, it is infrequently used.
The fruit can be used as a light, cooling cleanser or moisturiser for the skin.
The fruit is used in a variety of homeopathic remedies, including as a first-aid treatment for burns and abrasions.
Several IgE-binding proteins, ranging between 13 and 60 kDa, have been detected in melon extract by means of pooled sera from patients with melon allergy. A 13 kDa allergen was the main reactive protein band detected, and was identified as a profilin. (2)
The following allergens have been characterised:
A lipid transfer protein (LTP) has also been detected. (20) It is highly resistant to pepsin digestion and is heat-stable, making it a potentially potent allergen.
In a study of melon profilin, sera from 71% of 21 patients with oral allergy syndrome after melon ingestion recognised melon profilin. This profilin was shown to be highly digestible in gastric juice. (2) In a study of 23 melon-allergic patients, specific IgE to nCuc m 2 (natural melon profilin) and rCuc m 2 (its recombinant counterpart) was found in 100% and 78% respectively of the 23 individual sera analysed. In in vivo tests of 10 patients, nCuc m 2 resulted in a positive skin-prick test in all (10/10) patients tested. Simulated gastric fluid readily inactivated rCuc m 2, but heat treatment did not affect the IgE-binding capacity of rCuc m 2. (10)
Cuc m 3 is a minor allergen. Cuc m 3 bound IgE from 12 of 17 sera from melon-allergic patients, and inhibited approximately 40% and 70% respectively of the IgE binding to melon pulp and juice extract. Positive skin-prick test responses to purified Cuc m 3 were demonstrated in 2 of 14 allergic patients. The allergen accumulates mainly in the juice of the central part of melon, where Cuc m 1 is also located. (15)
Chitin oligosaccharides have been shown to elicit chitinase activity in melon plants within 6 hours after treatment, with maximal levels at 12-24 hours. Chitinase induction was both local and systemic. (21) Whether this chitinase has allergenic potential was not evaluated.
Extensive cross-reactivity between the different individual species of the Cucurbitaceae (gourd) family could be expected. The family includes melon, watermelon, squashes and pumpkin. (22) Cross-reactivity has been demonstrated in vitro: 13 kDa proteins of zucchini, cucumber, and watermelon extracts were strongly recognised by the IgE antibodies of patients with melon allergy. These proteins were identified as profilins. (2)
Profilins are highly cross-reactive allergens, which bind IgE antibodies of almost 20% of plant-allergic patients. Cross-reactivity of melon profilin with other plant profilins was evaluated utilising 17 patients with melon allergy attested by clinical history and a positive skin-prick test. Amino acid sequence analysis of melon profilin alongside other profilins showed the most identity with watermelon profilin, and substantial cross-reactivity with profilin from tomato, peach and grape, and with profilin from the pollen of Bermuda grass. Serum IgE reacted only with melon profilin. The study concluded that IgE reactivity to melon profilin strongly depended on the highly conserved conformational structure, rather than on a high degree of amino acid sequence identity or even linear epitope identity. (9)
Hypersensitivity to the birch tree profilin Bet v 2 has been strongly associated with clinical allergy to melon and watermelon. A history of allergy to gourd fruits, citrus fruits, tomato, banana – or a combination of these – is a sensitive means to detect profilin-hypersensitive patients, predictive in 85% (41/48). The authors suggested that in clinical settings in which laboratory investigations are not easily accessible, allergy to melon, watermelon, citrus fruits, tomato, and banana could be used as a marker of profilin hypersensitivity, once a sensitisation to natural rubber latex and lipid transfer protein has been ruled out. (23)
A study evaluated sensitisation to profilin in patients in central Portugal suffering from respiratory allergy who were sensitised to pollens. A total of 370 patients were evaluated; 65.9% showed positive skin-prick tests, and 76.2% were positive to pollens. All the patients sensitised to pollens had rhinitis. Four profilin- and pollen-sensitised patients experienced oral allergy syndrome with melon. (24) Other studies have reported the relevance of profilin in melon allergy and OAS. (25)
Cuc m 3, a minor component of melon juice, was shown to have greater than 60% sequence identity with PR-1 proteins from grape and cucumber. (15)
As a lipid transfer protein allergen is present in melon, cross-reactivity with other fruits and vegetables containing this allergen is possible. (20)
In an evaluation of the clinical characteristics of melon allergy in 66 melon-allergic patients, 48% self-reported allergy to fig. Skin-specific IgE was most frequently demonstrated to (after pollen) peach, fig, and kiwi. About 82% of patients were shown to have skin-specific IgE to fig. (26)
An association between grass pollinosis and sensitisation to tomato, potato, pea, peanut, watermelon, melon, apple, orange and kiwi has also been reported, (27) as well as between watermelon, melon and ragweed. (28, 29) A number of patients with allergy to birch, grass, and mugwort pollen have been reported to be allergic to melon; (30) another study connected birch-allergic patients with melon allergy. (31) The common allergen was not isolated. Furthermore, in 3 patients with confirmed allergy to melon, analysis revealed that several distinct protein bands were shared by melon with Plantago and Dactylis pollen. All allergens of melon blotting were almost completely inhibited by grass and Plantago pollen extracts – evidence of the presence of structurally similar allergens in melon. (32, 33)
Although allergy to plant-derived fresh food has usually been reported in geographical areas where birch or ragweed pollens are common, and has been attributed to cross-reactivity to pollens, in a study that evaluated plant-derived fresh foods’ effects on pollen-allergic patients from a birch- and ragweed-free area, it was demonstrated that, of 95 pollen-allergic patients, 35 had positive skin-specific IgE to some plant-derived fresh foods, the most frequent being to peach and pear (26%), followed by melon (14%). (34)
An association between sensitisation to olive-tree (Olea europaea) pollen and plant-derived food allergy has also been demonstrated. In 134 patients with allergy to olive pollen, 40 reported adverse reactions to plant-derived food. Twenty-one (group A) reported symptoms of oral allergy syndrome, and 19 (group B) anaphylaxis. In skin-specific IgE tests, sensitisation to Ole e 7 was more frequent in patients from group B. Oral challenges confirmed the association with melon allergy. (35)
Among 463 Japanese patients with allergic rhinitis in reaction to Japanese cedar tree pollen, 45 patients (10%) were diagnosed with oral allergy syndrome (OAS). The foods that most often provoked a reaction were (in order of frequency) melon, kiwi, crab and shrimp. The prevalence of OAS was higher in patients with Japanese-cedar-allergic rhinitis than in those without Japanese-cedar-allergic rhinitis. A higher prevalence of OAS was also found in house dust mite antibody-positive patients than in house dust mite antibody-negative patients. (36)
An association of latex-allergic individuals with fruit allergy has been reported by a number of studies. Fruits often associated include melon, peach, and banana. (37) Importantly, fruit-specific IgE antibodies may not always be detected, regardless of clinical allergy to the fruit. (38)
Melon may commonly induce symptoms of food allergy in sensitised individuals; (15, 31, 34, 39, 40) in particular, in latex-allergic individuals. (37)
Melon has been reported to be a frequent allergy-eliciting fruit in some areas in the United States, (29) and the second-most-frequent allergy-eliciting fruit in Spain, (34) where fruit allergy is the most important food allergy in adult patients. (26, 41, 42)
The allergic reactions are usually immediate. Oral allergy syndrome is the most common manifestation of allergy to melon, but urticaria, and gastrointestinal symptoms, including nausea, vomiting and diarrhoea, have been reported. Dermatitis, angioedema and anaphylaxis are possible. Melon allergy is commonly associated with oral allergy syndrome (OAS) and with hypersensitivity to pollens and other plant foods, as a result of the presence of profilin, a panallergen. (10, 25)
The most common clinical feature of melon allergy is oral allergy syndrome (OAS). (2, 10, 20, 43, 44, 45, 46) OAS associated with the onset of immediate laryngeal oedema after the ingestion of melon has been reported. In this instance, treatment with pollen-specific injection immunotherapy was successful. (47) A Japanese study of 16 cases of childhood OAS concluded that childhood OAS does not always accompany pollen allergy, and that the most frequent allergen was kiwi fruit, followed by tomato, orange and melon. (48) In a Japanese review of 63 patients with OAS aged 2 to 61 who were evaluated over 6 years, the most frequent causative foods were found to be apple, peach, kiwi, and melon, affecting 13, 12, 12, and 11 patients respectively. (49)
In a Spanish study of melon allergy, 161 patients were included: 66 with melon allergy, and 95 in the pollen-allergic control group. Patients were aged between 5 and 61 years. Although all patients of the melon allergy group had oral symptoms, 13 (20%) had extra-oral symptoms, but none experienced generalised urticaria or anaphylaxis. Five patients (8%) reported gastrointestinal symptoms, 3 patients (5%) reported conjunctivitis, 3 patients (5%) reported contact urticaria, 1 patient (2%) reported rhinitis, and 1 patient (2%) reported contact urticaria and conjunctivitis. Oral symptoms preceded extra-oral symptoms. A total of 22 patients (33%) had rhinoconjunctivitis, and 44 (67%) had rhinoconjunctivitis and asthma. Skin-prick-prick tests with fresh melon pulp were positive in all patients in the melon allergy group. Skin testing with 3 commercially available melon extracts resulted in positive skin tests in 12%, 17% and 90%, the outcome being dependent on the commercial extract. Up to 14% of pollen-allergic patients had a positive skin-prick-prick test result to fresh melon pulp; however, only 7% of the patients in the pollen allergy group had melon allergy, a judgment based on positive results on the skin test and an oral challenge test. The fruits most frequently self-reported by the melon-allergic patients to elicit symptoms were peach (62% of patients), fig (48%) and kiwi (42%). Forty-seven per cent of patients reported symptoms caused by some nuts, with walnut (35%) and hazelnut (18%) most frequently implicated. Excluding other Cucurbitaceae fruits, peach, fig, and kiwi elicited positive skin test results and symptoms most frequently. Up to 23% of melon-allergic patients had a concomitant latex sensitisation. Melon allergy was especially strongly linked to pollen allergy, since all the melon-allergic patients were also allergic to pollen. (26)
In many cases, melon allergy cannot be detected by skin-specific or serum-specific IgE. In 53 consecutive adult patients complaining of adverse reactions to melon, actual clinical reactivity was confirmed in 19 (36%), using DBPCFC. The most frequent symptom was oral allergy syndrome (in 14), but 2 patients experienced life-threatening reactions, including respiratory symptoms and hypotension. The positive predictive value for a skin-specific IgE test was 42%; for serum-specific IgE measurement, it was 44%. The authors reported that isolated melon allergy is rare, with most patients having either allergic rhinitis, asthma, or both, or associated food allergies. (50) The detection of specific IgE may also not be clinically relevant. (51)
Anaphylaxis following ingestion of melon has been reported. (52, 53)
Occupational protein contact dermatitis due to melon has been described. (54)
A study reports on a 24-year-old woman with ethanol-induced anaphylaxis who developed anaphylaxis following ingestion of overripe rock melon (Cucumis melo). The accumulation of endogenous ethanol in overripe fruit may occur. (55)