Presentday Cultivation And Usage

Currently, 50 varieties of watermelon are known; some of these are seedless. The fruit pulp is usually red, but yellow-orange melons are also available. Owing to its desert origin, it is cultivated throughout the tropics as a long-season plant. The growing literature cites its multifaceted uses. It is a calorific food with a high water content, also containing sugar, minerals, B-complex vitamins, and special amino acids, while its seed oils contain triglycerides and saturated and unsaturated fatty acids with therapeutic values. The seed tea has anti-helminthetic, diuretic and laxative effects, and is anticarcinogenic at the level of the epithelial cells of glands.

In the field of cosmetics, too, watermelon seed oils are popular. Their moisturizing, non-clogging, cleansing, and semi-drying features are useful in preparing skin-care cosmetics and lotions. The abundant u-PUFAs lead to the above properties, and baby formulations, creams, lotions, soaps, eye creams, facial oils, and skin- and hair-care preparations are also being made and commercialized. Above all, the u-PUFAs have led to watermelon seed oil's popularity in treating cardiovascular and carcinogenic complications.

Watermelon seeds

There are a few hundred watermelon seeds in total in a mature fruit (Figures 136.1—136.3), although the number may vary from variety to variety and cultivar to cultivar. When the melon

FIGURE 136.1

Morphology of watermelon fruits. A heap of watermelon fruits, of different sizes, shapes, and stripes, for sale at a market in Coimbatore, a southern part of India.

FIGURE 136.1

Morphology of watermelon fruits. A heap of watermelon fruits, of different sizes, shapes, and stripes, for sale at a market in Coimbatore, a southern part of India.

FIGURE 136.2

Longitudinal section of watermelon fruit, showing bright red watery flesh with seeds buried in it.

FIGURE 136.2

Longitudinal section of watermelon fruit, showing bright red watery flesh with seeds buried in it.

FIGURE 136.3

Morphology of watermelon seeds. Stored watermelon seeds showing dark reflective and rough surfaces of seed coats.

FIGURE 136.3

Morphology of watermelon seeds. Stored watermelon seeds showing dark reflective and rough surfaces of seed coats.

is freshly cut, the seeds comprise approximately 2—3% of the fruit's total weight. The seeds are slightly pear-shaped, with a strong light brown to brown or black color, sometimes with a mottled surface. The seeds are in parietal placentation, and are covered with mucilage when afresh.

Seed chemistry

Watermelon seeds are procured in tonnes in African and Middle Eastern countries, as delicious 1152 cakes can be made from them, or food grade oil pressed from them. The protein composites of the seeds are mostly of amino acids, such as tryptophan, lysine, and glutamic acid. The seeds also contain arginine, which is often used to regulate blood pressure and cure cardiac ailments. The seeds also contain several B vitamins, including folate, thiamin, riboflavin, pantothenate, vitamin B6, and niacin, totaling 3.8 mg in 31 g of seed — equivalent to 19% of the daily requirement. The prevalent elements are calcium, iron, magnesium, manganese, and zinc. Magnesium regulates blood pressure, and is also involved in controlling the carbohydrate metabolism, thus affecting plasma sugar levels. The fatty acids of watermelon seeds and their health benefits are discussed elsewhere in this chapter.

The seeds can be roasted to make tea or soups. They have diuretic effects, and hence improve kidney and bladder function, particularly during hot weather. They are also anti-inflammatory, chiefly affecting the urinary system. They regulate blood pressure by dilating capillaries, especially in post-menopausal, senile, and obesity-related hypertension.

Water absorption and retention aspects of watermelon seeds

The water absorption and retention aspects of watermelon seeds have been studied, using an average weight of a small cup of about 20 seeds. The fresh seeds weighed 1760 mg and the stored ones 1200 mg. The average weight of the fully dried ones was 1137 mg, and for the fully imbibed ones was 2300 mg (Table 136.1). It was found that water-imbibing capacity is about one-third of the fresh weight. The water-holding capacity improves upon storage (Table 136.2, Figure 136.4). The water retained by the fully dried and stored seeds is double the imbibitional suction power of fresh seeds, suggesting a greater water imbibitional power for watermelon seeds. This evidences the readiness of watermelon seeds for the first and crucial stage of germination. However, germinability tests alone will reveal the successful percentage of germination. Observations of cut stored and totally dried seeds revealed the higher oil content of the kernel (Figure 136.5).

TABLE 136.1 Responses of Watermelon Seeds to Different Storage Conditions*

Seed Type

Average Weight of

20 Seeds (mg)

Fresh

1760

Stored

1200

Fully dried

1137

Fully turgid

2300

All data are as per the study conducted at the author's laboratory.

All data are as per the study conducted at the author's laboratory.

TABLE 136.2 Responses of Watermelon Seeds to Soaking, Total Drying, and Storage

Water loss upon storage FSW - SSW 1760 - 1200 560

Water loss upon total drying FSW - TDSW 1760 - 1137 623

Water gained upon soaking TUSW - FSW 2300 - 1760 540

Water gained upon soaking TUSW - TDSW 2300 - 1137 1163

Water gained upon soaking TUSW - SSW 2300 - 1200 1100

Response of watermelon seeds to 12 hours' soaking or total drying over a storage period of 15 days.

FSW, fresh seed weight; TUSW, turgid seed weight; SSW, stored seed weight without drying; TDSW, totally dried seed weight. The seed behavior is recorded as differences in the average weight of 20 seeds, in mg. All the data are as per the study conducted at the author's laboratory.

Response of watermelon seeds to 12 hours' soaking or total drying over a storage period of 15 days.

FSW, fresh seed weight; TUSW, turgid seed weight; SSW, stored seed weight without drying; TDSW, totally dried seed weight. The seed behavior is recorded as differences in the average weight of 20 seeds, in mg. All the data are as per the study conducted at the author's laboratory.

FIGURE 136.4

Morphometry of turgid (upper row) and dry (lower row) watermelon seeds.

FIGURE 136.4

Morphometry of turgid (upper row) and dry (lower row) watermelon seeds.

There was not much difference in the seed length between soaked, stored, and fully dried seeds (Table 136.3). There was no difference in the breadth of the kernels between fresh and stored ones, but the totally dried seeds showed a decrease in breadth of 0.25 mm. This suggests that the seeds are mainly composed of oil and other reserves, and the water content is of no great value.

However, the imbibitional capacity of the fully dried seeds suggests that, as well as intra-seed factors, there may be some extra-seed factors responsible for this. It may be that the thick, dried mucilage coat on the dry seed testa absorbs a great amount of water. This must be confirmed by the complete removal of the mucilage coat and recording imbibitional results

FIGURE 136.5

Longitudinal and transverse sections of watermelon seeds, showing thick testa and heavy oil content.

FIGURE 136.5

Longitudinal and transverse sections of watermelon seeds, showing thick testa and heavy oil content.

TABLE 136.3 Morphometric Differences of Watermelon Seeds with Soaking, Total Drying, and Storage*

Seed Type

Length (mm)

Breadth (mm)

TUSW

TDSW

1154 Response of watermelon seeds to 12 hours' soaking or total drying over a storage period of 15 days.

SSW, stored seed weight without drying; TUSW, turgid seed weight; TDSW, totally dried seed weight. The seed behavior is recorded as differences in the average length and breadth of 20 seeds, in mm. *All the data are as per the study conducted at the author's laboratory.

thereafter. The data in Tables 136.1—136.3, and the discussion here, are the outcome of the water-relationship studies conducted in the author's laboratory.

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