Luffa

Luffa
Egyptian luffa with nearly mature fruit
Scientific classification
Kingdom:	Plantae
Clade:	Tracheophytes
Clade:	Angiosperms
Clade:	Eudicots
Clade:	Rosids
Order:	Cucurbitales
Family:	Cucurbitaceae
Subfamily:	Cucurbitoideae
Tribe:	Sicyoeae
Genus:	Luffa Mill.[1]
Species[2]
Luffa acutangula (L.) Roxb. (angled luffa, ridged luffa, vegetable gourd) Luffa aegyptiaca Mill. (smooth luffa, Egyptian luffa, dishrag gourd, gourd loofa) Luffa astorii Svenson Luffa echinata Roxb. Luffa graveolens Roxb. Luffa operculata (L.) Cogn. (wild loofa, sponge cucumber) Luffa quinquefida (Hook. & Arn.) Seem. Luffa saccata F.Muell. ex I.Telford Luffa sepium (G.Mey.) C.Jeffrey
Synonyms[2]
Poppya Neck. Trevouxia Scop. Turia Forssk. ex J.F.Gmel.

Luffa is a genus of tropical and subtropical vines in the pumpkin, squash and gourd family (Cucurbitaceae).

In everyday non-technical usage, the luffa, also spelled loofah^[3] or less frequently loofa,^[4] usually refers to the fruits of the species Luffa aegyptiaca and Luffa acutangula. It is cultivated and eaten as a vegetable, but must be harvested at a young stage of development to be edible. The vegetable is popular in India, China, Nepal, Bhutan, Bangladesh and Vietnam.^[5] When the fruit is fully ripened, it is very fibrous. The fully developed fruit is the source of the loofah scrubbing sponge.

Names

The name luffa was taken by European botanists in the 17th century from the Arabic name لوف lūf.^[1]

In North America it is sometimes known as "Chinese okra",^[6] and in Spanish as estropajo.^[7]

Uses

Fibers

The fruit section of L. aegyptiaca may be allowed to mature and used as a bath or kitchen

fibers. If the loofah is allowed to fully ripen and then dried on the vine, the flesh disappears, leaving only the fibrous skeleton and seeds, which can be easily shaken out. Marketed as luffa or loofah, the sponge is used as a body scrub in the shower.

In Paraguay, panels are made out of luffa combined with other vegetable matter and recycled plastic. These can be used to create furniture and construct houses.[8]

Food

Luffa is a very popular food item. There are various ways to prepare it including in soups or stir frys.

Indian subcontinent

In Hindi-speaking North Indian states, it is called torai (तोरई), and cooked as vegetable. In eastern-UP it is also called nenua. But in central/Western India, specially in Madhya Pradesh, it is called gilki (गिल्की). Torai is reserved for ridge gourd and is less popular than gilki in central western India.

In

speaking regions it is called ghiura. Apart from the fruit of the vegetable, flowers are also used as a vegetable as chokha, tarua, pakoda, etc.

In Nepal and Nepali language speaking Indian states, it is called ghiraula (घिरौंला). It is a popular vegetable usually cooked with tomato and potatoes and served with rice.

In Gujarat it is known as turia or turya (તુરીયા) as well as ghissori or ghissora in the Kutchi language. It is a simple but very popular vegetable usually made with a plentiful tomato gravy and garnished with green chillies and fresh coriander. When cooked roti is shredded by hand and mixed into it, it is colloquially known as "rotli shaak ma bhuseli". Alternatively this dish is also eaten mixed with plain cooked rice.

In Bengali-speaking Bangladesh and the Indian state of West Bengal, it is known as dhudhul (ধুঁধুল) and a popular vegetable. It is eaten fried or cooked with shrimp, fish, or meat.

In Assam, it is called bhul (ভুল) and is cooked with sour fish curry along with taro.^[9]

In

Even the skin is used to make chutney.

In Karnataka's Malenadu (Western Ghats) it is known as tuppadahirekayi, which literally translates as "buttersquash", also known as hirekayi in Kannada. It grows naturally in this region and is consumed when it is still tender and green. It is used as a vegetable in curries, but also as a snack, bhajji, dipped in chickpea batter and deep fried. In Tulu language it is known as Peere and is used to prepare chutney and ajethna.^[12]

In Telangana, it is called beerakaya. It is used in making Dal, Fry, Roti Pacchadi, and wet curry.

In Andhra Pradesh, it is called nethi beerakaya or beerakaya. And in Assam it is called jika (জিকা, Luffa acutangula) and bhula (ভোল, Luffa aegyptiaca). It is used as a vegetable in a curry, chutney and stir fry.

In

, it grows as a creeper on fences.

In Maharashtra, India, dodka (ridge gourd luffa) and ghosavala (smooth luffa) are common vegetables prepared with either crushed dried peanuts or with beans.

In Manipur, India, sebot is cooked with other ingredients like potato, dried fish, fermented fish and served. It is also steamed and consumed or crushed (ironba) with other ingredients and served with steamed rice (chaak). Fried ones (kaanghou) are also favorites for many. Sebot is also eaten as a green vegetable.

Other Asian cuisines

In Vietnamese cuisine, the gourd is called "mướp hương" and is a common ingredient in soups and stir-fried dishes.

In China and Taiwan (where it is called

]

In Japan it is called hechima (へちま) and is cultivated all over the country during summer. It is commonly used as a green vegetable in traditional dishes of the Ryukyu Islands (where it is called naabeeraa). In other regions it is also grown for uses other than food.

In Nepal it is called ghiraula and consumed as a vegetable at a young age. When it becomes ripe and dried, it is used as a body scrubbing material during bathing.

Western cuisines

Luffa is also known as "Chinese okra" in Canada and the U.S.

Other uses

In Japan, in regions other than the Ryukyu Islands and Kyushu, it is predominantly grown for use as a sponge or for applying soap, shampoo, and lotion. As with

]

Role in food chain

Luffa species are used as food plants by the larvae of some Lepidoptera species, including Hypercompe albicornis and Zeugodacus tau.^[13]

Mechanical properties

The luffa sponge is a biological cellular material. These materials often exhibit exceptional mechanical properties at low densities. While their mechanical performance tends to fall behind manmade materials, such as alloys, ceramics, plastics, and composites, as a structural material, they have long term sustainability for the natural environment. When compressed longitudinally, a luffa sponge is able to absorb comparable energy per unit mass as aluminum foam.^[14] Luffa sponges are composed of a complex network of fiber bundles connected to form a 3-dimensional, highly-porous network.^[15]

The hierarchical structure of luffa sponges results in mechanical properties that vary with the component of sponge tested. Specifically, the mechanical properties of fiber bundles differ from those of blocks from the bulk of the sponge, which differ from those of the cross sections of the entire sponge.^[15]

Fiber-bundles

Uniaxial tensile tests of fiber bundles isolated from the inner surface provide insight this basic strut element of the luffa sponges. These fiber bundles vary in diameter from 0.3 to 0.5 mm.^[15] Each fiber bundle has a low density core region not occupied by fibers.^[16] The stress-strain response of the fiber bundles is nearly linear elastic all the way until fracture, suggesting the absence of work hardening. The slope of the linear region of the stress-strain curve, or Young’s modulus, is 236* MPa. The highest stress achieved before fracture, or ultimate tensile strength, is 103 MPa. The strain at which failure occurs, or failure strain, is small at only 5%. The mechanical properties of fiber bundles decrease dramatically when the size of the hollow region inside the bundle increases. Despite their low tensile strength, the fiber bundles have a high specific modulus of 2.07– 4.05 MPa⋅m³/kg, and their overall properties are improved when a high ratio of their cross sectional area is occupied by fibers, they are evenly distributed, and there is strong adhesion between fibers.^[15][16]

Bulk-sponge

Block samples (height: 12.69 ± 2.35mm, width: 11.30 ± 2.88mm, length: 13.10 ± 2.64mm) cut from the core region and hoop region of the luffa sponge exhibit different mechanical behaviors under compression depending on both the orientation they are loaded in as well as the location in the sponge they are sampled from. The hoop region consists of the section of sponge located around the outside between the inner and outer surfaces, while the core region is from the sponge center. Samples from both the hoop and core regions exhibited yielding when compressed in the longitudinal direction due to the buckling of fibers. With the highly aligned fibers from the inner surface removed from the hoop region block samples, this yield behavior disappears. In general, the inner surface fibers most significant impact the longitudinal properties of the luffa sponge column followed by the circumferential properties. There is no noticeable contribution to the radial properties. Additionally, the core region exhibits lower yield stress and energy absorption (as determined by the area under the stress-strain curve) compared to the hoop region due to its greater porosity.^[15]

Overall, the stress-strain curves of block samples exhibit three stages of mechanical behavior common to porous materials. Namely, the samples follow linear elasticity for strains less than 10%, followed by a plateau for strains from 10% to 60%, and finally a stress increase associated with densification at strains greater than 60%. Segment samples created from cross sections of the entire luffa sponge (diameter: 92.51 ± 6.15mm, height: 19.76 ± 4.95mm) when tested in compression exhibit this same characteristic behavior.^[15] The three stages can be described by the equations:

1. Linear elasticity region: ${\displaystyle \sigma =E^{*}\varepsilon }$ for ${\displaystyle \varepsilon \leq \varepsilon _{e}}$
2. Plateau region: ${\displaystyle \sigma =\sigma _{p}^{*}}$ for ${\displaystyle \varepsilon _{e}<\varepsilon \leq \varepsilon _{D}(1-1/D)}$
3. Densification region: ${\displaystyle \sigma =\sigma _{p}^{*}/D{(\varepsilon _{D}/\varepsilon _{D}-\varepsilon )}^{m}}$ for ${\displaystyle \varepsilon >\varepsilon _{D}(1-1/D)}$ ^[17]

In the above equations, ${\displaystyle E^{*}}$ is the Young's modulus and ${\displaystyle \sigma _{p}^{*}}$ the yield strength of the sponge material. These are chosen to best fit experimental data. The strain at the elastic limit, where the plateau region begins, is denoted as ${\displaystyle \varepsilon _{e}}$, while the strain at the onset of the densification region is ${\displaystyle \varepsilon _{D}}$.^[17]

${\displaystyle \varepsilon _{D}=1-1.4(\rho ^{*}/\rho _{s})}$

Here ${\displaystyle \rho ^{*}}$ is the density of the bulk sponge ${\displaystyle \rho _{s}}$ is the density of its constituent, the fiber bundle. The constant D defines the strain at the onset of densification as well as the stress relationship in the densification region. It is determined by fitting experimental data.^[17]

Dynamic loading

The mechanical properties of Luffa sponges change under different strain rates. Specifically, energy adsorption, compressive stress, and plateau stress (which is in the case of foam materials corresponds to the yield stress) are enhanced by increasing the strain rate.^[15][18] One explanation for this is that the luffa fibers undergo more axial deformation when dynamically loaded (high strain rates) than when quasi-statically loaded (low strain rates).^[18]

Gallery

• 
  Luffa (right), illustration from the Japanese agricultural encyclopedia Seikei Zusetsu (1804)
• 
  Habitus of the vine
• 
  Luffa in a coconut tree
• 
  Commonly known as Ridge Gourd from Southern India
• 
  Extrafloral nectar glands^[19] in Luffa acutangula and Oecophylla smaragdina ants
• 
  Luffa leaf
• 
  A bag of dried mature luffa fruits.
• 
  Luffa aegyptiaca, fruit and seeds -

  MHNT
• 
  Luffa operculata, fruit - MHNT
• 
  A luffa sponge whose coarse texture helps with skin polishing
• 
  Luffa aegyptiaca sponge section magnified 100 times
• 
  Luffa acutangula seeds. Each division of the ruler is 1 mm. Seeds of Luffa aegyptica look very similar.
• 
  Pollen grains of Luffa
• 
  Luffa flowers
• 
  Sponges made of sponge gourd

References

External links

Wikimedia Commons has media related to Luffa.

• Multilingual taxonomic information from the University of Melbourne