The genus Eucheuma, is an important carrageenophyte which is abundant in the Philippines, tropical Asia and the Western Pacific region. It occurs in the regions of the south of China, for example, Hainan Island, the Xisha Islands and Taiwan. Eucheuma is a genus of tropical seaweeds which grows on coral reefs, most abundantly from the lowest tide level to 1-2m deep in the sublittoral zone. This genus belongs to the Family Solieriaceae, of the Order Gigartinales. The thalli of Eucheuma are very cartilaginous, prostrate or erect, and consist of cylindrical to compressed branches.

The life cycle of Eucheuma consists of an alternation of three somatic stages, namely the tetrasporophyte (asexual), the gametophyte (sexual) and the carposporophyte. The tetrasporophyte (2n) and the gametophyte (n) are large and isomorphic (they have the same thallus form). The carposporophyte (2n) is microscopic and parasitic on the female gametophyte.

Eucheuma denticulatum is presently cultivated in the Philippines, Indonesia, Western Central Pacific Islands and several other tropical countries. This species is also commercially farmed in northern Bohol and other areas, and forms part of the Philippines seaweed export. Eucheuma denticulatum, is farmed using the following methods of culture:

1. the fixed, off-bottom monoline method , and

2. the raft or long-line method.

The fixed, off-bottom monoline method is the most common method used in the culture of Eucheuma. This method has many advantages over other methods used in the past, such as the net method. The farm is cheaper to maintain and easier to install. The stakes which are spaced at 10m intervals, in rows that are 1m apart, are driven deep into the substratum. Tied to the one stake, is one end of the nylon monofilament line, which is stretched so that the other end can be tied to another stake in the opposite row. Eucheuma cuttings which are approximately 50-100g, are tied to the monolines at 25-30cm intervals using soft plastic tying material, such as soft plastic straw, also referred to as "tie-tie".

These plants are allowed to grow to 1kg or more before they are harvested, and depending on the growth rate, may be harvested after 2-3 months. Whole plants of Eucheuma are harvested and replaced by new cuttings. Floating methods involve Raft or long-lines. The raft and long-line methods can only be used in areas where the water currents are weak, or in protected areas where the water movement is mainly due to wave action generated by wind.

In the raft method, the monolines are attached to a wooden frame (3x4m), and the bamboo is used as a flotation device. In some areas, plastic bags filled with air are used as flotation devices. Fifteen monolines, which are 4,5m long, and spaced at 20m intervals are attached to the wooden frame. Five rafts are joined together as one unit, which is then anchored to the bottom from the corner of each unit using wooden stakes. Three to four hundred cuttings can be planted on one raft.

The long-line, floating method comprises 6 nylon monofilament lines (10m or longer), are attached to bamboo (2m long), which are set at 5m intervals. The nylon lines are attached to the bamboo at 30cm intervals. Each long-line unit can be planted with 400 cuttings, which are tied to the nylon lines at 15cm intervals. The four corners of the unit are anchored to the wooden stakes.

Factors such as intense grazing and/or seasonality in growth, disease and changes in the degree of water movement brought about monsoons, and also a space shortage, prevents the fixed, off-bottom monoline method, but allows for the floating methods.

The advantages of these floating methods over the fixed,off-bottom method are:

1. grazing by bottom-associated animals is minimized or eliminated because the plants are raised out of reach of benthic grazers,

2. plants being near the surface of the water column are exposed to more moderate water movement caused by waves.

USES OF EUCHEUMA

Eucheuma is presently exported in four forms:

1. As dried, raw seaweed,

2. As alkali-treated chips,

3. As a semi-processed powder, and

4. As pure carrageenan.

There are three main types of carrageenan, lambda, kappa and iota, each having their own characteristics. There is a great demand for kappa-carrageenan. The different forms of the phycocolloid are extracted from different species and genera of red seaweeds, e.g. Chondrus is harvested and provides a mixture of lambda and kappa forms, Gigartina from southern Europe is a good source of lambda. Eucheuma cottonii yields good kappa-carrageenan whilst E. spinosum gives good yields of the iota form.

Carrageenan is used mainly in food applications, largely in convenience foods. Small amounts of carrageenan are employed by the pharmaceutical and cosmetic industries. The major industrial use of carrageenan is in air-freshener gels. They are valuable gelling and stabilizing agents in foods, and they are effective at respectively low concentrations. Carrageenans are used to improve and balance the behavior of other gums, especially guar gum, locust bean gums and carboxymethyl cellulose. As carrageenan retain a strong negative charge over the normal pH range, they are used extensively in ‘milk reactivity' which has been one of the major advantages of this group of phycocolloids. Lambda-carrageenan is used for the stabilization of cold-milk products, and kappa-carrageenan with pasteurized products.

Big processors prefer the semi-processed material such as alkali-treated chips, because the quality of the raw material is good and they can avoid pollution problems associated with the disposal of processing wastes in their own countries. Chips are then made by heating the seaweed for 2 hours at 85°C in a 2-N KOH solution, which increases the gel strength of the carrageenan. The plants are washed to remove the alkali, chopped wet, and then dried to form chips. The chips can be ground to produce seaweed flour. The flour is used in products not intended for human consumption, such as gelation of pet foods and air fresheners.

The gels and solutions of seaweed flour are cloudy and grainy because it has a 9-15% fibre content. Alcohol-precipitated carrageenan solutions are clear. Still, manufacturers prefer the seaweed flour to the extracted carrageenan for human foods, because it is cheaper.