BIOLOGY O F SEAWEEDS OF ECONOMIC IMPORTANCE
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B. Terminology associated with the extractives
Agar (agar-agar) : a term now used to describe the water-soluble gel
extracted from agarophytes. Originally a Malayan term for a seaweed
which yielded the gel (Eucheuma) it then became synonymous with jelly
and hence to the general usage mentioned above.
Akin (alginic acid): a cell wall constituent of brown seaweeds.
Alkali soluble, and a polymer of mannuronic acid (Mautner, 1964).
The source of alginates, important products of the seaweed industry.
Carrageenan: a galactose-sulphate derivative extracted from the
Carrageens. The terms phycowlloids (Tseng, 1947) and polysacolloid8
(Stoloff, 1962) are both used to describe the polymerized extractives
referred to in the earlier paragraphs.
Knowledge of the chemical nature of the extractives mentioned
above is now available. Agar has been taken to mean all watersoluble gels extractable from red algae, but in recent work there have
been attempts at arriving at a more precise definition, since in their
physical properties many of the gel-like extractives differ markedly.
Yaphe (1969) has defined it as an extract soluble in hot water and
requiring only a 1% solution to set as a gel on cooling. Its main
properties are due to agarose and this is a linear polymer of D-galactose
and anhydro-L-galactose. It also contains agaropectin, a sulphated
polysaccharide about which there is limited knowledge. These compounds are extracted from the agarophytes defined above. A more
critical identification is now possible with the isolation by Yaphe (1957)
of an agarase from Pseudomonas atlantica. This was found to be specific
for agar, and only hydrolysed the gel-like extracts from species of
Gelidium, Pterocladia pyramidale, Gracilaria verrucosa and Suhria
vittata.
The use of the term agaroid has already been indicated. By Yaphe’s
(1969) definition the extractives from Chondrus, Gigartina and related
genera are not true agars. These agaroid extractives (called carrageenans) have been found to consist of two components, the lambdaand kappa- fractions. Yaphe (1969) isolated kappa-carrageenase from
Pseudomonas atlantica and P . carrageenovera, an enzyme specific for
hydrolysis of the kappa-fraction. Use of this enzyme also enabled
quantitative differences to be shown for the kappa-fraction of different
extracts, e.g. the reducing properties of some hydrolyzed extracts were
greater than those of others. With two specific enzyme reactions it is
thus possible to distinguish between agar and carrageenan in plant
extractives.
A further development has been the attempts to link the bio-
111
B. Terminology associated with the extractives
Agar (agar-agar) : a term now used to describe the water-soluble gel
extracted from agarophytes. Originally a Malayan term for a seaweed
which yielded the gel (Eucheuma) it then became synonymous with jelly
and hence to the general usage mentioned above.
Akin (alginic acid): a cell wall constituent of brown seaweeds.
Alkali soluble, and a polymer of mannuronic acid (Mautner, 1964).
The source of alginates, important products of the seaweed industry.
Carrageenan: a galactose-sulphate derivative extracted from the
Carrageens. The terms phycowlloids (Tseng, 1947) and polysacolloid8
(Stoloff, 1962) are both used to describe the polymerized extractives
referred to in the earlier paragraphs.
Knowledge of the chemical nature of the extractives mentioned
above is now available. Agar has been taken to mean all watersoluble gels extractable from red algae, but in recent work there have
been attempts at arriving at a more precise definition, since in their
physical properties many of the gel-like extractives differ markedly.
Yaphe (1969) has defined it as an extract soluble in hot water and
requiring only a 1% solution to set as a gel on cooling. Its main
properties are due to agarose and this is a linear polymer of D-galactose
and anhydro-L-galactose. It also contains agaropectin, a sulphated
polysaccharide about which there is limited knowledge. These compounds are extracted from the agarophytes defined above. A more
critical identification is now possible with the isolation by Yaphe (1957)
of an agarase from Pseudomonas atlantica. This was found to be specific
for agar, and only hydrolysed the gel-like extracts from species of
Gelidium, Pterocladia pyramidale, Gracilaria verrucosa and Suhria
vittata.
The use of the term agaroid has already been indicated. By Yaphe’s
(1969) definition the extractives from Chondrus, Gigartina and related
genera are not true agars. These agaroid extractives (called carrageenans) have been found to consist of two components, the lambdaand kappa- fractions. Yaphe (1969) isolated kappa-carrageenase from
Pseudomonas atlantica and P . carrageenovera, an enzyme specific for
hydrolysis of the kappa-fraction. Use of this enzyme also enabled
quantitative differences to be shown for the kappa-fraction of different
extracts, e.g. the reducing properties of some hydrolyzed extracts were
greater than those of others. With two specific enzyme reactions it is
thus possible to distinguish between agar and carrageenan in plant
extractives.
A further development has been the attempts to link the bio-