Environmental Engineering Reference
In-Depth Information
Table 1
(continued)
Species
packaging material, photography, leather industry,
plywood manufacturing, cosmetics, and pharma-
ceutical industry.
Uses
Countries
Sargassum
spp.
Ag
Brazil, Vietnam, India,
China, South Africa,
Australia
5.1.1 Method of Agar Production
from Seaweed
A brief account of the extraction of agar from
Gracilaria
/
Gelidium
is given below (McHugh
2003
). Collected and dried seaweeds are washed
with water to remove adhering mud and sand. It
is soaked in acidifi ed water (0.5 N HCl) for 24 h.
It is then washed, taken, and introduced into
boiling potable water at 100 °C. The ratio of
seaweed to water is 1:40. The pH at the begin-
ning of the extraction is adjusted to slightly acidic
after introducing seaweeds. This will facilitate
easy extraction of the gel. Extraction was carried
out at 100 °C for 1 h at this temperature, and then
the liquid is allowed to simmer for another hour.
Finally, the extract is left in a warm chamber to
cool gradually, permitting the sedimentation of
suspended particles. The clear supernatant liquid
was separated, kept at ambient temperature for
some time, and then cooled. The gel is formed
and is slightly warmed to melt. Or the gel is
removed, melted in water, and poured in to
enamel trays to form the gel again. Upper layer of
the gel is suffi ciently scored using a cutter to
increase the surface area to enable to freeze
immediately. It is frozen at temperature between
0 and −5 °C for 24 h and it is allowed to thaw at
room temperature. The process is repeated till
complete water is removed. It is then drained
off; the gel is placed on plastic screen and then
in galvanized wire netting and is dried either in
shade or in hot air at 65 °C in most of the agar
manufacturing plants, and it is bleached using
mild chlorine water when it is thawed. It is
washed free of chlorine using potable water. The
dried agar is powdered and packed in polyethyl-
ene bags. Agar can also be packed in the form of
agar shreds. The agar obtained is of good quality,
and the yield is about 13-15 % of the dry seaweeds.
The processing method is slightly different when
the bacteriological grade is manufactured. Gel
solution is fi ltered using a fi lter press and drying
is done at a low temperature. It is pulverized
using a pulverizer fi ne mesh. Gel strength is the
Al
Vietnam
F
Bangladesh, Hawaii,
Malaysia, Myanmar,
Philippines, Thailand,
Vietnam
M
Brazil, Vietnam
Sargassum fi lipendula
F
Egypt
Sargassum
graminifolium
Al
Vietnam
Sargassum
henslowianum
Al
Vietnam
Sargassum horneri
F
Korea
Sargassum ilicifolium
Al
India
Sargassum mcclurei
Al
Vietnam
Sargassum myriocystum
Al
India
Sargassum oligosystum
F
Thailand
Sargassum polycystum
F
Indonesia, Thailand
AL,
M
Vietnam
Sargassum siliquosum
Al
Vietnam
F, M
Indonesia
Sargassum wightii
Al
India
Sargassum
vachelliannum
Al
Vietnam
Turbinaria
spp. Ag Vietnam
M Philippines
Turbinaria conoides
Al India
Turbinaria decurrens
Al India
Turbinaria ornata
Al India
Undaria pinnatifi da
F Australia, China,
France, Japan, Korea
Undaria peterseniana
F Korea, Japan, China
F
food,
A
agar,
C
carrageenan,
Al
alginate,
M
medicine,
RoK
roe on kelp,
Ag
agricultural,
P
paper (Zemke-White
and Ohno
1999
)
5
Seaweeds for Industrial
Applications
5.1
Agar-Agar Production
Agar is the major constituent of the cell walls of
certain red algae especially members of the
Gelidiaceae and Gracilariaceae. Agar is widely
used in paper manufacturing, culture media,
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