Seasonal agar yield and quality in Journal t~fApplied Phycology 7: 141-144, 1995.
(~) 1995 Kluwer Academic Publishers. Printed in Belgium.
141
Seasonal agar yield and quality in Gelidium canariensis (Grunow)
Seoane-Camba (Gelidiales, Rhodophyta) from Gran Canaria, Spain
Y. Freile-Pelegrfn 1,2,*, D. R. Robledo 2 & G. G a r c f a - R e i n a 1
i Instituto de Algologfa Aplicada, Instituto Tecnoldgico de Canarias, Box 550 Las Palmas de Gran Canaria, Spain
2 CINVESTAV- Unidad M#rida, AP, 73 Cordemex 97310, M#rida, Yucatdn, Mdxico (E-mail:
freile @kin. cieamer, conacyt, mx)
(* Author for correspondence; 2 present address)
Received 7 October 1994; revised 19 January 1995; accepted 23 January 1995
Key words: Gelidium canariensis, agar, seasonality
Abstract
The seasonal effects on yield and gel properties of Gelidium canariensis agar were investigated at two intertidal
populations at the northern coast of Gran Canaria. Physical and rheological properties were measured in 1.5% w/v
solutions after treatment with alkali. No significant differences were found on agar characteristics between the two
sites studied. The highest yields were obtained during summer with a maximum in June (27.8%) and minimum
during late autumn and winter (18-18.6%). Overall quality was highest in winter (November-January), when gel
strength peaked above 850 g cm -2. The results showed an agar of industrial quality.
Introduction
Gelidium and Pterocladia species are usually regarded as yielding the best quality agar and the highest
prices. The former genera constitute about 47.3% of
the world's annual use for agar extraction, estimated
to be about 6683 t (Armis6n, 1994). Species of Gelidium are extremely important because their extract best
meets the requirements of gel strength and temperature
hysteresis for bacteriological agar, along with that from
Pterocladia which is available in only small amounts
(Armis6n & Galatas, 1987).
Most resources of Gelidium are obtained from
Spain, Portugal, North Africa and Korea with the Spanish harvest accounting for 20% of the world total Gelidium harvest (McHugh, 1991). Estimated agar production in Spain is around 890 t y-1 representing approximately 65% of European production (Indergaard &
Ostgaard, 1991). Although the main agar source is G.
sesquipedale (Clemente) Thuret, there are other less
known species that could be used by local industries.
G. canariensis (Grunow) Seoane-Camba is an agarophyte restricted to the northen coasts of some of the
Canary Islands. There have been no published studies
on the agar content and quality of this seaweed.
According to Santelices (1988), a comprehensive
management model based on seasonal changes in the
rheological and physical properties of agar should precede intensive harvesting and exploitation of agarophytes. It is well known that agar composition and
content in agarophytes depends on the season of the
year; these changes are usually associated with variations in water temperature, light intensity, photoperiod
and geography (Santelices, 1988). Seasonal changes
in the yield and quality of agar in Gelidiales have been
reported by several authors (Carter & Anderson, 1986;
Onra~t & Robertson, 1987; Garcfa, 1988; MouradiGivernaud et al., 1992), but differences in the results
exist because different methods used for agar extraction. Also, Armis6n (1994) has noted the need to consider the level of 'pure seaweed' within a normal harvest in order to determine realistic yields.
The present study was undertaken to ascertain
whether seasonal variation occurs in the yield and rheological and physical properties of the agar obtained
from G. canariensis growing at two populations in the
northern coast of Gran Canaria and to evaluate whether
142
this seaweed could be of importance to the agar industry.
Materials and methods
Plant collection
Gelidium canariensis plants were collected monthly at Bocabarranco (28°09'N, 15°40'W) and Agaete
(28006 ' N, 15°43 ' W) from August 1991 to July 1992
at an exposed northern rocky shore of Gran Canaria
Island. Seawater temperature was recorded in situ during the monthly sampling. Plants were collected during
low tide, transported to the laboratory, washed thoroughly with tap water, centrifuged to remove excess
water, weighed and oven dried (60-70 °C) overnight.
Samples were stored in sealed plastic bags until agar
extraction. To determine levels of pure seaweed, subsamples of fresh material were weighed, cleaned and
reweighed. Three samples (1 g each) of fresh pure seaweed were oven dried for 24 h at 60 °C to estimate
monthly changes of percent dry weight.
(room temperature) until the glass bead ceased moving. The gel temperature in the tube was immediately
measured introducing a precision thermometer (0.1 °C
divisions). Melting temperature of the gel in a test tube
(2.3 cm diameter, 16.5 cm height) was measured by
placing a lead bead (9 mm diameter) on the gel surface. The test tube was clamped in a water-bath and
the temperature raised from 50 to 100 °C; the melting
point was recorded with a precision thermometer when
the bead sank into the solution.
Statistical analysis
The data were tested for normality (KolmogorovSmirnov) and homogeneity of variance (Bartlett test)
using a statistical software package. Simple linear correlation analysis were use to correlate data. Statistical
significant differences in yield, gel strength and dry
weight between months and localities were tested using
a multiple analysis of variance (MANOVA) followed
by a least significant difference test.
Results
Agar extraction
Seaweeds were exposed to a 0.5% solution of Na2CO3
at 85-90 °C for 30 min prior to extraction and washed
with running tap water for 10 min. Agar was extracted
(n = 3) with distilled water at a pH between 6.0-6.5 and
autoclaved at 120 °C for 2 h. The extract was ground
with a commercial blender and heated at 90 °C with
diatomaceous earth for 30 min and pressured filtered.
The filtrate was allowed to gel at room temperature,
frozen overnight and thawed. Finally the agar was oven
dried for 24 h at 60 °C, cooled and weighed to calculate
percent agar.
Gel properties
The dry agar was ground in a Tecator mill and reconstituted into 1.5% w/v solutions to measure gel strength,
melting and gelling temperature (n = 3). Gel strength
was measured after gelling overnight at room temperature by measuring the load (g cm -2) that causes a cylindrical plunger (1 cm 2 cross section) to break a standard
gel in 20 s (Armis6n & Galatas, 1987). Gelling temperature was obtained by the addition of 10 ml hot agar
solution into a test tube (2.3 cm diameter, 6 cm height).
A glass bead (5 mm diameter) was placed in the test
tube. The tube was tilted up and down in a water bath
The Gelidium canariensis population at Bocabarranco
was more homogeneous than the population located at
the northwest. In Agaete, the plants were shorter (5-10
cm) with obvious epiphyte cover throughout the year
with a mean value of 13.9% fresh weight corresponding to epiphytes, when compared with Bocabarranco
plants (8.86% fresh weight).
The dry weight oscillated around 30% depending
on the season, with a peak in September for Agaete
(52%) and in October for Bocabarranco (65%). Agar
yield and percent dry weight were generally inversely
related (Fig. 1). Sea water temperature ranged between
17.7 to 23.5 °C and was correlated positively with dry
weight values (p < 0.05, r = 0.57 and r = 0.72, Agaete
and Bocabarranco respectively).
Agar yield from G. canariensis fluctuated seasonally in both localities from 16.7% to 32.6% with a mean
value of 23.1% (Fig. 1). The mean agar yield values in
Agaete were slightly higher (23.4%) than in Bocabarranco (22.7%). The highest yields were obtained from
plants harvested during summer with a maximum value
in June for Agaete (32.6%) and in August for Bocabarranco (30.2%). Agar content was minimal at both sites
during November and January-February with values
of 18.2%-17% in Bocabarranco, and 16.6-16.8% in
Agaete.
143
900
a
40
a
60
8O0
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\
7O0
N
600
E
o
500
Y'
o
o~
c
400
.-
900
r
l
i
~
f
~
~
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t
~
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600
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15 ~ ,
A
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~
,
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r
,
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400A
Fig. I. Seasonal variation of the agar content (-) and dry weight
(- -) of Gelidium canariensis in a. Agaete ( I ) and b. Bocabarranco
S
D
1991
1992
d
F M A
a
d
1992
Fig. 2. Seasonal variation of the agar gel strength from Gelidium
Canariensis in a. Agaete (Q) and in b. Bocabarranco (O).
(o).
Gel strength varied from 513 g c m -2 to 903 g
cm -2 for Agaete and between 470 to 873 g c m -2 for
Bocabarranco (Fig. 2). In both localities the higher gel
strength occurred in November, December and January coinciding with the lowest yield values (p < 0.05,
r = -0.25). Minimum gel strength values were found
during March (513 g cm -2) and July (588 g c m -2) in
Agaete, while in Bocabarranco were recorded during
February (492 g cm -2) and July (502 g cm-2).
Gelling temperature ranged from 35.7 °C to 39.3 °C
with a mean value of 37.5 °C for Agaete and from
34.6 °C to 37.5 °C with amean of 36.4 °C for Bocabarranco, while melting temperature ranged from 85.1 °C
to 93.7 °C with a mean of 89.2 °C for Agaete and
85.5 °C to 92.1 °C with a mean of 89.5 °C for Bocabarranco. There was a positive correlation between gel
strength and melting temperature in Agaete (p < 0.05,
r=0.39) and in Bocabarranco (p < 0.05, r=0.44).
Multiple analysis of variance showed a significant difference in the variables studied (gel strength, yield, dry
weight) both seasonally (p < 0.000 I) or between localities (p < 0.005), confirming the annual variation in the
agar characteristics. However, when the locality was
used as the main effect for the same variables, the only
significant difference between Agaete and Bocabarranco was for the dry weight (p < 0.005).
Discussion
There were substantial seasonal changes in agar characteristics of G. canariensis at Gran Canaria, but
no significant differences in the agar characteristics
between the two populations. Dry weight was found
to differ between localities probably due to the plants
from Agaete being smaller than those from Bocabarranco. Betancort and Gonzzilez (1991) found that G.
canariensis was larger in the Bocabarranco population
(size classes 10-15 cm and > 15 cm) than the Agaete
population where there were no individuals > 15 cm
and with the medium size class (5-10 cm) predominating.
High agar yield occurred during late spring and
summer, with a minimum during winter similar to
G. sesquipedale (Garcfa, 1988). Mouradi-Givernaud
144
et al. (1992) also reported high yield during summer
for G. latifolium, but they found another maximum
in November. The highest agar yields may be related
to the development of the thermocline and the lowest
nutrient concentrations at that season of the year. An
increase in agar content with nutrient deficiency has
been also found by Carter and Anderson (1986).
The inverse relationship between agar yield and
dry weight suggests that agar synthesis occurs at the
expense of biomass production (Fig. 1). Similar results
have been found by Mouradi-Givernaud et al. (1992)
for Gelidium latifolium. Increased biomass was also
related to an increased in sea water temperature based
on dry weight changes. Sosa et al. (1993) reported
superior photosynthetic performance at 25 °C for G.
canariensis.
Seasonal changes in gel strength of G. canariensis
agar are comparable with those obtained for Onikusa
pristoides (Onra6t & Robertson, 1987) and for Gelidium latifolium (Mouradi-Givernaud et al., 1992). In
contrast, there have been reports of high values in gel
strength for summer and low ones for winter from
G. sesquipedale (Establier, 1964). The relationship
between gel strength and melting temperature has been
known for many years, and both measurements are usually considered when agar quality is of interest (Selby
& Wynne, 1973). Higher melting temperatures and
higher gel strength have been related with decreasing amounts of sulfate in agar (Yaphe & Duckworth,
1972). The sulfate content in agar from G. canariensis was inversely correlated with gel strength in both
localities (data not shown).
Gel properties of G. sesquipedale are higher than
those obtained for G. canariensis: gel strength and
agar yields ranged between 920 to 1500 g cm -2 and
29-35%, respectively (Establier, 1964; Garcfa, 1988)
while in G. canariensis they were 700 g cm - 2 and
23%. Thus, G. canariensis is a potential a source for
bacteriological agar. The best period for harvest to
obtain high gel strength occurs in the winter months,
but studies on biomass are needed before an optimum
harvesting programme can be recommended.
Acknowledgments
This study was supported by a fellowship from Fundaci6n Universitaria de Las Palmas to Y. FreilePelegrfn. C O N A C y T (M6xico) is acknowledge for
financial support to D. Robledo. We express our sin-
cere thanks to D. Rafael Armis6n for fruitful support
and advice.
References
Armis6nR, GalatasF (1987) Production,properties and uses of agar.
In McHughDJ (ed.), Productionand Utilizationof Products from
Commercial Seaweeds. FAO Fish. Tech. Pap. 288:1-57
Armis6n R (1994) Productos derivados del Gelidium: producci6n,
estructura y aplicaciones.In Juanes JA, GonztllezS (eds), Gelidium: de los Recusos alas Aplicaciones.Diputaci6nGeneral de
Cantabria (in press).
Betancort MJ, Gonz,51ezMN (1991) Estudio preliminar sobre la
biologfa de las poblaciones de Gelidium canariensis (Grunow)
Seoane en Gran Canaria. Acta BotfmicaMalacitana 16: 51-58.
Carter AR, AndersonRJ (1986) Seasonalgrowth and agar contentsin
Gelidium pristoides (Gelidiales,Rhodophyta) from Port Alfred,
South Africa. Bot. mar. 29:117-123.
Establier R (1964) Variaci6nestacionalde la composici6nqulmica,
extracci6ny caracteristicas del agar-agarde algunasalgas (g6nero
Gelidium) de la costa sudatl~nticaespafiola. Inv. Pesq. 26: 165194.
Garcfa I (1988) Estudio de la variaci6n estacional de la calidad y
el rendimientodel agar obtenidodel alga Gelidium sesquipedale
(Clem.) Born. et Thur. en la costa guipuzcoana(N. de Espafia).
Inf. Tecn. Inv. Pesq. 146: 3-19.
Indergaard M, Ostgaard K (1991) Polysaccharides for food and
pharmaceutical uses. In Guiry MD, Blunden G (eds), Seaweed
Resources in Europe: Uses and Potential. Wiley & Sons: 169183.
McHughDJ (1991) Worldwidedistributionof commercialresources
of seaweeds includingGelidium. Hydrobiologia221: 19-29.
Mouradi-GivernandA, GivernaudT, Morvan H, Cosson J (1992)
Agar from Gelidium latiJolium (Rhodophyceae, Gelidiales):Biochemicalcompositionand seasonalvariations.Bot. mar. 35: 153159.
Onra~t AC, Robertson BL (1987) Seasonal variation in yield and
properties of agar from sporophytic and gametophyticphases of
Onikusa pristoides (Turner)Akatsuka (Gelidiaceae, Rhodophyta). Bot. mar. 30: 491-495.
Santelices B (1988) Synopsisof biologicaldata on the seaweed genera Gelidium and Pterocladia (Rhodophyta). FAO Fish. Synop.
145:55 pp.
Selby HH, WynneWH (1973) Agar. In WhistlerRL (ed.), Industrial
gums, polysaccharides and their derivatives. Academic Press,
New York: 22-48.
Sosa P, Jim6nez del Rfo M, Garcia-Reina G (1993) Physiological comparison between gametophytes and tetrasporophytes of
Gelidium canariensis (Gelidiaceae: Rhodophyta). Hydrobiologia 260/261 (Dev. Hydrobiol. 85): 445-449.
Yaphe W, Duckworth M (1972) The relationshipbetween structures
and biologicalproperties of agars. Proc. 7th Int. Seaweed Symp.
7:15--22
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