SUMMARYSeasonal variation of agar f

SUMMARY
Seasonal variation of agar from specimens of a commercially exploited population ofGracilaria gracilis
(Stackhouse) Steentoft, Irvine & Farnham in the Patagonian coast of Argentina was studied. For each seasonal harvest, random samples of plants were pooled
for subsequent polysaccharide extraction at different water temperatures and agar physico-chemical
properties and composition were determined.
Both spring and summer plants yielded 30% and 41%
of agar, respectively, which differed slightly in theirat
rest rheological behavior. Spring and summer plants
produced strong gels (238 and 218 g cm
-2
, respectively), but the latter gels had nil adhesiveness. In
autumn plants, agar yield decayed to 19%, though
the product still maintained similar gel strength
(210 g cm
-2
). Adhesiveness in this product was at least
an order of magnitude higher than in the others, concomitant with a peak in the formation of tetraspores
and carpospores. This suggests a biological role for the
galactan in the initial attachment of spores to the
substrate. But since fall corresponds to the settling of
reproductive structures, caution should be taken to
harvest the algae once spores have been shed from
mother plants.
Key words: agar,Gracilaria gracilis, rheological behavior,
seasonal variation.
INTRODUCTION
The genusGracilariaGreville (Gracilariales, Gracilariaceae, Rhodophyta) includes worldwide species of economical significance (Smit 2004) in the phycocolloid
industry. Due to its agar’s high yield and quality,G. gracilis(Stackhouse) Steentoft, Irvine & Farnham together
withG. chilensisBird, McLachlan & Oliveira are the
most frequently exploited species (Oliveira et al.,
2000). In Argentina,G. gracilisgrows exclusively in the
Chubut Province, where the agar industry is based on
collection from the commercial beds located in small
bays in the north of Golfo San Jorge, such as Bahía
Bustamante, Bahía Melo and Bahía Arredondo. Being
the most productive, the population of Bahía Bustamante has been exploited since the end of the 1960s,
leading to a notorious decrease in annual production
(Boraso et al., 2006). Aiming to achieve a sustainable
exploitation of natural beds, a monitoring of the annual
cycle of the population was undertaken (Martínet al.,
2010) in order to design the appropriate harvest schedule to promote resource renewal and/or propagation.
Summer plants produce a good quality agarose with
a 71% yield, which does not require alkaline pretreatment, even when extracted at 70°C (Rodríguez
et al., 2009).
Composition and properties of Gracilaria agars
depend on, among others, the species, physiological
factors, life cycle stage, environmental conditions
including seasonal and geographical aspects, extraction
procedures and post-harvest storage (Marinho-Soriano
& Bourret 2003; Marinho-Sorianoet al., 2006; Romero
et al., 2008). Yet, knowledge on seasonal variation in
chemical composition and physical properties of agar
extracted fromG. gracilisfrom Bahía Bustamante has
not been informed