Biology and agar composition of Gelidium sesquipedale harvested along the Atlantic coast of Morocco

Abstract

Gelidium sesquipedale (Clem.) Bornet et Thuret is the main raw material used for agar production in Morocco. The biology and biochemistry of this slow growing alga collected monthly over one year has been studied. The agar content varied around 40% of algal dry weight and reached a maximum of 44.5% in November. Agar gel strength was maximum in May and July (1000 g cm-2), and melting (90 °C) and gelling (35 °C) temperatures varied slightly. The agar contained a high 3,6-anhydrogalactose content (40-45 mol%) and low amounts of 6-O-methylgalactose (around 1 mol%) and sulphate (1.0-1.6% of dry weight). The reproductive status of the alga affected the agar synthesis and quality. The phycocolloid gel strength was related to the mean polysaccharide chain length but not to its chemical substitution.