Rheological properties of agar from Gracilariopsis heteroclada (Zhang et Xia) Zhang et Xia (Gracilariales, Rhodophyta) treated with powdered commercial lime and aqueous alkaline solution
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Rheological properties were measured for 1.5% agar gels from Gracilariopsis heteroclada pre-treated with powdered commercial lime (CaCO3) during sun drying, and a combination of two alkaline solutions during water-bath heating in the laboratory. All samples were subjected to a one or three hours of heating prior to extraction. Slightly higher agar yield were obtained from samples treated with lime while drying (2.9-4.5%) than from seaweed (2.1-3.8%) treated with alkaline solutions in the laboratory. Better rheological (breaking strength,cohesiveness, breaking energy, and rigidity) and physical properties (dynamic gelling and melting temperatures) were obtained from laboratory treated seaweed after a 3-hour treatment. No effect of collection site, alkali treatment and treatment time on the yield of agar, was observed. However, significant (P ≤ 0.01) effects were recorded for collection site, alkali treatment and treatment time both on rheological properties and on gelling and melting temperatures.