Rheological properties of agar from Gracilariopsis heteroclada (Zhang et Xia) Zhang et Xia (Gracilariales, Rhodophyta) treated with powdered commercial lime and aqueous alkaline solution

Abstract

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.