Effects of partial acid hydrolysis on physical and chemical properties of agar from a newly reported Japanese agarophyte (Gracilariopsis lemaneiformis)

Abstract

Physical and chemical properties of alkali-treated agar polymers extracted from Gracilariopsis lemaneiformis, newly reported Japanese agarophyte, were investigated after partial acid hydrolysis. The alkali-treated agar was hydrolyzed in boiling 0.1 N, 0.01 N, and 0.001 N sulfuric acid, oxalic acid, acetic acid, and citric acid solutions, for 1, 2, and 3 h at 100 °C. Partial acid hydrolysis of the agar polymers indicated strong effects on the physical properties. Different kinds of acid used for hydrolysis gave different agar properties. Gelling polymers were obtained from the agar hydrolysed in boiling 0.001 N acetic acid, oxalic acid, and citric acid solutions, and in 0.01 N acetic acid solution. High gel strength (715 ± 74.6 g cm-2) with low viscosity (2.47 cP) was obtained from 1 h treatment by 0.001 N acetic acid on hydrolysed agar. The results indicated that partial hydrolysis of agar under appropriate conditions probably improve agar quality and produce good grade agar from the Japanese agarophyte.