Impact of alkali pretreatment on yield, physico-chemical and gelling properties of high quality agar from Gracilaria tenuistipitata

Abstract

Yield, physico-chemical and gelling properties of agar from Gracilaria tenuistipitata as affected by alkaline treatments conditions at various levels were investigated. Agar with alkaline treatment, especially at higher alkali concentration, showed better gelling property as evidenced by higher gel strength (624.4–1250.8 g cm−2), gelling (28.1–43.2 °C) and melting (96.4–99.6 °C) temperatures with coincidentally increased 3,6-anhydrogalactose content (38.93%–44.78%) and decreased sulphate content (7.79%–3.48%), but reducing yield (22.34%–15.61%). Treatment temperature or time has a positive influence on agar properties in appropriate range, while higher temperature or longer time might result in yield reducing. Alkaline treatment with 6% alkali at 80 °C for 1.5 h was the optimal pretreatment process, with the gel strength reached to 1068.15 g cm−2 and obtained high yield (23.14%), which are higher than the earlier reports. Meanwhile, the study of the correlation between physico-chemical and gelling properties of agar confirmed that the gel strength has negative correlation relationship with sulphate content (p < 0.05), while positive correlation with 3,6-anhydrogalactose content (p < 0.01) and gelling (p > 0.05) or melting temperatures (p > 0.05). Overall, this work suggested the feasibility of the exploitation of G. tenuistipitata for production of superior quality agar, which are mainly from Gelidium species.