Effect of dark and salinity treatment in the yield and quality of agar from Gracilaria cornea (Rhodophyceae)

Abstract

The alkali treatment used previous to agar extractions from the Gracilaria genus reduces, among other reactions, the sulphate content and improves the gel strength; however, at an industrial level it requires expensive effluent processing to reduce its polluting charge. The red alga Gracilaria cornea was cultivated under dark and salinity treatments to replace this alkali treatment. The different treatments tested were: (a) darkness and 33‰ salinity for 8 days, [dark treatment]; (b) darkness and 50‰ salinity for 4 days, followed by darkness and 25‰ salinity for 4 days, [4+4]; and (c) darkness and 50‰ salinity for 8 days, followed by darkness and 25‰ salinity for 4 days, [8+4]. The treatment [4+4] increased the agar yield in 26% (from 36.6 to 46.1%). All treatments reduced the sulphate content of the agar in approximately 24% when compared with agar obtained without any treatment. For G. cornea the [4+4] treatment might become in the future an additional treatment to a mild alkali treatment using less alkaline reagents for agar extraction.