Pretreatment Techniques and Green Extraction Technologies for Agar from Gracilaria lemaneiformis

Optimizing the alkali treatment process alone without tracking the changes of algae and agar quality with each pretreatment process will not achieve the optimal agar yield and final quality. In this study, we monitored the changes of the morphology and weight of algae with each treatment process, and comprehensively analyzed the effects of each pretreatment process on the quality of agar by combining the changes of the physicochemical properties of agar. In conventional alkaliextraction technology, alkali treatment (7%, w/v) alone significantly reduced the weight of algae (52%), but hindered the dissolution of algae, resulting in a lower yield (4%). Acidification could solve the problem of algal hardening after alkali treatment to improve the yield (12%). In enzymatic extraction technology, agar with high purity cannot be obtained by enzyme treatment alone, but low gel strength (405 g/cm(2)) and high sulfate content (3.4%) can be obtained by subsequent acidification and bleaching. In enzyme-assisted extraction technology, enzyme damage to the surface fiber of algae promoted the penetration of low-concentration alkali (3%, w/v), which ensured a high desulfurization efficiency and a low gel degradation rate, thus improving yield (24.7%) and gel strength (706 g/cm(2)), which has the potential to replace the traditional alkali-extraction technology.

Automated summary

Optimizing alkali treatment process alone is not sufficient to achieve the best agar yield and quality. Changes in algae morphology and weight, as well as the physicochemical properties of agar, need to be monitored and analyzed comprehensively during pretreatment processes. Acidification can improve yield by solving the problem of algae hardening after alkali treatment, and enzyme-assisted extraction technology shows potential to replace traditional alkali-extraction technology by promoting desulfurization efficiency and gel strength.