Pilot plant scale extraction of alginate from Macrocystis pyrifera. 1. Effect of pre-extraction treatments on yield and quality of alginate

In the extraction of alginate from brown seaweeds, the acid pre-extraction treatment has been considered by many authors as an essential step because it makes the alginate more readily soluble in an alkaline solution. At pilot plant level, extractions were made (i) using formalin treatment prior to the acid pre-extraction treatment (ii) using different acid treatments so the calcium ions exchanged varied from 83% to 4%. The use of formalin treatment gave a product with less color. During the acid pre-extraction treatment, it was possible to reduce the calcium exchanged from 33.4% to almost zero with a maximum reduction in alginate yield of 7%. The degree of acid treatment was positively correlated to calcium exchanged and yield but negatively correlated with alginate viscosity. Using strong acid conditions the viscosity was 168 mPa s, while mild acid conditions produced an alginate with 623 mPa s. The direct extraction from calcium alginate to sodium alginate is possible because strong alkaline conditions were used, pH 10 at 80 °C for two hours and with a low water volume. The best pre-extraction treatment to obtain an alginate with high viscoity is to hydrate the alga with 0.1% formalin overnight, then wash the alga once with hydrochloric acid at pH 4 using a batch system with continuous agitation during 15 min.