Developing a production process for agarose from Gracilaria sp. seaweed without using filter aids

Agar-like polysaccharides consist of two main components: a nonionic polysaccharide (agarose) and an ionic polysaccharide (agaropectin). Therefore, the process of producing agarose from seaweed includes two main stages: producing agar from seaweed and extracting agarose from agar.

Methods to separate agarose from agar typically involve precipitating agaropectin using quaternary ammonium salts or precipitating agarose using polyethylene glycol of various molecular weights. Other methods include the use of ion-exchange resins such as DEAE-Sephadex A-50 or 1-ethyl-3-methylimidazolium acetate, choline acetate and 1-ethyl-3-methylimidazolium diethyl phosphate, or a combination of precipitation and ion-exchange techniques. All these methods generally require high concentrations of agar solution (2-10%). Therefore, the process of producing agarose from seaweed involves several steps: (i) treating the seaweed with alkali, extracting the treated seaweed, and filtering the seaweed extract; (ii) subjecting the extract to multiple freeze-thaw cycles to isolate the agar product; and (iii) obtaining the agarose through solvent/chemical treatment and/or chromatography to remove impurities and residual agaropectin.

As a result, obtaining agarose consumes significant energy and time in converting seaweed extract into agar powder, followed by further chemical purification. This is the main reason for the high cost of agarose. To overcome this drawback, the project "Research and Development of an Agarose Production Process from Gracilaria sp. Seaweed Without Using Filter Aids," carried out by the Nha Trang Institute of Research and Application of Technology, introduced a technique to bypass the freeze-thaw cycle used in agar production and directly extract agarose from the seaweed extract.

Agar gel properties are strongly influenced by surfactants. Freezing strength and freezing-melting temperatures increase in the presence of ionic surfactants, while neutral surfactants have the opposite effect. The weakening of the agar gel network with neutral surfactants results in reduced gel strength due to the formation of micellar aggregates. In these aggregates, the hydrophobic aromatic core is surrounded by hydrophilic ethoxylate chains, which form hydrogen bonds with the hydroxyl groups of galactose monomers in agarose. Based on this scientific foundation, the research group developed a process to directly extract agarose from the seaweed extract, omitting the agar production step, thereby reducing energy costs and time.

The task achieved several key results:

Two species of seaweed, Gracilaria tenuistipitata and Gracilaria bailiniae, were selected as raw materials for agarose production after surveying the chemical composition and gel properties of seven species of seaweed collected from Vietnamese waters (Figure 1).

Figure 1. Images of the two species Gracilaria tenuistipitata and Gracilaria bailiniae collected from the waters of Khanh Hoa for agarose production.

A process was developed for extracting agarose from certain seaweed species without using filter aids, saving energy during the dewatering process. The specific parameters were as follows: Production scale: 0.1 kg to 3.0 kg of seaweed, using two species of seaweed. Alkali treatment conditions: NaOH concentration: 10.0%, temperature: 80.0 ºC; extraction time: 3.0 hours. Extraction conditions: Temperature: 90.0 ºC; extraction time: 3.0 hours at pH = 9; using a centrifugal filtration system at 10,000 rpm. Agarose precipitation conditions: Agar extract carbohydrate concentration: >0.7%, sulfate concentration: <1.0%, Synperonic 91/6 concentration: 4.0%. Agarose purification: Agarose precipitates were washed with an IPA: H2O solvent mixture, varying from a 1:1 to 1:0 ratio. The resulting agarose had the following chemical composition and gel properties: sulfate content: 0.35%, ash content: 0.5%, gel strength: 1200 g/cm², and melting temperature: 39.5°C. This agarose is suitable for DNA electrophoresis.

Figure 2. Diagram of the agarose extraction process from seaweed

The task's results were recognized by the Intellectual Property Office of Vietnam, granting two exclusive utility solutions (Patent 3314 and Decision 26612/SHTT-SC) regarding patent protection and fee payment.

Translated by Phuong Huyen
Link to Vietnamese version