Keyword: extraction, carrageenan, gel strength, sulfate, Eucheuma cottonii
By: Sperisa Distantina*, Fadilah, Rochmadi, Moh. Fahrurrozi, Wiratni
Carrageenan, as biopolymer, has excellent physical properties to form gel thermo-reversible, therefore the carrageenans are widely utilized, such as thickening, gelling, and stabilities ability. The formation of 3,6-anhydro-α-D-galactose (DA) units from α-D-galactose-6-sulfate residue by alkaline treatment is an important and well-known reaction of carageenans, and is used to commercially enhance gelation behavior. Previous works of the rate of DA formation had not studied extraction rate and reaction rate simultaneously. Practically, both mechanisms are simultaneously, where the seaweeds are extracted using alkali as the solvent. The aim of this research is to study the effects of alkali in carrageenan extraction from Eucheuma cottonii on the rate of extraction and sulfate content reduction simultaneously and the gel properties.
Kappa carrageenan extraction process was developed for Eucheuma cottonii collected from South Sulawesi, Indonesia, by investigating the effects of water and KOH solution (concentration 0.1-0.3N) as the solvent upon physicochemical properties of carrageenan. Extraction process was carried out in water bath equipped by shaker with a constant ratio of seaweed weight to solvent volume ( 1: 30 g/mL) at 100oC and at various extraction different time. The extract was then precipitated in 3 volume of cold 90% ethanol, oven dried at 60oC to constant weight. Percent sulfate content was determined using method of sulfate hydrolysis followed by precipitation sulfate as barium sulfate. The gel properties, namely gel strength, melting and gelling temperature, were determined using tecniques described Falshaw with minor modifications. Assessment of the extracted carrageenan chemical structure was performed by Fourier transform infrared spectroscopy (FTIR) Shimadzu. Commercial carrageenans (Type I), supplied by Sigma, were used as reference samples. Yield was defined as weight ratio of dried carrageenan with dried seaweed. Based on experimental data, pure water was the most efficient solvent with regard to yield but certainly not gel strength. Distilled water as the solvent led higher yield (approximately 45%) than KOH solution when the mass transfer equilibrium time (30 - 40 minutes) was reached. Sulfate content in carrageenan extracted using aquadest was 18-24.7%. Alkali significantly influenced carrageenan yield and properties. Increasing the KOH concentration led to carrageenan containing less sulfate content. Using KOH solution, sulfate decreased quickly in the first 20 minute of extraction. The carrageenan gel properties were significantly affected by sulfate content. The gel strength increased along with the increasing KOH concentration. Also, the sulfate content decreased with the increasing extraction time. The extraction product was found to have essentially identical FTIR spectra to the reference
samples of kappa-carrageenan