Mat Hashim, Dzulkifly

Muhammad, Kharidah

Wongsuban, Benchamaporn

Yusof, Salmah

Universiti Putra Malaysia Institutional Repository

OPTIMISATION OF METHODS FOR AGAREXTRACTION FROM GRACILARIA SP.FOR Category F10800: Biological SciencesKharidah Muhammad, Benchamaporn Wongsuban,Salmah Yusof and Dzulkifly Mat HashimFaculty of Food Science and BiotechnologyUniversiti Putra Malaysia, 43400 UPM, Serdang, Selangor,MalaysiaKeywords: Gracilaria chang ii, Gracilaria fisheri,Gracilaria tenuistipitata, seaweeds, sodium hydroxide.IntroductionIn Malaysia, the demand for agar is increasing every year.Efforts should thus be made to produce agar locally. Agar iscommercially produced from red seaweeds and various ex-traction methods have been employed which involve heatingsun-bleached seaweeds in various extraction solutions. Themethods differed either in the type of extraction solution, itsconcentration, the heating temperature or heating time used.The gel strength of agar produced from red seaweeds is usu-ally very weak. Alkali pre-treatment of the seaweeds hasbeen performed in order to improve the agar gel strength.Sodium hydroxide has been used and the conditions werevaried in terms of sodium hydroxide concentration, andsoaking temperature and time. The objective of this study wasto determine the optimum conditions for extraction of agarfrom Gracilaria sp. with high yield and high gel strength.Materials and MethodsThree species of red seaweeds were used in this study.Gracilaria changii was collected from Ban Merbok, Kedahand was grown in a pond under the supervision of FisheriesResearch Institute, Pulau Pinang. Gracilaria fisheri andGracilaria tenuistipitata were collected from Pattani Bay,Pattani Province, Thailand. After the seaweeds were har-vested, they were washed and sun-dried, and stored for fur-ther processing. Agar was extracted from the seaweeds withdifferent extraction solutions. They were distilled water, sul-phuric acid, acetic acid and sodium hexametaphosphate. Theconcentrations of sulphuric acid and acetic acid were in therange of 0.005-0.03% while the concentrations of sodiumhexametaphosphate were in the range of 0.0005-0.003 M.The extraction temperature was 121°C while the extractiontime was varied from 10 to 60 min. After the optimum ex-traction conditions were established, the seaweeds were pre-treated with sodium hydroxide and the parameters studiedwere sodium hydroxide concentration which ranged from Ito 9%, soaking time of 1 to 3 hours, and soaking temperatureof 80 to 100°C.Results and DiscussionUsing distilled water, it was observed that the yield increasedwhen the extraction time was increased. After the optimumextraction time was reached the yield plateau off (as in G.changii and G. fisheri) or decreased slightly (G. tenuistipi-tata) when the extraction time was further increased. Theoptimum extraction times for G. changii, G. fisheri and G.tenuistipitata were 40 min, 30 min and 20 min, respectively.Using the optimum extraction times, the highest yield ob-tained with G. changii, G. fisheri and G. tenuistipitata were35%, 32% and 25%, respectively. When the agar was ex-tracted using sulphuric acid and acetic acid, the yield tendedto increase when the concentration of acid and extractiontime were increased, and then decreased. This is due to thefact that agar is a polysaccharide in the cell wall of seaweeds.Acid helped destroy the cell wall but in the same time it wasdestructive to the agar. Therefore, there was a certain periodof time to extract the agar and after that the agar would bedestroyed because it was present in the acid solution for toolong. When sodium hexametaphosphate was used, the yieldtended to increase and the gel strength slightly decreasedwhen the concentration and extraction time were increased.Employing 0.0005 M sodium hexametaphosphate, 121°C~d 10 min extraction temperature and time, respectively, theYIeldof agar from G. changii decreased gradually when thetemperature of the sodium hydroxide pre-treatment of theseaweeds was increased from 60°C to 100°C but the reduc-tion was not significant. The gel strength increased when thesodium hydroxide pre-treatment temperature was increasedfrom 60°C to 80°C. The concentration of sodium hydroxidesignificantly affected the yield and gel strength of agar. Theyield decreased gradually when sodium hydroxide concen-tration was increased from 1 to 9%. The gel strength of agarincreased when the sodium hydroxide concentration was in-creased from 1 to 3% but further increment in the sodiumhydroxide concentration led to a decrease in the gel strength.The temperature of sodium hydroxide pre-treatment had nosignificant effect on the yield of agar from G. fisheri. How-ever, the value was found to be lower than that of G. changiiagar. The gel strength of extracted agar increased signifi-cantly when the sodium hydroxide pre-treatment temperaturewas increased from 60 to 80°C and then leveled off when thetemperature was further increased. The concentration of so-dium hy~roxide used did affect the yield and gel strength ofagar obtained from G. fisheri. The gel strength was increasedwhen the concentration of sodium hydroxide was increasedfrom 1 ~o 7% and .~en decreased at 9% sodium hydroxide.The optimum conditions for alkali pre-treatment of G. fisheriwere at 80-90°C with 7% sodium hydroxide.ConclusionsThe utilisation of sulphuric acid, acetic acid and sodium hex-ametaph~sphate increased the yield of agar from G. changii,G. fisheri and G. tenuistipitata but have a negative effect onthe agar gel strength. An extraction method which employed0.0005M sodium hexametaphosphate, 121°C and 10 min re-s~lted in a high yield of agar with a high gel strength. AgarWItha gel strength of 661-838 g/cm2 could be obtained fromG.changii after pre-treatment with 3-5% sodium hydroxide at80-90°C for 1-2 ho~. For Gjisheri, a high gel strengthagar (612-713 glcm) could be obtained after 5-7% sodiumhydroxide treatment at 80-90°C for 2-3 hours.Supported by IRPA Grant 01-02-04-0200203

Optimisation of methods for agar extraction from Gracilaria sp.

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Optimisation of methods for agar extraction from Gracilaria sp.

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