Optimization of Refined Carrageenan Extraction from Locally Produced Kappaphycus alvarezii (Doty): A Comparative Analysis of Yield and Physicochemical Quality

Carrageenan is a commercially important polysaccharide extracted from seaweeds and widely used in the food, pharmaceutical, and cosmetic industries due to its gelling, thickening, and viscosity-enhancing properties. This study aimed to compare the quantity and quality of extracted refined carrageenan using four common extraction methods: conventional Ca(OH)₂ autoclaving, 6% (w/v) Ca(OH)₂, 6% (w/v) KOH, and 6% (w/v) NaOH. Forty-five days old brown color morphotype of Kappaphycus alvarezii grown in Jaffna was used as a seaweed source. Carrageenan yield, transmittance under Fourier Transform Infrared (FTIR), gel strength, water holding capacity, and L*a*b* color values were measured across extraction methods. Kappaphycus alvarezii cultivated in Jaffna yielded a carrageenan content exceeding 25%, with the highest recovery (37.20%) obtained using the KOH extraction method, which was significantly greater (P<0.05) than yields obtained with the other three extraction methods. However, the FTIR spectra for four extracted carrageenan samples displayed similar patterns with the commercial carrageenan sample, with slight deviations at 845 cm^-1, 925-930 cm^-1, and 1220-1260 cm^-1 wave ranges indicating different types of kappa-, iota- and lambda-carrageenan fractions of different extraction methods.  The highest (P<0.05) gel strength (1745.86 g/cm2) was recorded in the KOH method, whereas the conventional method recorded the significantly lowest gel strength (706.26 g/cm²). Moreover, conventional and KOH-treated carrageenan samples showed the highest (P<0.05) water holding capacity (98.59% and 97.42%) along with the highest a* and b* values. By contrast, lightness (L*) did not show a significant difference among carrageenan extracted from four methods. Therefore, it can be concluded that treatment with 6% KOH produces refined carrageenan with the highest yield and desirable physicochemical properties, outperforming the other methods when K. alvarezii is used as the seaweed source. Furthermore, this study highlights the potential for significant advancement in the use of 6% KOH method for domestic superior carrageenan production in Sri Lanka.