Effect of decolorization treatment on the gel strength of seaweed (Eucheuma cottonii) for food product development

Abstract

Seaweeds, Eucheuma cottonii, is widely recognized for its nutritional and industrial value due to its high content of bioactive compounds, including carrageenan. In this study, E. cottonii was sourced from the coastal area of Mannar, Sri Lanka, where it is cultivated by local seaweed farmers. Carrageenan, a water-soluble polysaccharide, is extensively utilized in the food industry as a gelling, thickening, and stabilizing agent. However, E. cottonii's dark brown color and odor limits its food applications despite its valuable carrageenan and mineral content. This study optimized decolorization methods to preserve gel strength while effectively removing color and odor, thereby maintaining functionality. Three 3% solutions, hydrogen peroxide, sodium metabisulfite andascorbic acid were tested in 24h ambient dips, followed by hot water extraction at 70-75°C. Hydrogen peroxide exhibited the highest gel strength among the treatments, along with effective decolorization. According to hedonic scale evaluation, it also achieved the highest deodorization scores, indicating the greatest reduction in undesirable odor as perceived by panelists. Further optimization trials tested H₂O₂ concentrations of 0.5%, 1%, and 3% over 24, 48, and 72 hours to determine the ideal balance between decolorization and gel strength. At 0.5% H₂O₂, the 48-hour dipping method was identified as optimal, achieving effective decolorization with an L value of 18.58 while maintaining a high gel strength of 0.18N. In contrast, extending the treatment to 72 hours improved decolorization slightly (L value of 20.21) but significantly reducedgel strength to 0.11N. This demonstrates that prolonged exposure beyond 48 hours compromises gel strength despite increased color removal. Treatment duration was strongly correlated with gel strength at 0.5% H₂O₂ (r = 0.912, p < 0.001), highlighting the critical role of optimizing dipping time. Therefore, 48 hours was selected as the best treatment duration to maximize decolorization while preserving the gel strength of E. cottonii, supporting its application in developing high-quality food products.