Abstract
Hypnea bryoidescollected from the Arabian Sea on the southern coast of Oman was investigated forκ-carrageenan optimal extraction conditions. The effects of different conditions of alkali treatment (4, 6, and 8% w/v NaOH), temperatures (70, 75, and 80°C), and time (2, 2.75, 3.5 hours) on carrageenan yield and chemical and thermal properties were evaluated. Yield was significantly affected by alkaline concentration and temperature, with highest value of 26.74 ± 5.01%. Molecular weights of the extracted carrageenan were significantly reduced by increased temperatures and ranged from 5.95 ± 0.49 × 105 Da to 13.90 ± 0.14 × 105. FTIR showed that samples under all extraction conditions were similar and confirmed the presence ofκ-carrageenan with no traces ofμ-precursor. Sulfate content was also significantly reduced by alkaline concentration (from 4% to 6%) and ranged from 7.62 ± 5.52% to 17.02 ± 0.14. Thermal properties showed more sensitivity towards temperature and alkaline strength parameter than time. In addition, melting and gelling temperatures were significantly correlated with the molecular weight, but not sulfate content. In conclusion, mild extraction conditions were found to be more efficient in introducing the intended structural modification while getting the highest yield and quality.
Highlights
Among marine macroorganisms, seaweed gained considerable significance due to its utilizations as a rich raw material for extraction of various valuable materials, for instance, polyphenols, organic pigments, proteins, unsaturated fatty acids, and polysaccharides [1, 2]
The results demonstrate that the total yield value obtained from different alkali treatments extraction conditions ranged between 6.59 ± 0.09% and 26.74 ± 5.01%, obtained by the treatment with 8% NaOH, 3.5h, 80∘C and 6% NaOH, 2.75h, 70∘C, respectively
Some of the carrageenan yields obtained in this study were in the same range of those extracted in aqueous media obtained by Yermak et al [29] from C. pinnulatus (20.5%-18.2), Reis et al [30] from H. musciformis (48%21%), and Webber et al [31] from K. alvarezii (35.8%-18%)
Summary
Among marine macroorganisms, seaweed gained considerable significance due to its utilizations as a rich raw material for extraction of various valuable materials, for instance, polyphenols, organic pigments, proteins, unsaturated fatty acids, and polysaccharides [1, 2]. Carrageenans, which are a family of linear sulfated polysaccharides, are found and extracted from the cell wall of certain species of red seaweeds (Rhodophyta) [4]. These natural polymers are capable of forming thermoreversible gels or viscous solutions when added in small concentration to salt solutions. They are commonly used as texturing, thickening, suspending, or stabilizing agents in a variety of industrial applications ranging from food products, pharmaceutics, and cosmetics to experimental medicine [5,6,7]
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