Development of clean and green extraction technologies for biomolecules from Irish seaweeds

Seaweeds are rich in valuable biomolecules that possess antioxidant, anti-inflammatory and anti-tumor properties. Extracting these biomolecules from seaweed is difficult and typically requires the use of non eco-friendly solvents. This thesis aims to develop innovative clean and green extraction technologies for fucoidan, alginate, phenolics, protein, and umami free amino acids from Irish seaweeds. Study 1 investigated the use of conventional and green solvents (0.1 M HCl, 1% citric acid, and distilled water) for extracting protein, free amino acids, and umami amino acids from Fucus vesiculosus and Ascophyllum nodosum seaweeds. Results showed that extract yields were influenced by seaweed species, solvent, and extraction time. Both seaweeds were found to be excellent sources of proteins and amino acids, with potential applications in the food industry. Sustainable solvents, such as deionised water and citric acid, were found to result in higher compound recoveries compared to HCl. Study 2 compared the ultrasound-assisted extraction (UAE) method with conventional extraction to obtain phenolic compounds from 11 brown seaweeds. The study optimized the process parameters using ultrasound (US) frequency, sonication treatment time and ethanol concentration to obtain maximum yields of the compounds and determine their associated antioxidant activities. The results showed that optimised UAE (35 kHz, 30 min sonication treatment time and 50% ethanol) method resulted in higher extraction yield and values for all compounds studied, as well as higher antioxidant activity, compared to conventional solvent extraction. Study 3 examined the conventional extraction of fucoidan followed by depolymerization using 20 kHz US amplitude (40, 70, 100%), solvents (distilled water, 0.1% citric acid, and Fenton reagent) and 30 min sonication time. US proved to be an effective method of reducing molecular weight. Lower Mw fucoidan demonstrated higher cytotoxic effects against glioblastoma cells. Study 4 used UAE to obtain alginate from a by-product of large-scale fucoidan production using seaweed F. vesiculosus. The extraction process was optimized using response surface methodology, resulting in an optimal condition of 69% US amplitude and 30 min treatment time. Increasing the US amplitude and sonication time led to increased alginate content and crude alginate yield. The crude alginate obtained through optimized UAE showed similar thermogravimetric analysis, differential scanning calorimetry, fourier-transform infrared spectroscopy results to commercial sodium alginate. The study suggests that this by-product has potential as a source of high-quality alginate, contributing to the sustainability of the seaweed industry. Study 5 investigated a biorefinery approach to extract fucoidan, mannitol, laminarin, alginate and protein from F. vesiculosus and A. nodosum seaweeds, both fresh and dry. Conventional extraction methods were used, followed by ultrafiltration to obtain retentate for fucoidan analysis and permeate for mannitol and laminarin analysis. Fresh F. vesiculosus samples yielded more fucoidan, while dried samples had more fucoidan in A. nodosum. The choice of solvent affected the extraction of fucoidan, mannitol and laminarin. Residual by-product was used to extract alginate with US treatment (20 kHz, 64% amplitude and 32 min). This green extraction process highlights the ability to effectively utilize by-products for high value biomolecules. Overall this thesis demonstrated the feasibility of using green solvents and extraction methods to obtain high value biomolecules from seaweeds via a biorefinery approach. US was shown to be an effective, low-cost and eco-friendly technique to extract alginates and polyphenols from brown seaweed species and depolymerize fucoidan. The thesis outcomes will facilitate the establishment of a sustainable biorefinery approach in seaweed processing.