**4. Conclusions**

The yields of compounds extracted from *F. vesiculosus* (173.33 to 354.67 mg dried extract per g macroalgae) were higher when compared to *P. canaliculata* (147.00 to 240.33 mg dried extract/g macroalgae). The yields were influenced by the technology used and, overall, the highest were achieved using UMAE (354.67 ± 2.33 for *F. vesiculosus* and 240.33 ± 1.20 for *P. canaliculata*), followed by UAE (316.33 ± 4.63 and 214.33 ± 2.60 for *F. vesiculosus* and *P. canaliculata*, respectively). Following the extraction treatment, additional extraction (24 h) did not improve the yields of phytochemicals or the antioxidant properties of the extracts, indicating possible precipitation or degradation loss of the compounds dissolved for prolonged periods of time in ethanolic solutions. When analysing the extraction of phytochemicals using multiple novel technologies without additional extraction after extraction, overall UAE achieved the highest yields of most phytochemicals from both *F. vesiculosus* (445.0 ± 4.6 mg GAE/g, 362.9 ± 3.7 mg PGE/g, 286.3 ± 7.8 mg QE/g, and 189.1 ± 4.4 mg ChE/g) and *P. canaliculata* (250.6 ± 6 mg GAE/g, 203.9 ± 4.9 mg PGE/g, 122.6 ± 3.4 mg QE/g and 79.5 ± 4.6 mg ChE/g). Moreover, UMAE also achieved high yields of TPC, TPhC and TFC from *P. canaliculata*. Overall, the extraction procedures using 50% ethanol as solvent achieved low TSC yields, except when using HAE, from both macroalgae. In the case of the antioxidant properties, the extracts with the highest DPPH radical scavenging activities were extracted by UAE and UMAE and the lowest by MAE from both *F. vesiculosus* and *P. canaliculata*. Meanwhile, strong variations were appreciated depending on the extraction technology and macroalgal species considered in the case of FRAP activity. Both DPPH and FRAP were positively correlated with the levels of TPC, TPhC, TFC and TTC in both macroalgal species. This study evaluated the effectiveness of multiple extraction technologies for the recovery of phytochemicals (keeping a fixed solvent type, concentration and extraction time) from macroalgae. Further, studies are needed optimising the use of novel extraction technologies, varying extraction time and the polarity of the extraction solvents targeting multiple compounds from macroalgae in order to establish efficient extraction protocols to allow the future commercialisation of these compounds. Moreover, further chemical characterisation of the extracted compounds as well as confirmation of their biological effects in vivo will also be needed in order to commercialise these compounds. Based on the results of this study, the use of UAE combined with 50% ethanolic solution as an extraction solvent could be a promising strategy targeting the extraction of TPC, TPhC, TFC and TTC, while reducing the coextraction of undesirable carbohydrates from both *F. vesiculosus* and *P. canaliculata*, with promising applications when using these compounds as pharmaceuticals, nutraceuticals and cosmeceuticals.

**Author Contributions:** M.G.-V. collaborated in designing the work, performed the extraction experiments and the statistical treatment of the data, and wrote and reviewed the manuscript. O.W. and R.R. performed the chemical analyses of the extracts and helped in writing the first draft of the manuscript. J.O. and B.K.T. contributed to the revision of the manuscript and provided funds for the work. A.K.J. and G.R. designed and supervised the work and revised the manuscript. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research work was supported by Science Foundation Ireland (SFI). Grant numbers: [16/RC/3889] and [14/IA/2548].

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable. **Data Availability Statement:** Not applicable as all the data is contained in the manuscript.

**Conflicts of Interest:** The authors declare no conflict of interest.
