Pressurized Liquid Extraction of Antioxidant and α-Amylase-Inhibitory Compounds from Red Seaweed Using Water–Ethanol Mixtures

Red seaweeds from the coastal shores of Ilo (Peru) are a natural source of high-value compounds beneficial to health due to their high antioxidant capacity. Thus, this work evaluated the effect of water-ethanol mixtures (0, 15, and 30%; <i>v</i>/<i>v</i>) at high temperatures (90, 120, and 150 °C) on the polyphenol content, antioxidant capacity, and polyphenols profile of red seaweed (<i>Chondracanthus chamissoi</i>) during a pressurized liquid extraction process, whose parameters were set at 10 atm, with a single cycle of extraction and a volume of 150%. An increase in temperature and ethanol had a positive effect on antioxidant compounds. Thus, the best processing conditions were established at 150 °C and 30% ethanol, allowing for the extraction of a high polyphenol content (2.04 mg GAE/g dw) and antioxidant capacity (IC50: 7.46 mg/mL, ORAC: 148.98 μmol TE/g dw). High ethanol concentrations (30%) effectively recovered phenolic acids, flavonols, and phlorotannins for the polyphenols profile. However, the use of pure water was more effective in recovering flavonols. Interestingly, using pure water as an extraction solvent at high temperatures allowed for a more significant inhibition of the α-amylase enzyme than water-ethanol mixtures under the same conditions. Finally, the results can be utilized for future industrial scaling and the potential utilization of extracts in developing diabetes treatments.