Extraction of bioactive compounds from Mastocarpus stellatus using ultrasound and microwave-assisted extraction: a comparative study

The ocean environment is a rich and largely unexplored reservoir of biodiversity, comprising several species of seaweeds. Seaweeds are commonly classified in three main groups, depending on their main pigments, in green, brown, or red seaweeds. Red seaweeds (Rodophyta) include a wide variety of species, such as Mastocarpus stellatus (Stackhouse) Guiry, and are known as beneficial for consumers health due to their content in micronutrients, vitamins, omega-3 fatty acids and other bioactive compounds 1. With this knowledge, the aim of this work was to optimize the bioactive compounds extraction from M. stellatus seaweed. For that purpose, microwave-assisted extraction (MAE), ultrasound assisted extraction (UAE) and a combination of both methods (MAE + UAE) were tested. For each treatment, 1.2 g of homogenized M. stellatus seaweed were accurately weighted and 30 mL of 60% (v/v) distilled water-ethanol solution was added. Samples were submitted to MAE (MARS-X, 1500 from CEM), power 600 W, for 20 min at 90ºC, to UAE (Sonics & Materials VCX750), power 750 W, for 20 min at 70ºC, and to sequential MAE-UAE treatment using the previous conditions. The obtained extracts were analyzed (in triplicate) for carotenoids, chlorophylls, proteins and total phenolics (TPC) contents, as well as for antioxidant capacity through the ABTS•+ scavenging assay. The results for the three extraction methods (MAE, UAE, and MAE + UAE) presented some differences. Concerning pigments extraction, the contents of carotenoids ranged between 0.4 μg/mL (UAE) and 0.8 μg/mL (MAE + UAE), while total chlorophylls concentrations ranged between 2.6 μg/mL (UAE) and 4.0 μg/mL (MAE +UAE). Regarding protein extraction, concentration values between 89 μg/mL (UAE) and 157 μg/mL (MAE + UAE) were achieved. About TPC results, values ranged between 154 mg/mL (UAE) and 177 mg/mL (MAE + UAE). Concerning antioxidant capacity (ABTS•+ results), values were between 61 μg/mL (UAE) and 86 μg/mL (MAE + UAE). These results suggest that the combined MAE-UAE treatment is the best extraction technique to recover carotenoids, chlorophylls, proteins, phenolics and antioxidant compounds from the M. stellatus seaweed species. Further work should be done to optimize the best MAE-UAE conditions to maximize the extraction of valuable bioactive compounds from M. stellatus. The optimum extract will be also characterized regarding the carotenoids and phenolics profiles and in vitro bioactivities.