A greener alternative using subcritical water extraction to valorize the brown macroalgae Ecklonia maxima for bioactive compounds

Abstract

This work aimed to optimize the subcritical water extraction (SWE) parameters from the brown macroalga Ecklonia maxima for yields, total phenolic content (TPC), antioxidant activity (ABTS), sulphate content and alginate yields using response surface methodology (RSM). A central composite experimental design evaluated the impact of temperature (100–180 °C), extraction time (5–30 min) and solvent to feed (S/F) ratio (10–50 mL g−1) operated at 40 bar. The predicted model accuracy for all the variables was good with R2 values ranging from 0.76 to 0.97. All response variables showed a high dependence on the hydrolysis temperature followed by S/F ratio and extraction time. The optimized levels for the total phenolic content coupled with antioxidant activities and yield was 180 °C, extraction time of 23.75 min and a S/F ratio of 30 mL g−1 with an yield of 76.02 ± 0.51%, TPC of 41.20 ± 0.42 GAE g−1 and antioxidant activity of 1.81 ± 0.01 mmol TE g−1. The optimized levels for the polysaccharide fractions were 120 °C for 5 min at S/F ratio of 30 mL g−1 giving a yield of 58.25 ± 0.93%, sulphate content of 48.53 ± 1.19 mg SO42− g−1 and 15.65 ± 0.42% alginate. These results show that there is a variance in optimal operational conditions based on the target compounds of interest and it links operational conditions to both functional properties and product type. Overall, SWE is a promising green extraction technology for isolating bioactive compounds from E. maxima which can find potential applications in food and cosmetic industry.