Characterization of functional materials derived from tropical red seaweed Hypnea musciformis produced by subcritical water extraction systems

Hypnea musciformis is an edible tropical red seaweed species and still considered as an underexploited seaweed species in Indonesia. In this study, H. musciformis was hydrolyzed using the subcritical water extraction (SCWE) system. Different solid to liquid ratios (S/L ratios 1:150, 1:100, and 1:50) and six different temperature conditions (120-270 degrees C with 30 degrees C increments) were applied to obtain the best functional materials. Hypnea musciformis hydrolysate (HMH) was further analyzed for total sugar, protein, phenol, and flavonoid content. The antioxidant capacity and functional material contents varied significantly based on extraction conditions, with HMH hydrolyzed at S/L ratio 1:50 and temperature 210 degrees C showing the highest antioxidant activity with values of 0.97 +/- 0.02 Trolox equivalent (TE) mg g(-1), 2.23 +/- 0.05 ascorbic acid (AA) equivalent mg g(-1), and 0.92 +/- 0.00 TE mg g(-1)for DPPH, total antioxidant, and ABTS, respectively. Pearson analyses showed that the phenolic contents were closely associated with DPPH scavenging activities with a value of 0.983. High-performance liquid chromatography analysis revealed that the highest phenolic acids in H. musciformis were chlorogenic acid (27.98 +/- 0.57 mg g(-1)) and gallic acid (1.22 +/- 0.20 mg g(-1)), with the highest content obtained by SCWE (S/L ratio 1:50) at a temperature of 210 degrees C. Further, the emulsifying properties of HMH in corn oil and sunflower oil were analyzed. HMH demonstrated thermostable emulsifying properties. Moreover, H. musciformis could be developed as a potential antioxidant additive and also as an emulsifying agent in the food, pharmacy, cosmetics, and other industries. Collectively, this study shows the potential of underexploited red seaweed resources in Indonesia using SCWE.