Ultrasound-assisted dieckol extraction from Eisenia bicyclis and its evaluation as a functional ingredient for bacterial cellulose-based desserts.

Dieckol is a brown algal phlorotannin with potent bioactivities such as hepatoprotective effects. This study aimed to produce dieckol-rich extract from Eisenia bicyclis and apply them as a functional ingredient for a novel bacterial cellulose (BC)-based dessert. The modeling and optimization of the ultrasound-assisted extraction (UAE) process were performed. The developed model showed that at least one of the linear or quadratic terms of all variables (amplitude, solvent concentration, temperature, and time) affected dieckol recovery (p < 0.05). Following numerical optimization, dieckol recovery achieved 17.3 mg/g biomass under optimal conditions (62 % amplitude, 35 % solvent concentration, 70 °C, and 6 min), similar to the model-predicted value (18.3 mg/g). Then, BC-dieckol (BC-D) pellicles were fabricated by ex situ loading 25, 50, 75, and 100 % of the liquid extract with 9.954 mg dieckol (recommended intake level). All BC-D pellicles showed high dieckol loading (98.16 - 100 %), and BC-D100 meets the acceptable level. The FTIR and SEM analyses confirmed the impregnation of the extract, especially the signature peaks of dieckol, related to aromatic ether stretch and aromatic ring structure of phlorotannin by the FTIR spectra. The crystallinity index and water absorption capacity of BC-D100 were determined to be about 83.9 % and 415.6 %, respectively, which were slightly decreased compared to BC-control, but not significantly. In addition, BC-D100 has shown antioxidant activity making it valuable as a food material. This study provides valuable information for the food industry, paving the way for developing novel BC-based foods using brown algal extracts.