Ultrasound-assisted extraction and microencapsulation of phenolic compounds from Caesalpinia sappan wood: Physicochemical characterisation and in vitro bioaccessibility

Caesalpinia sappan (red sappan wood) is a rich source of phenolic compounds with significant antioxidant potential; however, efficient extraction and stabilization remain challenging. This study compared maceration (MA), microwave-assisted extraction (MWE) and ultrasound-assisted extraction (USE) for phenolic compound extraction and the extracts were encapsulated to enhance bioaccessibility of phenolic compounds. USE produced significantly higher (p < 0.05) total phenolic content (87.67 ± 1.37 mg GAE/g extract), total flavonoid content (41.57 ± 0.70 mg QE/g extract), yielding around a 1.6–1.7-fold higher antioxidant activity across DPPH, ABTS and FRAP assays compared to maceration and microwave-assisted extraction as determined by DPPH (61.46 ± 1.06 mg QE/g extract), ABTS (68.27 ± 0.81 mg QE/g extract), and FRAP (79.2 ± 0.6 μmoL Fe2+/g extract) assays. The enhanced extraction efficiency may be attributed to acoustic cavitation, which is reported to facilitate cell disruption and mass transfer. LC-MS/MS analysis tentatively identified the presence of key phenolic constituents. The optimized extract was microencapsulated using maltodextrin, β-cyclodextrin, and locust bean gum via the freeze-drying method. Among the carriers, β-cyclodextrin exhibited the highest encapsulation efficiency (88.54%). Structural characterisation (FT-IR, XRD, and FE-SEM) confirmed successful encapsulation and interactions between core and wall materials. In vitro gastrointestinal digestion revealed improved solubility with maltodextrin and enhanced intestinal retention with β-cyclodextrin (67.60%). These findings demonstrate that USE is a promising green technique for efficient extraction of phenolic compounds while microencapsulation further enhances their bioaccessibility, providing a basis for further studies on functional food applications.