Ultrasonic and Glycation-Modified Soy Protein Isolate Delivery System Enhances the Antioxidant Activity of Antrodia cinnamomea Triterpenoids

triterpenoids) exhibit notable hepatoprotective, antioxidant, anticancer, and immunomodulatory activities. However, their poor aqueous solubility and low dispersibility in aqueous media have limited their practical applications. In this study, the conditions for ultrasonic treatment and xylo-oligosaccharide (XOS)-mediated glycation for soy protein isolate (SPI) were optimized; ACT was then encapsulated into the modified SPI carrier to prepare XOS-SPI-ACT nanoparticles. The delivery system was systematically characterized in terms of encapsulation efficiency (74.22 ± 2.15)%, drug-loading capacity (71.19 ± 4.67)%, storage stability, thermal stability, Fourier transform infrared (FTIR) spectroscopy, UV fluorescence spectroscopy, circular dichroism (CD) spectroscopy, and surface morphological features. The results showed that ACT was effectively embedded in XOS-SPI to form a stable complex with excellent thermal stability and favorable storage stability over a 28-day period. The in vitro antioxidant activities of XOS-SPI-ACT, XOS-SPI, and free ACT were comparatively evaluated. XOS-SPI-ACT exhibited significantly higher scavenging capacities against DPPH radicals, ABTS radicals, hydroxyl radicals, and superoxide anions, as well as higher FRAP values (94%, 74%, 75%, 68%, and 2 mmol/g), compared with free ACT (48%, 17%, 21%, 32%, and 1 mmol/g). Furthermore, XOS-SPI-ACT effectively inhibited lipid peroxidation in the β-carotene/linoleic acid oxidation model, with an overall antioxidant performance of 72%, markedly higher than the 20% of free ACT. This study effectively improves the aqueous solubility and dispersibility of ACT, expands their application potential, and provides a foundation for developing ACT-based natural antioxidants and functional foods.