Ultrasound-enzyme-assisted extraction of flavonoids, polysaccharides, and triterpenes from Gualou and Xiebai: optimization, bioactivity, in vitro digestive stability, and impact on lipid digestion

Gualou (Trichosanthes kirilowii Maxim) and Xiebai (Allium macrostemon Bunge) have been extensively studied for their diverse active ingredients, which include flavonoids, polysaccharides, and triterpenoids. This study employed a single-factor experiment alongside the Plackett–Burman design and utilized response surface methodology to optimize the ultrasonic-enzyme-assisted extraction (U-EAT) method for the functional components in Gualou and Xiebai (GLXB). The optimal extraction conditions were identified as a solid-to-liquid ratio of 1:11 g/mL, an alcohol concentration of 55%, an enzyme concentration of 1.2%, and an extraction temperature of 40°C. The yields of flavonoids, polysaccharides, and triterpenoids obtained were 0.94 ± 0.05, 260.46 ± 1.78, and 118.69 ± 0.71 mg/g, respectively, demonstrating increases of 59.19%, 29.03%, and 46.10% compared to HL (HL, the traditional reflux extraction method). Furthermore, in vitro digestion of the GLXB extract demonstrated significant lipid-lowering and hypoglycemic effects. The GLXB extract facilitated the flocculation of lipid droplets during lipid digestion and exhibited the capacity to reduce the rate of fat digestion. These findings indicate that the U-EAT significantly enhanced the content of active ingredients in GLXB and improved the hypoglycemic and lipid-lowering activities of the GLXB extract, highlighting its potential for further development and application in functional foods.