Effect of in Vitro Simulated Digestion on Changes in Chemical Composition, Functional Activity and Saponins of Panax notoginseng Leaves

In this study, an in vitro digestive model was established to determine changes in the contents of total saponins, total phenols, polysaccharides, and total flavonoids in Panax notogiseng leaves (PNL) during simulated digestion.Meanwhile, changes in the in vitro antioxidant activity and α-glucosidase-inhibiting activity were assessed. Ultra-high performance liquid chromatography-quadrupole time-of-flight mass spectrometry (UPLC-Q-TOF-MS) was employed to further analyze the pattern of changes in 24 monomer saponins in PNL. The results showed that the contents of total saponins and total phenols were the highest at the intestinal digestion stage, reaching up to 188.32 and 17.43 mg/g, respectively. The change in polysaccharide content was insignificant during the entire digestion process. The content of total flavonoids was the highest in the oral digestion stage at 23.76 mg/g. Similarly, the antioxidant and α-glucosidase-inhibiting capacity of PNL were both the strongest in the intestinal digestion stage. The 2,2’-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radical cation scavenging activity, iron-reducing capacity, and α-glucosidase-inhibiting capacity all showed a trend of initial decrease and then increase and reached the highest values of 84.97%, 37.80 mg/g, and 72.5%, respectively in the intestinal digestion stage. Furthermore, the large-molecular-mass ginsenosides Rb₁, Rb₂, Rb₃, Re, and Rd were cleaved into small-molecular-mass rare saponins such as compound K, Rg₃, Rg₅, and Rk₁. In conclusion, PNL still exhibited significant functional activity after digestion. The functional activities of PNL, such as antioxidant and α-glucosidase-inhibiting activity, increased as the digestion process proceeded, reaching their highest levels in the intestinal digestion stage. This might be related to the release of active ingredients and the production of small-molecule rare saponins. This study could provide a scientific basis for applying PNL to develop functional foods.