Highly Promiscuous Flavonoid Di-O-glycosyltransferases from Carthamus tinctorius L.

Safflower (Carthamus tinctorius L.) has been recognized for its medicinal value, but there have been limited studies on the glycosyltransferases involved in the biosynthesis of flavonoid glycosides from safflower. In this research, we identified two highly efficient flavonoid O-glycosyltransferases, CtOGT1 and CtOGT2, from safflower performing local BLAST alignment. By constructing a prokaryotic expression vector, we conducted in vitro enzymatic reactions and discovered that these enzymes were capable of catalyzing two-step O-glycosylation using substrates such as kaempferol, quercetin, and eriodictyol. Moreover, they exhibited efficient catalytic activity towards various compounds, including flavones (apigenin, scutellarein), dihydrochalcone (phloretin), isoflavones (genistein, daidzein), flavanones (naringenin, glycyrrhizin), and flavanonols (dihydrokaempferol), leading to the formation of O-glycosides. The broad substrate specificity of these enzymes is noteworthy. This study provides valuable insights into the biosynthetic pathways of flavonoid glycosides in safflower. The discovery of CtOGT1 and CtOGT2 enhances our understanding of the enzymatic processes involved in synthesizing flavonoid glycosides in safflower, contributing to the overall comprehension of secondary metabolite biosynthesis in this plant species.

Study on structural characteristics, physicochemical properties, and in vitro digestibility of Kudzu-resistant starch prepared by different methods.

Three different methods, including autoclaving, autoclaving-debranching, and purification, were used to prepare Kudzu-resistant starch (KRS) from Kudzu starch (KS). The physicochemical properties, such as thermodynamic properties, pasting properties, solubility, swelling, and coagulability, as well as the in vitro digestive characteristics of the three kinds of KRS were studied. The results showed that the morphology of starch granules of KRS prepared by autoclave, autoclave enzymatic hydrolysis, and purification methods was changed and the relative crystallinity was significantly decreased compared with the original starch. X-ray diffraction (XRD) showed that KRS exists in the form of C and C+V crystalline form. There was a significant increase in the pasting temperature and a remarkable decrease in the peak viscosity and the expansion degree of the KRS prepared by all three methods. The solubility of the resistant starch (RS) obtained by autoclaving-debranching and that by purification were both increased compared to that of native KS, while the solubility of the RS obtained by autoclaving was decreased. Meanwhile, the retrogradation of the three RS was also improved to varying degrees. The contents of RS in the samples were: P-KRS (71%) > DA-KRS (43%) > A-KRS (42%) > KS (9%). Simulated human in vitro digestion experiments showed that RS has stronger antidigestibility properties than native starch. Among them, the RS prepared by the purification method has stronger antidigestive properties, and it is predicted that it may have a better potential value in regulating blood glucose. These results indicated that the processing properties of KRS, especially the digestibility, are significantly improved and can be used as a new functional food ingredient, which deserves thorough study.

Kudzu Resistant Starch: An Effective Regulator of Type 2 Diabetes Mellitus.

Kudzu is a traditional medicinal dietary supplement, and recent research has shown its significant benefits in the prevention/treatment of type 2 diabetes mellitus (T2DM). Starch is one of the main substances in Kudzu that contribute decisively to the treatment of T2DM. However, the underlying mechanism of the hypoglycemic activity is not clear. In this study, the effect of Kudzu resistant starch supplementation on the insulin resistance, gut physical barrier, and gut microbiota was investigated in T2DM mice. The result showed that Kudzu resistant starch could significantly decrease the value of fasting blood glucose and the levels of total cholesterol, total triglyceride, and high-density lipoprotein, as well as low-density lipoprotein, in the blood of T2DM mice. The insulin signaling sensitivity in liver tissue was analyzed; the result indicated that intake of different doses of Kudzu resistant starch can help restore the expression of IRS-1, p-PI3K, p-Akt, and Glut4 and thus enhance the efficiency of insulin synthesis. Furthermore, the intestinal microorganism changes before and after ingestion of Kudzu resistant starch were also analyzed; the result revealed that supplementation of KRS helps to alleviate and improve the dysbiosis of the gut microbiota caused by T2DM. These results validated that Kudzu resistant starch could improve the glucose sensitivity of T2DM mice by modulating IRS-1/PI3K/AKT/Glut4 signaling transduction. Kudzu resistant starch can be used as a promising prebiotic, and it also has beneficial effects on the gut microbiota structure of T2DM mice.