Bouhee Kang

Effect of Black Tea and Black Tea Pomace Polyphenols on α-Glucosidase and α-Amylase Inhibition, Relevant to Type 2 Diabetes Prevention

This study evaluates the potential mechanism of action and bioactivity of black tea and black tea pomace for type 2 diabetes prevention via inhibition of carbohydrate hydrolyzing enzymes. Black tea leaves were extracted in hot water and black tea pomace was extracted in 70% acetone. The phenolic content of the water extract (WBT) and pomace acetone extracts (AOBT) were 5.77 and 8.9 mg/mL, respectively, both based on the same concentration of solid tea in the extract. The water extract was subjected to C18 extraction and the resulting hydrophobic fraction (HBBT) was further subjected to LH-20 extraction to recover a low molecular weight phenolic enriched fraction (LMW) and a high molecular weight enriched fraction (HMW). The phenolic content of the LMW and HMW fraction were 1.42 and 2.66 mg/mL, respectively. Among water extracts the HMW fraction was most bioactive against α-glucosidase (IC50 = 8.97 μg/mL) followed by HBBT fraction (IC50 = 14.83 μg/mL). However, the HBBT fraction was the most bioactive fraction against α-amylase (IC50 = 0.049 mg/mL). The black tea pomace (AOBT) had significant α-glucosidase inhibitory activity (IC50 = 14.72 μg/mL) but lower α-amylase inhibitory activity (IC50 = 0.21 mg/mL). The phenolic profiles for LMW and HMW fractions were evaluated using HPLC and the differences between the two profiles were identified. Further research is underway to identify and evaluate the phenolic compounds that are present in the HMW fraction. Our findings suggest that black tea and black tea pomace has potential for carbohydrate hydrolyzing enzyme inhibition and this activity depends on high molecular weight phenolic compounds.

In Vitro and In Vivo Antihyperglycemic Effect of 2 Amadori Rearrangement Compounds, Arginyl-Fructose and Arginyl-Fructosyl-Glucose

During the heat processing of raw ginseng to produce red ginseng, amino acid derivatives such as arginyl-fructose (AF) and arginyl-fructosyl-glucose (AFG) are formed at high levels, through amadori rearrangement, the early step of Maillard reaction, from arginine and glucose or maltose, respectively. However, very limited information is available about the effect of the structural difference between AF and AFG on various biological activities. This is the first report of the mode of action and effect of AF and AFG on the type 2 diabetes management related inhibition of postprandial hyperglycemia in vitro and in animal model. In our previous study, standards AF and AFG were chemically synthesized and in this study their inhibitory activities against rat intestinal α-glucosidases and porcine pancreatic α-amylase were investigated in vitro. The IC(50) value of the in vitro inhibitory activity of AF and AFG on rat intestinal sucrase was high and in similar levels (6.40 and 6.20 mM, respectively). Additionally, a mild pancreatic α-amylase inhibitory activity was observed, with IC(50) values 36.30 and 37.60 mM for AF and AFG, respectively. The effect of AF and AFG on the postprandial blood glucose increase after meal was investigated in Sprague Dawley rats fed on starch or sucrose meals. Both amadori compounds significantly reduced the postprandial blood glucose levels after starch or sucrose loading. These results indicate that AF and AFG, Maillard reaction products, may have antidiabetic effect by suppressing carbohydrate absorption in the gastrointestinal level, and thereby reducing the postprandial increase of blood glucose.

Seasonal influence on phenolic-mediated antihyperglycemic properties of Canadian sugar and red maple leaves using in vitro assay models

Red and sugar maple leaves collected in the summer and fall from Canada, were evaluated for phenolic content, antioxidant, α-glucosidase, and α-amylase inhibitory activities variation. The phenolic contents of summer red maple leaves (RML-S) and summer sugar maple leaves (SML-S) were higher than red and sugar maple leaves collected in fall (RML-F and SML-F, respectively). HPLC analyses showed differences in phenolic compounds present in the SML samples compared to the RML samples. The extracts were assayed for yeast and rat α-glucosidase inhibitory activities. Both results showed that SML-S extracts had the highest inhibitory activity which could possibly be attributed to the unique phenolics present therein. Milder effects were observed in terms of α-amylase inhibitory activity, with RML-F having the highest inhibitory activity. These results suggest that maple tree leaf extracts may have potential for phenolic-mediated α-glucosidase inhibition, relevant to type 2 diabetes management, with SML-S extract having the highest bioactivity.