Study on the in vitro inhibitory activity of blueberry leaf polyphenols on alpha amylase and alpha glucosidase
Blueberries are small berries with a sweet and sour taste that is delicious for fresh consumption. They belong to the Ericaceae family and the Vaccinium genus. There are abundant wild blueberries in the forests of Changbai Mountain, Daxing’an Mountains, and Xiaoxing’an Mountains in northeastern China. Blueberries are rich in compounds such as sugars, terpenes, amino acids, and a large amount of polyphenols, which have high nutritional value and health benefits. In recent years, there has been an increasing amount of research on its active ingredients. Compared to the fruits and flowers of blueberries, blueberry leaves have a higher content of phenolic substances. At present, there are many studies on the antioxidant capacity, blood pressure lowering, and antibacterial effects of blueberry leaf polyphenols, but there is little research on blood sugar lowering. Nowadays, diabetes has become one of the major diseases threatening human health. Alpha amylase and alpha glucosidase can promote the breakdown of food in the mouth, stomach, and intestines, releasing glucose into the bloodstream and raising blood sugar levels. Taking inhibitors is the first choice for the treatment of diabetes at present. Chemical drugs on the market are prone to side effects such as bloating and indigestion, and it is safer to extract inhibitors from natural substances. Previous studies have reported that plant extracts contain polyphenols, terpenoid derivatives, polysaccharides, phenylpropanoids, and other compounds that exhibit excellent α – amylase and α – glucosidase inhibitory activity. Polyphenols have great potential in the prevention and treatment of diabetes. Liu et al showed that polyphenols in green tea extracts have inhibitory effects, and can inhibit the uptake and transport of glucose by intestinal epithelial cells Caco-2. Sun et al. explored through molecular docking that polyphenols can bind to amino acid residues at the active site of alpha amylase, altering the enzyme’s molecular conformation and inhibiting its binding to substrates. This article investigates the inhibitory effects and types of blueberry leaf polyphenols on alpha amylase and alpha glucosidase, providing a theoretical basis for the development of blueberry leaf related products.

The main components of the blueberry leaf polyphenol extract studied in this article include chlorogenic acid, 5,6,7,3 ‘, 4’ – pentahydroperoxide, quercetin, anthocyanins, etc. In vitro hypoglycemic activity evaluation showed that blueberry leaf polyphenols have good inhibitory effects on alpha amylase and alpha glucosidase, and the inhibitory activity is positively correlated with total phenolic content. By exploring the effects of temperature and pH on the inhibitory activity of blueberry leaf polyphenols, it was found that blueberry leaf polyphenols are relatively stable at low temperatures (30-50 ℃) and slightly acidic environments (pH 2.0-8.0 and 3.0-5.0), and can maintain high levels of α – amylase and α – glucosidase inhibitory activity. The half maximal inhibitory concentrations (IC50) of blueberry leaf polyphenols on alpha amylase and alpha glucosidase were 10.926 and 7.276 μ g/mL, respectively. In addition, kinetic studies showed that their inhibition on both enzymes was a mixed reversible inhibition with greater competition than non competition.
In summary, blueberry leaves are rich in polyphenols and have good in vitro α – amylase and α – glucosidase inhibitory effects, revealing the potential hypoglycemic effect of blueberry leaf polyphenols and providing a theoretical basis for the development of blueberry leaf related products.