Optimization of flavonoids extraction from Tartary buckwheat rice and analysis of its hypoglycemic activity

Abstract: Due to the presence of high content of proteins, polyphenols, and minerals, tartary buckwheat has been widely recognized for its nutritional values. Various parts of the globe buckwheat are used as a bran, groats, flour and rice. There are two types of buckwheat cultivated around the world including common buckwheat (Fagopyrum esculentum) and tartary buckwheat (Fagopyrum tataricum). Recent studies have reported that Tartary buckwheat contained multiple bioactive components, especially rich in flavonoids. It was also reported that Tartary buckwheat contained more bioactive components than common buckwheat. The potential health benefits of buckwheat have been paid attention to in the forms of food, dietary supplements and pharmaceutical drugs. However, no detailed study on various factors which can influence the activity of flavonoid content of buckwheat has been found. Therefore, the present study was aimed to optimize the extraction procedures of flavonoids from tartary buckwheat rice. Firstly, we analyzed the impact of multiple factors such as ethanol concentration, liquid/solid ratio, extraction time and temperature on the yield of flavonoids. Further response surface methodology (RSM) was applied to determine the optimum conditions for the flavonoid extraction from tartary buckwheat rice. Graphical representation of flavonoid yield on 3D response surface graph indicated that the optimum factors including ethanol concentration, liquid/solid ratio, extraction time and temperature were tentatively 54%, 1:24 g/mL, 62 min and 71 ℃ respectively. Total flavonoid content of tartary buckwheat rice was 2.20 %. Moreover, we evaluated the anti-diabetic activity of flavonoids from tartary buckwheat rice using α- amylase inhibition assay and cellular glucose uptake assay. α-Amylase inhibition activity of flavonoids from tartary buckwheat rice was compared with a widely used pharmacological amylase inhibitor metformin. Our results indicated that 7.5 mg/mL flavonoids showed 54.05% inhibition of α-amylase activity, which is nearly equal to 5 mg/mL of metformin. Further cellular glucose consumption assay showed that flavonoids from tartary buckwheat rice significantly increased the glucose consumption by 48.73% in HpeG2 cells as compared to control group. In order to study the possible mechanism that the flavonoids from tartary buckwheat rice could improve glucose consumption in HepG2 cells, we next measured the intracellular glycogen content. Our results showed that glycogen content in HepG2 cells was increased to 311% after treated with 50 μg/mL of flavonoids compared with that in control group, which indicated that flavonoids from tartary buckwheat rice can significantly promote the synthesis of glycogen. Taken together, these results suggested that the ability of flavonoids from tartary buckwheat rice to promote the glucose consumption in HepG2 cells may be due to the increase of glycogen synthesis. In summary, we optimized the extraction process of flavonoids from tartary buckwheat rice. Besides, we also evaluated the inhibition ability of flavonoids on α-amylase and demonstrated that tartary buckwheat flavonoids could significantly inhibit the activity of α-amylase. We employed cell glucose consumption assay and glycogen assay to further evaluate the antidiabetic effect in cellular level, and found that tartary buckwheat flavonoids could effectively improve the consumption of glucose and the synthesis of glycogen. Our results indicated that tartary buckwheat flavonoids have an auxiliary effect of hypoglycemic.