Preparation and characterization of metal-tea polysaccharide complexes and their inhibition on α-glucosidase

The preparation method and the sources of metal elements may affect the activity of the metal-polysaccharide complex. In this study, four Fe-tea polysaccharide complexes were prepared and three tea polysaccharides (TPSs) from different seasons were extracted. Moreover, the binding mode of TPSs with internal and external metallic elements as well as their inhibitory effect on alpha-glucosidase was explored. The results revealed that the binding mode (-C-O-Fe and -C-Fe) of the Fe-TPS complex prepared at pH 5.0 was closer to TPS with internal metallic elements. The TPS with the least amount of internal metallic elements (61.72 mg/g) exhibited a high inhibitory activity on alpha-glucosidase (37.90%). The inhibitory activity of Fe-TPS on alpha-glucosidase was lower than that without Fe. But the quenching effect and the inhibition type of TPSs on alpha-glucosidase were not affected by metallic elements. Therefore, the metallic elements have the potential to reduce the hypoglycemic activity of TPS. Practical applications In this paper, TPS was extracted from crude tea in different seasons, and the effects of metallic elements in TPS on hypoglycemic activity, physicochemical properties, and structure of TPS were discussed. TPS metal complexes were prepared by adding Fe3+ or removing metallic elements, and the differences of internal metallic elements in TPS were discussed. It is of great academic significance to use tea pruned leaves and crude tea as potential resources to develop polysaccharide hypoglycemic products and to reveal the relationship between TPS metal ions and their structure and activity. In addition, it has guiding value for consumers to choose tea-producing regions and growers to choose chemical fertilizer.

Automated summary

The study investigated the effects of metal elements on the activity of metal-polysaccharide complexes, showing that metallic elements may reduce the hypoglycemic activity of polysaccharides. Four Fe-tea polysaccharide complexes were prepared and three tea polysaccharides were extracted to explore their binding modes with metallic elements and inhibitory effects on alpha-glucosidase. The results revealed that the activity of Fe-TPS on alpha-glucosidase was lower than that without Fe, suggesting that metallic elements have the potential to decrease the hypoglycemic activity of TPS.