Chemical Characterization and Evaluation of the Antihyperglycemic Effect of Lychee (Litchi chinensis Sonn.) cv. Brewster

Lychee is a fruit of Asian origin with an exquisite flavor and an attractive reddish color. However, according to recent reports, the consumption of this fruit reduces the levels of blood glucose with adverse effects on human health such as encephalopathy and hypoglycemic. The objective of this work was to determine if the peel, pulp, and seed of "Brewster" lychee fruits harvested at two stages of maturity had antihyperglycemic effect. This effect was determined by an oral glucose tolerance test using Wistar rats. In addition, ultraviolet-visible spectrophotometry and high-resolution liquid chromatography were used to quantify phenolic compounds, flavonoids, organic acids (OAs), sugars, and antioxidant activity. Results indicated that stage I pulp (immature fruits) and stage II peel and seed (export mature fruits) reduced blood glucose levels, and the effects of the former two were synergistic with metformin. The pulp of mature fruits (stage II), however, lacked a hypoglycemic effect. Additionally, the peel and the seeds of these fruits presented a high antioxidant activity (as determined by DPPH [2,2-diphenyl-2-picryl-hydracyl] and ABTS+ [2,2-azino-bis-(3-ethylbenzothiazoline)-6-sulfonic acid] methods), which correlated well with the total content of phenolic compounds. The highest content of polyphenolics, flavonoids, and OAs was found in the extracts of the peel and seeds of both stages of maturity. It was therefore concluded that "Brewster" mature lychees are safe for human consumption, and both the seed and the peel can be useful sources for obtaining new compounds with antihyperglycemic activity.