Abstract
Litchi (Litchi chinensis Sonn.) fruit is known for its rich source of phenolics. Litchi pericarp contains high levels of epicatechin that may form oligomers of various lengths. Except for several A or B type epicatechin dimers, other soluble oligomers have rarely been identified in the pericarp. Here, bioassay-guided column fractionation was applied to isolate bioactive phenolics from aqueous pericarp extract. A fraction (S3) was obtained by two rounds of Sephadex LH-20 column chromatography, and showed higher antioxidant activity and inhibition on the proliferation of human lung cancer cells (A549) than Litchi anthocyanins. S3 was further separated to isolate fractions P1–P4, which all showed higher antioxidant activity than vitamin C. P3 showed 32.9% inhibition on A549 cells at 30 μg/mL, higher than other fractions and cis-Dichlorodiamineplatinum (DDP, 0.5 μg/mL), but not as high as the combination of the four fractions. Using HPLC-Q-TOF-MS/MS, one B-type and complex A/B type epicatechin trimers were identified in P3; another B-type and two A/B-type trimers were identified in P4. P1 and P2, containing epicatechin and proanthocyanidin B2, respectively, showed no cell inhibition at 30 μg/mL. It is the first time that the two B type trimers of epicatechins (Litchitannin B1 and B2), have been found in Litchi species. The identified proanthocyanidins were detected in the pericarp of the young fruit, and the levels of the compounds decreased as the fruit developed, correlating to the decreasing patterns of the expression of LcLAR and LcANR, two key genes in the catechin biosynthesis pathway.
Highlights
Litchi (Litchi chinensis Sonn.) fruit has a bright red and attractive pericarp surrounding a white and translucent fleshy aril, having delicious and great nutritional value [1]
The major components of fresh Litchi pericarp extract were anthocyanins, proanthocyanidins, phenolic acids, and coumarins, etc., which are associated with high antioxidant activity and a lower incidence of cancers [7]
The phenolics in Litchi pericarp were extracted with 0.1 mol/L HCl aqueous solution
Summary
Litchi (Litchi chinensis Sonn.) fruit has a bright red and attractive pericarp surrounding a white and translucent fleshy aril, having delicious and great nutritional value [1]. Some Litchi cultivars exhibit a high yield of fruits and are promising sources for bioactive compound extraction. The major components of fresh Litchi pericarp extract were anthocyanins, proanthocyanidins, phenolic acids, and coumarins, etc., which are associated with high antioxidant activity and a lower incidence of cancers [7]. Other extraction/isolation strategies and investigations of the effect of tissue status/developmental stage may help to identify more bio-functional oligomers of proanthocyanidin in the Litchi pericarp. Combinatorial chemistry and bioassay-guided fractionation was suggested for the purification of pharmacologically active phytochemicals [13] Based on this strategy, phenolic compounds were extracted and purified from freshly frozen Litchi pericarp by 0.1 M aqueous solution. We analyzed the accumulation profiles of four catechin-type compounds during fruit development and the expression patterns of relevant biosynthesis-related genes
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