Phenolic composition of litchi fruit pericarp.

Abstract

Litchi (Litchi chinensis, Sapindaceae) is a nonclimacteric subtropical fruit that, once harvested, loses its red pericarp color because of browning reactions probably involving polyphenols. Low-pressure chromatography, high-pressure liquid chromatography, UV-visible spectral analysis, mass spectrometry, and nuclear magnetic resonance studies have allowed the determination and quantification of the polyphenolic composition of litchi pericarp. Litchi skins contain significant amounts of polyphenolic compounds. The principal characteristic of the litchi skin polyphenolic compounds is their ortho-diphenolic structure, which gives them high oxidability. Four major pigments were formally identified as cyanidin 3-rutinoside, cyanidin glucoside, quercetin 3-rutinoside (rutin), and quercetin glucoside. The tannin content was characterized after the depolymerization thiolysis reaction. Tannins (polymeric proanthocyanidins) are mainly constituted with epicatechin units linked by A- and B-type bonds. The different phenolic compounds of litchi cv. Kwai Mi were quantified by HPLC. Condensed tannins were the most abundant (4 mg x g(-1) of fresh skin), followed by epicatechin and procyanidin A2 (1.7 and 0.7 mg x g(-1) of fresh pericarp, respectively). The amount of anthocyanins was found to be comparable to that of flavonols, with a value of approximately 0.4 mg x g(-1) of fresh pericarp.