Abstract
Content of total proanthocyanidins as well as total phenolics, flavonoids, antioxidant activities were evaluated for litchi (Litchi chinensis Sonn.) pulp of 32 cultivars. One cultivar, Hemaoli, showed the highest total proanthocyanidins and total phenolics, and DPPH or ABTS radical scavenging activities. ESI-MS and NMR analysis of the Hemaoli pulp crude extracts (HPCE) showed that procyandins composed of (epi)catechin unites with degree of polymerization (DP) of 2–6 were dominant proanthocyanidins in HPCE. After the HPCE was fractionated by a Sephadex LH-20 column, 32 procyanidins were identified by LC-ESI-Q-TOF-MS in litchi pulp for the first time. Quantification of individual procyanidin in HPCE indicated that epicatechin, procyanidin B2, procyanidin C1 and A-type procyanidin trimer were the main procyanidins. The radical scavenging activities of different fractions of HPCE as well as six procyanidins standards were evaluated by both DPPH and ABTS assays. HPCE fractions showed similar antioxidant activities with those of Vc and six individual procyanidins, the IC50 of which ranged from 1.88 ± 0.01 to 2.82 ± 0.10 μg/ml for DPPH assay, and from 1.52 ± 0.17 to 2.71 ± 0.15 μg/ml for ABTS assay. Such results indicate that litchi cultivars rich in proanthocyanidins are good resources of dietary antioxidants and have the potential to contribute to human health.
Highlights
Proanthocyanidins are oligomers or polymers of flavan-3-ol units that are widely distributed in plants kingdom, e.g., apple, blueberry, chocolate, grape, and bark of pine [1,2,3,4,5]
For the DPPH and ABTS radical scavenging activities of Hemaoli pulp crude extracts (HPCE) fractions and individual proanthocyanidins, IC50 values were calculated as the concentrations that inhibited 50% of the ABTS radicals in the reaction, where radical scavenging activity was calculated as: Scavenging rate (%) = (A0 – A1)/A0 × 100%
In a recent study investigating the oligomeric proanthocyanidins in plant products such as grape seed extracts by using UHPLC-PDA-ESI/HRMSn, proanthocyanidins accounted for 48.79% of the grape seed extract (w/w on dry weight basis), among which mononers such as catechin, epicatechin, epicatechin-gallate, and catechin-gallate accounted for 16.63%, dimmers accounted for 17.44%, trimer accounted for 14.24% of the extract [3]
Summary
Proanthocyanidins (condensed tannins) are oligomers or polymers of flavan-3-ol units that are widely distributed in plants kingdom, e.g., apple, blueberry, chocolate, grape, and bark of pine [1,2,3,4,5]. Based on the hydroxylation patterns of their constitutive units, proanthocyanidins can be divided into several classes. Proanthocyanidins exclusively constituted of (epi)catechins units were procyandins, while proanthocyanidins consisted of (epi)afzelechin units and (epi) gallocatechins units were designated as propelargonidins and prodelphinidins, respectively. Proanthocyanidins in Litchi Pulp and Their Antioxidant Activity
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