Changes in Flavonoids and Nonphenolic Pigments during On-Tree Maturation and Postharvest Pericarp Browning of Litchi (Litchi chinensis Sonn.) As Shown by HPLC-MSn

Polyphenols, chlorophylls, and carotenoids were characterized by HPLC-DAD-MSn in the pericarp of unripe to over-ripe 'Hong Huey' and 'Chacapat' litchi fruit at harvest and during subsequent storage (5 °C, 90% RH, 21 days). (−)-Epicatechin and A-type procyanidins always predominated quantitatively. Besides these ortho-diphenolic compounds, minor novel litchi flavonoids included monohydroxylated structures. Chlorophyll degradation by 73−92% and 7−38-fold anthocyanin accumulation affected pericarp color throughout the last 15−20 days of on-tree maturation. Postharvest, anthocyanins and (−)-epicatechin largely degraded within the first 3 days, accompanied by severe pericarp browning. Without packaging of the fruit, desiccation initially accelerated polyphenol oxidase-induced oxidation of (−)-epicatechin, but then hindered its further progress. Constant levels of the monohydroxylated (epi)afzelechin indicated no involvement of peroxidase. Acting as antioxidants, anthocyanins retarded (−)-epicatechin degradation. Hence, pinkish-red fruit with a molar ratio of cyanidin 3-O-rutinoside to (−)-epicatechin of >3:100 retained flavonoids best. However, brown polymers masked remaining red pigments.