Impact of thermal processing and storage temperature on the phenolic profile and antioxidant activity of different varieties of lychee juice

Abstract Lychee pulp is rich in phenolic compounds and has a variety of biological activities. However, their thermal stability are unknown. The results showed that after heat-treated at 121 °C (HT121), the total phenolic content (TPC) and total flavonoid content of the lychee juices were significantly increased compared to those of the unheated (UH) and 70 °C heat-treated (HT70) lychee juices. Nine individual phenolic compounds, gallic acid, (-)-gallocatechin, procyanidin B2, vanillic acid, quercetin-3-rutinose-7-rhamnoside, syringic acid, procyanidin A2, ferulic acid and rutin, were detected in lychee juice by HPLC-DAD. After heat treatment at 121 °C and high temperature storage at 45 °C, the gallic acid content in lychee juice was increased. In particular, (-)-gallocatechin was generated after thermal processing at 121 °C. (-)-Gallocatechin accounted for 89.50% of the total phenolic compounds in HT121 lychee juice. However, with prolonged storage time (72 h) and increased storage temperature (45 °C), the (-)-gallocatechin degraded and disappeared. In summary, the thermal stability of most phenolic compounds in lychee pulp is good, and heat treatment could promote the release of phenolic compounds in lychee juice and improve their antioxidant activity. The variety of Guiwei lychee is more suitable for fruit juice manufacturing.