Quality changes of litchi (Litchi chinensis Sonn.) in syrup due to thermal and high pressure processes

- HHP could maintain the original color parameters of litchi.
- HHP slightly affected the textural properties of litchi.
- HHP litchi retained ascorbic acid and phenolic compounds better than TP litchi.
- Highest antioxidant activities were noted for HHP litchi.

This study purposed to determine endogenous enzymes, color parameters, phytochemicals, antioxidant capacity, indicator microbes and acceptability of litchi pulps in syrup after pasteurization (90 °C/5 min) and pressurization (100-600 MPa/25 °C/20 min). The results showed that the polyphenoloxidase (PPO) and peroxidase (POD) activities in litchi still remained after pressurization, while pasteurization completely inactivated both enzymes. Moreover, the levels of ascorbic acid, total anthocyanins, total polyphenols and antioxidant activities (DPPH and FRAP assays) in pressurized samples were significant higher than those in heated one. Also, pressurization could preserve the natural color better than pasteurization. The microbiological contamination was noticeably inhibited after pasteurization and pressurization at 400-600 MPa. Pressurized pulps were shown to have the liking scores apparently higher than pasteurized pulp. In overall, pressurization at 600 MPa was an appropriate condition for decreasing the PPO and POD activities as well as the indicator microbes of litchi pulps in syrup. During refrigerated storage, browning index (BI) of pressurized pulp (600 MPa) was higher than that of thermally treated pulp, while the degradation of the phytochemicals and antioxidant activities in both processed products were observed. However, residual levels of both endogenous enzymes and antioxidant properties in pressurized pulp were still higher than those of pasteurized pulp throughout the storage period.