Alterations in the phytochemical composition and antioxidant activity of Ligustrum robustum according to continuous wet- and dry-heat treatment.

Small-leaved Kuding tea (SLKDT) obtained from Ligustrum robustum is a traditional tea substitute in southern China and has a range of physiological effects. However, the changes in its phytochemical composition after various heat treatments are not reported yet. Thus, the phytochemical composition and antioxidant activities of fresh leaves of SLKDT (LrF1) and SLKDT after high-temperature wet-heat treatment (LrF2) and wet- and dry-heat treatments (LrF3) were assessed using liquid chromatography-mass spectrometry, and 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonate (ABTS) and 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activities and lipid peroxidation inhibition activity of LrF1 and LrF3 were investigated. The results indicated that the phytochemical composition of LrF1, LrF2, and LrF3 was significantly different. Overall, 258 and 83 differential constituents, respectively, were obtained in LrF1 versus LrF2 and LrF2 versus LrF3. The differential constituents mainly included amino acids and their derivatives, nucleosides, flavonoids, terpenoids, simple phenylpropanoids, and coumarins. After heat treatment, SLKDT exhibited obvious changes in sensory characteristics and physiological properties, which may be related to the changes in the levels of amino acids, linalool, beta-geraniol, myricetin, naringin, fraxetin, and isoacteoside. Moreover, the antioxidant activities significantly changed after heat treatment of SLKDT. Overall, our study demonstrated that heat treatment can alter the phytochemical composition of SLKDT, thus affecting its sensory properties and physiological properties. PRACTICAL APPLICATION: This study preliminarily assessed the changes in the composition of small-leaved Kuding tea (SLKDT) after various heat treatments and revealed that the composition of SLKDT tea can be adjusted by various heat and temperature treatments.