Kinetic degradation of total phenolic content, DPPH radical scavenging and xanthine oxidase inhibitory activities in Yanang (Tiliacora triandra) leaf extract during preparation process

Abstract

Presently, canned bamboo shoots in Yanang (Tiliacora triandra (Colebr.) Diels) leaf extract is produced in order to expand shelf-life and ease to prepare food. The objectives of this research were to investigate the effect of different thermal processing during Yanang leaf extract preparation on total phenolic content, DPPH radical scavenging and xanthine oxidase inhibitory activities and to determine kinetics of the extract’s quality alterations. The preparation included 1:12 (w/v) leaves to water ratio, 32,000 rpm blending speed and different heating temperature at 60, 70 or 80 ˚C for 15 minutes. Data were collected at 0, 1, 3, 6, 9, 12 and 15 minutes of heating time. The results showed that fresh Yanang leaf extract had total phenolic content of 680.16 ± 19.57 mg GAE/100 mg db. and it possessed DPPH radical scavenging and xanthine oxidase inhibitory activities at 163.53 ± 0.87 μg BHT/mL and 78.58 ± 0.17%, respectively. The results revealed that an increase in heating temperature and time decreased total phenolic content and the DPPH radical scavenging and xanthine oxidase inhibitory activities of Yanang leaf extract. During 15 minutes heating, the total phenolic content of Yanang leaf extract ranged from 526.33 ± 28.79 to 638.93 ± 29.69 mg GAE/100 mg db., DPPH radical scavenging activity ranged from 92.86 ± 1.66 to 136.41 ± 5.70 μg BHT/mL and xanthine oxidase inhibitory activity ranged from 72.64 ± 0.34 to 76.65 ± 0.50%. The change of total phenolic content (R2 = 0.809-0.959) followed zero-order kinetic model and that of DPPH radical scavenging activity (R2 = 0.783-0.920) while xanthine oxidase inhibitory activity (R2 = 0.864-0.922) followed second-order kinetic model.